Search

Magnetar-like activity has been observed in a large variety of neutron stars. PSR J1846−0258 is a young 327 ms radio-quiet pulsar with a large rotational power (∼8 × 1036 erg s−1), and resides at the center of the supernova remnant Kes 75. It is one of the rare examples of a high-magnetic-field pulsar showing characteristics both of magnetars and radio pulsars, and can thus provide important clues on the differences in the emission mechanisms between these two classes. In 2006, PSR J1846−0258 was detected to undergo an outburst for the first time, accompanied by a large flux increase, millisecond X-ray bursts, significant spectral changes, and a large timing glitch. In the period between 2020 May and June, after 14 yr of quiescent stable emission, the source underwent a second magnetar-like outburst, which was followed up with several observations by Neutron Star Interior Composition Explorer, XMM-Newton, NuSTAR, and Swift. In this work, we report on the long-term timing and X-ray spectral properties of the source following the 2020 outburst, and place upper limits on any source activity at radio wavelengths. We demonstrate that the pulsed flux increased by a factor >6 during the outburst, followed by nontrivial variability in the spin-down rate. Our timing analysis shows that the spin frequency and its derivative are clearly affected by magnetospheric activity due to the outburst. We find hints for an oscillation in the frequency derivative with a timescale of 50–60 days, recovering later on to stable quiescence. [ABSTRACT FROM AUTHOR]

The origin of an extraordinary X-ray burst (XRB) associated with a fast radio burst (FRB) such as FRB 20200428 is still unclear, though several models, such as the emission of a trapped fireball modified by resonant cyclotron scattering, the outflow from a polar trapped-expanding fireball, and the synchrotron radiation of a far-away relativistic shock, have been proposed. To determine which model is true, we study the possible X-ray polarization signature for each model, inspired by the importance of radio polarization in identifying the FRB origin. We first numerically simulate or calculate the XRB spectrum for each model and fit it to the observed data, then compute the corresponding polarization signal based on the fit. We find that these three models predict different polarization patterns in terms of phase/time and energy variations. The differences can be used to test the models with future X-ray polarization observations. [ABSTRACT FROM AUTHOR]

In this paper, we present rapid follow-up observations of the short GRB 201006A, consistent with being a compact binary merger, using the LOw Frequency ARray (LOFAR). We have detected a candidate 5.6 |$\sigma$|⁠ , short, coherent radio flash at 144 MHz at 76.6 min post-GRB with a 3 |$\sigma$| duration of 38 s. This radio flash is 27 arcsec offset from the GRB location, which has a probability of being co-located with the GRB of |$\sim$| 0.05 per cent (3.8 |$\sigma$|⁠) when accounting for measurement uncertainties. Despite the offset, we show that the probability of finding an unrelated transient within 40 arcsec of the GRB location is |$\lt 10^{-6}$| and conclude that this is a candidate radio counterpart to GRB 201006A. We performed image plane dedispersion and the radio flash is tentatively (2.4 |$\sigma$|⁠) shown to be highly dispersed, allowing a distance estimate, corresponding to a redshift of |$0.58\pm 0.06$|⁠. The corresponding luminosity of the event at this distance is |$6.7^{+6.6}_{-4.4} \times 10^{32}$| erg s |$^{-1}$| Hz |$^{-1}$|⁠. If associated with GRB 201006A, this emission would indicate prolonged activity from the central engine that is consistent with being a newborn, supramassive, likely highly magnetized, millisecond spin neutron star (a magnetar). [ABSTRACT FROM AUTHOR]

Millisecond magnetars are widely suggested as the central engines powering hydrogen-poor superluminous supernovae (SLSNe). These magnetars primarily lose huge rotational energy through gravitational wave radiation (GWR) and magnetic dipole radiation (MDR), with MDR serving as an energy source for SLSNe. We study the evolution of the magnetar spin, magnetic inclination angle, and the resulting thermal radiative luminosity of the SLSNe, where the impacts of the nucleon–nucleon short-range correlation, the mass and initial spin of the magnetar, and the density-dependent symmetry energy of the dense nuclear matter on the evolution are discussed. The relativistic mean-field theory is employed to calculate the nuclear matter properties, and we particularly concentrate on the time- and space-dependent bulk viscosity, which is crucial for the magnetic inclination angle evolution. It is found that the nucleon–nucleon short-range correlation weakens the damping of bulk viscosity of dense matter and therefore inhibits the growth of magnetic inclination angle, and it reduces the MDR (GWR) peak luminosity of a canonical magnetar by several times while it raises the peak thermal radiation luminosity of SLSNe by several times. For magnetars with non-rotating mass obviously lower than the |$1.4 \, \rm M_\odot$| with slow initial rotation, the magnetic inclination angle is more likely to evolve towards 0 deg quickly, and these magnetars are not suitable as the central engine for SLSNe. Within the 'family' of FSUGarnet interaction, a stiffer symmetry energy gives a lower threshold of direct Urca process and hence gives a much larger bulk viscosity coefficient, and thus it promotes the growth of the magnetic inclination angle and the GWR for canonical stars but reduces the peak brightness of SLSNe significantly. [ABSTRACT FROM AUTHOR]

