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1. A Growing Braking Index and Spin-down Swings for the Pulsar PSR B0540–69

Author: Cristóbal M. Espinoza, Lucien Kuiper, Wynn C. G. Ho, Danai Antonopoulou, Zaven Arzoumanian, Alice K. Harding, Paul S. Ray, and George Younes
Subjects: Compact objects, Neutron stars, Pulsars, Rotation powered pulsars, Astrophysics, QB460-466
Abstract: The way pulsars spin down is not understood in detail, but a number of possible physical mechanisms produce a spin-down rate that scales as a power of the rotation rate ( $\dot{\nu }\propto -{\nu }^{n}$ ), with the power-law index n called the braking index. PSR B0540−69 is a pulsar that in 2011, after 16 yr of spinning down with a constant braking index of 2.1, experienced a giant spin-down change and a reduction of its braking index to nearly zero. Here, we show that, following this episode, the braking index monotonically increased during a period of at least 4 yr and stabilized at ∼1.1. We also present an alternative interpretation of a more modest rotational irregularity that occurred in 2023, which was modeled as an anomalous negative step of the rotation rate. Our analysis shows that the 2023 observations can be equally well described as a transient swing of the spin-down rate (lasting ∼65 days), and the Bayesian evidence indicates that this model is strongly preferred.
Published: 2024
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2. First Detection of Polarization in X-Rays for PSR B0540-69 and Its Nebula

Author: Fei Xie, Josephine Wong, Fabio La Monaca, Roger W. Romani, Jeremy Heyl, Philip Kaaret, Alessandro Di Marco, Niccolò Bucciantini, Kuan Liu, Chi-Yung Ng, Niccolò Di Lalla, Martin C. Weisskopf, Enrico Costa, Paolo Soffitta, Fabio Muleri, Matteo Bachetti, Maura Pilia, John Rankin, Sergio Fabiani, Iván Agudo, Lucio A. Antonelli, Luca Baldini, Wayne H. Baumgartner, Ronaldo Bellazzini, Stefano Bianchi, Stephen D. Bongiorno, Raffaella Bonino, Alessandro Brez, Fiamma Capitanio, Simone Castellano, Elisabetta Cavazzuti, Chien-Ting Chen, Stefano Ciprini, Alessandra De Rosa, Ettore Del Monte, Laura Di Gesu, Immacolata Donnarumma, Victor Doroshenko, Michal Dovčiak, Steven R. Ehlert, Teruaki Enoto, Yuri Evangelista, Riccardo Ferrazzoli, Javier A. Garcia, Shuichi Gunji, Kiyoshi Hayashida, Wataru Iwakiri, Svetlana G. Jorstad, Vladimir Karas, Fabian Kislat, Takao Kitaguchi, Jeffery J. Kolodziejczak, Henric Krawczynski, Luca Latronico, Ioannis Liodakis, Simone Maldera, Alberto Manfreda, Frédéric Marin, Andrea Marinucci, Alan P. Marscher, Herman L. Marshall, Francesco Massaro, Giorgio Matt, Ikuyuki Mitsuishi, Tsunefumi Mizuno, Michela Negro, Stephen L. O’Dell, Nicola Omodei, Chiara Oppedisano, Alessandro Papitto, George G. Pavlov, Abel L. Peirson, Matteo Perri, Melissa Pesce-Rollins, Pierre-Olivier Petrucci, Andrea Possenti, Juri Poutanen, Simonetta Puccetti, Brian D. Ramsey, Ajay Ratheesh, Oliver J. Roberts, Carmelo Sgrò, Patrick Slane, Gloria Spandre, Douglas A. Swartz, Toru Tamagawa, Fabrizio Tavecchio, Roberto Taverna, Yuzuru Tawara, Allyn F. Tennant, Nicholas E. Thomas, Francesco Tombesi, Alessio Trois, Sergey S. Tsygankov, Roberto Turolla, Jacco Vink, Kinwah Wu, Silvia Zane, IXPE Collaboration, Zorawar Wadiasingh, Wynn C. G. Ho, Alice K. Harding, Keith C. Gendreau, and Zaven Arzoumanian
Subjects: Pulsars, Pulsar wind nebulae, Polarimetry, Astrophysics, QB460-466
Abstract: We report on X-ray polarization measurements of the extragalactic Crab-like PSR B0540-69 and its Pulsar Wind Nebula (PWN) in the Large Magellanic Cloud, using a ∼850 ks Imaging X-ray Polarimetry Explorer (IXPE) exposure. The PWN is unresolved by IXPE. No statistically significant polarization is detected for the image-averaged data, giving a 99% confidence polarization upper limit (MDP _99 ) of 5.3% in the 2–8 keV energy range. However, a phase-resolved analysis detects polarization for both the nebula and pulsar in the 4–6 keV energy range. For the PWN defined as the off-pulse phases, the polarization degree (PD) of (24.5 ± 5.3)% and polarization angle (PA) of (78.1 ± 6.2)° is detected at 4.6 σ significance level, consistent with the PA observed in the optical band. In a single on-pulse window, a hint of polarization is measured at 3.8 σ with PD of (50.0 ± 13.1)% and PA of (6.2 ± 7.4)°. A “simultaneous” PSR/PWN analysis finds two bins at the edges of the pulse exceeding 3 σ PD significance, with PD of (68 ± 20)% and (62 ± 20)%; intervening bins at 2–3 σ significance have lower PD, hinting at additional polarization structure.
Published: 2024
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3. The Gamma-Ray Pulsar Phenomenology in View of 3D Kinetic Global Magnetosphere Models

Author: Constantinos Kalapotharakos, Zorawar Wadiasingh, Alice K. Harding, and Demosthenes Kazanas
Subjects: Pulsars, Gamma-rays, Gamma-ray telescopes, Computational methods, Neutron stars, Astrophysics, QB460-466
Abstract: We develop kinetic plasma models of pulsar magnetospheres with magnetic-field-line-dependent plasma injection that reveal the importance of various magnetosphere regions in regulating the γ -ray emission. We set different particle injection rates for the so-called open, closed, and separatrix zones. Moderate particle injection rates in open and closed zones ensure a global field structure close to the force-free structure, while the dissipation occurs mainly in and around the equatorial current sheet. The particles that are injected into the separatrix zone affect the particle populations that enter the equatorial current sheet region, and therefore the corresponding accelerating electric fields, particle energies, the spectral cutoff energy, and γ -ray efficiency. The separatrix zone models reproduce the recently discovered fundamental plane of γ -ray pulsars consistent with curvature radiation emission, the γ -ray light-curve shapes, and the radio-lag versus peak-separation correlation reported in the Fermi second pulsar catalog. The model beaming factors indicate that the pulsar total γ -ray luminosities listed in the Fermi catalogs are overestimations of the actual ones. We find that the radiation reaction limited regime starts ceasing to govern the high-energy emission for $\dot{{ \mathcal E }}\lesssim {10}^{34}\,\mathrm{erg}\,\,{{\rm{s}}}^{-1}$ . Our results also indicate that toward high magnetic inclination angles, the Y point around the rotational equator migrates well inside the light cylinder, sparking additional peaks in the γ -ray pulse profiles. We find that an equivalent enhanced particle injection beyond the Y point strengthens these features, making the model γ -ray light curves inconsistent with those observed.
Published: 2023
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4. A NICER View on the 2020 Magnetar-like Outburst of PSR J1846−0258

Author: Chin-Ping Hu, Lucien Kuiper, Alice K. Harding, George Younes, Harsha Blumer, Wynn C. G. Ho, Teruaki Enoto, Cristóbal M. Espinoza, and Keith Gendreau
Subjects: Neutron stars, Astrophysics, QB460-466
Abstract: We report on our monitoring of the strong-field magnetar-like pulsar PSR J1846−0258 with the Neutron Star Interior Composition Explorer (NICER) and the timing and spectral evolution during its outburst in 2020 August. Phase-coherent timing solutions were maintained from 2017 March through 2021 November, including a coherent solution throughout the outburst. We detected a large spin-up glitch of magnitude Δ ν / ν = 3 × 10 ^−6 at the start of the outburst and observed an increase in pulsed flux that reached a factor of more than 10 times the quiescent level, a behavior similar to that of the 2006 outburst. Our monitoring observations in 2020 June and July indicate that the flux was rising prior to the Swift announcement of the outburst on 2020 August 1. We also observed several sharp rises in the pulsed flux following the outburst and the flux reached quiescent level by 2020 November. The pulse profile was observed to change shape during the outburst, returning to the preoutburst shape by 2021. Spectral analysis of the pulsed emission of NICER data shows that the flux increases result entirely from a new blackbody component that gradually fades away while the power law remains nearly constant at its quiescent level throughout the outburst. Joint spectral analysis of NICER and simultaneous NuSTAR data confirms this picture. We discuss the interpretation of the magnetar-like outburst and origin of the transient thermal component in the context of both a pulsar-like and a magnetar-like model.
Published: 2023
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5. Pulsar Polar Cap and Slot Gap Models: Confronting Fermi Data

Author: Alice K. Harding
Subjects: pulsars, gamma-rays, Astronomy, QB1-991
Abstract: Rotation-powered pulsars are excellent laboratories for studying particle acceleration as well as fundamental physics of strong gravity, strong magnetic fields and relativity. Particle acceleration and high-energy emission from the polar caps is expected to occur in connection with electron-positron pair cascades. I will review acceleration and gamma-ray emission from the pulsar polar cap and associated slot gap. Predictions of these models can be tested with the data set on pulsars collected by the Large Area Telescope on the Fermi Gamma-Ray Telescope over the last four years, using both detailed light curve fitting, population synthesis and phase-resolved spectroscopy.
Published: 2013
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6. High-energy Photon Opacity in the Twisted Magnetospheres of Magnetars

Author: Kun Hu, Matthew Baring, Alice K. Harding, and Zorawar Wadiasingh
Subjects: Space Radiation
Abstract: Magnetars are neutron stars characterized by strong surface magnetic fields generally exceeding the quantum critical value of 44.1 TG. High-energy photons propagating in their magnetospheres can be attenuated by QED processes like photon splitting and magnetic pair creation. In this paper, we compute the opacities due to photon splitting and pair creation by photons emitted anywhere in the magnetosphere of a magnetar. Axisymmetric, twisted dipole field configurations embedded in the Schwarzschild metric are treated. The paper computes the maximum energies for photon transparency that permit propagation to infinity in curved spacetime. Special emphasis is given to cases where photons are generated along magnetic field loops and/or in polar regions; these cases directly relate to resonant inverse Compton scattering models for the hard X-ray emission from magnetars and Comptonized soft gamma-ray emission from giant flares. We find that increases in magnetospheric twists raise or lower photon opacities, depending on both the emission locale and the competition between field-line straightening and field strength enhancement. Consequently, given the implicit spectral transparency of hard X-ray bursts and persistent "tail" emission of magnetars, photon splitting considerations constrain their emission region locales and the twist angle of the magnetosphere; these constraints can be probed by future soft gamma-ray telescopes such as COSI and AMEGO. The inclusion of twists generally increases the opaque volume of pair creation by photons above its threshold, except when photons are emitted in polar regions and approximately parallel to the field.
Published: 2022
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7. Exploring the MeV Sky With A Combined Coded Mask and Compton Telescope: the Galactic Explorer With A Coded Aperture Mask Compton Telescope (GECCO)

