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1. Constraining the Dense Matter Equation of State with New NICER Mass–Radius Measurements and New Chiral Effective Field Theory Inputs

Author

Nathan Rutherford, Melissa Mendes, Isak Svensson, Achim Schwenk, Anna L. Watts, Kai Hebeler, Jonas Keller, Chanda Prescod-Weinstein, Devarshi Choudhury, Geert Raaijmakers, Tuomo Salmi, Patrick Timmerman, Serena Vinciguerra, Sebastien Guillot, and James M. Lattimer

Subjects
Gravitational wave sources, Neutron stars, Neutron star cores, X-ray sources, Nuclear astrophysics, Astrophysics, QB460-466
Abstract

Pulse profile modeling of X-ray data from the Neutron Star Interior Composition Explorer is now enabling precision inference of neutron star mass and radius. Combined with nuclear physics constraints from chiral effective field theory ( χ EFT), and masses and tidal deformabilities inferred from gravitational-wave detections of binary neutron star mergers, this has led to a steady improvement in our understanding of the dense matter equation of state (EOS). Here, we consider the impact of several new results: the radius measurement for the 1.42 M _⊙ pulsar PSR J0437−4715 presented by Choudhury et al., updates to the masses and radii of PSR J0740+6620 and PSR J0030+0451, and new χ EFT results for neutron star matter up to 1.5 times nuclear saturation density. Using two different high-density EOS extensions—a piecewise-polytropic (PP) model and a model based on the speed of sound in a neutron star (CS)—we find the radius of a 1.4 M _⊙ (2.0 M _⊙ ) neutron star to be constrained to the 95% credible ranges ${12.28}_{-0.76}^{+0.50}$ km ( ${12.33}_{-1.34}^{+0.70}$ km) for the PP model and ${12.01}_{-0.75}^{+0.56}$ km ( ${11.55}_{-1.09}^{+0.94}$ km) for the CS model. The maximum neutron star mass is predicted to be ${2.15}_{-0.16}^{+0.14}$ M _⊙ and ${2.08}_{-0.16}^{+0.28}$ M _⊙ for the PP and CS models, respectively. We explore the sensitivity of our results to different orders and different densities up to which χ EFT is used, and show how the astrophysical observations provide constraints for the pressure at intermediate densities. Moreover, we investigate the difference R _2.0 − R _1.4 of the radius of 2 M _⊙ and 1.4 M _⊙ neutron stars within our EOS inference.

Published
2024
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2. A NICER View of the Nearest and Brightest Millisecond Pulsar: PSR J0437–4715

Author

Devarshi Choudhury, Tuomo Salmi, Serena Vinciguerra, Thomas E. Riley, Yves Kini, Anna L. Watts, Bas Dorsman, Slavko Bogdanov, Sebastien Guillot, Paul S. Ray, Daniel J. Reardon, Ronald A. Remillard, Anna V. Bilous, Daniela Huppenkothen, James M. Lattimer, Nathan Rutherford, Zaven Arzoumanian, Keith C. Gendreau, Sharon M. Morsink, and Wynn C. G. Ho

Subjects
Neutron stars, Pulsars, Rotation powered pulsars, Millisecond pulsars, Neutron star cores, Nuclear astrophysics, Astrophysics, QB460-466
Abstract

We report Bayesian inference of the mass, radius, and hot X-ray emitting region properties—using data from the Neutron Star Interior Composition ExploreR (NICER)—for the brightest rotation-powered millisecond X-ray pulsar, PSR J0437−4715. Our modeling is conditional on informative tight priors on mass, distance, and binary inclination obtained from radio pulsar timing using the Parkes Pulsar Timing Array (PPTA; Reardon et al.), and we use NICER background models to constrain the nonsource background, cross-checking with data from XMM-Newton. We assume two distinct hot emitting regions and various parameterized hot region geometries that are defined in terms of overlapping circles; while simplified, these capture many of the possibilities suggested by detailed modeling of return current heating. For the preferred model identified by our analysis, we infer a mass of M = 1.418 ± 0.037 M _⊙ (largely informed by the PPTA mass prior) and an equatorial radius of $R={11.36}_{-0.63}^{+0.95}$ km, each reported as the posterior credible interval bounded by the 16% and 84% quantiles. This radius favors softer dense matter equations of state and is highly consistent with constraints derived from gravitational wave measurements of neutron star binary mergers. The hot regions are inferred to be nonantipodal and hence inconsistent with a pure centered dipole magnetic field.

Published
2024
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3. NICER Discovery that SRGA J144459.2–604207 Is an Accreting Millisecond X-Ray Pulsar

Author

Mason Ng, Paul S. Ray, Andrea Sanna, Tod E. Strohmayer, Alessandro Papitto, Giulia Illiano, Arianna C. Albayati, Diego Altamirano, Tuğba Boztepe, Tolga Güver, Deepto Chakrabarty, Zaven Arzoumanian, D. J. K. Buisson, Elizabeth C. Ferrara, Keith C. Gendreau, Sebastien Guillot, Jeremy Hare, Gaurava K. Jaisawal, Christian Malacaria, and Michael T. Wolff

Subjects
Neutron stars, X-ray transient sources, Millisecond pulsars, X-ray bursts, Low-mass x-ray binary stars, Astrophysics, QB460-466
Abstract

We present the discovery, with the Neutron Star Interior Composition Explorer (NICER), that SRGA J144459.2−604207 is a 447.9 Hz accreting millisecond X-ray pulsar (AMXP), which underwent a 4 week long outburst starting on 2024 February 15. The AMXP resides in a 5.22 hr binary, orbiting a low-mass companion donor with M _d > 0.1 M _⊙ . We report on the temporal and spectral properties from NICER observations during the early days of the outburst, from 2024 February 21 through 2024 February 23, during which NICER also detected a type I X-ray burst that exhibited a plateau lasting ∼6 s. The spectra of the persistent emission were well described by an absorbed thermal blackbody and power-law model, with blackbody temperature kT ≈ 0.9 keV and power-law photon index Γ ≈ 1.9. Time-resolved burst spectroscopy confirmed the thermonuclear nature of the burst, where an additional blackbody component reached a maximum temperature of nearly kT ≈ 3 keV at the peak of the burst. We discuss the nature of the companion as well as the type I X-ray burst.

Published
2024
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4. X-Ray and Radio Monitoring of the Neutron Star Low-mass X-Ray Binary 1A 1744-361: Quasiperiodic Oscillations, Transient Ejections, and a Disk Atmosphere

Author

Mason Ng, Andrew K. Hughes, Jeroen Homan, Jon M. Miller, Sean N. Pike, Diego Altamirano, Peter Bult, Deepto Chakrabarty, D. J. K. Buisson, Benjamin M. Coughenour, Rob Fender, Sebastien Guillot, Tolga Güver, Gaurava K. Jaisawal, Amruta D. Jaodand, Christian Malacaria, James C. A. Miller-Jones, Andrea Sanna, Gregory R. Sivakoff, Tod E. Strohmayer, John A. Tomsick, and Jakob van den Eijnden

Subjects
High energy astrophysics, Transient sources, Low-mass x-ray binary stars, Neutron stars, Pulsars, Accretion, Astrophysics, QB460-466
Abstract

We report on X-ray (NICER/NuSTAR/MAXI/Swift) and radio (MeerKAT) timing and spectroscopic analysis from a 3 month monitoring campaign in 2022 of a high-intensity outburst of the dipping neutron star low-mass X-ray binary 1A 1744−361. The 0.5–6.8 keV NICER X-ray hardness–intensity and color–color diagrams of the observations throughout the outburst suggest that 1A 1744−361 spent most of its outburst in an atoll-state, but we show that the source exhibited Z-state-like properties at the peak of the outburst, similar to a small sample of other atoll-state sources. A timing analysis with NICER data revealed several instances of an ≈8 Hz quasiperiodic oscillation (QPO; fractional rms amplitudes of ∼5%) around the peak of the outburst, the first from this source, which we connect to the normal branch QPOs seen in the Z-state. Our observations of 1A 1744−361 are fully consistent with the idea of the mass accretion rate being the main distinguishing parameter between atoll- and Z-states. Radio monitoring data by MeerKAT suggests that the source was at its radio-brightest during the outburst peak, and that the source transitioned from the “island” spectral state to the “banana” state within ∼3 days of the outburst onset, launching transient jet ejecta. The observations present the strongest evidence for radio flaring, including jet ejecta, during the island-to-banana spectral state transition at low accretion rates (atoll-state). The source also exhibited Fe xxv , Fe xxvi K α , and K β X-ray absorption lines, whose origins likely lie in an accretion disk atmosphere.