We present an extensive contemporaneous X-ray and radio campaign performed on the repeating fast radio burst (FRB) source FRB 20220912A for 8 weeks immediately following the source's detection by CHIME/FRB. This includes X-ray data from XMM-Newton, NICER, and Swift, and radio detections of FRB 20220912A from CHIME/Pulsar and Effelsberg. We detect no significant X-ray emission at the time of 30 radio bursts with upper limits on a 0.5–10.0 keV X-ray fluence of (1.5–14.5) × 10−10 erg cm−2 (99.7% credible interval, unabsorbed) on a timescale of 100 ms. Translated into a fluence ratio η x/r = F X-ray/ F radio, this corresponds to η x/r < 7 × 106. For persistent emission from the location of FRB 20220912A, we derive a 99.7% 0.5–10.0 keV isotropic flux limit of 8.8 × 10−15 erg cm−2 s−1 (unabsorbed) or an isotropic luminosity limit of 1.4 × 1041 erg s−1 at a distance of 362.4 Mpc. We derive a hierarchical extension to the standard Bayesian treatment of low-count and background-contaminated X-ray data, which allows the robust combination of multiple observations. This methodology allows us to place the best (lowest) 99.7% credible interval upper limit on an FRB η x/r to date, η x/r < 2 × 106, assuming that all 30 detected radio bursts are associated with X-ray bursts with the same fluence ratio. If we instead adopt an X-ray spectrum similar to the X-ray burst observed contemporaneously with FRB-like emission from the Galactic magnetar SGR 1935+2154 detected on 2020 April 28, we derive a 99.7% credible interval upper limit on η x/r of 8 × 105, which is only 3 times the observed value of η x/r for SGR 1935+2154. [ABSTRACT FROM AUTHOR]

The neutrino-driven wind cooling phase of proto-neutron stars (PNSs) follows successful supernovae. Wind models without magnetic fields or rotation fail to achieve the necessary conditions for production of the third r -process peak, but robustly produce a weak r- process in neutron-rich winds. Using 2D magnetohydrodynamic simulations with magnetar-strength magnetic fields and rotation, we show that the PNS rotation rate significantly affects the thermodynamic conditions of the wind. We show that high-entropy material is quasiperiodically ejected from the closed zone of the PNS magnetosphere with the required thermodynamic conditions to produce heavy elements. We show that maximum entropy S of the material ejected depends systematically on the magnetar spin period P ⋆ and scales as S ∝ P ⋆ − 5 / 6 for sufficiently rapid rotation. We present results from simulations at a constant neutrino luminosity representative of ∼1–2 s after the onset of cooling for P ⋆ ranging from 5–200 ms and a few simulations with evolving neutrino luminosity where we follow the evolution of the magnetar wind until 10–14 s after the onset of cooling. We estimate at magnetar polar magnetic field strength B 0 = 3 × 1015 G and 1015 G that neutron-rich magnetar winds can, respectively, produce at least ∼1–5 × 10−5 M ⊙ and ∼1–4 × 10−7 M ⊙ of material with the required parameters for synthesis of the third r -process peak, within 1–2 s and 10 s, respectively, in that order after the onset of cooling. We show that proton-rich magnetar winds can have favorable conditions for production of p- nuclei, even at a modest B 0 = 5 × 1014 G. [ABSTRACT FROM AUTHOR]

The Sculptor Galaxy (NGC 253), located in the Southern Hemisphere, far off the Galactic Plane, has a relatively high star-formation rate of about 7 M |$_{\odot }$|  yr−1 and hosts a young and bright stellar population, including several super star clusters and supernova remnants. It is also the first galaxy, apart from the Milky Way Galaxy to be associated with two giant magnetar flares. As such, it is a potential host of pulsars and/or fast radio bursts in the nearby Universe. The instantaneous sensitivity and multibeam sky coverage offered by MeerKAT therefore make it a favourable target. We searched for pulsars, radio-emitting magnetars, and fast radio bursts in NGC 253 as part of the TRAPUM large survey project with MeerKAT. We did not find any pulsars during a 4 h observation, and derive a flux density limit of 4.4 µJy at 1400 MHz, limiting the pseudo-luminosity of the brightest putative pulsar in this galaxy to 54 Jy kpc2. Assuming universality of pulsar populations between galaxies, we estimate that detecting a pulsar as bright as this limit requires NGC 253 to contain a pulsar population of ⪞20 000. We also did not detect any single pulses, and our single pulse search flux density limit is 62 mJy at 1284 MHz. Our search is sensitive enough to have detected any fast radio bursts and radio emission similar to the brighter pulses seen from the magnetar SGR J1935+2154 if they had occurred during our observation. [ABSTRACT FROM AUTHOR]