Author: Elena Orlando, Eugenio Bottacini, A.A. Moiseev, Arash Bodaghee, Werner Collmar, Torsten Ensslin, Igor V. Moskalenko, Michela Negro, Stefano Profumo, Seth W. Digel, David J. Thompson, Matthew G. Baring, Aleksey Bolotnikov, Nicholas Cannady, Gabriella A. Carini, Vincent Eberle, Isabelle A. Grenier, Alice K. Harding, Dieter Hartmann, Sven Herrmann, Matthew Kerr, Roman Krivonos, Philippe Laurent, Francesco Longo, Aldo Morselli, Bernard Philips, Makoto Sasaki, Peter Shawhan, Daniel Shy, Gerry Skinner, Lucas D. Smith, Floyd W. Stecker, Andrew Strong, Steven Sturner, John A. Tomsick, Zorawar Wadiasingh, Ricahrd S. Woolf, Eric Yates, Klaus-Peter Ziock, and Andreas Zoglauer
Subjects: Astrophysics, Physics of Elementary Particles and Fields
Abstract: The sky at MeV energies is currently poorly explored. Here we present an innovative mission concept that builds upon the heritage of past and current missions improving the sensitivity and, very importantly, the angular resolution. This consists in combining a Compton telescope and a coded-mask telescope. We delineate the motivation for such a concept and we define the scientific goals for such a mission. The Galactic Explorer with a Coded Aperture Mask Compton Telescope (GECCO) is a novel concept for a next-generation telescope covering hard X-ray and soft gamma-ray energies. The potential and importance of this approach that bridges the observational gap in the MeV energy range are presented. With the unprecedented angular resolution of the coded mask telescope combined with the sensitive Compton telescope, a mission such as GECCO can disentangle the discrete sources from the truly diffuse emission. Individual Galactic and extragalactic sources are detected. This also allows to understand the gamma-ray Galactic center excess and the Fermi Bubbles, and to trace the low-energy cosmic rays, and their propagation in the Galaxy. Nuclear and annihilation lines are spatially and spectrally resolved from the continuum emission and from sources, addressing the role of low-energy cosmic rays in star formation and galaxy evolution, the origin of the 511 keV positron line, fundamental physics, and the chemical enrichment in the Galaxy. Such an instrument also detects explosive transient gamma-ray sources, which, in turn, enables identifying and studying the astrophysical objects that produce gravitational waves and neutrinos in a multi-messenger context. By looking at a poorly explored energy band it also allows discoveries of new astrophysical phenomena.
Published: 2022
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8. Probing the High-energy Gamma-Ray Emission Mechanism in the Vela Pulsar via Phase-resolved Spectral and Energy-dependent Light-curve Modeling

Author: Monica Barnard, Christo Venter, Alice K. Harding, Constantinos Kalapotharakos, and Tyrel J. Johnson
Subjects: Instrumentation And Photography
Abstract: Recent kinetic simulations sparked a debate regarding the emission mechanism responsible for pulsed GeV γ-ray emission from pulsars. Some models invoke curvature radiation, while other models assume synchrotron radiation in the current sheet. We interpret the curved spectrum of the Vela pulsar as seen by H.E.S.S. II (up to ∼100 GeV) and the Fermi Large Area Telescope to be the result of curvature radiation due to primary particles in the pulsar magnetosphere and current sheet. We present phase-resolved spectra and energy-dependent light curves using an extended slot gap and current-sheet model, invoking a step function for the accelerating electric field as motivated by kinetic simulations. We include a refined calculation of the curvature radius of particle trajectories in the lab frame, impacting the particle transport, predicted light curves, and spectra. Our model reproduces the decrease of the flux of the first peak relative to the second one, evolution of the bridge emission, near-constant phase positions of peaks, and narrowing of pulses with increasing energy. We can explain the first of these trends because we find that the curvature radii of the particle trajectories in regions where the second γ-ray light-curve peak originates are systematically larger than those associated with the first peak, implying that the spectral cutoff of the second peak is correspondingly larger. However, an unknown azimuthal dependence of the E field, as well as uncertainty in the precise spatial origin of the GeV emission, precludes a simplistic discrimination of emission mechanisms.
Published: 2022
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9. X-Ray Burst and Persistent Emission Properties of the Magnetar SGR 1830-0645 in Outburst

Author: George Younes, Chin-Ping Hu, Karishma Bansal, Paul S. Ray, Aaron B. Pearlman, Franz Kirsten, Zorawar Wadiasingh, Ersin Göğüş, Matthew G. Baring, Teruaki Enoto, Zaven Arzoumanian, Keith C. Gendreau, Chryssa Kouveliotou, Tolga Güver, Alice K. Harding, Walid A. Majid, Harsha Blumer, Jason W. T. Hessels, Marcin P. Gawroński, Vladislavs Bezrukovs, and Arturs Orbidans
Subjects: Astrophysics
Abstract: We report on NICER X-ray monitoring of the magnetar SGR 1830−0645 covering 223 days following its 2020 October outburst, as well as Chandra and radio observations. We present the most accurate spin ephemerides of the source so far: ν = 0.096008680(2) Hz, $\dot{\n𝜈}=-6.2(1) x (10)^(-14) Hz/s, and significant second and third frequency derivative terms indicative of nonnegligible timing noise. The phase-averaged 0.8–7 keV spectrum is well fit with a double-blackbody (BB) model throughout the campaign. The BB temperatures remain constant at 0.46 and 1.2 keV. The areas and flux of each component decreased by a factor of 6, initially through a steep decay trend lasting about 46 days, followed by a shallow long-term one. The pulse shape in the same energy range is initially complex, exhibiting three distinct peaks, yet with clear continuous evolution throughout the outburst toward a simpler, single-pulse shape. The rms pulsed fraction is high and increases from about 40% to 50%. We find no dependence of pulse shape or fraction on energy. These results suggest that multiple hot spots, possibly possessing temperature gradients, emerged at outburst onset and shrank as the outburst decayed. We detect 84 faint bursts with NICER, having a strong preference for occurring close to the surface emission pulse maximum—the first time this phenomenon is detected in such a large burst sample. This likely implies a very low altitude for the burst emission region and a triggering mechanism connected to the surface active zone. Finally, our radio observations at several epochs and multiple frequencies reveal no evidence of pulsed or burst-like radio emission.
Published: 2022
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10. Very-high-energy Emission from Pulsars

Author: Alice K. Harding, Christo Venter, and Konstantinos Kalapotharakos
Subjects: Astrophysics
Abstract: Air-Cherenkov telescopes have detected pulsations at energies above 50 GeV from a growing number of Fermi pulsars. These include the Crab, Vela, PSR B1706−44, and Geminga, with the first two having pulsed detections above 1 TeV. In some cases, there appears to be very-high-energy (VHE) emission that is an extension of the Fermi spectra to high energies, while in other cases, additional higher-energy spectral components that require a separate emission mechanism may be present. We present results of broadband spectral modeling using global magnetospheric fields and multiple emission mechanisms that include synchro-curvature (SC) and inverse Compton scattered (ICS) radiation from accelerated particles (primaries) and synchrotron self-Compton (SSC) emission from lower-energy pairs. Our models predict three distinct VHE components: SC from primaries whose high-energy tail can extend to 100 GeV, SSC from pairs that can extend to several TeV, and ICS from primary particles accelerated in the current sheet that scatter pair synchrotron radiation, which appears beyond 10 TeV. Our models suggest that H.E.S.S.-II and MAGIC have detected the high-energy tail of the primary SC component that produces the Fermi spectrum in Vela, Geminga, and PSR B1706−44. We argue that the ICS component peaking above 10 TeV from Vela has been seen by H.E.S.S. Detection of this emission component from the Crab and other pulsars is possible with the High Altitude Water Cherenkov Observatory and Cherenkov Telescope Array, and will directly measure the maximum particle energy in pulsars.
Published: 2021
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11. Timing Six Energetic Rotation-powered X-Ray Pulsars, Including the Fast-spinning Young PSR J0058-7218 and Big Glitcher PSR J0537-6910

Author: Wynn C. G. Ho, Lucien Kuiper, Cristóbal M. Espinoza, Sebastien Guillot, Paul S. Ray, D. A. Smith, Slavko Bogdanov, Danai Antonopoulou, Zaven Arzoumanian, Michał Bejger, Teruaki Enoto, Paolo Esposito, Alice K. Harding, Brynmor Haskell, Natalia Lewandowska, Chandreyee Maitra, and Georgios Vasilopoulos
Published: 2022
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12. Constraining the Neutron Star Mass–Radius Relation and Dense Matter Equation of State with NICER. III. Model Description and Verification of Parameter Estimation Codes

Author: Slavko Bogdanov, Alexander J. Dittmann, Wynn C. G. Ho, Frederick K. Lamb, Simin Mahmoodifar, M. Coleman Miller, Sharon M. Morsink, Thomas E. Riley, Tod E. Strohmayer, Anna L. Watts, Devarshi Choudhury, Sebastien Guillot, Alice K Harding, Paul S. Ray, Zorawar Wadiasingh, Michael T. Wolff, Craig B. Markwardt, Zaven Arzoumanian, and Keith C. Gendreau
Subjects: Astrophysics
Abstract: We describe the X-ray pulse profile models we use and how we use them to analyze Neutron Star Interior Composition Explorer(NICER)observations of rotation-powered millisecond pulsars to obtain information about the mass–radius relation of neutron stars and the equation of state of the dense matter in their cores. Here we detail our modeling of the observed profile of PSR J0030+0451 that we analyzed in Miller et al. and Riley et al. and describe a cross-verification of computations of the pulse profiles of a star with R/M 3, in case stars this compact need to be considered in future analyses. We also present our early cross-verification efforts of the parameter estimation procedures used by Miller et al. and Riley et al. by analyzing two distinct synthetic data sets. Both codes yielded credible regions in the mass–radius plane that are statistically consistent with one another, and both gave posterior distributions for model parameter values consistent with the values that were used to generate the data. We also summarize the additional tests of the parameter estimation procedure of Miller et al. that used synthetic pulse profiles and the NICER pulse profile of PSR J0030+0451. We then illustrate how the precision of mass and radius estimates depends on the pulsar’s spin rate and the size of its hot spot by analyzing four different synthetic pulse profiles. Finally, we assess possible sources of systematic error in the estimates made using this technique, some of which may warrant further investigation.
Published: 2021
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13. Opacities for photon splitting and pair creation in neutron star magnetospheres

Author: Kun Hu, Matthew G Baring, Zorawar Wadiasingh, and Alice K Harding
Published: 2019
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14. The Fundamental Plane Relation for Gamma-Ray Pulsars Implied by 4FGL

Author: Constantinos Kalapotharakos, Zorawar Wadiasingh, Alice K. Harding, and Demosthenes Kazanas
Published: 2022
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15. Pulse Peak Migration during the Outburst Decay of the Magnetar SGR 1830-0645: Crustal Motion and Magnetospheric Untwisting

Author: George Younes, Samuel K Lander, Matthew G. Baring, Teruaki Enoto, Chryssa Kouveliotou, Zorawar Wadiasingh, Wynn C. G. Ho, Alice K. Harding, Zaven Arzoumanian, Keith Gendreau, Tolga Güver, Chin-Ping Hu, Christian Malacaria, Paul S. Ray, and Tod E. Strohmayer
Published: 2022
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16. Timing six energetic rotation-powered X-ray pulsars, including the fast-spinning young PSR J0058-7218 and Big Glitcher PSR J0537-6910

Author: Wynn C. G. Ho, Lucien Kuiper, Cristóbal M. Espinoza, Sebastien Guillot, Paul S. Ray, D. A. Smith, Slavko Bogdanov, Danai Antonopoulou, Zaven Arzoumanian, Michał Bejger, Teruaki Enoto, Paolo Esposito, Alice K. Harding, Brynmor Haskell, Natalia Lewandowska, Chandreyee Maitra, Georgios Vasilopoulos, Institut de recherche en astrophysique et planétologie (IRAP), Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Centre National d'Études Spatiales [Toulouse] (CNES), Laboratoire d'Astrophysique de Bordeaux [Pessac] (LAB), Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Observatoire astronomique de Strasbourg (ObAS), and Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Solar and Stellar Astrophysics (astro-ph.SR)
Abstract: Measuring a pulsar's rotational evolution is crucial to understanding the nature of the pulsar. Here we provide updated timing models for the rotational evolution of six pulsars, five of which are rotation phase-connected using primarily NICER X-ray data. For the newly-discovered fast energetic young pulsar, PSR J0058-7218, we increase the baseline of its timing model from 1.4 days to 8 months and not only measure more precisely its spin-down rate nudot = (-6.2324+/-0.0001)x10^-11 Hz s^-1 but also for the first time the second time derivative of spin rate nuddot = (4.2+/-0.2)x10^-21 Hz s^-2. For the fastest and most energetic young pulsar, PSR J0537-6910 (with 16 ms spin period), we detect 4 more glitches, for a total of 15 glitches over 4.5 years of NICER monitoring, and show that its spin-down behavior continues to set this pulsar apart from all others, including a long-term braking index n = -1.234+/-0.009 and interglitch braking indices that asymptote to, 18 pages, 17 figures; accepted for publication in ApJ; very minor edits and no changes to numbers
Published: 2023
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17. Discovery of Soft X-ray Pulsations from PSR J1231-1411 using NICER