Published
2024
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5. An Updated Mass–Radius Analysis of the 2017–2018 NICER Data Set of PSR J0030+0451

Author

Serena Vinciguerra, Tuomo Salmi, Anna L. Watts, Devarshi Choudhury, Thomas E. Riley, Paul S. Ray, Slavko Bogdanov, Yves Kini, Sebastien Guillot, Deepto Chakrabarty, Wynn C. G. Ho, Daniela Huppenkothen, Sharon M. Morsink, Zorawar Wadiasingh, and Michael T. Wolff

Subjects
Neutron stars, Nuclear astrophysics, Astronomy data analysis, High energy astrophysics, X-ray astronomy, Astrophysics, QB460-466
Abstract

In 2019 the NICER collaboration published the first mass and radius inferred for PSR J0030+0451, thanks to NICER observations, and consequent constraints on the equation of state characterizing dense matter. Two independent analyses found a mass of ∼1.3–1.4 M _⊙ and a radius of ∼13 km. They also both found that the hot spots were all located on the same hemisphere, opposite to the observer, and that at least one of them had a significantly elongated shape. Here we reanalyze, in greater detail, the same NICER data set, incorporating the effects of an updated NICER response matrix and using an upgraded analysis framework. We expand the adopted models and also jointly analyze XMM-Newton data, which enables us to better constrain the fraction of observed counts coming from PSR J0030+0451. Adopting the same models used in previous publications, we find consistent results, although with more stringent inference requirements. We also find a multimodal structure in the posterior surface. This becomes crucial when XMM-Newton data is accounted for. Including the corresponding constraints disfavors the main solutions found previously, in favor of the new and more complex models. These have inferred masses and radii of ∼[1.4 M _⊙ , 11.5 km] and ∼[1.7 M _⊙ , 14.5 km], depending on the assumed model. They display configurations that do not require the two hot spots generating the observed X-rays to be on the same hemisphere, nor to show very elongated features, and point instead to the presence of temperature gradients and the need to account for them.

Published
2024
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6. NICER Observations of Thermonuclear Bursts from 4U 1728-34: Detection of Oscillations prior to the Onset of Two Bursts

Author

Z. Funda Bostancı, Tuğba Boztepe, Tolga Güver, Tod E. Strohmayer, Yuri Cavecchi, Ersin Göğüş, Diego Altamirano, Peter Bult, Deepto Chakrabarty, Sebastien Guillot, Gaurava K. Jaisawal, Christian Malacaria, Giulio C. Mancuso, Andrea Sanna, and Jean H. Swank

Subjects
Neutron stars, X-ray bursts, Low-mass x-ray binary stars, Astrophysics, QB460-466
Abstract

We present temporal and time-resolved spectral analyses of all the thermonuclear X-ray bursts observed from the neutron star low-mass X-ray binary 4U 1728−34 with NICER from 2017 June to 2019 September. In total, we detected 11 X-ray bursts from the source and performed time-resolved spectroscopy. Unlike some of the earlier results for other bursting sources from NICER, our spectral results indicate that the use of a scaling factor for the persistent emission is not statistically necessary. This is primarily a result of the strong interstellar absorption in the line of sight toward 4U 1728−34, which causes the count rates to be significantly lower at low energies. We also searched for burst oscillations and detected modulations in six different bursts at around the previously known burst oscillation frequency of 363 Hz. Finally, we report the detection of oscillations prior to two bursts at 356 and 359 Hz, respectively. This is the first time in the literature where burst oscillations are detected before the rapid rise in X-ray flux, from any known burster. These oscillations disappear as soon as the burst starts to rise and occur at a somewhat lower frequency than the oscillations we detect during the bursts.

Published
2023
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7. Atmospheric Effects on Neutron Star Parameter Constraints with NICER

Author

Tuomo Salmi, Serena Vinciguerra, Devarshi Choudhury, Anna L. Watts, Wynn C. G. Ho, Sebastien Guillot, Yves Kini, Bas Dorsman, Sharon M. Morsink, and Slavko Bogdanov

Subjects
Neutron stars, X-ray astronomy, Astrophysics, QB460-466
Abstract

We present an analysis of the effects of uncertainties in the atmosphere models on the radius, mass, and other neutron star parameter constraints for the NICER observations of rotation-powered millisecond pulsars. To date, NICER has applied the X-ray pulse profile modeling technique to two millisecond-period pulsars: PSR J0030+0451 and the high-mass pulsar PSR J0740+6620. These studies have commonly assumed a deep-heated, fully ionized hydrogen atmosphere model, although they have explored the effects of partial ionization and helium composition in some cases. Here, we extend that exploration and also include new models with partially ionized carbon composition, externally heated hydrogen, and an empirical atmospheric beaming parameterization to explore deviations in the expected anisotropy of the emitted radiation. None of the studied atmosphere cases have any significant influence on the inferred radius of PSR J0740+6620, possibly due to its X-ray faintness, tighter external constraints, and/or viewing geometry. In the case of PSR J0030+0451, both the composition and ionization state could significantly alter the inferred radius. However, based on the evidence (prior predictive probability of the data), partially ionized hydrogen and carbon atmospheres are disfavored. The difference in the evidence for ionized hydrogen and helium atmospheres is too small to be decisive for most cases, but the inferred radius for helium models trends to larger sizes around or above 14–15 km. External heating or deviations in the beaming that are less than 5% at emission angles smaller than 60°, on the other hand, have no significant effect on the inferred radius.

Published
2023
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8. The 2022 High-energy Outburst and Radio Disappearing Act of the Magnetar 1E 1547.0–5408

Author

Marcus E. Lower, George Younes, Paul Scholz, Fernando Camilo, Liam Dunn, Simon Johnston, Teruaki Enoto, John M. Sarkissian, John E. Reynolds, David M. Palmer, Zaven Arzoumanian, Matthew G. Baring, Keith Gendreau, Ersin Göğüş, Sebastien Guillot, Alexander J. van der Horst, Chin-Ping Hu, Chryssa Kouveliotou, Lin Lin, Christian Malacaria, Rachael Stewart, and Zorawar Wadiasingh

Subjects
Magnetars, Pulsars, Radio pulsars, High energy astrophysics, Neutron stars, Astrophysics, QB460-466
Abstract

We report the radio and high-energy properties of a new outburst from the radio-loud magnetar 1E 1547.0−5408. Following the detection of a short burst from the source with Swift-BAT on 2022 April 7, observations by NICER detected an increased flux peaking at (6.0 ± 0.4) × 10 ^−11 erg s ^−1 cm ^−2 in the soft X-ray band, falling to a baseline level of 1.7 × 10 ^−11 erg s ^−1 cm ^−2 over a 17 day period. Joint spectroscopic measurements by NICER and NuSTAR indicated no change in the hard nonthermal tail despite the prominent increase in soft X-rays. Observations at radio wavelengths with Murriyang, the 64 m Parkes radio telescope, revealed that the persistent radio emission from the magnetar disappeared at least 22 days prior to the initial Swift-BAT detection and was redetected two weeks later. Such behavior is unprecedented in a radio-loud magnetar, and may point to an unnoticed slow rise in the high-energy activity prior to the detected short bursts. Finally, our combined radio and X-ray timing revealed the outburst coincided with a spin-up glitch, where the spin frequency and spin-down rate increased by 0.2 ± 0.1 μ Hz and (−2.4 ± 0.1) × 10 ^−12 s ^−2 , respectively. A linear increase in the spin-down rate of (−2.0 ± 0.1) × 10 ^−19 s ^−3 was also observed over 147 days of postoutburst timing. Our results suggest that the outburst may have been associated with a reconfiguration of the quasi-polar field lines, likely signaling a changing twist, accompanied by spatially broader heating of the surface and a brief quenching of the radio signal, yet without any measurable impact on the hard X-ray properties.

Published
2023
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9. The Radius of PSR J0740+6620 from NICER with NICER Background Estimates

Author

Tuomo Salmi, Serena Vinciguerra, Devarshi Choudhury, Thomas E. Riley, Anna L. Watts, Ronald A. Remillard, Paul S. Ray, Slavko Bogdanov, Sebastien Guillot, Zaven Arzoumanian, Cecilia Chirenti, Alexander J. Dittmann, Keith C. Gendreau, Wynn C. G. Ho, M. Coleman Miller, Sharon M. Morsink, Zorawar Wadiasingh, and Michael T. Wolff

Subjects
X-ray astronomy, Neutron stars, Astrophysics, QB460-466
Abstract

We report a revised analysis for the radius, mass, and hot surface regions of the massive millisecond pulsar PSR J0740+6620, studied previously with joint fits to NICER and XMM-Newton data by Riley et al. (2021) and Miller et al. (2021). We perform a similar Bayesian estimation for the pulse-profile model parameters, except that instead of fitting simultaneously the XMM-Newton data, we use the best available NICER background estimates to constrain the number of photons detected from the source. This approach eliminates any potential issues in the cross-calibration between these two instruments, providing thus an independent check of the robustness of the analysis. The obtained neutron star parameter constraints are compatible with the already published results, with a slight dependence on how conservative the imposed background limits are. A tighter lower limit causes the inferred radius to increase, and a tighter upper limit causes it to decrease. We also extend the study of the inferred emission geometry to examine the degree of deviation from antipodality of the hot regions. We show that there is a significant offset to an antipodal spot configuration, mainly due to the non-half-cycle azimuthal separation of the two emitting spots. The offset angle from the antipode is inferred to be above 25° with 84% probability. This seems to exclude a centered-dipolar magnetic field in PSR J0740+6620.