Among the more than 60 sources observed in the first two years of operations, IXPE addressed four magnetars, neutron stars believed to host ultra-strong magnetic fields. We report here the main implication coming from IXPE measurements for the physics of magnetars. Polarimetric observations confirmed the expectations of high polarization degrees, up to ≈ 80 % , values which have not been detected in any other source so far, providing further proof (independent from the P- P ˙ estimate) that magnetars host indeed ultra-magnetized neutron stars. Polarization measurements also indicate that softer X-rays likely come from surface regions where the overlying atmosphere underwent magnetic condensation. The agreement of the phase-dependent polarization angle with a simple rotating vector model strongly supports the presence of vacuum birefringence around the star. [ABSTRACT FROM AUTHOR]

While the appeal of their extraordinary radio luminosity to our curiosity is undiminished, the nature of fast radio bursts (FRBs) has remained unclear. The challenge has been due in part to small sample sizes and limited understanding of telescope selection effects. We here present the first inclusion of the entire set of one-off FRBs from CHIME/FRB Catalog 1 in frbpoppy. Where previous work had to curate this data set, and fit for few model parameters, we have developed full multi-dimensional Markov chain Monte Carlo (MCMC) capabilities for frbpoppy – the comprehensive, open-science FRB population synthesis code – that allow us to include all one-off CHIME bursts. Through the combination of these two advances we now find the best description of the real, underlying FRB population, with higher confidence than before. We show that 4 ± 3 × 103 one-off FRBs go off every second between Earth and z = 1; and we provide a mock catalog based on our best model, for straightforward inclusion in other studies. We investigate CHIME side-lobe detection fractions, and FRB luminosity characteristics, to show that some bright, local FRBs are still being missed. We find strong evidence that FRB birth rates evolve with the star formation rate of the Universe, even with a hint of a short (0.1−1 Gyr) delay time. The preferred contribution of the hosts to the FRB dispersion agrees with a progenitor birth location in the host disk. This population-based evidence solidly aligns with magnetar-like burst sources, and we conclude FRBs are emitted by neutron stars. [ABSTRACT FROM AUTHOR]

Context. Fast radio bursts (FRBs) are energetic, millisecond-duration radio pulses observed at extragalactic distances and whose origins are still a subject of heated debate. A fraction of the FRB population have shown repeating bursts, however it's still unclear whether these represent a distinct class of sources. Aims. We investigated the bursting behaviour of FRB 20220912A, one of the most active repeating FRBs known thus far. In particular, we focused on its burst energy distribution, linked to the source energetics, and its emission spectrum, with the latter directly related to the underlying emission mechanism. Methods. We monitored FRB 20220912A at 408 MHz with the Northern Cross radio telescope and at 1.4 GHz using the 32-m Medicina Grueff radio telescope. Additionally, we conducted 1.2 GHz observations taken with the upgraded Giant Meter Wave Radio Telescope (uGMRT) searching for a persistent radio source coincident with FRB 20220912A, and included high energy observations in the 0.3–10 keV, 0.4–100 MeV and 0.03–30 GeV energy range. Results. We report 16 new bursts from FRB 20220912A at 408 MHz during the period between October 16th 2022 and December 31st 2023. Their cumulative spectral energy distribution follows a power law with slope αE = −1.3 ± 0.2 and we measured a repetition rate of 0.19 ± 0.03 hr−1 for bursts having a fluence of ℱ ≥ 17 Jy ms. Furthermore, we report no detections at 1.4 GHz for ℱ ≥ 20 Jy ms. These non-detections imply an upper limit of β < −2.3, with β being the 408 MHz – 1.4 GHz spectral index of FRB 20220912A. This is inconsistent with positive β values found for the only two known cases in which an FRB has been detected in separate spectral bands. We find that FRB 20220912A shows a decline of four orders of magnitude in its bursting activity at 1.4 GHz over a timescale of one year, while remaining active at 408 MHz. The cumulative spectral energy distribution (SED) shows a flattening for spectral energy Eν ≥ 1031 erg Hz−1, a feature seen thus far in only two hyperactive repeaters. In particular, we highlight a strong similarity between FRB 20220912A and FRB 20201124A, with respect to both the energy and repetition rate ranges. We also find a radio continuum source with 240 ± 36 μJy flux density at 1.2 GHz, centered on the FRB 20220912A coordinates. Finally, we place an upper limit on the γ to radio burst efficiency η to be η < 1.5 × 109 at 99.7% confidence level, in the 0.4–30 MeV energy range. Conclusions. The strong similarity between the cumulative energy distributions of FRB 20220912A and FRB 20201124A indicate that bursts from these sources are generated via similar emission mechanisms. Our upper limit on β suggests that the spectrum of FRB 20220912A is intrinsically narrow-band. The radio continuum source detected at 1.2 GHz is likely due to a star formation environment surrounding the FRB, given the absence of a source compact on millisecond scales brighter than 48 μJy beam−1. Finally, the upper limit on the ratio between the γ and radio burst fluence disfavours a giant flare origin for the radio bursts unlike observed for the Galactic magnetar SGR 1806-20. [ABSTRACT FROM AUTHOR]