Author: Paul S Ray, Sebastien Guillot, Scott M Ransom, Matthew Kerr, Slavko Bogdanov, Alice K Harding, Michael T Wolff, Christian Malacaria, Keith C Gendreau, Zaven Arzoumanian, Craig Markwardt, Yang Soong, and John P Doty
Subjects: Astrophysics
Abstract: We report the discovery of soft X-ray pulsations from the nearby millisecond pulsar PSR J1231−1411 using the Neutron Star Interior Composition Explorer (NICER). The pulsed emission is characterized by a broad and asymmetric main pulse and a much fainter secondary interpulse, with a total pulsed count rate of 0.055 c s−1 in the 0.35–1.5 keV band. We analyzed Fermi Large Area Telescope (LAT) data to update the pulse timing model covering 10 yr of data and used that model to coherently combine NICER data over a year of observations. Spectral modeling suggests that the flux is dominated by thermal emission from a hot spot (or spots) on the neutron star surface. The phase relationship between the X-ray pulse and the radio and γ rays provides insight into the geometry of the system.
Published: 2019
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18. Neutron Star Interior Composition Explorer X-Ray Timing of the Radio and Gamma-ray Quiet Pulsars PSR J1412+7922 and PRS J1849-0001

Author: Slavko Bogdanov, Wynn C G Ho, Teruaki Enoto, Sebastien Guillot, Alice K Harding, Guarava K Jaiswal, Christian Malacaria, Sridhar Manthripragada, Zaven Arzoumanian, and Keith C Gendreau
Subjects: Astrophysics
Abstract: We present new timing and spectral analyses of PSR J1412+7922 (Calvera) and PSR J1849−0001, which are only seen as pulsars in X-rays, based on observations conducted with the Neutron Star Interior Composition Explorer. We obtain updated and substantially improved pulse ephemerides compared to previous X-ray studies, as well as spectra that can be well fit by simple blackbodies and/or a power law. Our refined timing measurements enable deeper searches for pulsations at other wavelengths and sensitive targeted searches by the Laser Interferometer Gravitational-Wave Observatory (LIGO)/Virgo for continuous gravitational waves from these neutron stars. Using the sensitivity of LIGO’s first observing run, we estimate constraints that a gravitational wave search of these pulsars would be obtained on the size of their mass deformation and r-mode fluid oscillation.
Published: 2019
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19. Probing the non-thermal emission geometry of AR Sco via optical phase-resolved polarimetry

Author: Louis du Plessis, Christo Venter, Zorawar Wadiasingh, Alice K Harding, David A H Buckley, Stephen B Potter, and P J Meintjes
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Space and Planetary Science, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics::Solar and Stellar Astrophysics, Astronomy and Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics - High Energy Astrophysical Phenomena
Abstract: AR Sco is a binary system that contains a white and red dwarf. The rotation rate of the white dwarf has been observed to slow down, analogous to rotation-powered radio pulsars; it has thus been dubbed a "white dwarf pulsar". We previously fit the traditional radio pulsar rotating vector model to the linearly polarised optical data from this source, constraining the system geometry as well as the white dwarf mass. Using a much more extensive dataset, we now explore the application of the same model to binary phase-resolved optical polarimetric data, thought to be the result of non-thermal synchrotron radiation, and derive the magnetic inclination angle $\alpha$ and the observer angle $\zeta$ at different orbital phases. We obtain a $\sim 10^{\circ}$ variation in $\alpha$ and $\sim 30^{\circ}$ variation in $\zeta$ over the orbital period. The variation patterns in these two parameters is robust, regardless of the binning and epoch of data used. We speculate that the observer is detecting radiation from an asymmetric emission region that is a stable structure over several orbital periods. The success of this simple model lastly implies that the pitch angles of the particles are small and the pulsed, non-thermal emission originates relatively close to the white dwarf surface., Comment: 13 pages, 14 figures, accepted by MNRAS
Published: 2021
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20. NICER View of the 2020 Burst Storm and Persistent Emission of SGR 1935+2154

Author: George Younes, Tolga Güver, Chryssa Kouveliotou, Matthew G. Baring, Chin-Ping Hu, Zorawar Wadiasingh, Beste Begiçarslan, Teruaki Enoto, Ersin Göğüş, Lin Lin, Alice K. Harding, Alexander J. van der Horst, Walid A. Majid, Sebastien Guillot, and Christian Malacaria
Published: 2020
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21. A Radiatively Quiet Glitch and Anti-glitch in the Magnetar 1E 2259+586

Author: George Younes, Paul S. Ray, Matthew G. Baring, Chryssa Kouveliotou, Corinne Fletcher, Zorawar Wadiasingh, Alice K. Harding, and Adam Goldstein
Published: 2020
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22. Simultaneous Magnetic Polar Cap Heating during a Flaring Episode from the Magnetar 1RXS J170849.0–400910

Author: George Younes, Matthew G. Baring, Chryssa Kouveliotou, Zorawar Wadiasingh, Daniela Huppenkothen, and Alice K. Harding
Published: 2020
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23. Broadband X-ray burst spectroscopy of the fast-radio-burst-emitting Galactic magnetar

Author: Gaurava K. Jaisawal, Keith C. Gendreau, Alice K. Harding, Chin-Ping Hu, George Younes, Beverly LaMarr, Lin Lin, Teruaki Enoto, J. Pope, Matthew G. Baring, Zaven Arzoumanian, Wynn C. G. Ho, Yuki Kaneko, James F. Steiner, Ersin Gogus, Zorawar Wadiasingh, J. Doty, Takashi Okajima, Walid A. Majid, Tolga Guver, Chryssa Kouveliotou, M. Saylor, Paul S. Ray, A. J. van der Horst, Sebastien Guillot, Oliver J. Roberts, Institut de recherche en astrophysique et planétologie (IRAP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), and Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)
Subjects: Physics, Neutron Star Interior Composition Explorer, 010504 meteorology & atmospheric sciences, Fast radio burst, Astrophysics::High Energy Astrophysical Phenomena, Milky Way, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Magnetar, 01 natural sciences, Spectral line, Neutron star, 13. Climate action, 0103 physical sciences, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Spectroscopy, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Fermi Gamma-ray Space Telescope
Abstract: Magnetars are young, magnetically powered neutron stars that possess the strongest magnetic fields in the Universe. Fast radio bursts (FRBs) are extremely intense millisecond-long radio pulses of primarily extragalactic origin, and a leading attribution for their genesis focuses on magnetars. A hallmark signature of magnetars is their emission of bright, hard X-ray bursts of sub-second duration. On 27 April 2020, the Galactic magnetar SGR J1935+2154 emitted hundreds of X-ray bursts within a few hours. One of these temporally coincided with an FRB, the first known detection of an FRB from the Milky Way. Here, we present spectral and temporal analyses of 24 X-ray bursts emitted 13 hours prior to the FRB and seen simultaneously with the Neutron Star Interior Composition Explorer (NICER) mission of the National Aeronautics and Space Administration and with the Fermi Gamma-ray Burst Monitor (GBM) mission in their combined energy range of 0.2 keV to 30 MeV. These broadband spectra permit direct comparison with the spectrum of the FRB-associated X-ray burst (FRB-X). We demonstrate that all 24 NICER and GBM bursts are very similar temporally to the FRB-X, but strikingly different spectrally. The singularity of the FRB-X burst is perhaps indicative of an uncommon locale for its origin. We suggest that this event originated in quasi-polar open or closed magnetic field lines that extend to high altitudes. Twenty-four X-ray bursts from a Galactic magnetar simultaneously observed with NICER and Fermi permit a direct comparison to a later X-ray burst that was coincident with a fast radio burst (FRB). The FRB-related burst is spectrally distinct, pointing to an unusual point of emission.
Published: 2021
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24. Evidence for a compact object in the aftermath of the extragalactic transient AT2018cow

Author: Francesco Tombesi, Zaven Arzoumanian, James F. Steiner, Jeroen Homan, M. Ng, Edward M. Cackett, Tod E. Strohmayer, Ronald A. Remillard, Diego Altamirano, Keith C. Gendreau, William Alston, Dheeraj R. Pasham, Deepto Chakrabarty, Jon M. Miller, Peter Bult, Alice K. Harding, Andrew C. Fabian, Brian Metzger, and Wynn C. G. Ho
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Computer science, Settore FIS/05, Astrophysics::High Energy Astrophysical Phenomena, Astronomy, FOS: Physical sciences, Transient (computer programming), Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Compact star, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics::Galaxy Astrophysics
Abstract: The brightest Fast Blue Optical Transients (FBOTs) are mysterious extragalactic explosions that may represent a new class of astrophysical phenomena. Their fast time to maximum brightness of less than a week and decline over several months and atypical optical spectra and evolution are difficult to explain within the context of core-collapse of massive stars which are powered by radioactive decay of Nickel-56 and evolve more slowly. AT2018cow (at redshift of 0.014) is an extreme FBOT in terms of rapid evolution and high luminosities. Here we present evidence for a high-amplitude quasi-periodic oscillation (QPO) of AT2018cow's soft X-rays with a frequency of 224 Hz (at 3.7$\sigma$ significance level or false alarm probability of 0.02%) and fractional root-mean-squared amplitude of >30%. This signal is found in the average power density spectrum taken over the entire 60-day outburst and suggests a highly persistent signal that lasts for a billion cycles. The high frequency (rapid timescale) of 224 Hz (4.4 ms) argues for a compact object in AT2018cow, which can be a neutron star or black hole with a mass less than 850 solar masses. If the QPO is the spin period of a neutron star, we can set limits on the star's magnetic field strength. Our work highlights a new way of using high time-resolution X-ray observations to study FBOTs., Comment: Published in Nature astronomy on 13th December 2021
Published: 2022

25. The Emission Physics of Millisecond Pulsars

Author: Alice K. Harding
Published: 2021
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26. Probing the High-energy $\gamma$-ray Emission Mechanism in the Vela Pulsar via Phase-resolved Spectral and Energy-dependent Light Curve Modeling

Author: Monica Barnard, Christo Venter, Alice K. Harding, Constantinos Kalapotharakos, and Tyrel J. Johnson
Subjects: Space and Planetary Science, Astrophysics::High Energy Astrophysical Phenomena, Astronomy and Astrophysics, Astrophysics - High Energy Astrophysical Phenomena
Abstract: Recent kinetic simulations sparked a debate regarding the emission mechanism responsible for pulsed GeV $\gamma$-ray emission from pulsars. Some models invoke curvature radiation, while other models assume synchrotron radiation in the current-sheet. We interpret the curved spectrum of the Vela pulsar as seen by H.E.S.S. II (up to $\sim$100 GeV) and the $Fermi$ Large Area Telescope (LAT) to be the result of curvature radiation due to primary particles in the pulsar magnetosphere and current sheet. We present phase-resolved spectra and energy-dependent light curves using an extended slot gap and current sheet model, invoking a step function for the accelerating electric field as motivated by kinetic simulations. We include a refined calculation of the curvature radius of particle trajectories in the lab frame, impacting the particle transport, predicted light curves, and spectra. Our model reproduces the decrease of the flux of the first peak relative to the second one, evolution of the bridge emission, near-constant phase positions of peaks, and narrowing of pulses with increasing energy. We can explain the first of these trends because we find that the curvature radii of the particle trajectories in regions where the second $\gamma$-ray light curve peak originates are systematically larger than those associated with the first peak, implying that the spectral cutoff of the second peak is correspondingly larger. However, an unknown azimuthal dependence of the $E$-field as well as uncertainty in the precise spatial origin of the GeV emission, precludes a simplistic discrimination of emission mechanisms., Comment: 24 pages, 19 figures, accepted by ApJ
Published: 2021

27. Modelling Phase-resolved Spectra and Energy-dependent Light Curves of the Vela Pulsar to Scrutinize its GeV Emission Mechanism

Author: Monica Barnard, Constantinos Kalapotharakos, Christo Venter, Alice K. Harding, and Tyrel J. Johnson
Subjects: Energy dependent, Physics, Pulsar, Phase (waves), Astrophysics, Light curve, Vela, Mechanism (sociology), Spectral line
Published: 2021
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28. 'Spider' Millisecond Pulsar Binaries as Potential TeV Emitters

Author: Alice K. Harding, Matthew G. Baring, Christian J. T. van der Merwe, Christo Venter, and Zorawar Wadiasingh
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Light curve, Synchrotron, Spectral line, Galaxy, law.invention, Particle acceleration, Positron, Astrophysics - Solar and Stellar Astrophysics, Pulsar, Millisecond pulsar, law, Physics::Accelerator Physics, Astrophysics - High Energy Astrophysical Phenomena, Solar and Stellar Astrophysics (astro-ph.SR)
Abstract: Pulsar winds interacting with sources of external pressure are well-established as efficient and prolific TeV accelerators in our Galaxy. Yet, enabled by observations from Fermi-LAT, a growing class of non-accreting pulsars in binaries has emerged and these are likely to become apparent as TeV emitters in the CTA era. This class consists of the black widows and redbacks, binaries in which a millisecond pulsar interacts with its low-mass companion. In such systems, an intrabinary shock can form as a site of particle acceleration and associated nonthermal emission. We motivate why these sources are particularly interesting for understanding pulsar winds. We also describe our new multizone code which models the X-ray and gamma-ray synchrotron and inverse Compton spectral components for select spider binaries, including diffusion, convection, and radiative energy losses in an axially symmetric, steady-state approach. This new multizone code simultaneously yields energy-dependent light curves and orbital-phase-resolved spectra. It also better constrains the multiplicity of electron/positron pairs that have been accelerated up to TeV energies and are necessary to power orbitally-modulated synchrotron emission components between the X-rays and MeV/GeV bands potentially observed in some systems. This affords a more robust prediction of the expected high-energy and VHE gamma-ray flux. Nearby MSPs with hot or flaring companions may be promising targets for CTA, and it is possible that spider binaries could contribute to the observed AMS-02 energetic positron excess., Comment: Presented at the 37th International Cosmic Ray Conference (ICRC 2021)
Published: 2021
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29. Modeling Very-High-Energy Emission from Pulsars