Published
2022
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11. Discovery, Timing, and Multiwavelength Observations of the Black Widow Millisecond Pulsar PSR J1555–2908

Author

Paul S Ray, Lars Nieder, Colin J Clark, Scott M Ransom, H Thankful Cromartie, Dale A Frail, Kunal P Mooley, Huib Intema, Preshanth Jagannathan, Paul Demorest, Kevin Stovall, Jules P Halpern, Julia S Deneva, Sebastien Guillot, Matthew Kerr, Samuel J Swihart, Philippe Bruel, Ben W Stappers, Andrew Lyne, Mitch Mickaliger, Fernando Camilo, Elizabeth C Ferrara, Michael T Wolff, and P F Michelson

Subjects
Astronomy
Abstract

We report the discovery of PSR J1555−2908, a 1.79 ms radio and gamma-ray pulsar in a 5.6 hr binary system with a minimum companion mass of 0.052 M⊙. This fast and energetic ((E =3 ×10(exp 35)) ̇ erg s(exp -1) millisecond pulsar was first detected as a gamma-ray point source in Fermi Large Area Telescope (LAT) sky survey observations. Guided by a steep-spectrum radio point source in the Fermi error region, we performed a search at 820 MHz with the Green Bank Telescope that first discovered the pulsations. The initial radio pulse timing observations provided enough information to seed a search for gamma-ray pulsations in the LAT data, from which we derive a timing solution valid for the full Fermi mission. In addition to the discovery and timing of radio and gamma-ray pulsations, we searched for X-ray pulsations using NICER but no significant pulsations were detected. We also obtained time-series r-band photometry that indicates strong heating of the companion star by the pulsar wind. Material blown off the heated companion eclipses the 820 MHz radio pulse during inferior conjunction of the companion for ≈10% of the orbit, which is twice the angle subtended by its Roche lobe in an edge-on system.

Published
2022
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14. A NICER Look at Thermonuclear X-ray Bursts from Aql X-1

Author

Tolga Güver, Tugba Boztepe, D R Ballantyne, Z Funda Bostanci, Peter Bult, Gaurava K Jaisawal, Ersin Göğüş, Tod E Strohmayer, Diego Altamirano, Sebastien Guillot, and Deepto Chakrabarty

Subjects
Astronomy
Abstract

We present spectral and temporal properties of all the thermonuclear X-ray bursts observed from Aql X-1 by the Neutron StarInterior and Composition Explorer (NICER) between 2017 July and 2021 April. This is the first systematic investigation of alarge sample of type I X-ray bursts from Aql X-1 with improved sensitivity at low energies. We detect 22 X-ray bursts includingtwo short recurrence burst events in which the separation was only 451 s and 496 s. We perform time resolved spectroscopy of thebursts using the fixed and scaled background (fa method) approaches. We show that the use of a scaling factor to the pre-burstemission is the statistically preferred model in about 68% of all the spectra compared to the fixed background approach. Typically the fa values are clustered around 1–3, but can reach up to 11 in a burst where photospheric radius expansion is observed. Such fa values indicate a very significant increase in the pre-burst emission especially at around the peak flux moments of the bursts.We show that the use of the fa factor alters the best fit spectral parameters of the burst emission. Finally, we employed a reflectionmodel instead of scaling the pre-burst emission. We show that reflection models also do fit the spectra and improve the goodnessof the fits. In all cases we see that the disc is highly ionized by the burst emission and the fraction of the reprocessed emission tothe incident burst flux is typically clustered around 20%

Published
2021
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17. 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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18. Timing the Pulsations of The Accreting Millisecond Pulsar SAX J1808.4-3658 During Its 2019 Outburst

Author

Peter Bult, Deepto Chakrabarty, Zaven Arzoumanian, Keith C Gendreau, Sebastien Guillot, Christian Malacaria, Paul S Ray, and Tod E Strohmayer

Subjects
Astrophysics
Abstract

In this paper we present a coherent timing analysis of the 401 Hz pulsations of the accreting millisecond X-ray pulsar SAX J1808.4-3658 during its 2019 outburst. Using observations collected with the Neutron Star Interior Composition Explorer (NICER), we establish the pulsar spin frequency and orbital phase during its latest epoch. We find that the 2019 outburst shows a pronounced evolution in pulse phase over the course of the outburst. These phase shifts are found to correlate with the source flux, and are interpreted in terms of hot-spot drift on the stellar surface, driven by changes in the mass accretion rate. Additionally, we find that the long-term evolution of the pulsar spin frequency shows evidence for a modulation at the Earth's orbital period, enabling pulsar timing based astrometry of this accreting millisecond pulsar.

Published
2020
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19. A NICER View of Spectral and Profile Evolution for Three X-ray-Emitting Millisecond Pulsars

Author

Dominick M Rowan, Zaynab Ghazi, Lauren Lugo, Elizabeth Spano, Andrea Lommen, Alice Harding, Christo Venter, Renee Ludlam, Paul S Ray, Matthew Kerr, Zaven Arzoumanian, Slavko Bogdanov, Julia Deneva, Sebastien Guillot, Natalia Lewandowska, Craig B Markwardt, Scott Ransom, Teruaki Enoto, Kent S Wood, and Keith C Gendreau

Subjects
Astrophysics
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 >3σ 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.

Published
2020
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20. Constraining the Neutron Star Mass–Radius Relation and Dense Matter Equation of State with NICER. I. The Millisecond Pulsar X-Ray Data Set

Author

Keith C Gendreau, Slavko Bogdanov, Sebastien Guillot, Paul S. Ray, Michael T Wolff, Deepto Chakrabarty, Wynn C G Ho, Matthew Kerr, Frederick K. Lamb, Andrea Lommen, Renee M. Ludlam, Reilly Milburn, Sergio Montano, M. Coleman Miller, Michi Bauböck, Feryal Özel, Dimitrios Psaltis, Ronald A Remillard, Thomas E. Riley, James F. Steiner, Tod E Strohmayer, Anna L. Watts, Kent S. Wood, Jesse Zeldes, Teruaki Enoto, Takashi Okajima, James W Kellogg, Charles Baker, Craig Bishop Markwardt, and Zaven Arzoumanian

Subjects
Astronomy
Abstract

We present the set of deep Neutron Star Interior Composition Explorer (NICER) X-ray timing observations of the nearby rotation-powered millisecond pulsars PSRs J0437−4715, J0030+0451, J1231−1411, and J2124−3358, selected as targets for constraining the mass–radius relation of neutron stars and the dense matter equation of state (EoS) via modeling of their pulsed thermal X-ray emission. We describe the instrument, observations, and data processing/reduction procedures, as well as the series of investigations conducted to ensure that the properties of the data sets are suitable for parameter estimation analyses to produce reliable constraints on the neutron star mass–radius relation and the dense matter EoS. We find that the long-term timing and flux behavior and the Fourier domain properties of the event data do not exhibit any anomalies that could adversely affect the intended measurements. From phase-selected spectroscopy, we find that emission from the individual pulse peaks is well described by a single-temperature hydrogen atmosphere spectrum, with the exception of PSR J0437−4715, for which multiple temperatures are required.