Context. There is a growing number of peculiar events that cannot be assigned to any of the main classes. SN 1987A and a handful of similar objects, thought to be explosive outcomes of blue supergiant stars, is one of them: while their spectra closely resemble those of H-rich (IIP) SNe, their light curve (LC) evolution is very different. Aims. Here we present the detailed photometric and spectroscopic analysis of SN 2021aatd, a peculiar Type II explosion. While its early-time evolution resembles that of the slowly evolving double-peaked SN 2020faa (although at a lower luminosity scale), after ∼40 days its LC shape becomes similar to that of SN 1987A-like explosions. Methods. In addition to comparing LCs, color curves, and spectra of SN 2021aatd to those of SNe 2020faa, 1987A, and other objects, we compared the observed spectra with our own SYN++ models and with the outputs of published radiative transfer models. We also carried out a detailed modeling of the pseudo-bolometric LCs of SNe 2021aatd and 1987A with a self-developed semi-analytical code, assuming a two-component ejecta (core + shell), and involving the rotational energy of a newborn magnetar in addition to radioactive decay. Results. We find that the photometric and the spectroscopic evolution of SN 2021aatd can be well described with the explosion of a ∼15 M⊙ blue supergiant star. Nevertheless, SN 2021aatd shows higher temperatures and weaker Na I D and Ba II 6142 Å lines than SN 1987A, which is instead reminiscent of IIP-like atmospheres. With the applied two-component ejecta model (accounting for decay and magnetar energy), we can successfully describe the bolometric LC of SN 2021aatd, including the first ∼40-day phase showing an excess compared to 87A-like SNe, but being strikingly similar to that of the long-lived SN 2020faa. Nevertheless, finding a unified model that also explains the LCs of more luminous events (e.g., SN 2020faa) is still a matter of debate. [ABSTRACT FROM AUTHOR]

Crustal quakes of highly magnetized neutron stars can disrupt their magnetospheres, triggering energetic phenomena like X-ray and fast radio bursts. Understanding plasma wave dynamics in these extreme environments is vital for predicting energy transport across scales to the radiation length. This study models relativistic plasma wave interaction in magnetar magnetospheres with force-free electrodynamics simulations. For propagation along curved magnetic field lines, we observe the continuous conversion of Alfvén waves to fast magnetosonic (FMS) waves. The conversion efficiency can be up to three times higher when counter-propagating Alfvén waves interact in the equatorial region. Alfvén waves generate FMS waves of twice their frequency during their first crossing of the magnetosphere. After the initial transient burst of FMS waves, Alfvén waves convert to FMS waves periodically, generating variations on timescales of the magnetospheric Alfvén wave crossing time. This decaying FMS wave tail carries a significant portion (half) of the total energy emitted. Plastic damping of "bouncing" Alfvén waves by the magnetar crust has minimal impact on the FMS efficiency. We discuss the implications of the identified wave phenomena for magnetar observations. Outgoing FMS waves can develop electric zones, potential sources of coherent radiation. Long wavelength FMS waves could generate FRBs through reconnection beyond the light cylinder. [ABSTRACT FROM AUTHOR]

Utilizing four archival X-ray data sets taken with the Hard X-ray Detector onboard Suzaku , timing studies were performed on three magnetars, 1E 1841−045 (observed in 2006), SGR 0501+4516 (2008), and 1RXS J170849.0−400910 (2009 and 2010). Their pulsations were reconfirmed, typically in an energy range of 12–50 keV. The 11.783 s pulses of 1E 1841−045 and those of SGR 0501+4516 at 5.762 s were periodically phase modulated, with a long period of |$\approx 23.4$| and |$\approx 16.4$|  ks, respectively. The pulse-phase modulation was also observed, at |$\approx 46.5$|  ks, from two data sets of 1RXS J170849.0−400910. In all these cases, the modulation amplitude was 6 per cent to 16 per cent of the pulse cycle. Including previously confirmed four objects, this characteristic timing behaviour is now detected from seven magnetars in total, and interpreted as a result of free precession of neutron stars that are deformed to an asphericity of |$\sim 10^{-4}$|⁠. Assuming that the deformation is due to magnetic stress, these magnetars are inferred to harbour toroidal magnetic fields of |$B_{\rm t}\sim 10^{16}$|  G. By comparing the estimated |$B_{\rm t}$| of these objects with their poloidal dipole field |$B_{\rm d}$|⁠ , the |$B_{\rm t}/B_{\rm d}$| ratio is found to increase with their characteristic age. Therefore, the toroidal fields of magnetars are likely to last longer than their poloidal fields. This explains the presence of some classes of neutron stars that have relatively weak |$B_{\rm d}$| but are suspected to hide strong |$B_{\rm t}$| inside them. [ABSTRACT FROM AUTHOR]