Author: Alice K. Harding, Constantinos Kalapotharakos, and Christo Venter
Subjects: Physics, Pulsar, law, Millisecond pulsar, Astrophysics::High Energy Astrophysical Phenomena, Synchrotron radiation, Astrophysics, MAGIC (telescope), Vela, Spectral line, Synchrotron, Fermi Gamma-ray Space Telescope, law.invention
Abstract: Ground-based Air-Cherenkov telescopes have detected pulsations at energies above 50 GeV from a growing number of {\sl Fermi} pulsars. These include the Crab, Vela, PSR~B1706-44 and Geminga pulsar, with the first two having pulsed detections above 1 TeV. In some cases, there appears to be very-high-energy (VHE) emission that is an extension of the {\sl Fermi} spectra to higher energies, while in other cases, additional higher-energy spectral components that require a separate emission mechanism may be present. We will present results of broadband spectral modeling using global magnetosphere fields and multiple emission mechanisms that include synchro-curvature (SC) and inverse Compton scattered (ICS) radiation from accelerated particles (primaries) and synchrotron self-Compton (SSC) emission from lower-energy pairs. Our models predict three distinct VHE components: SC from primaries whose high-energy tail can extend to 100 GeV, SSC from pairs that can extend to several TeV and ICS from primary particles accelerated in the current sheet, scattering pair synchrotron radiation, that appears beyond 10 TeV. Model spectra show a wide range of VHE flux, with detectable pair SSC and primary ICS components expected for Crab-like pulsars and some millisecond pulsars but only a primary ICS component for Vela. Our models suggest that H.E.S.S.-II and MAGIC have detected the high-energy tail of the primary SC component that produces the {\sl Fermi} spectrum in Vela, Geminga and PSR B1706$-$44. We argue that the ICS component peaking above 10 TeV from Vela has been seen by H.E.S.S. Detection of this emission component from the Crab and other pulsars is possible with HAWC and CTA, and directly measures the maximum particle energy in pulsars.
Published: 2021
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30. A NICER View of the Massive Pulsar PSR J0740+6620 Informed by Radio Timing and XMM-Newton Spectroscopy

Author: Keith C. Gendreau, Sebastien Guillot, Ismaël Cognard, Anna L. Watts, Zaven Arzoumanian, Anna V. Bilous, Ronald A. Remillard, Julia Deneva, Takashi Okajima, Matthew Kerr, James M. Lattimer, Michael Loewenstein, Chanda Prescod-Weinstein, Renee M. Ludlam, Aditya Parthasarathy, Lucas Guillemot, Sharon M. Morsink, Wynn C. G. Ho, Timothy T. Pennucci, Ingrid H. Stairs, Slavko Bogdanov, Paul S. Ray, Scott M. Ransom, Devarshi Choudhury, Emmanuel Fonseca, Michael T. Wolff, Alice K. Harding, H. Thankful Cromartie, Craig B. Markwardt, Thomas E. Riley, Institut de recherche en astrophysique et planétologie (IRAP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Centre National d'Études Spatiales [Toulouse] (CNES), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), and High Energy Astrophys. & Astropart. Phys (API, FNWI)
Subjects: Photon, [PHYS.NUCL]Physics [physics]/Nuclear Theory [nucl-th], Nuclear Theory, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, 01 natural sciences, Orbital inclination, Nuclear Theory (nucl-th), Pulsar, Millisecond pulsar, 0103 physical sciences, 010303 astronomy & astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Neutron Star Interior Composition Explorer, 010308 nuclear & particles physics, Astronomy and Astrophysics, Radius, Effective temperature, Astrophysics - Solar and Stellar Astrophysics, [SDU]Sciences of the Universe [physics], 13. Climate action, Space and Planetary Science, Astrophysics::Earth and Planetary Astrophysics, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Astrophysics - High Energy Astrophysical Phenomena, Likelihood function
Abstract: We report on Bayesian estimation of the radius, mass, and hot surface regions of the massive millisecond pulsar PSR J0740$+$6620, conditional on pulse-profile modeling of Neutron Star Interior Composition Explorer X-ray Timing Instrument (NICER XTI) event data. We condition on informative pulsar mass, distance, and orbital inclination priors derived from the joint NANOGrav and CHIME/Pulsar wideband radio timing measurements of arXiv:2104.00880. We use XMM European Photon Imaging Camera spectroscopic event data to inform our X-ray likelihood function. The prior support of the pulsar radius is truncated at 16 km to ensure coverage of current dense matter models. We assume conservative priors on instrument calibration uncertainty. We constrain the equatorial radius and mass of PSR J0740$+$6620 to be $12.39_{-0.98}^{+1.30}$ km and $2.072_{-0.066}^{+0.067}$ M$_{\odot}$ respectively, each reported as the posterior credible interval bounded by the 16% and 84% quantiles, conditional on surface hot regions that are non-overlapping spherical caps of fully-ionized hydrogen atmosphere with uniform effective temperature; a posteriori, the temperature is $\log_{10}(T$ [K]$)=5.99_{-0.06}^{+0.05}$ for each hot region. All software for the X-ray modeling framework is open-source and all data, model, and sample information is publicly available, including analysis notebooks and model modules in the Python language. Our marginal likelihood function of mass and equatorial radius is proportional to the marginal joint posterior density of those parameters (within the prior support) and can thus be computed from the posterior samples., Comment: 40 pages, 16 figures (3 of which are figure sets), 1 animation, 2 tables. ApJL accepted version. Software: https://github.com/ThomasEdwardRiley/xpsi. Zenodo: https://doi.org/10.5281/zenodo.4697624. (v1 = submitted version; v2 = accepted version; v3 = metadata edits)
Published: 2021
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31. Enhanced x-ray emission coinciding with giant radio pulses from the Crab Pulsar

Author: Keith C. Gendreau, Alice K. Harding, Slavko Bogdanov, Yoshinori Yonekura, Hiroaki Misawa, Takahiko Aoki, Sebastien Guillot, Zaven Arzoumanian, Tomoaki Oyama, Steve Kenyon, Kazuhiro Takefuji, Zorawar Wadiasingh, Tolga Guver, R. S. Foster, Mamoru Sekido, Katsuaki Asano, Christian Malacaria, Shuta J. Tanaka, Yang Soong, Craig B. Markwardt, Takashi Okajima, Shota Kisaka, Natalia Lewandowska, Chin-Ping Hu, Fuminori Tsuchiya, Paul S. Ray, Hiroshi Takeuchi, Teruaki Enoto, Toshio Terasawa, Shinpei Shibata, Osamu Kameya, Munetoshi Tokumaru, Gaurava K. Jaisawal, Mareki Honma, Wynn C. G. Ho, Yasuhiro Murata, Walid A. Majid, Institut de recherche en astrophysique et planétologie (IRAP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), and Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Multidisciplinary, Crab Pulsar, Astrophysics::High Energy Astrophysical Phenomena, X-ray, Astrophysics::Instrumentation and Methods for Astrophysics, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Wavelength, Microsecond, Pulsar, 0103 physical sciences, Optical emission spectroscopy, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], 010306 general physics, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics
Abstract: Giant radio pulses (GRPs) are sporadic bursts emitted by some pulsars, lasting a few microseconds. GRPs are hundreds to thousands of times brighter than regular pulses from these sources. The only GRP-associated emission outside radio wavelengths is from the Crab Pulsar, where optical emission is enhanced by a few percent during GRPs. We observed the Crab Pulsar simultaneously at X-ray and radio wavelengths, finding enhancement of the X-ray emission by $3.8\pm0.7\%$ (a 5.4$\sigma$ detection) coinciding with GRPs. This implies that the total emitted energy from GRPs is tens to hundreds of times higher than previously known. We discuss the implications for the pulsar emission mechanism and extragalactic fast radio bursts., Comment: 63 pages, 23 figures, 7 Tables. Published in Science
Published: 2021
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32. Einstein@Home discovery of the gamma-ray millisecond pulsar PSR J2039–5617 confirms its predicted redback nature

Author: Mark Kennedy, O. Behnke, V. S. Dhillon, C. Choquet, D. Mata Sánchez, Jingwen Wu, Heinz-Bernd Eggenstein, T. R. Marsh, Alessandro Corongiu, Zorawar Wadiasingh, Guillaume Voisin, Rene P. Breton, Lucas Guillemot, L. Nieder, C. Aulbert, Roberto Mignani, J. Stringer, C. J. Clark, Alice K. Harding, H. Fehrmann, Benjamin William Allen, B. Machenschalk, ITA, USA, GBR, FRA, DEU, ESP, POL, Laboratoire Univers et Théories (LUTH (UMR_8102)), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), and Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)
Subjects: gamma-rays: stars, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, pulsars: individual (PSR J2039–5617), 01 natural sciences, stars: neutron, Pulsar, Millisecond pulsar, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, 010303 astronomy & astrophysics, QC, QB, Physics, Orbital elements, High Energy Astrophysical Phenomena (astro-ph.HE), binaries: close, 010308 nuclear & particles physics, Compton scattering, Astronomy and Astrophysics, Orbital period, Light curve, Space and Planetary Science, Quadrupole, Astrophysics::Earth and Planetary Astrophysics, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Astrophysics - High Energy Astrophysical Phenomena, Fermi Gamma-ray Space Telescope
Abstract: The Fermi Large Area Telescope gamma-ray source 3FGL J2039.6$-$5618 contains a periodic optical and X-ray source that was predicted to be a "redback" millisecond pulsar (MSP) binary system. However, the conclusive identification required the detection of pulsations from the putative MSP. To better constrain the orbital parameters for a directed search for gamma-ray pulsations, we obtained new optical light curves in 2017 and 2018, which revealed long-term variability from the companion star. The resulting orbital parameter constraints were used to perform a targeted gamma-ray pulsation search using the Einstein@Home distributed volunteer computing system. This search discovered pulsations with a period of 2.65 ms, confirming the source as a binary MSP now known as PSR J2039$-$5617. Optical light curve modelling is complicated, and likely biased, by asymmetric heating on the companion star and long-term variability, but we find an inclination $i > 60��$, for a low pulsar mass between $1.1 M_{\odot} < M_{\rm psr} < 1.6 M_{\odot}$ and a companion mass of 0.15--0.22 $M_{\odot}$, confirming the redback classification. Timing the gamma-ray pulsations also revealed significant variability in the orbital period, which we find to be consistent with quadrupole moment variations in the companion star, suggestive of convective activity. We also find that the pulsed flux is modulated at the orbital period, potentially due to inverse Compton scattering between high-energy leptons in the pulsar wind and the companion star's optical photon field., 21 pages, 11 figures, published in MNRAS
Published: 2021
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33. Constraining the Neutron Star Mass-Radius Relation and Dense Matter Equation of State with NICER. III. Model Description and Verification of Parameter Estimation Codes