Published
2019
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21. NICER X-ray Observations of Seven Nearby Rotation-powered Millisecond Pulsars

Author

Sebastien Guillot, Matthew Kerr, Paul S Ray, Slavko Bogdanov, Scott M Ransom, Julia S Deneva, Zaven Arzoumanian, Petrus Bult, Deepto Chakrabarty, Keith C Gendreau, Wynn C G Ho, Gaurava K. Jaisawal, Christian Malacaria, M. Coleman Miller, Tod E Strohmayer, Michael T Wolff, Kent S. Wood, Natalie A. Webb, Lucas Guillemot, Ismael Cognard, and Gilles Theureau

Subjects
Astrophysics
Abstract

The Neutron star Interior Composition Explorer observed several rotation-powered millisecond pulsars (MSPs) to search for or confirm the presence of X-ray pulsations. When broad and sine-like, these pulsations may indicate thermal emission from hot polar caps at the magnetic poles on the neutron star surface. We report confident detections (≥4.7σ after background filtering) of X-ray pulsations for five of the seven pulsars in our target sample: PSR J0614−3329, PSR J0636+5129, PSR J0751+1807, PSR J1012+5307, and PSR J2241−5236, while PSR J1552+5437 and PSR J1744−1134 remain undetected. Of those, only PSR J0751+1807 and PSR J1012+5307 had pulsations previously detected at the 1.7σ and almost 3σ confidence levels, respectively, in XMM-Newton data. All detected sources exhibit broad sine-like pulses, which are indicative of surface thermal radiation. As such, these MSPs are promising targets for future X-ray observations aimed at constraining the neutron star mass–radius relation and the dense matter equation of state using detailed pulse profile modeling. Furthermore, we find that three of the detected MSPs exhibit a significant phase offset between their X-ray and radio pulses.

Published
2019
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22. 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

23. An Evolving Broad Iron Line from the First Galactic Ultraluminous X-Ray Pulsar Swift J0243.6+6124

Author

Gaurava K. Jaisawal, Colleen Wilson-hodge, Andrew C. Fabian, Sachindra Naik, Deepto Chakrabarty, Peter Kretschmar, David R. Ballantyne, Renee M. Ludlam, Jérôme Chenevez, Diego Altamirano, Zaven Arzoumanian, Felix Fürst, Keith C Gendreau, Sebastien Guillot, Christian Malacaria, Jon M. Miller, Abigail L. Stevens, and Michael T Wolff

Subjects
Astrophysics
Abstract

We present a spectral study of the ultraluminous Be/X-ray transient pulsar Swift J0243.6+6124 using Neutron Star Interior Composition Explorer (NICER) observations during the system's 2017–2018 giant outburst. The 1.2–10 keV energy spectrum of the source can be approximated with an absorbed cutoff power-law model. We detect strong, luminosity-dependent emission lines in the 6–7 keV energy range. A narrow 6.42 keV line, observed in the sub-Eddington regime, is seen to evolve into a broad Fe-line profile in the super-Eddington regime. Other features are found at 6.67 and 6.97 keV in the Fe-line complex. An asymmetric broad-line profile, peaking at 6.67 keV, is possibly due to Doppler effects and gravitational redshift. The 1.2–79 keV broadband spectrum from Nuclear Spectroscopic Telescope Array (NuSTAR) and NICER observations at the outburst peak is well described by an absorbed cutoff power law plus multiple Gaussian lines and a blackbody component. Physical reflection models are also tested to probe the broad iron-line feature. Depending on the mass accretion rate, we found emission sites that are evolving from ~5000 km to a range closer to the surface of the neutron star. Our findings are discussed in the framework of the accretion disk and its implication on the magnetic field, the presence of optically thick accretion curtain in the magnetosphere, jet emission, and the massive, ultrafast outflow expected at super-Eddington accretion rates. We do not detect any signatures of a cyclotron absorption line in the NICER or NuSTAR data.

Published
2019
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24. NICER Observes a Secondary Peak in the Decay of a Thermonuclear Burst from 4U 1608-52

Author

Gaurava K. Jaisawal, Jérôme Chenevez, Peter Bult, Jean J. M. in’t Zand, Duncan K. Galloway, Tod E. Strohmayer, Tolga Güver, Phillip Adkins, Diego Altamirano, Zaven Arzoumanian, Deepto Chakrabarty, Jonathan Coopersmith, Keith C. Gendreau, Sebastien Guillot, Laurens Keek, Renee M. Ludlam, and Christian Malacaria

Subjects
Astronomy, Astrophysics
Abstract

We report for the first time below 1.5 keV, the detection of a secondary peak in an Eddington-limited thermonuclear X-ray burst observed by the Neutron Star Interior Composition Explorer (NICER) from the low-mass X-ray binary 4U 1608–52. Our time-resolved spectroscopy of the burst is consistent with a model consisting of a varying-temperature blackbody, and an evolving persistent flux contribution, likely attributed to the accretion process. The dip in the burst intensity before the secondary peak is also visible in the bolometric flux. Prior to the dip, the blackbody temperature reached a maximum of ≈3 keV. Our analysis suggests that the dip and secondary peak are not related to photospheric expansion, varying circumstellar absorption, or scattering. Instead, we discuss the observation in the context of hydrodynamical instabilities, thermonuclear flame spreading models, and reburning in the cooling tail of the burst.

Published
2019
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25. A Joint NICER and XMM-Newton View of the 'Magnificent' Thermally Emitting X-ray Isolated Neutron Star RX J1605.3+3249

Author

Christian Malacaria, Slavko Bogdanov, Wynn C G Ho, Teruaki Enoto, Paul S Ray, Zaven Arzoumanian, Thoniel Cazeau, Keith C Gendreau, Sebastien Guillot, Tolga Guver, Gaurava K Jaisawal, and Michael T Wolff

Subjects
Astrophysics
Abstract

Thermally emitting X-ray isolated neutron stars (NSs) represent excellent targets for testing cooling surface emission and atmosphere models, which are used to infer the physical parameters of the NS. Among the seven known members of this class, RXJ1605.3+3249 is the only one that still lacks confirmation of its spin period. Here we analyze NICER and XMM-Newton observations of RXJ1605.3+3249, in order to address its timing and spectral behavior. Contrary to a previous tentative detection, but in agreement with the recent work by Pires et al., we find no significant pulsation with a pulsed fraction higher than 1.3% (3σ) for periods above 150 ms. We also find a limit of 2.6% for periods above 2 ms, despite searches in different energy bands. The X-ray spectrum can be fit by either a double-blackbody model or by a single-temperature magnetized atmosphere model, both modified by a Gaussian absorption line at ∼0.44 keV. The origin of the absorption feature as a proton cyclotron line or as an atomic transition in the NS atmosphere is discussed. The predictions of the best-fit X-ray models extended to IR, optical, and UV bands, are compared with archival data. Our results are interpreted in the framework of a fallback disk scenario.

Published
2019
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26. Anti-Glitches in the Ultraluminous Accreting Pulsar NGC 300 ULX-1 Observed with NICER

Author

Paul S Ray, Sebastien Guillot, Wynn C G Ho, Matthew Kerr, Teruaki Enoto, Keith C Gendreau, Zaven Arzoumanian, Diego Altamirano, Slavko Bogdanov, Robert Campion, Deepto Chakrabarty, Julia S Deneva, Gaurava K Jaisawal, Robert Kozon, Christian Malacaria, Tod E Strohmayer, and Michael T Wolff

Subjects
Lunar And Planetary Science And Exploration
Abstract

We present evidence for three spin-down glitches (or “anti-glitches”) in the ultraluminous accreting X-ray pulsar NGC 300 ULX-1, in timing observations made with the Neutron Star Interior Composition Explorer. Our timing analysis reveals three sudden spin-down events of magnitudes Δν=−23, −30, and −43 μHz (fractional amplitudes Δν/ν=−4.4, −5.5, and −7.7×10−4). We determined fully phase-coherent timing solutions through the first two glitches, giving us high confidence in their detection, while the third candidate glitch is somewhat less secure. These are larger in magnitude (and opposite in sign) than any known radio pulsar glitch. This may be caused by the prolonged rapid spin up of the pulsar, causing a sudden transfer of angular momentum between the superfluid and non-superfluid components of the star. We find no evidence for profile or spectral changes at the epochs of the glitches, supporting the conclusion that these are due to the same process as in normal pulsar glitches, but in reverse.

Published
2019
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27. 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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28. NICER Observations of the 2018 Outburst of XTE J1810-197

Author

Tolga Guver, Ersin Gogus, Eda Vurgun, Teruaki Enoto, K C Gendreau, Takanori Sakamoto, Eric V Gotthelf, Zaven Arzoumanian, Sebastien Guillot, Gaurava K Jaisawal, Christian Malacaria, and Walid A Majid

Subjects
Astrophysics
Abstract

We present the earliest available soft X-ray observations of XTE J1810−197, the prototypical transient magnetar, obtained 75–84 days after its 2018 outburst with the Neutron Star Interior Composition Explorer. Using a series of observations covering eight days we find that its decreasing X-ray flux is well described by either a blackbody plus power law or a two-blackbody spectral model. The 2–10 keV flux of the source varied from (1.206 ± 0.007) × 10−10 to (1.125 ± 0.004) x 10-10 erg s-1 cm-2, a decrease of about 7% within our observations and 44% from that measured 7–14 days after the outburst with NuSTAR. We confirm that the pulsed fraction and spin pulse phase of the neutron star are energy dependent up to at least 8 keV. Phase-resolved spectroscopy of the pulsar suggests magnetospheric variations relative to the line of sight.