The ultra-high-energy cosmic ray (UHECR) puzzle is reviewed under the hints of a few basic results: clustering, anisotropy, asymmetry, bending, and composition changes with energies. We show how the lightest UHECR nuclei from the nearest AGN or Star-Burst sources, located inside a few Mpc Local Sheets, may explain, at best, the observed clustering of Hot Spots at tens EeV energy. Among the possible local extragalactic candidate sources, we derived the main contribution of very few galactic sources. These are located in the Local Sheet plane within a distance of a few Mpc, ejecting UHECR at a few tens of EeV energy. UHECR also shine at lower energies of several EeV, partially feeding the Auger dipole by LMC and possibly a few nearer galactic sources. For the very recent highest energy UHECR event, if a nucleon, it may be explained by a model based on the scattering of UHE ZeV neutrinos on low-mass relic neutrinos. Such scatterings are capable of correlating, via Z boson resonance, the most distant cosmic sources above the GZK bound with such an enigmatic UHECR event. Otherwise, these extreme events, if made by the heaviest composition, could originate from the largest bending trajectory of heaviest nuclei or from nearby sources, even galactic ones. In summary, the present lightest to heavy nuclei model UHECR from the Local Sheet could successfully correlate UHECR clustering with the nearest galaxies and AGN. Heavy UHECR may shine by being widely deflected from the Local Sheet or from past galactic, GRB, or SGR explosive ejection. [ABSTRACT FROM AUTHOR]

Four X-ray datasets of the soft gamma repeater SGR 1806−20, taken with the Gas Imaging Spectrometer (GIS) onboad ASCA, were analyzed. Three of them were acquired over 1993 October 9–20, the last one in 1995 October. Epoch-folding analysis of the 2.8–12 keV signals confirmed the ∼7.6 s pulses in these data, which Kouveliotou et al. (1998, Nature, 393, 235) reported as one of the earliest pulse detections from this object. In the 1995 observation, 3–12 keV pulses were phase modulated with a period of T  = 16.4 ± 0.4 ks, and an amplitude of ∼1 s. This makes a fourth example of the behavior observed from magnetars. As in the previous three sources, the pulse-phase modulation of SGR 1806−20 disappeared at ≲2.5 keV, where the soft X-ray component dominates. In the 1993 datasets, this periodic modulation was reconfirmed, and successfully phase-connected coherently across the 11 d interval. As a result, the modulation period was refined to T  = 16.435 ± 0.024 ks. The implied high stability of the phenomenon strengthens its interpretation in terms of free precession of the neutron star, which is deformed to an asphericity of ∼10−4, presumably by the stress of toroidal magnetic fields reaching ∼1016 G. Toroidal fields of this level can be common among magnetars. [ABSTRACT FROM AUTHOR]

The August 2024 issue of Astronomy & Geophysics covers a wide range of topics in astronomy. It includes information about the upcoming Caroline Herschel Prize Lecture, which will discuss the use of artificial intelligence in finding exploding stars and black holes. The winners of the 2023 RAS Thesis Prize are also announced, and details about National Astronomy Week in 2025 are provided. The issue features scientific discoveries such as the most distant known galaxy, the cause of water loss on Venus, evidence of space weathering on asteroid Ryugu, and the presence of liquid rock droplet clouds on exoplanet WASP-43b. Other topics covered include sunspots, Pluto's heart-shaped feature, alternative eclipse observation methods, quasar mergers, planet-forming disks, gas outflows in galaxies, supermassive black hole growth, early galaxy mergers, magnetar bursts, the Sun's magnetic field formation, a vent near the Milky Way's black hole, and a new model explaining phosphorus abundance. A new Earth-sized exoplanet called SPECULOOS-3 b has been discovered orbiting a nearby ultra-cool dwarf star, and researchers found that primordial inhomogeneities in molecular clouds can create chemical differences in stars with the same origin. Another study suggests that massive stars can collapse into black holes without becoming supernovae. [Extracted from the article]

We present photometric and spectroscopic observations and analysis of the Type IIb supernova (SN) SN 2019tua, which exhibits multiple bumps in its declining light curves between 40 and 65 days after discovery. SN 2019tua shows a time to peak of about 25 days, similar to other Type IIb SNe. Our observations indicate a decrease in its brightness of about 1 mag in the 60 days after the peak. At about days 50 and 60, its multiband light curves exhibit bumpy behavior. The complex luminosity evolution of SN 2019tua could not be well modeled with a single currently popular energy source model, e.g., radioactive decay of 56Ni, magnetar, interaction between the ejecta and a circumstellar shell. Even though the magnetar model has a smaller χ 2/dof value, the complex changes in SN 2019tua's brightness suggest that more than one physical process might be involved. We propose a hybrid circumstellar medium (CSM) interaction plus 56Ni model to explain the bolometric light curve of SN 2019tua. The fitting results show that the ejecta mass M ej ≈ 2.4 M ⊙, the total CSM mass M CSM ≈ 1.0 M ⊙, and the 56Ni mass M Ni ≈ 0.4 M ⊙. The total kinetic energy of the ejecta is E k ≈ 0.5 × 1051 erg. Preexisting multiple shells suggest that the progenitor of SN 2019tua experienced mass ejections within approximately ∼6–44 yr prior to the explosion. [ABSTRACT FROM AUTHOR]