Author: Alexander J. Dittmann, Anna L. Watts, M. Coleman Miller, Frederick K. Lamb, Keith C. Gendreau, Sharon M. Morsink, Simin Mahmoodifar, Sebastien Guillot, Craig B. Markwardt, Michael T. Wolff, Zorawar Wadiasingh, Alice K. Harding, Devarshi Choudhury, Wynn C. G. Ho, Slavko Bogdanov, Paul S. Ray, Zaven Arzoumanian, Thomas E. Riley, Tod E. Strohmayer, Institut de recherche en astrophysique et planétologie (IRAP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), and High Energy Astrophys. & Astropart. Phys (API, FNWI)
Subjects: Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Equation of state, Neutron Star Interior Composition Explorer, 010504 meteorology & atmospheric sciences, FOS: Physical sciences, Astronomy and Astrophysics, Radius, 16. Peace & justice, 01 natural sciences, Pulse (physics), Computational physics, Stars, Neutron star, Pulsar, Space and Planetary Science, Millisecond pulsar, 0103 physical sciences, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], 010303 astronomy & astrophysics, 0105 earth and related environmental sciences
Abstract: We describe the X-ray pulse profile models we use, and how we use them, to analyze Neutron Star Interior Composition Explorer (NICER) observations of rotation-powered millisecond pulsars to obtain information about the mass-radius relation of neutron stars and the equation of state of the dense matter in their cores. Here we detail our modeling of the observed profile of PSR J0030+0451 that we analyzed in Miller et al. (2019) and Riley et al. (2019) and describe a cross-verification of computations of the pulse profiles of a star with R/M 3, in case stars this compact need to be considered in future analyses. We also present our early cross-verification efforts of the parameter estimation procedures used by Miller et al. (2019) and Riley et al. (2019) by analyzing two distinct synthetic data sets. Both codes yielded credible regions in the mass-radius plane that are statistically consistent with one another and both gave posterior distributions for model parameter values consistent with the values that were used to generate the data. We also summarize the additional tests of the parameter estimation procedure of Miller et al. (2019) that used synthetic pulse profiles and the NICER pulse profile of PSR J0030+0451. We then illustrate how the precision of mass and radius estimates depends on the pulsar's spin rate and the size of its hot spot by analyzing four different synthetic pulse profiles. Finally, we assess possible sources of systematic error in these estimates made using this technique, some of which may warrant further investigation., Comment: 26 pages, 5 figures; submitted for publication in the Astrophysical Journal Letters
Published: 2021
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34. The Mysterious Magnetospheres of Magnetars (INVITED)

Author: Zorawar Wadiasingh, Kun Hu, Alice K. Harding, Peter L. Gonthier, and Matthew G. Baring
Subjects: Physics, Neutron star, Photon, Stellar mass, Astrophysics::High Energy Astrophysical Phenomena, Milky Way, Dissipative system, Astrophysics, Polarization (waves), Magnetar, Astrophysics::Galaxy Astrophysics
Abstract: Magnetars are the most powerful compact objects in the stellar mass range observed in the Milky Way. Periodicity seen in magnetar persistent emission and also in the temporal tails of powerful giant flares detected from three soft gamma repeaters, and distinctive "spin-down" lengthening of the period have driven the paradigm that strongly-magnetized neutron stars constitute these fascinating sources. The steady X-ray emission includes both thermal atmospheric components and magnetospheric contributions that masquerade as hard X-ray "tails." This paper addresses observational and theoretical elements pertinent to the steady hard X-ray emission of magnetars, focusing on dissipative processes in their magnetospheres, and elements of Comptonization and polarization. It also discusses the action and possible signatures of exotic QED mechanisms like photon splitting and magnetic pair creation, and the quest for their observational vindication.
Published: 2020
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35. The NICER View of the 2020 Burst Storm and Persistent Emission of SGR 1935+2154

Author: Teruaki Enoto, Matthew G. Baring, Zorawar Wadiasingh, Chryssa Kouveliotou, Sebastien Guillot, Beste Begiçarslan, George Younes, Alice K. Harding, Alexander J. van der Horst, Chin-Ping Hu, Ersin Gogus, Walid A. Majid, C. Malacaria, Lin Lin, Tolga Guver, Institut de recherche en astrophysique et planétologie (IRAP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), and Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Physics, 010504 meteorology & atmospheric sciences, Fast radio burst, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Magnetar, 01 natural sciences, Spectral line, Pulse (physics), Neutron star, Orders of magnitude (time), 13. Climate action, Space and Planetary Science, 0103 physical sciences, Log-normal distribution, Black-body radiation, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Astrophysics - High Energy Astrophysical Phenomena, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences
Abstract: We report on NICER observations of the Magnetar SGR~1935+2154, covering its 2020 burst storm and long-term persistent emission evolution up to $\sim90$ days post outburst. During the first 1120~seconds taken on April 28 00:40:58 UTC we detect over 217 bursts, corresponding to a burst rate of $>0.2$ bursts s$^{-1}$. Three hours later the rate is at 0.008 bursts s$^{-1}$, remaining at a comparatively low level thereafter. The $T_{90}$ burst duration distribution peaks at 840~ms; the distribution of waiting times to the next burst is fit with a log-normal with an average of 2.1 s. The 1-10 keV burst spectra are well fit by a blackbody, with an average temperature and area of $kT=1.7$ keV and $R^2=53$ km$^2$. The differential burst fluence distribution over $\sim3$ orders of magnitude is well modeled with a power-law form $dN/dF\propto F^{-1.5\pm0.1}$. The source persistent emission pulse profile is double-peaked hours after the burst storm. We find that the bursts peak arrival times follow a uniform distribution in pulse phase, though the fast radio burst associated with the source aligns in phase with the brighter peak. We measure the source spin-down from heavy-cadence observations covering days 21 to 39 post-outburst, $\dot��=-3.72(3)\times10^{-12}$ Hz s$^{-1}$; a factor 2.7 larger than the value measured after the 2014 outburst. Finally, the persistent emission flux and blackbody temperature decrease rapidly in the early stages of the outburst, reaching quiescence 40 days later, while the size of the emitting area remains unchanged., Accepted for publication in the Astrophysical Journal Letters
Published: 2020
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36. Erratum: 'Searches for Gravitational Waves from Known Pulsars at Two Harmonics in 2015–2017 LIGO Data' (2019, ApJ, 879, 10)