Published
2019
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29. 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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31. Dense matter with eXTP

Author

Anna L. Watts, WenFei Yu, Juri Poutanen, Shu Zhang, Sudip Bhattacharyya, Slavko Bogdanov, Long Ji, Alessandro Patruno, Thomas E. Riley, Pavel Bakala, Altan Baykal, Federico Bernardini, Ignazio Bombaci, Edward Brown, Yuri Cavecchi, Deepto Chakrabarty, Jérôme Chenevez, Nathalie Degenaar, Melania Del Santo, Tiziana Di Salvo, Victor Doroshenko, Maurizio Falanga, Robert D. Ferdman, Marco Feroci, Angelo F. Gambino, MingYu Ge, Svenja K. Greif, Sebastien Guillot, Can Gungor, Dieter H. Hartmann, Kai Hebeler, Alexander Heger, Jeroen Homan, Rosario Iaria, Jean in’t Zand, Oleg Kargaltsev, Aleksi Kurkela, XiaoYu Lai, Ang Li, XiangDong Li, ZhaoSheng Li, Manuel Linares, FangJun Lu, Simin Mahmoodifar, Mariano Méndez, M. Coleman Miller, Sharon Morsink, Joonas Nättilä, Andrea Possenti, Chanda Prescod-Weinstein, JinLu Qu, Alessandro Riggio, Tuomo Salmi, Andrea Sanna, Andrea Santangelo, Hendrik Schatz, Achim Schwenk, LiMing Song, Eva Šrámková, Benjamin Stappers, Holger Stiele, Tod Strohmayer, Ingo Tews, Laura Tolos, Gabriel Török, David Tsang, Martin Urbanec, Andrea Vacchi, RenXin Xu, YuPeng Xu, Silvia Zane, GuoBao Zhang, ShuangNan Zhang, WenDa Zhang, ShiJie Zheng, and Xia Zhou

Subjects
Physics (General), Astronomy
Abstract

In this White Paper we present the potential of the Enhanced X-ray Timing and Polarimetry (eXTP) mission for determining the nature of dense matter; neutron star cores host an extreme density regime which cannot be replicated in a terrestrial laboratory. The tightest statistical constraints on the dense matter equation of state will come from pulse profile modelling of accretion-powered pulsars, burst oscillation sources, and rotation-powered pulsars. Additional constraints will derive from spin measurements, burst spectra, and properties of the accretion flows in the vicinity of the neutron star. Under development by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Science, the eXTP mission is expected to be launched in the mid 2020s.

Published
2018
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32. 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

33. Discovery of thermonuclear (Type I) X-ray bursts in the X-ray binary Swift J1858.6–0814 observed with NICER and NuSTAR

Author

N. Castro Segura, Francesco Tombesi, Tod E. Strohmayer, Zaven Arzoumanian, Jon M. Miller, Keith C. Gendreau, A. C. Albayati, D. J. K. Buisson, Deepto Chakrabarty, Poshak Gandhi, Dom Walton, Tolga Guver, Diego Altamirano, Sebastien Guillot, John A. Tomsick, C. Malacaria, F. M. Vincentelli, Ron Remillard, Jeroen Homan, Jeremy Hare, Jiachen Jiang, Gaurava K. Jaisawal, M. Ozbey Arabaci, Peter Bult, G. C. Mancuso, 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
Ciencias Astronómicas, Accretion, bursts [X-rays], Ciencias Físicas, Astrophysics::High Energy Astrophysical Phenomena, X-ray binary, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Compact star, 01 natural sciences, Luminosity, purl.org/becyt/ford/1 [https], X-rays: binaries, stars: neutron, accretion, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, ACCRETION, ACCRETION DISCS, X-rays: bursts, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Accretion (meteorology), Settore FIS/05, 010308 nuclear & particles physics, neutron [Stars], Astronomy and Astrophysics, purl.org/becyt/ford/1.3 [https], Radius, Light curve, accretion discs, Astronomía, Neutron star, Amplitude, Space and Planetary Science, accretion, accretion discs, binaries [X-rays], [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Astrophysics - High Energy Astrophysical Phenomena, CIENCIAS NATURALES Y EXACTAS, Accretion discs
Abstract

Swift J1858.6-0814 is a recently discovered X-ray binary notable for extremely strong variability (by factors $>100$ in soft X-rays) in its discovery state. We present the detection of five thermonuclear (Type I) X-ray bursts from Swift J1858.6-0814, implying that the compact object in the system is a neutron star. Some of the bursts show photospheric radius expansion, so their peak flux can be used to estimate the distance to the system. The peak luminosity, and hence distance, can depend on several system parameters; for the most likely values, a high inclination and a helium atmosphere, $D=12.8_{-0.6}^{+0.8}$ kpc, although systematic effects allow a conservative range of $9-18$ kpc. Before one burst, we detect a QPO at $9.6\pm0.5$ mHz with a fractional rms amplitude of $2.2\pm0.2$% ($0.5-10$ keV), likely due to marginally stable burning of helium; similar oscillations may be present before the other bursts but the light curves are not long enough to allow their detection. We also search for burst oscillations but do not detect any, with an upper limit in the best case of 15% fractional amplitude (over $1-8$ keV). Finally, we discuss the implications of the neutron star accretor and this distance on other inferences which have been made about the system. In particular, we find that Swift J1858.6-0814 was observed at super-Eddington luminosities at least during bright flares during the variable stage of its outburst., 14 pages, 8 figures, 2 tables, MNRAS accepted

Published
2020

34. The SUrvey for Pulsars and Extragalactic Radio Bursts – IV. Discovery and polarimetry of a 12.1-s radio pulsar

Author

Teruaki Enoto, R. Remillard, Michael Kramer, Evan Keane, Zaven Arzoumanian, Andrew Jameson, Simon Johnston, Matthew Bailes, Paul S. Ray, Wynn C. G. Ho, Shivani Bhandari, M. Caleb, Benjamin Stappers, Sebastien Guillot, Vincent Morello, W. van Straten, Ewan Barr, C. Malacaria, C.M.L. Flynn, Slavko Bogdanov, Fabian Jankowski, Keith C. 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), and Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)

Subjects
Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Parameter space, Magnetar, 01 natural sciences, Upper and lower bounds, stars: neutron, Pulsar, pulsars: general, 0103 physical sciences, pulsars: individual: PSR J2251−3711, 010306 general physics, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Astronomy and Astrophysics, Position angle, Polarization (waves), Magnetic field, Neutron star, Space and Planetary Science, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract

We report the discovery of PSR~J2251$-$3711, a radio pulsar with a spin period of 12.1 seconds, the second longest currently known. Its timing parameters imply a characteristic age of 15 Myr, a surface magnetic field of $1.3 \times 10^{13}$~G and a spin-down luminosity of $2.9 \times 10^{29}~\mathrm{erg~s}^{-1}$. Its dispersion measure of 12.12(1)~$\mathrm{pc}~\mathrm{cm}^{-3}$ leads to distance estimates of 0.5 and 1.3 kpc according to the NE2001 and YMW16 Galactic free electron density models, respectively. Some of its single pulses show an uninterrupted 180 degree sweep of the phase-resolved polarization position angle, with an S-shape reminiscent of the rotating vector model prediction. However, the fact that this sweep occurs at different phases from one pulse to another is remarkable and without straightforward explanation. Although PSR~J2251$-$3711 lies in the region of the $P-\dot{P}$ parameter space occupied by the X-ray Isolated Neutron Stars (XINS), there is no evidence for an X-ray counterpart in our Swift XRT observation; this places a 99\%-confidence upper bound on its unabsorbed bolometric thermal luminosity of $1.1 \times 10^{31}~(d / 1~\mathrm{kpc})^2~\mathrm{erg/s}$ for an assumed temperature of 85 eV, where $d$ is the distance to the pulsar. Further observations are needed to determine whether it is a rotation-powered pulsar with a true age of at least several Myr, or a much younger object such as an XINS or a recently cooled magnetar. Extreme specimens like PSR J2251$-$3711 help bridge populations in the so-called neutron star zoo in an attempt to understand their origins and evolution., Accepted for publication in MNRAS, 13 pages, 8 figures

Published
2020

35. The Discovery of the 528.6 Hz Accreting Millisecond X-Ray Pulsar MAXI J1816–195

Author

Peter Bult, Diego Altamirano, Zaven Arzoumanian, Deepto Chakrabarty, Jérôme Chenevez, Elizabeth C. Ferrara, Keith C. Gendreau, Sebastien Guillot, Tolga Güver, Wataru Iwakiri, Gaurava K. Jaisawal, Giulio C. Mancuso, Christian Malacaria, Mason Ng, Andrea Sanna, Tod E. Strohmayer, Zorawar Wadiasingh, Michael T. Wolff, 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), and 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)