Time-domain and multimessenger astronomy (TDAMM) involves the study of transient and time-variable phenomena across various wavelengths and messengers. The Astro2020 Decadal Survey has identified TDAMM as the top priority for NASA in this decade, emphasizing its crucial role in advancing our understanding of the universe and driving new discoveries in astrophysics. The TDAMM community has come together to provide further guidance to funding agencies, aiming to define a clear path toward optimizing scientific returns in this research domain. This encompasses not only astronomy but also fundamental physics, offering insights into properties of gravity, the formation of heavy elements, the equation of state of dense matter, and quantum effects associated with extreme magnetic fields. Magnetars, neutron stars with the strongest magnetic fields in the universe, play a critical role in this context. We aim to underscore the significance of magnetars in TDAMM, highlighting the necessity of ensuring observational continuity, addressing current limitations, and outlining essential requirements to expand our knowledge in this field. [ABSTRACT FROM AUTHOR]

The milestone discovery of GW170817-GRB 170817A-AT 2017gfo has shown that gravitational waves (GWs) could be produced during the merger of a neutron star–neutron star/black hole and that in electromagnetic (EM) waves, a gamma-ray burst (GRB) and a kilonova (KN) are generated in sequence after the merger. Observationally, however, EM properties before the merger phase are still unclear. Here we report a peculiar precursor in a KN-associated long-duration GRB 211211A, providing evidence of the EM before the merger. This precursor lasts ∼0.2 s, and the waiting time between the precursor and the main burst is ∼1 s, comparable to that between GW170817 and GRB 170817A. The spectrum of the precursor could be well fit with a nonthermal cutoff power-law model instead of a blackbody. In particular, a ∼22 Hz quasiperiodic oscillation candidate (∼3 σ) is detected in the precursor. These temporal and spectral properties indicate that this precursor is probably produced by a catastrophic flare accompanied with magnetoelastic or crustal oscillations of a magnetar in a binary compact merger. The strong magnetic field of the magnetar can also account for the prolonged duration of GRB 211211A. However, it poses a challenge to reconcile the rather short lifetime of a magnetar with the rather long spiraling time of a binary neutron star system only by the GW radiation before the merger. [ABSTRACT FROM AUTHOR]

The fallback disk model is widely accepted to explain long-period neutron stars (NSs) that cannot be simulated by magnetic dipole radiation. However, there was no confirmed detection of disks from the newly discovered long-period pulsars GLEAM-X 162759.5-523504.3 and GPM J1839-10 and the slowest known isolated NS 1E 161348-5055. This might be because the disks have either been in a noninteracting/inactive state where their emission is too weak to be detected or have been disrupted. In this work, we conduct simulations to examine the lifetime of supernova fallback disks around isolated NSs. We assume that the disks' mass varies in a self-similar way, and their interaction with the NS occurs only in an interacting/active state. Our results reveal that nearly all the interacting lifetimes for the disks are shorter than 105 yr, while the existence lifetimes are considerably longer. [ABSTRACT FROM AUTHOR]

Magnetars are slowly rotating neutron stars that possess the strongest magnetic fields known in the cosmos (1014 − 1015 G). They display a range of transient high-energy electromagnetic activity. The brightest and most energetic of these events are the gamma-ray bursts (GRBs) known as magnetar giant flares (MGFs), with isotropic energies Eiso ≈ 1044 − 1046 erg. Only seven MGF detections have been made to date: three unambiguous events occurred in our Galaxy and the Magellanic Clouds, and the other four MGF candidates are associated with nearby star-forming galaxies. As all seven identified MGFs are bright at Earth, additional weaker events likely remain unidentified in archival data. We conducted a search of the Fermi Gamma-ray Burst Monitor database for candidate extragalactic MGFs and, when possible, collected localization data from the Interplanetary Network (IPN) satellites. Our search yielded one convincing event, GRB 180128A. IPN localizes this burst within NGC 253, commonly known as the Sculptor Galaxy. The event is the second MGF in modern astronomy to be associated with this galaxy and the first time two bursts have been associated with a single galaxy outside our own. Here we detail the archival search criteria that uncovered this event and its spectral and temporal properties, which are consistent with expectations for a MGF. We also discuss the theoretical implications and finer burst structures resolved from various binning methods. Our analysis provides observational evidence of an eighth identified MGF. [ABSTRACT FROM AUTHOR]