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Howell, Ej, Hoy, Cg, Huang, Y, Hubner, Mt, Huerta, Ea, Huet, D, Hughey, B, Hui, V, Husa, S, Huttner, Sh, Huynh-Dinh, T, Idzkowski, B, Iess, A, Inchauspe, H, Ingram, C, Inta, R, Intini, G, Irwin, B, Isa, Hn, Isac, Jm, Isi, M, Iyer, Br, Jacqmin, T, Jadhav, Sj, Jani, K, Janthalur, Nn, Jaranowski, P, Jariwala, D, Jenkins, Ac, Jiang, J, Johnson, D, Jones, Aw, Jones, Di, Jones, Jd, Jones, R, Jonker, Rjg, Ju, L, Junker, J, Kalaghatgi, Cv, Kalogera, V, Kamai, B, Kandhasamy, S, Kang, G, Kanner, Jb, Kapadia, Sj, Karki, S, Kashyap, R, Kasprzack, M, Katsanevas, S, Katsavounidis, E, Katzman, W, Kaufer, S, Kawabe, K, Keerthana, Nv, Kefelian, F, Keitel, D, Kennedy, R, Key, J, Khalili, Fy, Khan, I, Khan, S, Khazanov, Ea, Khetan, N, Khursheed, M, Kijbunchoo, N, Kim, C, Kim, Jc, Kim, K, Kim, W, Kim, Ym, Kimball, C, King, Pj, Kinley-Hanlon, M, Kirchhoff, R, Kissel, J, Kleybolte, L, Klika, Jh, Klimenko, S, Knowles, Td, Koch, P, Koehlenbeck, Sm, Koekoek, G, Koley, S, Kondrashov, V, Kontos, A, Koper, N, Korobko, M, Korth, Wz, Kovalam, M, Kozak, Db, Kramer, C, Kringel, V, Krishnendu, N, Krolak, A, Krupinski, N, Kuehn, G, Kumar, A, Kumar, P, Kumar, R, Kuo, L, Kutynia, A, Kwang, S, Lackey, Bd, Laghi, D, Lai, Kh, Lam, Tl, Landry, M, Lane, Bb, Lang, Rn, Lange, J, Lantz, B, Lanza, Rk, Lartaux-Vollard, A, Lasky, Pd, Laxen, M, Lazzarini, A, Lazzaro, C, Leaci, P, Leavey, S, Lecoeuche, K, Lee, Ch, Lee, Hk, Lee, Hm, Lee, Hw, Lee, J, Lee, K, Lehmann, J, Lenon, Ak, Leroy, N, Letendre, N, Levin, Y, Li, A, Li, J, Li, Kjl, Li, Tgf, Li, X, Lin, F, Linde, F, Linker, Sd, Littenberg, Tb, Liu, J, Liu, X, Llorens-Monteagudo, M, Lo, Rkl, London, Lt, Longo, A, Lorenzini, M, Loriette, V, Lormand, M, Losurdo, G, Lough, Jd, Lousto, Co, Lovelace, G, Lower, Me, Luck, H, Lumaca, D, Lundgren, Ap, Lynch, R, Ma, Y, Macas, R, Macfoy, S, Macinnis, M, Macleod, Dm, Macquet, A, Hernandez, Im, Magana-Sandoval, F, Magee, Rm, Majorana, E, Maksimovic, I, Malik, A, Man, N, Mandic, V, Mangano, V, Mansell, Gl, Manske, M, Mantovani, M, Mapelli, M, Marchesoni, F, Marion, F, Marka, S, Marka, Z, Markakis, C, Markosyan, A, Markowitz, A, Maros, E, Marquina, A, Marsat, S, Martelli, F, Martin, Iw, Martin, Rm, Martinez, V, Martynov, Dv, Masalehdan, H, Mason, K, Massera, E, Masserot, A, Massinger, Tj, Masso-Reid, M, Mastrogiovanni, S, Matas, A, Matichard, F, Matone, L, Mavalvala, N, Mccann, Jj, Mccarthy, R, Mcclelland, De, Mccormick, S, Mcculler, L, Mcguire, Sc, Mcisaac, C, Mciver, J, Mcmanus, Dj, Mcrae, T, Mcwilliams, St, Meacher, D, Meadors, Gd, Mehmet, M, Mehta, Ak, Meidam, J, Villa, Em, Melatos, A, Mendell, G, Mercer, Ra, Mereni, L, Merfeld, K, Merilh, El, Merzougui, M, Meshkov, S, Messenger, C, Messick, C, Messina, F, Metzdorff, R, Meyers, Pm, Meylahn, F, Miani, A, Miao, H, Michel, C, Middleton, H, Milano, L, Miller, L, Millhouse, M, Mills, Jc, Milovich-Goff, Mc, Minazzoli, O, Minenkov, Y, Mishkin, A, Mishra, C, Mistry, T, Mitra, S, Mitrofanov, Vp, Mitselmakher, G, Mittleman, R, Mo, G, Moffa, D, Mogushi, K, Mohapatra, Srp, Molina-Ruiz, M, Mondin, M, Montani, M, Moore, Cj, Moraru, D, Morawski, F, Moreno, G, Morisaki, S, Mours, B, Mow-Lowry, M, Muciaccia, F, Mukherjee, A, Mukherjee, D, Mukherjee, S, Mukund, N, Mullavey, A, Munch, J, Muniz, Ea, Muratore, M, Murray, Pg, Nagar, A, Nardecchia, I, Naticchioni, L, Nayak, Rk, Neil, Bf, Neilson, J, Nelemans, G, Nelson, Tjn, Nery, M, Neunzert, A, Nevin, L, Ng, Ky, Ng, S, Nguyen, C, Nguyen, P, Nichols, D, Nichols, Sa, Nissanke, S, Nocera, F, North, C, Nuttall, Lk, Obergaulinger, M, Oberling, J, O'Brien, Bd, Oganesyan, G, Ogin, Gh, Oh, Jj, Oh, Sh, Ohme, F, Ohta, H, Okada, Ma, Oliver, M, Oppermann, P, Oram, Rj, O'Reilly, B, Ormiston, Rg, Ortega, Lf, O'Shaughnessy, R, Ossokine, S, Ottaway, Dj, Overmier, H, Owen, Bj, Pace, Ae, Pagano, G, Page, Ma, Pagliaroli, G, Pai, A, Pai, Sa, Palamos, Jr, Palashov, O, Palomba, C, Pan, H, Panda, Pk, Pang, Pth, Pankow, C, Pannarale, F, Pant, Bc, Paoletti, F, Paoli, A, Parida, A, Parker, W, Pascucci, D, Pasqualetti, A, Passaquieti, R, Passuello, D, Patil, M, Patricelli, B, Payne, E, Pearlstone, Bl, Pechsiri, Tc, Pedersen, Aj, Pedraza, M, Pedurand, R, Pele, A, Penn, S, Perego, A, Perez, Cj, Perigois, C, Perreca, A, Petermann, J, Pfeiffer, Hp, Phelps, M, Phukon, K, Piccinni, Oj, Pichot, M, Piergiovanni, F, Pierro, V, Pillant, G, Pinard, L, Pinto, Im, Pirello, M, Pitkin, M, Plastino, W, Pong, Dyt, Ponrathnam, S, Popolizio, P, Porter, Ek, Powell, J, Prajapati, Ak, Prasad, J, Prasai, K, Prasanna, R, Pratten, G, Prestegard, T, Principe, M, Prodi, Ga, Prokhorov, L, Punturo, M, Puppo, P, Purrer, M, Qi, H, Quetschke, V, Quinonez, Pj, Raab, Fj, Raaijmakers, G, Radkins, H, Radulesco, N, Raffai, P, Raja, S, Rajan, C, Rajbhandari, B, Rakhmanov, M, Ramirez, Ke, Ramos-Buades, A, Rana, J, Rao, K, Rapagnani, P, Raymond, V, Razzano, M, Read, J, Regimbau, T, Rei, L, Reid, S, Reitze, Dh, Rettegno, P, Ricci, F, Richardson, Cj, Richardson, Jw, Ricker, Pm, Riemenschneider, G, Riles, K, Rizzo, M, Robertson, Na, Robinet, F, Rocchi, A, Rolland, L, Rollins, Jg, Roma, Vj, Romanelli, M, Romano, R, Romel, Cl, Romie, Jh, Rose, Ca, Rose, D, Rose, K, Rosinska, D, Rosofsky, Sg, Ross, Mp, Rowan, S, Rudiger, A, Ruggi, P, Rutins, G, Ryan, K, Sachdev, S, Sadecki, T, Sakellariadou, M, Salafia, O, Salconi, L, Saleem, M, Samajdar, A, Sammut, L, Sanchez, Ej, Sanchez, Le, Sanchis-Gual, N, Sanders, Jr, Santiago, Ka, Santos, E, Sarin, N, Sassolas, B, Saulson, Pr, Sauter, O, Savage, Rl, Schale, P, Scheel, M, Scheuer, J, Schmidt, P, Schnabel, R, Schofield, Rm, Schonbeck, A, Schreiber, E, Schulte, Bw, Schutz, Bf, Scott, J, Scott, Sm, Seidel, E, Sellers, D, Sengupta, A, Sennett, N, Sentenac, D, Sequino, V, Sergeev, A, Setyawati, Y, Shaddock, Da, Shaffer, T, Shahriar, M, Shaner, Mb, Sharma, A, Sharma, P, Shawhan, P, Shen, H, Shink, R, Shoemaker, Dh, Shoemaker, Dm, Shukla, K, Shyamsundar, S, Siellez, K, Sieniawska, M, Sigg, D, Singer, Lp, Singh, D, Singh, N, Singhal, A, Sintes, Am, Sitmukhambetov, S, Skliris, V, Slagmolen, Bjj, Slaven-Blair, Tj, Smith, Jr, Smith, Rje, Somala, S, Son, Ej, Soni, S, Sorazu, B, Sorrentino, F, Souradeep, T, Sowell, E, Spencer, Ap, Spera, M, Srivastava, Ak, Srivastava, V, Staats, K, Stachie, C, Standke, M, Steer, Da, Steinke, M, Steinlechner, J, Steinlechner, S, Steinmeyer, D, Stevenson, Sp, Stocks, D, Stone, R, Stops, Dj, Strain, Ka, Stratta, G, Strigin, Se, Strunk, A, Sturani, R, Stuver, Al, Sudhir, V, Summerscales, Tz, Sun, L, Sunil, S, Sur, A, Suresh, J, Sutton, Pj, Swinkels, Bl, Szczepanczyk, Mj, Tacca, M, Tait, Sc, Talbot, C, Tanner, Db, Tao, D, Tapai, M, Tapia, A, Tasson, Jd, Taylor, R, Tenorio, R, Terkowski, L, Thomas, M, Thomas, P, Thondapu, Sr, Thorne, Ka, Thrane, E, Tiwari, S, Tiwari, V, Toland, K, Tonelli, M, Tornasi, Z, Torres-Forne, A, Torrie, Ci, Toyra, D, Travasso, F, Traylor, G, Tringali, Mc, Tripathee, A, Trovato, A, Trozzo, L, Tsang, Kw, Tse, M, Tso, R, Tsukada, L, Tsuna, D, Tsutsui, T, Tuyenbayev, D, Ueno, K, Ugolini, D, Unnikrishnan, C, Urban, Al, Usman, Sa, Vahlbruch, H, Vajente, G, Valdes, G, Valentini, M, van Bakel, N, van Beuzekom, M, van den Brand, Jfj, Van Den Broeck, C, Vander-Hyde, Dc, van der Schaaf, L, Vanheijningen, Jv, van Veggel, Aa, Vardaro, M, Varma, V, Vass, S, Vasuth, M, Vecchio, A, Vedovato, G, Veitch, J, Veitch, Pj, Venkateswara, K, Venugopalan, G, Verkindt, D, Vetrano, F, Vicere, A, Viets, Ad, Vinciguerra, S, Vine, Dj, Vinet, Jy, Vitale, S, Vo, T, Vocca, H, Vorvick, C, Vyatchanin, Sp, Wade, Ar, Wade, Le, Wade, M, Walet, R, Walker, M, Wallace, L, Walsh, S, Wang, H, Wang, Jz, Wang, S, Wang, Wh, Wang, Yf, Ward, Rl, Warden, Za, Warner, J, Was, M, Watchi, J, Weaver, B, Wei, Lw, Weinert, M, Weinstein, Aj, Weiss, R, Wellmann, F, Wen, L, Wessel, K, Wessels, P, Westhouse, Jw, Wette, K, Whelan, Jt, Whiting, Bf, Whittle, C, Wilken, Dm, Williams, D, Williamson, Ar, Willis, Jl, Willke, B, Winkler, W, Wipf, Cc, Wittel, H, Woan, G, Woehler, J, Wofford, Jk, Wright, Jl, Wu, D, Wysocki, Dm, Xiao, S, Xu, R, Yamamoto, H, Yancey, Cc, Yang, L, Yang, Y, Yang, Z, Yap, Mj, Yazback, M, Yeeles, Dw, Yu, H, Yu, Hc, Yuen, Shr, Zadrozny, Ak, Zadrozny, A, Zanolin, M, Zelenova, T, Zendri, Jp, Zevin, M, Zhang, J, Zhang, L, Zhang, T, Zhao, C, Zhao, G, Zhou, M, Zhou, Z, Zhu, Xj, Zimmerman, Ab, Zucker, Me, Zweizig, J, (Astro)-Particles Physics, Arzoumanian, Z, Bogdanov, S, Cognard, I, Corongiu, A, Enoto, T, Freire, P, Gendreau, Kc, Guillemot, L, Harding, Ak, Jankowski, F, Keith, Mj, Kerr, M, Lyne, A, Palfreyman, J, Possenti, A, Ridolfi, A, Stappers, B, Theureau, G, Weltervrede, P, Université de Lyon-Université de Lyon-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon, Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris-Sud - Paris 11 (UP11), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7)
Subjects: Known Pulsars, 010504 meteorology & atmospheric sciences, Astronomy, Astrophysics, Table (information), Vela, gravitational waves, pulsars, 01 natural sciences, Pulsar, 0103 physical sciences, Limit (mathematics), 010303 astronomy & astrophysics, gravitational wave, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, Physics, [PHYS]Physics [physics], Gravitational wave, Two Harmonics, Astronomy and Astrophysics, Gravitational Waves, Known Pulsars, Two Harmonics, Erratum, LIGO, Amplitude, Space and Planetary Science, Erratum, Glitch (astronomy), [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract: Two analysis errors have been identified that affect the results for a handful of the high-value pulsars given in Table 1 of Abbott et al. (2019). One affects the Bayesian analysis for the five pulsars that glitched during the analysis period, and the other affects the 5n-vector analysis for J0711-6830. Updated results after correcting the errors are shown in Table 1, which now supersedes the results given for those pulsars in Table 1 of Abbott et al. (2019). Updated versions of figures can be seen in Figures 1-4. Bayesian analysis.-For the glitching pulsars, the signal phase evolution caused by the glitch was wrongly applied twice and was therefore not consistent with our expected model of the pulsar phase. This error did not affect the F/G-statistic or 5n-vector analysis. Analyses of the five pulsars PSR J0205+6449, PSR J0534+2200, PSR J0835-4510, PSR J1028-5819, and PSR J1718-3825 have been repeated after correcting for the error. There are small quantitative differences in the results, but the changes do not affect the main conclusions of the paper. The largest differences are for PSR J0835-4510 (the Vela pulsar), for which the updated upper limits from the Bayesian method are found to be between 1.1 and 2 times larger than those obtained when the error was present. This appears primarily to be due to the error leading to the decohering of a strong spectral line in the LIGO Livingston detector and thus lowering the amplitude limit. 5n-vector analysis.-An error was also identified in the settings of the 5n-vector analysis, which affected the upper limit computation at the rotation frequency for C21 95% of J0711-6830. Specifically, we found an incorrect choice for the range of amplitudes used to inject simulated signals in the O2 data. The updated upper limit is about 2.5 times worse than that obtained when the error was present. This error did not affect the Bayesian or F/G-statistic results. (Table Presented) (Figure Presented).
Published: 2020
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37. Plasma Fluctuations Could Generate Bright Pulsar Emission

Author: Alice K. Harding
Subjects: Physics, Pulsar, Astrophysics, Plasma
Published: 2020
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38. VTXO: The Virtual Telescope for X-ray Observations

Author: Kyle Rankin, Asal Nasari, Chris R. Schrader, Alice K. Harding, Daniel T. Smith, Lloyd Purves, Krishna Kota, Michael F. Corcoran, Laura E. Boucheron, Neerav Shah, Philip C. Calhoun, Steven Stochaj, John F. Krizmanic, Cassandra Webster, and Hyeongjun Park
Subjects: Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Nebula, Crab Pulsar, Astronomy, FOS: Physical sciences, X-ray telescope, law.invention, Telescope, Supersynchronous orbit, law, Orbit (dynamics), Angular resolution, Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Instrumentation and Methods for Astrophysics (astro-ph.IM), Heliosphere
Abstract: The Virtual Telescope for X-ray Observations (VTXO) will use lightweight Phase Fresnel Lenses (PFLs) in a virtual X-ray telescope with $\sim$1 km focal length and with $\sim$50 milli-arcsecond angular resolution. VTXO is formed by using precision formation flying of two SmallSats: a smaller OpticsSat that houses the PFLs and navigation beacons while a larger DetectorSat contains an X-ray camera, a precision start tracker, and the propulsion for the formation flying. The baseline flight dynamics uses a highly elliptical supersynchronous orbit allow the formation to hold in an inertial frame around the 90,000 km apogee for 10 hours of the 32.5 hour orbit with nearly a year mission lifetime. VTXO's fine angular resolution enables measuring the environments close to the central engines of bright compact X-ray sources. This X-ray imaging capability allows for the study of the effects of dust scattering near to the central objects such as Cyg X-3 and GX 5-1, for the search for jet structure near to the compact object in X-ray novae such as Cyg X-1 and GRS 1915+105, and for the search for structure in the termination shock of in the Crab pulsar wind nebula. The VTXO SmallSat and instrument designs, mission parameters, and science performance are described. VTXO development was supported as one of the selected 2018 NASA Astrophysics SmallSat Study (AS$^3$) missions., Comment: 6 pages, 7 figures, corrected version, Proceedings Volume 11444, Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray; 114447V (2020). arXiv admin note: text overlap with arXiv:2006.12174
Published: 2020
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39. A NICER View of Spectral and Profile Evolution for Three X-ray Emitting Millisecond Pulsars

Author: Zaven Arzoumanian, Lauren Lugo, Paul S. Ray, Slavko Bogdanov, Julia Deneva, Scott M. Ransom, Matthew Kerr, Elizabeth Spano, Keith C. Gendreau, Christo Venter, Andrea N. Lommen, Sebastien Guillot, Kent S. Wood, Natalia Lewandowska, D. M. Rowan, Craig B. Markwardt, Alice K. Harding, Renee M. Ludlam, Zaynab Ghazi, Teruaki Enoto, Institut de recherche en astrophysique et planétologie (IRAP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Centre National d'Études Spatiales [Toulouse] (CNES), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS), and 12006653 - Venter, Christo
Subjects: 010504 meteorology & atmospheric sciences, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Context (language use), Astrophysics, 7. Clean energy, 01 natural sciences, Neutron stars, X-ray astronomy, Pulsar, Millisecond pulsar, 0103 physical sciences, Emission spectrum, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Millisecond pulsars, Neutron Star Interior Composition Explorer, Astronomy and Astrophysics, Pulse (physics), Neutron star, 13. Climate action, Space and Planetary Science, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract: We present two years of Neutron star Interior Composition Explorer (NICER) X-ray observations of three energetic rotation-powered millisecond pulsars (MSPs): PSRs B1937+21, B1821-24, and J0218+4232. We fit Gaussians and Lorentzians to the pulse profiles for different energy sub-bands of the soft X-ray regime to measure the energy dependence of pulse separation and width. We find that the separation between pulse components of PSR J0218+4232 decreases with increasing energy at $\gt 3\sigma$ confidence. The 95% upper limit on pulse separation evolution for PSRs B1937+21 and B1821-24 is less than 2 milliperiods per keV. Our phase-resolved spectral results provide updated constraints on the non-thermal X-ray emission of these three pulsars. The photon indices of the modeled X-ray emission spectra for each pulse component of PSR B1937+21 are inconsistent with each other at the 90% confidence level, suggesting different emission origins for each pulse. We find that the PSR B1821-24 and PSR J0218+4232 emission spectra are invariant with phase at the 90% confidence level. We describe the implications of our profile and spectral results in the context of equatorial current sheet emission models for these three MSPs with non-thermal, magnetospheric X-ray emission., Comment: 16 pages, 13 figures, accepted for publication in ApJ
Published: 2020
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40. Exploiting morphological data from Pulsar Wind Nebulae via a spatiotemporal leptonic transport code