Subjects
High Energy Astrophysical Phenomena (astro-ph.HE), Millisecond pulsars, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], Space and Planetary Science, [SDU]Sciences of the Universe [physics], X-ray bursts, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Low-mass x-ray binary stars
Abstract

We present the discovery of 528.6 Hz pulsations in the new X-ray transient MAXI J1816-195. Using NICER, we observed the first recorded transient outburst from the neutron star low-mass X-ray binary MAXI J1816-195 over a period of 28 days. From a timing analysis of the 528.6 Hz pulsations, we find that the binary system is well described as a circular orbit with an orbital period of 4.8 hours and a projected semi-major axis of 0.26 light-seconds for the pulsar, which constrains the mass of the donor star to $0.10-0.55 M_\odot$. Additionally, we observed 15 thermonuclear X-ray bursts showing a gradual evolution in morphology over time, and a recurrence time as short as 1.4 hours. We did not detect evidence for photospheric radius expansion, placing an upper limit on the source distance of 8.6 kpc., Comment: 8 pages, 3 figures, 2 tables. Accepted for publication in ApJ Letters

Published
2022

36. Burst-Disk Interaction in 4U 1636-536 as observed by NICER

Author

Tolga Güver, Z. Funda Bostancı, Tuğba Boztepe, Ersin Göğüş, Peter Bult, Unnati Kashyap, Manoneeta Chakraborty, David R. Ballantyne, R. M. Ludlam, C. Malacaria, Gaurava K. Jaisawal, Tod E. Strohmayer, Sebastien Guillot, Mason Ng, 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), and 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)

Subjects
Stellar accretion disks, High Energy Astrophysical Phenomena (astro-ph.HE), Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, Astrophysics::High Energy Astrophysical Phenomena, X-ray bursts, 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), Neutron stars
Abstract

We present the detection of 51 thermonuclear X-ray bursts observed from 4U 1636-536 by the Neutron Star Interior Composition Explorer (NICER) over the course of a three year monitoring campaign. We performed time resolved spectroscopy for 40 of these bursts and showed the existence of a strong soft excess in all the burst spectra. The excess emission can be characterized by the use of a scaling factor (f_a method) to the persistent emission of the source, which is attributed to the increased mass accretion rate on to the neutron star due to Poynting-Robertson drag. The soft excess emission can also be characterized by the use of a model taking into account the reflection of the burst emission off of the accretion disk. We also present time resolved spectral analysis of 5 X-ray bursts simultaneously observed by NICER and AstroSat, which confirm the main results with even greater precision. Finally, we present evidence for Compton cooling using 7 X-ray bursts observed contemporaneously with \nustar, by means of a correlated decrease in the hard X-ray lightcurve of 4U 1636-536 as the bursts start., Comment: Accepted for publication in the Astrophysical Journal

Published
2022
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37. The Thermonuclear X-Ray Bursts of 4U 1730–22

Author

Peter Bult, Giulio C. Mancuso, Tod E. Strohmayer, Arianna C. Albayati, Diego Altamirano, Douglas J. K. Buisson, Jérôme Chenevez, Sebastien Guillot, Tolga Güver, Wataru Iwakiri, Gaurava K. Jaisawal, Mason Ng, Andrea Sanna, and Jean H. Swank

Subjects
High Energy Astrophysical Phenomena (astro-ph.HE), Space and Planetary Science, X-ray bursts, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Low-mass x-ray binary stars
Abstract

We present observations of the historic transient 4U 1730-22 as observed with the Neutron Star Interior Composition Explorer (NICER). After remaining in quiescence since its 1972 discovery, this X-ray binary showed renewed outburst activity in 2021 and 2022. We observed 4U 1730-22 extensively with NICER, detecting a total of 17 thermonuclear X-ray bursts. From a spectroscopic analysis, we find that these X-ray bursts can be divided into a group of bright and weak bursts. All bright bursts showed $1\sim2$ second rise times and a photospheric radius expansion phase, while the weak bursts showed a slower $\sim5$ second rise with a tendency for concave shapes. From the photospheric radius expansion flux, we estimate the source distance at $6.9\pm0.2$ kpc. We consider various interpretations for our observations and suggest that they may be explained if accreted material is burning stably at the stellar equator, and unstable ignition occurs at a range of higher latitudes., 13 pages, 6 figures, 2 tables. Accepted for publication in ApJ

Published
2022

38. The Radius of PSR J0740+6620 from NICER and XMM-Newton Data

Author

Keith C. Gendreau, Michael Loewenstein, Michael T. Wolff, Sebastien Guillot, H. T. Cromartie, Paul S. Ray, Sridhar S. Manthripragada, Emmanuel Fonseca, Ingrid H. Stairs, Sharon M. Morsink, Matthew Kerr, Takashi Okajima, C. B. Markwardt, James M. Lattimer, Zaven Arzoumanian, Ismaël Cognard, Aditya Parthasarathy, Wynn C. G. Ho, Frederick K. Lamb, Scott M. Ransom, Alexander J. Dittmann, S. Pollard, Charles Baker, Lucas Guillemot, Thoniel Cazeau, M. C. Miller, Slavko Bogdanov, Timothy T. Pennucci, 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), 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), 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 d'Orléans (UO), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National d’Études Spatiales [Paris] (CNES)

Subjects
[PHYS.NUCL]Physics [physics]/Nuclear Theory [nucl-th], Nuclear Theory, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, General Relativity and Quantum Cosmology (gr-qc), Astrophysics::Cosmology and Extragalactic Astrophysics, [PHYS.NEXP]Physics [physics]/Nuclear Experiment [nucl-ex], 01 natural sciences, General Relativity and Quantum Cosmology, Nuclear Theory (nucl-th), Pulsar, Millisecond pulsar, 0103 physical sciences, Saturation (graph theory), Astrophysics::Solar and Stellar Astrophysics, Nuclear Experiment (nucl-ex), 010303 astronomy & astrophysics, Nuclear Experiment, Astrophysics::Galaxy Astrophysics, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Neutron Star Interior Composition Explorer, 010308 nuclear & particles physics, Gravitational wave, Equation of state (cosmology), Astronomy and Astrophysics, Radius, Neutron star, Space and Planetary Science, [SDU]Sciences of the Universe [physics], [PHYS.GRQC]Physics [physics]/General Relativity and Quantum Cosmology [gr-qc], Astrophysics::Earth and Planetary Astrophysics, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Astrophysics - High Energy Astrophysical Phenomena
Abstract

PSR J0740$+$6620 has a gravitational mass of $2.08\pm 0.07~M_\odot$, which is the highest reliably determined mass of any neutron star. As a result, a measurement of its radius will provide unique insight into the properties of neutron star core matter at high densities. Here we report a radius measurement based on fits of rotating hot spot patterns to Neutron Star Interior Composition Explorer (NICER) and X-ray Multi-Mirror (XMM-Newton) X-ray observations. We find that the equatorial circumferential radius of PSR J0740$+$6620 is $13.7^{+2.6}_{-1.5}$ km (68%). We apply our measurement, combined with the previous NICER mass and radius measurement of PSR J0030$+$0451, the masses of two other $\sim 2~M_\odot$ pulsars, and the tidal deformability constraints from two gravitational wave events, to three different frameworks for equation of state modeling, and find consistent results at $\sim 1.5-3$ times nuclear saturation density. For a given framework, when all measurements are included the radius of a $1.4~M_\odot$ neutron star is known to $\pm 4$% (68% credibility) and the radius of a $2.08~M_\odot$ neutron star is known to $\pm 5$%. The full radius range that spans the $\pm 1\sigma$ credible intervals of all the radius estimates in the three frameworks is $12.45\pm 0.65$ km for a $1.4~M_\odot$ neutron star and $12.35\pm 0.75$ km for a $2.08~M_\odot$ neutron star., Comment: 49 pages, 16 figures, submitted to The Astrophysical Journal Letters

Published
2021

39. 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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40. 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

41. NICER Detection of Thermal X-Ray Pulsations from the Massive Millisecond Pulsars PSR J0740+6620 and PSR J1614–2230

Author

Alexander J. Dittmann, M. Coleman Miller, Michael T. Wolff, Gilles Theureau, Keith C. Gendreau, Lucas Guillemot, Wynn C. G. Ho, Ismaël Cognard, Zaven Arzoumanian, Sebastien Guillot, Slavko Bogdanov, Kent S. Wood, Matthew Kerr, Paul S. Ray, 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), Laboratoire Univers et Théories (LUTH (UMR_8102)), 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), 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), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)