We present the semi-analytical light curve modelling of 13 supernovae associated with gamma-ray bursts (GRB-SNe) along with two relativistic broad-lined (Ic-BL) SNe without GRB association (SNe 2009bb and 2012ap), considering millisecond magnetars as central-engine-based power sources for these events. The bolometric light curves of all 15 SNe in our sample are well-regenerated utilizing a χ2-minimization code, MINIM , and numerous parameters are constrained. The median values of ejecta mass (M ej), magnetar's initial spin period (P i), and magnetic field (B) for GRB-SNe are determined to be ≈5.2 M⊙, 20.5 ms, and 20.1 × 1014 G, respectively. We leverage machine learning (ML) algorithms to comprehensively compare the three-dimensional parameter space encompassing M ej, P i, and B for GRB-SNe determined herein to those of H-deficient superluminous SNe (SLSNe-I), fast blue optical transients (FBOTs), long GRBs (LGRBs), and short GRBs (SGRBs) obtained from the literature. The application of unsupervized ML clustering algorithms on the parameters M ej, P i, and B for GRB-SNe, SLSNe-I, and FBOTs yields a classification accuracy of ∼95 per cent. Extending these methods to classify GRB-SNe, SLSNe-I, LGRBs, and SGRBs based on P i and B values results in an accuracy of ∼84 per cent. Our investigations show that GRB-SNe and relativistic Ic-BL SNe presented in this study occupy different parameter spaces for M ej, P i, and B than those of SLSNe-I, FBOTs, LGRBs, and SGRBs. This indicates that magnetars with different P i and B can give birth to distinct types of transients. [ABSTRACT FROM AUTHOR]

Core-collapse supernovae (CCSNe) are considered the primary magnetar formation channel, with 15 magnetars associated with supernova remnants (SNRs). A large fraction of these should occur in massive stellar binaries that are disrupted by the explosion, meaning that |$\sim 45~{{\ \rm per\ cent}}$| of magnetars should be nearby high-velocity stars. Here, we conduct a multiwavelength search for unbound stars, magnetar binaries, and SNR shells using public optical (uvgrizy bands), infrared (J, H, K , and Ks bands), and radio (888 MHz, 1.4 GHz, and 3 GHz) catalogues. We use Monte Carlo analyses of candidates to estimate the probability of association with a given magnetar based on their proximity, distance, proper motion, and magnitude. In addition to recovering a proposed magnetar binary, a proposed unbound binary, and 13 of 15 magnetar SNRs, we identify two new candidate unbound systems: an OB star from the Gaia catalogue we associate with SGR J1822.3−1606, and an X-ray pulsar we associate with 3XMM J185246.6 + 003317. Using a Markov Chain Monte Carlo simulation that assumes all magnetars descend from CCSNe, we constrain the fraction of magnetars with unbound companions to |$5\lesssim f_u \lesssim 24~{{\ \rm per\ cent}}$|⁠ , which disagrees with neutron star population synthesis results. Alternate formation channels are unlikely to wholly account for the lack of unbound binaries as this would require |$31\lesssim f_{nc} \lesssim 66~{{\ \rm per\ cent}}$| of magnetars to descend from such channels. Our results support a high fraction (⁠|$48\lesssim f_m \lesssim 86~{{\ \rm per\ cent}}$|⁠) of pre-CCSN mergers, which can amplify fossil magnetic fields to preferentially form magnetars. [ABSTRACT FROM AUTHOR]

A fast radio burst (FRB) localized to a globular cluster (GC) challenges FRB models involving ordinary young magnetars. In this paper, we examine the rapid spin-down millisecond neutron star (NS) scenario, which favours the dynamic environment in GCs. Fast spin-down corresponds to a larger magnetic field than regular millisecond pulsars, which empirically favours giant pulse (GP) emission. The kinetic energy in millisecond NSs can readily exceed the magnetic energy in magnetars. The high inferred isotropic luminosity of most FRBs is challenging to explain in spin-down powered pulsars. A recent observation of a GP from the Crab pulsar, on the other hand, suggests highly Doppler-beamed emission, making the required energy orders of magnitude smaller than estimated with isotropic assumptions. Considering this strong beaming effect, GPs from a recycled pulsar with a modest magnetic field could explain the energetics and burst rates for a wide range of FRBs. The short life span accounts for a paucity of bright FRBs in the Milky Way neighbourhood. We point out that tidal disruption spin-up from a main-sequence star can provide sufficient accretion rate to recycle an NS with mild magnetic field. It can also explain the observed source density and the spatial offset in the GC for FRB 20200120E. Frequency variation in the scattering tail for some of the brightest FRBs is expected in this scenario. [ABSTRACT FROM AUTHOR]