Author: Christo Venter, A. S. Seyffert, Alice K. Harding, C. van Rensburg, 21106266 - Van Rensburg, Carlo, 12006653 - Venter, Christo, and 20126999 - Seyffert, Albertus Stefanus
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Astroparticle physics, Physics, general [Gamma-rays], non-thermal [Radiation mechanisms], numerical [Methods], Astrophysics::High Energy Astrophysical Phenomena, supernova remnants [ISM], FOS: Physical sciences, Astronomy and Astrophysics, Radius, Astrophysics, law.invention, Telescope, Pulsar, Space and Planetary Science, law, Test statistic, Spectral energy distribution, Surface brightness, Astrophysics - High Energy Astrophysical Phenomena, Cherenkov radiation
Abstract: The next era of ground-based Cherenkov telescope development will see a great increase in both quantity and quality of $\gamma$-ray morphological data. This initiated the development of a spatio-temporal leptonic transport code to model pulsar wind nebulae. We present results from this code that predicts the evolution of the leptonic particle spectrum and radiation at different radii in a spherically-symmetric source. We simultaneously fit the overall broadband spectral energy distribution, the surface brightness profile and the X-ray photon index vs.\ radius for PWN 3C~58, PWN G21.5$-$0.9 and PWN G0.9+0.1. Such concurrent fitting of disparate data sets is non-trivial and we thus investigate the utility of different goodness-of-fit statistics, specifically the traditional $\chi^2$ test statistic and a newly developed scaled-flux-normalised test statistic to obtain best-fit parameters. We find reasonable fits to the spatial and spectral data of all three sources, but note some remaining degeneracies that will have to be broken by future observations., Comment: 13 Pages, 13 Figures. 4 Tables
Published: 2020

41. A NICER View of PSR J0030+0451: Evidence for a Global-scale Multipolar Magnetic Field

Author: Alice K. Harding, Slavko Bogdanov, Deepto Chakrabarty, Zaven Arzoumanian, Paul S. Ray, Thomas E. Riley, Anna V. Bilous, Anna L. Watts, Wynn C. G. Ho, Keith C. Gendreau, Sebastien Guillot, High Energy Astrophys. & Astropart. Phys (API, FNWI), Institut de recherche en astrophysique et planétologie (IRAP), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS), Centre National d'Études Spatiales [Toulouse] (CNES), Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), and Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Neutron Star Interior Composition Explorer, 010504 meteorology & atmospheric sciences, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Antipodal point, Magnetosphere, Astronomy and Astrophysics, Astrophysics, 16. Peace & justice, 01 natural sciences, Magnetic field, Neutron star, Dipole, Astrophysics - Solar and Stellar Astrophysics, Pulsar, Space and Planetary Science, Millisecond pulsar, 0103 physical sciences, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], 010303 astronomy & astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), 0105 earth and related environmental sciences
Abstract: Recent modeling of NICER observations of thermal X-ray pulsations from the surface of the isolated millisecond pulsar PSR J0030+0451 suggests that the hot emitting regions on the pulsar's surface are far from antipodal, which is at odds with the classical assumption that the magnetic field in the pulsar magnetosphere is predominantly that of a centered dipole. Here, we review these results and examine previous attempts to constrain the magnetospheric configuration of PSR J0030+0451. To the best of our knowledge, there is in fact no direct observational evidence that PSR J0030+0451's magnetic field is a centered dipole. Developing models of physically motivated, non-canonical magnetic field configurations and the currents that they can support poses a challenging task. However, such models may have profound implications for many aspects of pulsar research, including pulsar braking, estimates of birth velocities, and interpretations of multi-wavelength magnetospheric emission., Comment: Appears in ApJ Letters Focus Issue on NICER Constraints on the Dense Matter Equation of State
Published: 2019
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42. Hard Spectral Tails in Magnetars

Author: Matthew G. Baring, Peter L. Gonthier, Zorawar Wadiasingh, and Alice K. Harding
Subjects: Physics, Space and Planetary Science, Astrophysics::High Energy Astrophysical Phenomena, Astronomy and Astrophysics, Astrophysics, Magnetar
Abstract: Pulsed non-thermal quiescent emission between 10 keV and around 150 keV has been observed in ~10 magnetars. For inner magnetospheric models of such hard X-ray signals, resonant Compton upscattering of soft thermal photons from the neutron star surface is the most efficient radiative process. We present angle-dependent hard X-ray upscattering model spectra for uncooled monoenergetic relativistic electrons. The spectral cut-off energies are critically dependent on the observer viewing angles and electron Lorentz factor. We find that electrons with energies less than around 15 MeV will emit most of their radiation below 250 keV, consistent with the observed turnovers in magnetar hard X-ray tails. Moreover, electrons of higher energy still emit most of the radiation below around 1 MeV, except for quasi-equatorial emission locales for select pulses phases. Our spectral computations use new state-of-the-art, spin-dependent formalism for the QED Compton scattering cross section in strong magnetic fields.
Published: 2017
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43. Modelling the polarisation signatures detected from the first white dwarf pulsar AR Sco

Author: Zorawar Wadiasingh, Louis du Plessis, Christo Venter, Alice K. Harding, Pieter Meintjes, S. Chandra, 31125417 - Chandra, Sunil, 26594080 - Wadiasingh, Zorawar, 12006653 - Venter, Christo, and 25936328 - Du Plessis, Louis
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Magnetic dip, White dwarf, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Orbital period, Position angle, Pulsar, Phase angle (astronomy), Polar, Astrophysics::Solar and Stellar Astrophysics, Binary system, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics::Galaxy Astrophysics
Abstract: Marsh et al. detected radio and optical pulsations from the binary system AR Scorpii (AR Sco). This system, with an orbital period of 3.56 h, is composed of a cool, low-mass star and a white dwarf with a spin period of 1.95 min. Optical observations by Buckley et al. showed that the polarimetric emission from the white dwarf is strongly linearly polarised ( up to $\sim40\%$) with periodically changing intensities. This periodic non-thermal emission is thought to be powered by the highly magnetised ($ 5 \times 10^{8} $ G) white dwarf that is spinning down. The morphology of the polarisation signal, namely the position angle plotted against the phase angle, is similar to that seen in many radio pulsars. In this paper, we demonstrate that we can fit the traditional pulsar rotating vector model to the optical position angle. We used a Markov-chain-Monte-Carlo technique to find the best fit for the model yielding a magnetic inclination angle of $\alpha = (86.6^{+3.0}_{-2.8})^{\circ}$ and an observer angle of $\zeta = (60.5^{+5.3}_{-6.1})^{\circ}$. This modelling supports the scenario that the synchrotron emission originates above the polar caps of the white dwarf pulsar and that the latter is an orthogonal rotator., Comment: 6 pages, 2 figures, HEASA 2018 proceedings of science
Published: 2019

44. Probing the pulsar population of Terzan 5 via spectral modeling

Author: A. Kopp, D. J. van der Walt, Peter Eger, Alice K. Harding, Tyrel J. Johnson, David A. Smith, Christo Venter, Hambeleleni Ndiyavala, Centre d'Etudes Nucléaires de Bordeaux Gradignan (CENBG), Université Sciences et Technologies - Bordeaux 1-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), 24483818 - Kopp, Andreas, 10060499 - Van der Walt, Diederick Johannes, 12006653 - Venter, Christo, and 26403366 - Ndiyavala, Hambeleleni
Subjects: Physics, High Energy Astrophysical Phenomena (astro-ph.HE), education.field_of_study, non-thermal [Radiation mechanisms], 010308 nuclear & particles physics, Astrophysics::High Energy Astrophysical Phenomena, Population, general [Pulsars], FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Pulsar, Space and Planetary Science, 0103 physical sciences, individual (Terzan 5) [Globular clusters], education, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], 010303 astronomy & astrophysics
Abstract: Terzan 5 is the only Galactic globular cluster that has plausibly been detected at very-high energies by the High Energy Stereoscopic System. It has an unexpectedly asymmetric very-high-energy morphology that is offset from the cluster center, in addition to a large-scale, offset radio structure and compact diffuse X-ray emission associated with this cluster. We present new data from the Fermi Large Area Telescope on this source. We model the updated broadband spectral energy distribution, attributing this to cumulative pulsed emission from a population of embedded millisecond pulsars as well as unpulsed emission from the interaction of their leptonic winds with the ambient magnetic and soft-photon fields. In particular, our model invokes unpulsed synchrotron and inverse Compton components to model the radio and TeV data, cumulative pulsed curvature radiation to fit the Fermi data, and explains the hard Chandra X-ray spectrum via a "new" cumulative synchrotron component from electron-positron pairs within the pulsar magnetospheres that has not been implemented before. We find reasonable spectral fits for plausible model parameters. We also derive constraints on the millisecond pulsar luminosity function using the diffuse X-ray data and the Chandra sensitivity. Future higher-quality spectral and spatial data will help discriminate between competing scenarios (such as dark matter annihilation, white dwarf winds or hadronic interactions) proposed for the broadband emission as well as constrain degenerate model parameters., 17 pages, 1 figure, and 2 tables
Published: 2019
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45. A Fundamental Plane for Gamma-Ray Pulsars

Author: Zorawar Wadiasingh, Constantinos Kalapotharakos, Demosthenes Kazanas, and Alice K. Harding
Subjects: Physics, High Energy Astrophysical Phenomena (astro-ph.HE), 010504 meteorology & atmospheric sciences, Astrophysics::High Energy Astrophysical Phenomena, Gamma ray, Synchrotron radiation, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Curvature, 01 natural sciences, Current sheet, Pulsar, Space and Planetary Science, Millisecond pulsar, 0103 physical sciences, Fundamental plane (elliptical galaxies), Astrophysics - High Energy Astrophysical Phenomena, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences, Fermi Gamma-ray Space Telescope
Abstract: We show that the $\gamma$-ray pulsar observables, i.e., their total $\gamma$-ray luminosity, $L_{\gamma}$, spectral cut-off energy, $\epsilon_{\rm cut}$, stellar surface magnetic field, $B_{\star}$, and spin-down power $\dot{\mathcal{E}}$, obey a relation of the form $L_{\gamma}=f(\epsilon_{\rm cut},B_{\star},\dot{\mathcal{E}})$, which represents a 3D plane in their 4D log-space. Fitting the data of 88 pulsars of the second Fermi pulsar catalog, we show this relation to be $L_{\gamma}\propto \epsilon_{\rm cut}^{1.18\pm 0.24}B_{\star}^{0.17\pm 0.05}\dot{\mathcal{E}}^{0.41\pm 0.08}$, a pulsar fundamental plane (FP). We show that the observed FP is remarkably close to the theoretical relation $L_{\gamma}\propto \epsilon_{\rm cut}^{4/3}B_{\star}^{1/6}\dot{\mathcal{E}}^{5/12}$ obtained assuming that the pulsar $\gamma$-ray emission is due to curvature radiation by particles accelerated at the pulsar equatorial current sheet just outside the light cylinder. Interestingly, the FP seems incompatible with emission by synchrotron radiation. The corresponding scatter about the FP is $\sim 0.35$dex and can only partly be explained by the observational errors while the rest is probably due to the variation of the inclination and observer angles. We predict also that $\epsilon_{\rm cut}\propto \dot{\mathcal{E}}^{7/16}$ toward low $\dot{\mathcal{E}}$ for both young and millisecond pulsars implying that the observed death-line of $\gamma$-ray pulsars is due to $\epsilon_{\rm cut}$ dropping below the Fermi-band. Our results provide a comprehensive interpretation of the observations of $\gamma$-ray pulsars, setting requirement for successful theoretical modeling., Comment: 8 pages, 6 figures, accepted for publication in ApJL
Published: 2019