Subjects
[PHYS]Physics [physics], High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Neutron Star Interior Composition Explorer, 010308 nuclear & particles physics, Astrophysics::High Energy Astrophysical Phenomena, X-ray binary, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, 16. Peace & justice, 01 natural sciences, Spectral line, Neutron star, Pulsar, Space and Planetary Science, Millisecond pulsar, Thermal radiation, [SDU]Sciences of the Universe [physics], 0103 physical sciences, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Data reduction
Abstract

We report the detection of X-ray pulsations from the rotation-powered millisecond-period pulsars PSR J0740+6620 and PSR J1614-2230, two of the most massive neutron stars known, using observations with the Neutron Star Interior Composition Explorer (NICER). We also analyze X-ray Multi-Mirror Mission (XMM-Newton) data for both pulsars to obtain their time-averaged fluxes and study their respective X-ray fields. PSR J0740+6620 exhibits a broad double-peaked profile with a separation of ~0.4 in phase. PSR J1614-2230, on the other hand, has a broad single-peak profile. The broad modulations with soft X-ray spectra of both pulsars are indicative of thermal radiation from one or more small regions of the stellar surface. We show the NICER detections of X-ray pulsations for both pulsars and also discuss the phase relationship to their radio pulsations. In the case of PSR J0740+6620, this paper documents the data reduction performed to obtain the pulsation detection and prepare for pulse profile modeling analysis., Submitted to The Astrophysical Journal Letters

Published
2021

42. Discovery of thermonuclear Type-I X-ray bursts from the X-ray binary MAXI J1807+132

Author

Keith C. Gendreau, Gaurava K. Jaisawal, Jérôme Chenevez, Peter Bult, Tod E. Strohmayer, Tolga Guver, J. M. C. Court, C. Malacaria, S. Rapisarda, G. C. Mancuso, Laurens Keek, Diego Altamirano, A. C. Albayati, Zaven Arzoumanian, Sebastien Guillot, Deepto Chakrabarty, 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 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), and 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)

Subjects
Ciencias Astronómicas, 010504 meteorology & atmospheric sciences, bursts [X-rays], Astrophysics::High Energy Astrophysical Phenomena, X-ray binary, Neutron star, purl.org/becyt/ford/1.7 [https], FOS: Physical sciences, Astrophysics, Compact star, Eddington luminosity, Amplitude, 01 natural sciences, Luminosity, purl.org/becyt/ford/1 [https], symbols.namesake, X-rays: binaries, stars: neutron, Pulsar, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, X-rays: bursts, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), individual (MAXI J1807+132) [Stars], stars: individual (MAXI J1807+132), Astronomy and Astrophysics, neutron [Stars], Radius, 3. Good health, 13. Climate action, Space and Planetary Science, symbols, binaries [X-rays], Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract

MAXI J1807+132 is a low-mass X-ray binary (LMXB) first detected in outburst in 2017. Observations during the 2017 outburst did not allow for an unambiguous identification of the nature of the compact object. MAXI J1807+132 was detected in outburst again in 2019 and was monitored regularly with NICER. In this paper we report on five days of observations during which we detected three thermonuclear (Type-I) X-ray bursts, identifying the system as a neutron star LMXB. Time-resolved spectroscopy of the three Type-I bursts revealed typical characteristics expected for these phenomena. All three Type-I bursts show slow rises and long decays, indicative of mixed H/He fuel. We find no strong evidence that any of the Type-I bursts reached the Eddington Luminosity; however, under the assumption that the brightest X-ray burst underwent photospheric radius expansion, we estimate a, 9 pages, 4 figures

Published
2021

43. 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

44. 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

45. Constraining the Dense Matter Equation of State with Joint Analysis of NICER and LIGO/Virgo Measurements

Author

Samaya Nissanke, James M. Lattimer, Renee M. Ludlam, Anna L. Watts, Tanja Hinderer, G. Raaijmakers, Achim Schwenk, Sebastien Guillot, S. K. Greif, Kai Hebeler, Thomas E. Riley, IoP (FNWI), High Energy Astrophys. & Astropart. Phys (API, FNWI), Astroparticle Physics (IHEF, IoP, 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), 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), Sub String Theory Cosmology and ElemPart, and Theoretical Physics

Subjects
Equation of state, [PHYS.NUCL]Physics [physics]/Nuclear Theory [nucl-th], Nuclear Theory, 010504 meteorology & atmospheric sciences, Gaussian, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, 01 natural sciences, Nuclear Theory (nucl-th), symbols.namesake, Pulsar, 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, Gravitational wave, Starke Wechselwirkung und exotische Kerne – Abteilung Blaum, Astronomy and Astrophysics, Radius, LIGO, Stars, Space and Planetary Science, symbols, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Astrophysics - High Energy Astrophysical Phenomena
Abstract

The NICER collaboration recently published a joint estimate of the mass and the radius of PSR J0030+0451, derived via X-ray pulse-profile modeling. Raaijmakers et al. (2019) explored the implications of this measurement for the dense matter equation of state (EOS) using two parameterizations of the high-density EOS: a piecewise-polytropic model, and a model based on the speed of sound in neutron stars. In this work we obtain further constraints on the EOS following this approach, but we also include information about the tidal deformability of neutron stars from the gravitational wave signal of the compact binary merger GW170817. We compare the constraints on the EOS to those set by the recent measurement of a 2.14 solar mass pulsar, included as a likelihood function approximated by a Gaussian, and find a small increase in information gain. To show the flexibility of our method, we also explore the possibility that GW170817 was a neutron star-black hole merger, which yields weaker constraints on the EOS., 18 pages, 8 figures. Accepted for publication in ApJ Letters

Published
2020

46. The 2019 super-Eddington outburst of RX J0209.6-7427: Detection of pulsations and constraints on the magnetic field strength

Author

M. T. Wolff, Keith C. Gendreau, Tod E. Strohmayer, Diego Altamirano, P. A. Jenke, Georgios Vasilopoulos, Wataru Iwakiri, Paul S. Ray, Gaurava K. Jaisawal, A. L. Stevens, C. Malacaria, Colleen A. Wilson-Hodge, Sebastien Guillot, 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
Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Binary pulsar, individual: SMC [Galaxies], Luminosity, individual: RX J0209.6−7427 [Pulsars], symbols.namesake, stars: neutron, X-rays: binaries, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Accretion (meteorology), 010308 nuclear & particles physics, Astronomy and Astrophysics, neutron [Stars], Magnetic field, Neutron star, galaxies: individual: SMC, Space and Planetary Science, Eddington luminosity, symbols, binaries [X-rays], Small Magellanic Cloud, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Astrophysics - High Energy Astrophysical Phenomena, pulsars: individual: RX J0209.6–7427, Fermi Gamma-ray Space Telescope
Abstract

In November 2019, MAXI detected an X-ray outburst from the known Be X-ray binary system RX J0209.6-7427 located in the outer wing of the Small Magellanic Cloud. We followed the outburst of the system with NICER which led to the discovery of X-ray pulsations with a period of 9.3 s. We analyzed simultaneous X-ray data obtained with NuSTAR and NICER allowing us to characterize the spectrum and provide an accurate estimate of its bolometric luminosity. During the outburst the maximum broadband X-ray luminosity of the system reached $1-2\times10^{39}$ erg/s, thus exceeding by about one order of magnitude the Eddington limit for a typical 1.4 $M_{\odot}$ mass neutron star (NS). Monitoring observations with Fermi/GBM and NICER allowed us to study the spin evolution of the NS and compare it with standard accretion torque models. We found that the NS magnetic field should be of the order of $3\times10^{12}$ G. We conclude that RX J0209.6-7427 exhibited one of the brightest outbursts observed from a Be X-ray binary pulsar in the Magellanic Clouds, reaching similar luminosity level to the 2016 outburst of SMC X-3. Despite the super-Eddington luminosity of RX J0209.6-7427, the NS appears to have only a moderate magnetic field strength., 10 pages, 8 figures, accepted for publication in MNRAS

Published
2020

47. Disappearance of the Fe K$\alpha$ emission line in Ultra Compact X-ray Binaries 4U 1543-624 and Swift J1756.9-2508

Author

Filippos Koliopanos, Sebastien Guillot, N. A. Webb, Georgios Vasilopoulos, 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
Spectral shape analysis, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics, 01 natural sciences, Spectral line, X-rays: binaries, accretion, Ionization, 0103 physical sciences, Radiative transfer, Emission spectrum, 010303 astronomy & astrophysics, Line (formation), Physics, 010308 nuclear & particles physics, Astronomy and Astrophysics, accretion discs, radiative transfer, Space and Planetary Science, K-alpha, line: formation, methods: observational, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Astrophysics - High Energy Astrophysical Phenomena, Equivalent width, techniques: spectroscopic
Abstract

We investigate the long-term variability of the K$\alpha$ line of iron in the spectra of two Ultra Compact X-ray Sources (UCXBs) with C/O-rich donors. We revisit archival observations by five different X-ray telescopes, over a ~twenty year period. Adopting physically motivated models for the spectral continuum, we probe the long-term evolution of the source emission in a self-consistent manner enabling physical interpretation of potential variability in the primary X-ray emission continuum and/or any emission lines from reflection off the accretion disk. We find that the spectral shape and flux of the source emission (for both objects) has remained almost constant throughout all the observations, displaying only minor variability in some spectral parameters and the source flux (largest variation is a ~25% drop in the flux of Swift J1756.9-2508). We note a striking variability of the Fe K$\alpha$ line which fluctuates from a notable equivalent width of ~66-100 eV in 4U 1543-624 and ~170 eV in Swift J1756.9-2508, to non-detections with upper limits of 2-8 eV. We argue that the disappearance of the iron line is due to the screening of the Fe K$\alpha$ line by the overabundant oxygen in the C/O-rich UCXBs. This effect is cancelled when oxygen becomes fully ionized in the inner disk region, resulting in the variability of the Fe K$\alpha$ line in an otherwise unaltered spectral shape. This finding supports earlier predictions on the consequences of H-poor, C/O-rich accretion disk on reflection induced fluorescent lines in the spectra of UCXBs., Comment: Accepted for publication in MNRAS, 13 pages 8 figures

Published
2020

48. A deep Chandra survey for faint X-ray sources in the Galactic globular cluster M30, and searches for optical and radio counterparts

Author

James Miller-Jones, Yue Zhao, Thomas J. Maccarone, Laura Chomiuk, Phyllis M. Lugger, Arash Bahramian, Constanza Echiburú, Evangelia Tremou, Haldan N. Cohn, Jay Strader, Laura Shishkovsky, Craig O. Heinke, Gregory R. Sivakoff, Sebastien Guillot, 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 d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), 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), Laboratoire d'études spatiales et d'instrumentation en astrophysique = Laboratory of Space Studies and Instrumentation in Astrophysics (LESIA), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)

Subjects
Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Active galactic nucleus, 010308 nuclear & particles physics, galaxies: star clusters: individual: M30, X-ray, Binary number, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Radius, Type (model theory), 01 natural sciences, Jansky, X-rays: binaries, Space and Planetary Science, Millisecond pulsar, Globular cluster, 0103 physical sciences, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], 010303 astronomy & astrophysics
Abstract

We present a deep ($\sim 330~\mathrm{ks}$) {\it Chandra} survey of the Galactic globular cluster M30 (NGC 7099). Combining the new Cycle 18 with the previous Cycle 3 observations we report a total of 10 new X-ray point sources within the $1.03$ arcmin half-light radius, compiling an extended X-ray catalogue of a total of 23 sources. We incorporate imaging observations by the {\it Hubble Space Telescope} and the {\it Karl G. Jansky Very Large Array} from the MAVERIC survey to search for optical and radio counterparts to the new and old sources. Two X-ray sources are found to have a radio counterpart, including the known millisecond pulsar PSR J2140$-$2310A, the radio position of which also matches a previously reported faint optical counterpart which is slightly redder than the main sequence. We found optical counterparts to $18$ of the $23$ X-ray sources, identifying $2$ new cataclysmic variables (CVs), $5$ new CV candidates, $2$ new candidates of RS CVn type of active binary (AB), and $2$ new candidates of BY Dra type of AB. The remaining unclassified X-ray sources are likely background active galactic nuclei (AGN), as their number is consistent with the expected number of AGN at our X-ray sensitivity. Finally, our analysis of radial profiles of different source classes suggests that bright CVs are more centrally distributed than faint CVs in M30, consistent with other core-collapsed globular clusters., Comment: 24 pages, 12 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society

Published
2020
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49. NICER–NuSTAR Observations of the Neutron Star Low-mass X-Ray Binary 4U 1735–44

Author

Javier A. García, Christian Malacaria, A. C. Fabian, Edward M. Cackett, Gaurava K. Jaisawal, Peter Bult, Jonah Miller, Sebastien Guillot, C. B. Markwardt, Renee M. Ludlam, 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 Centre National d'Études Spatiales [Toulouse] (CNES)

Subjects
Physics, High Energy Astrophysical Phenomena (astro-ph.HE), 010504 meteorology & atmospheric sciences, Continuum (measurement), Astrophysics::High Energy Astrophysical Phenomena, X-ray binary, Binary number, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, K-line, Neutron star, Space and Planetary Science, 0103 physical sciences, Thermal, Low Mass, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], 010303 astronomy & astrophysics, Passband, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences
Abstract

We report on the first simultaneous $NICER$ and $NuSTAR$ observations of the neutron star (NS) low-mass X-ray binary 4U 1735$-$44, obtained in 2018 August. The source was at a luminosity of $\sim1.8~(D/5.6\ \mathrm{kpc})^{2}\times10^{37}$ ergs s$^{-1}$ in the $0.4-30$ keV band. We account for the continuum emission with two different continuum descriptions that have been used to model the source previously. Despite the choice in continuum model, the combined passband reveals a broad Fe K line indicative of reflection in the spectrum. In order to account for the reflection spectrum we utilize a modified version of the reflection model RELXILL that is tailored for thermal emission from accreting NSs. Alternatively, we also use the reflection convolution model of RFXCONV to model the reflected emission that would arise from a Comptonized thermal component for comparison. We determine that the innermost region of the accretion disk extends close to the innermost stable circular orbit ($R_{\mathrm{ISCO}}$) at the 90% confidence level regardless of reflection model. Moreover, the current flux calibration of $NICER$ is within 5% of the $NuSTAR$/FPMA(B)., Comment: Accepted for publication in ApJ, 8 pages, 1 table, 5 figures

Published
2020

50. Proper motion, spectra, and timing of PSR J1813–1749 using Chandra and NICER

Author

C. Malacaria, P. M. Saz Parkinson, Sebastien Guillot, Cristobal M. Espinoza, Wynn C. G. Ho, Brynmor Haskell, Gaurava K. Jaisawal, B. Limyansky, Micha l. Bejger, Chi-Yung Ng, 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), 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
Brightness, Proper motion, Photon, ISM: individual: G12.82–0.02, FOS: Physical sciences, X-rays: stars, Astrophysics, 01 natural sciences, Pulsar wind nebula, Article, Spectral line, Luminosity, HESS J1813–178, PSR J1813–1749, Pulsar, pulsars: general, 0103 physical sciences, 010306 general physics, 010303 astronomy & astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), pulsars: individual: CXOU J181335.16–174957.4, ISM: supernova remnants, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Astronomy and Astrophysics, Astrophysics - Solar and Stellar Astrophysics, 13. Climate action, Space and Planetary Science, Glitch (astronomy), Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract

PSR J1813-1749 is one of the most energetic rotation-powered pulsars known, producing a pulsar wind nebula (PWN) and gamma-ray and TeV emission, but whose spin period is only measurable in X-ray. We present analysis of two Chandra datasets that are separated by more than ten years and recent NICER data. The long baseline of the Chandra data allows us to derive a pulsar proper motion mu_R.A.=-(0.067"+/-0.010") yr^-1 and mu_decl.=-(0.014"+/-0.007") yr^-1 and velocity v_perp~900-1600 km/s (assuming a distance d=3-5 kpc), although we cannot exclude a contribution to the change in measured pulsar position due to a change in brightness structure of the PWN very near the pulsar. We model the PWN and pulsar spectra using an absorbed power law and obtain best-fit absorption NH=(13.1+/-0.9)x10^22 cm^-2, photon index Gamma=1.5+/-0.1, and 0.3-10 keV luminosity Lx~5.4x10^34 erg/s (d/5 kpc)^2 for the PWN and Gamma=1.2+/-0.1 and Lx~9.3x10^33 erg/s (d/5 kpc)^2 for PSR J1813-1749. These values do not change between the 2006 and 2016 observations. We use NICER observations from 2019 to obtain a timing model of PSR J1813-1749, with spin frequency nu=22.35 Hz and spin frequency time derivative nudot=(-6.428+/-0.003)x10^-11 Hz/s. We also fit nu measurements from 2009-2012 and our 2019 value and find a long-term spin-down rate nudot=(-6.3445+/-0.0004)x10^-11 Hz/s. We speculate that the difference in spin-down rates is due to glitch activity or emission mode switching., 9 pages, 5 figures; accepted for publication in MNRAS

Published
2020

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