46. Large High-precision X-Ray Timing of Three Millisecond Pulsars with $NICER$: Stability Estimates and Comparison with Radio

Author: Samuel R. Price, R. Spiewak, Paul Demorest, Sarah J. Vigeland, Slavko Bogdanov, W. W. Zhu, Timothy Dolch, Michael T. Lam, Julia S. Deneva, Peter A. Gentile, Cherry Ng, Zaven Arzoumanian, Harsha Blumer, D. R. Lorimer, N. Garver-Daniels, Maura McLaughlin, K. S. Wood, Matthew Kerr, J. Doty, Paul S. Ray, Scott M. Ransom, C. B. Markwardt, C. Malacaria, Joseph K. Swiggum, J. A. Ellis, Ingrid H. Stairs, M. L. Jones, Sebastien Guillot, Emmanuel Fonseca, Andrea N. Lommen, Paul R. Brook, Alice K. Harding, Kevin Stovall, Kevin Black, L. Guillemot, Robert D. Ferdman, David J. Nice, Timothy T. Pennucci, Luke M. Winternitz, Ismaël Cognard, M. T. Wolff, E. C. Ferrara, Ryan S. Lynch, H. T. Cromartie, M. E. DeCesar, Paul T. Baker, Natalia Lewandowska, Keith Gendreau, Institut de recherche en astrophysique et planétologie (IRAP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées, Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Université de Toulouse (UT), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Centre National d’Études Spatiales [Paris] (CNES), Université d'Orléans (UO)-Observatoire des Sciences de l'Univers en région Centre (OSUC), PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, and PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS)
Subjects: 010504 meteorology & atmospheric sciences, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, 01 natural sciences, 7. Clean energy, Stability (probability), stars: neutron, Pulsar, Millisecond pulsar, pulsars: general, 0103 physical sciences, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Neutron Star Interior Composition Explorer, Sigma, Order (ring theory), Astronomy and Astrophysics, Interstellar medium, pulsars: individual, 13. Climate action, Space and Planetary Science, [SDU]Sciences of the Universe [physics], Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Noise (radio)
Abstract: The Neutron Star Interior Composition Explorer (NICER) is an X-ray astrophysics payload on the International Space Station. It enables unprecedented high-precision timing of millisecond pulsars without the pulse broadening and delays due to dispersion and scattering within the interstellar medium that plague radio timing. We present initial timing results from a year of data on the millisecond pulsars PSR B1937+21 and PSR J0218+4232, and nine months of data on PSR B1821-24. NICER time-of-arrival uncertainties for the three pulsars are consistent with theoretical lower bounds and simulations based on their pulse shape templates and average source and background photon count rates. To estimate timing stability, we use the $\sigma_z$ measure, which is based on the average of the cubic coefficients of polynomial fits to subsets of timing residuals. So far we are achieving timing stabilities $\sigma_z \approx 3 \times 10^{-14}$ for PSR B1937+21 and on the order of $10^{-12}$ for PSRs B1821$-$24 and J0218+4232. Within the span of our \textit{NICER} data we do not yet see the characteristic break point in the slope of $\sigma_z$; detection of such a break would indicate that further improvement in the cumulative root-mean-square (RMS) timing residual is limited by timing noise. We see this break point in our comparison radio data sets for PSR B1821-24 and PSR B1937+21 on time scales of $> 2$ years., Comment: 30 pages, 15 figures; accepted to ApJ
Published: 2019
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47. Neutron Star Interior Composition Explorer X-Ray Timing of the Radio and $\gamma$-Ray Quiet Pulsars PSR J1412+7922 and PSR J1849-0001

Author: Alice K. Harding, Sridhar S. Manthripragada, Zaven Arzoumanian, Christian Malacaria, Slavko Bogdanov, Wynn C. G. Ho, Teruaki Enoto, Keith C. Gendreau, Sebastien Guillot, Gaurava K. Jaisawal, Institut de recherche en astrophysique et planétologie (IRAP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Centre National d'Études Spatiales [Toulouse] (CNES), Université Toulouse III - Paul Sabatier (UT3), and Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)
Subjects: 010504 meteorology & atmospheric sciences, individual (PSR J1412+7922, PSR J1849-0001) [Pulsars], Astrophysics::High Energy Astrophysical Phenomena, general [Pulsars], FOS: Physical sciences, X-rays: stars, Astrophysics, Ephemeris, 01 natural sciences, Spectral line, Gravitational waves, stars: neutron, Pulsar, pulsars: general, 0103 physical sciences, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, stars [X-rays], High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Neutron Star Interior Composition Explorer, Gravitational wave, Gamma ray, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, neutron [Stars], LIGO, Neutron star, pulsars: individual, gravitational waves, 13. Climate action, Space and Planetary Science, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract: We present new timing and spectral analyses of PSR J1412+7922 (Calvera) and PSR J1849-0001, which are only seen as pulsars in X-rays, based on observations conducted with the Neutron Star Interior Composition Explorer (NICER). We obtain updated and substantially improved pulse ephemerides compared to previous X-ray studies, as well as spectra that can be well-fit by simple blackbodies and/or a power law. Our refined timing measurements enable deeper searches for pulsations at other wavelengths and sensitive targeted searches by LIGO/Virgo for continuous gravitational waves from these neutron stars. Using the sensitivity of LIGO's first observing run, we estimate constraints that a gravitational wave search of these pulsars would obtain on the size of their mass deformation and r-mode fluid oscillation., 12 pages, 4 figures; submitted to the Astrophysical Journal
Published: 2019
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48. Multi-Wavelength Polarimetry of Isolated Pulsars

Author: Alice K. Harding
Subjects: Physics, Neutron star, Wavelength, Pulsar, Crab Pulsar, Astrophysics::High Energy Astrophysical Phenomena, Polarimetry, Magnetosphere, Astrophysics, Radiation, Magnetic field
Abstract: Isolated pulsars are ideal sources for polarisation studies since the radiation from pulsars generally covers a wide range of wavelengths from radio to very-high-energy γ-rays and the pulsed emission is closely tied to the local magnetic field direction. Although radio polarisation data exist for many pulsars, polarisation measurements at higher energies exist for only six sources. All six of these have optical polarisation measurements while only the Crab pulsar has measured polarisation in the X-ray band. One member of a small group of pulsars only visible at optical and X-ray wavelengths, thought to be powered by thermal emission from the cooling neutron star surface, has detected optical polarisation. This chapter will review the current multi-wavelength polarisation observations and the theoretical modelling by which we can probe the pulsar magnetosphere structure and emission mechanisms.
Published: 2019
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49. A NICER View of PSR J0030+0451: Millisecond Pulsar Parameter Estimation

Author: Zaven Arzoumanian, Sharon M. Morsink, Keith C. Gendreau, Alice K. Harding, Renee M. Ludlam, Tod E. Strohmayer, James M. Lattimer, Deepto Chakrabarty, Slavko Bogdanov, Anna V. Bilous, Sebastien Guillot, Wynn C. G. Ho, Paul S. Ray, Anna L. Watts, Thomas E. Riley, Charles Baker, Institut de recherche en astrophysique et planétologie (IRAP), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS), Centre National d'Études Spatiales [Toulouse] (CNES), Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), and High Energy Astrophys. & Astropart. Phys (API, FNWI)
Subjects: Nuclear Theory, 010504 meteorology & atmospheric sciences, Stellar mass, [PHYS.NUCL]Physics [physics]/Nuclear Theory [nucl-th], FOS: Physical sciences, Astrophysics, 01 natural sciences, Nuclear Theory (nucl-th), Pulsar, Millisecond pulsar, 0103 physical sciences, 010303 astronomy & astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), 0105 earth and related environmental sciences, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Neutron Star Interior Composition Explorer, Center (category theory), Spherical coordinate system, Astronomy and Astrophysics, Radius, Compact space, Astrophysics - Solar and Stellar Astrophysics, 13. Climate action, Space and Planetary Science, Astrophysics::Earth and Planetary Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract: We report on Bayesian parameter estimation of the mass and equatorial radius of the millisecond pulsar PSR J0030$+$0451, conditional on pulse-profile modeling of Neutron Star Interior Composition Explorer (NICER) X-ray spectral-timing event data. We perform relativistic ray-tracing of thermal emission from hot regions of the pulsar's surface. We assume two distinct hot regions based on two clear pulsed components in the phase-folded pulse-profile data; we explore a number of forms (morphologies and topologies) for each hot region, inferring their parameters in addition to the stellar mass and radius. For the family of models considered, the evidence (prior predictive probability of the data) strongly favors a model that permits both hot regions to be located in the same rotational hemisphere. Models wherein both hot regions are assumed to be simply-connected circular single-temperature spots, in particular those where the spots are assumed to be reflection-symmetric with respect to the stellar origin, are strongly disfavored. For the inferred configuration, one hot region subtends an angular extent of only a few degrees (in spherical coordinates with origin at the stellar center) and we are insensitive to other structural details; the second hot region is far more azimuthally extended in the form of a narrow arc, thus requiring a larger number of parameters to describe. The inferred mass $M$ and equatorial radius $R_\mathrm{eq}$ are, respectively, $1.34_{-0.16}^{+0.15}$ M$_{\odot}$ and $12.71_{-1.19}^{+1.14}$ km, whilst the compactness $GM/R_\mathrm{eq}c^2 = 0.156_{-0.010}^{+0.008}$ is more tightly constrained; the credible interval bounds reported here are approximately the $16\%$ and $84\%$ quantiles in marginal posterior mass., Comment: Appears in ApJ Letters Focus Issue on NICER Constraints on the Dense Matter Equation of State; 76 pages, 24 figures, 7 tables, 8 figure sets (available in the online journal or from the authors)
Published: 2019
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50. PSR J0030+0451 Mass and Radius from $NICER$ Data and Implications for the Properties of Neutron Star Matter

Author: Alexander J. Dittmann, Yang Soong, Frederick K. Lamb, Paul S. Ray, Keith C. Gendreau, R. S. Foster, Teruaki Enoto, Sharon M. Morsink, Sebastien Guillot, Alice K. Harding, K. S. Wood, Takashi Okajima, James M. Lattimer, Simin Mahmoodifar, Renee M. Ludlam, Wynn C. G. Ho, M. C. Miller, Slavko Bogdanov, Gregory Y. Prigozhin, Zaven Arzoumanian, Tod E. Strohmayer, Institut de recherche en astrophysique et planétologie (IRAP), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS), Centre National d'Études Spatiales [Toulouse] (CNES), Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), and Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)
Subjects: 010504 meteorology & atmospheric sciences, Nuclear Theory, [PHYS.NUCL]Physics [physics]/Nuclear Theory [nucl-th], Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 7. Clean energy, 01 natural sciences, Measure (mathematics), Gravitation, Nuclear Theory (nucl-th), Millisecond pulsar, 0103 physical sciences, Saturation (graph theory), 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Neutron Star Interior Composition Explorer, Equation of state (cosmology), Astronomy and Astrophysics, Radius, Neutron star, 13. Climate action, Space and Planetary Science, Astrophysics::Earth and Planetary Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract: Neutron stars are not only of astrophysical interest, but are also of great interest to nuclear physicists, because their attributes can be used to determine the properties of the dense matter in their cores. One of the most informative approaches for determining the equation of state of this dense matter is to measure both a star's equatorial circumferential radius $R_e$ and its gravitational mass $M$. Here we report estimates of the mass and radius of the isolated 205.53 Hz millisecond pulsar PSR J0030+0451 obtained using a Bayesian inference approach to analyze its energy-dependent thermal X-ray waveform, which was observed using the Neutron Star Interior Composition Explorer (NICER). This approach is thought to be less subject to systematic errors than other approaches for estimating neutron star radii. We explored a variety of emission patterns on the stellar surface. Our best-fit model has three oval, uniform-temperature emitting spots and provides an excellent description of the pulse waveform observed using NICER. The radius and mass estimates given by this model are $R_e = 13.02^{+1.24}_{-1.06}$ km and $M = 1.44^{+0.15}_{-0.14}\ M_\odot$ (68%). The independent analysis reported in the companion paper by Riley et al. (2019) explores different emitting spot models, but finds spot shapes and locations and estimates of $R_e$ and $M$ that are consistent with those found in this work. We show that our measurements of $R_e$ and $M$ for PSR J0030$+$0451 improve the astrophysical constraints on the equation of state of cold, catalyzed matter above nuclear saturation density., Comment: 49 pages, 16 figures, part of The Astrophysical Journal Letters focus issue on the Neutron Star Interior Composition Explorer
Published: 2019
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