Fast radio bursts (FRBs) are cosmological radio transients with millisecond durations and extremely high brightness temperatures. One FRB repeater, FRB 180916.J0158+65 (FRB 180916B), was confirmed to appear 16.35-day periodic activities with 5-day activity window. Another FRB repeater, FRB 121102, and two soft gamma-ray repeaters (SGRs), SGR 1935+2154 and SGR 1806−20, also show possible periodic activities. These periodicities might originate from the precession process of young magnetars due to the anisotropic pressure from the inner magnetic fields as proposed in the literature. In this work, we analyse a self-consistent model for the rotation evolution of magnetars and obtain the evolutions of magnetar precession and obliquity. We find that if the FRB repeaters and the SGRs with (possible) periodic activities originate from the magnetar precession, their ages would be constrained to be hundreds to tens of thousands of years, which is consistent with the typical ages of magnetars. Assuming that the FRB emission is beaming in the magnetosphere as proposed in the literature, we calculate the evolution of the observable probability and the duty cycle of the active window period. We find that for a given magnetar the observable probability increases with the magnetar age in the early stage and decreases with the magnetar age in the later stage; meanwhile, there are one or two active windows in one precession period if the emission is not perfectly axisymmetric with respect to the deformation axis of a magnetar, which could be tested by the future observation for repeating FRB sources. [ABSTRACT FROM AUTHOR]

Quantum electrodynamic (QED) plasmas, describing the intricate interplay of strong-field QED and collective pair plasma effects, play pivotal roles in astrophysical settings like those near black holes or magnetars. However, the creation of observable QED plasmas in laboratory conditions was thought to require ultra-intense lasers beyond the capabilities of existing technologies, hindering experimental verification of QED plasma theories. This paper provides a comprehensive review of recent studies outlining a viable approach to create and detect observable QED plasmas by combining existing electron beam facilities with state-of-the-art lasers. The collision between a high-density 30 GeV electron beam and a 3 PW laser initiates a QED cascade, resulting in a pair plasma with increasing density and decreasing energy. These conditions contribute to a higher plasma frequency, enabling the observation of ∼ 0.2 % laser frequency upshift. This solution of the joint production-observation problem should facilitate the near-term construction of ultra-intense laser facilities both to access and to observe the realm of strong-field QED plasmas. [ABSTRACT FROM AUTHOR]

Recently, two ultralong-period radio transients, GLEAM-X J162759.5-523504.3 (J1627) and GPM J1839-10 (J1839), were discovered with spin periods longer than 1000 s. The origin of these two ultralong-period radio transients is intriguing in understanding the spin evolution of neutron stars (NSs). In this work, we examine whether the interaction between strong magnetized NSs and fallback disks can spin NSs down to the observed ultralong period. Our simulations found that the magnetar + fallback disk model can account for the observed period, period derivative, and X-ray luminosity of J1627 in the quasi-spin-equilibrium stage. To evolve to the current state of J1627, the initial mass-accretion rate of the fallback disk and the magnetic field of the NS are in the range of (1.1–30) × 1024 g s−1 and (2–5) × 1014 G, respectively. In the active lifetime of the fallback disk, it is impossible for J1839 to achieve the observed upper limit of the period derivative. Therefore, we propose that J1839 may be in the second ejector phase after the fallback disk becomes inactive. Those NSs with a magnetic field of (2–6) × 1014 G and a fallback disk with an initial mass-accretion rate of ∼1024–1026 g s−1 are possible progenitors of J1839. [ABSTRACT FROM AUTHOR]

It was recently discovered that the time correlations of repeating fast radio bursts (FRBs) are similar to earthquake aftershocks. Motivated by the association between FRBs and magnetars, here we report correlation function analyses in the time-energy space for the 563 periodic radio pulses and the 579 X-ray short bursts from the magnetar SGR 1935+2154, which is known to have generated FRBs. Although radio pulses are concentrated near the fixed phase of the rotational cycle, we find that when multiple pulses occur within a single cycle, their correlation properties (aftershock production probability, aftershock rate decaying in power of time, and more) are similar to those of extragalactic FRBs and earthquakes. A possible interpretation is that the radio pulses are produced by rupture of the neutron star crust, and the first pulse within one cycle is triggered by external force periodically exerted on the crust. The periodic external force may be from the interaction of the magnetosphere with material ejected in an outburst. For X-ray bursts, we found no significant correlation signal, though correlation on the same time-scale as radio pulses may be hidden due to the long event duration. The aftershock similarity between the periodic radio pulsation and FRBs is surprising, given that the two are energetically very different, and therefore the energy sources would be different. This suggests that the essence of FRB-like phenomena is starquakes, regardless of the energy source, and it is important to search for FRB-like bursts from neutron stars with various properties or environments. [ABSTRACT FROM AUTHOR]

Fast radio bursts (FRBs) are luminous millisecond-duration radio pulses with extragalactic origin, which were discovered more than a decade ago. Despite the numerous samples, the physical origin of FRBs remains poorly understood. FRBs have been thought to originate from young magnetars or accreting compact objects (COs). Massive stars or COs are predicted to be embedded in the accretion discs of active galactic nuclei (AGNs). The dense disc absorbs FRBs severely, making them difficult to observe. However, progenitors' ejecta or outflow feedback from the accreting COs interact with the disc material to form a cavity. The existence of the cavity can reduce the absorption by the dense disc materials, making FRBs escape. Here, we investigate the production and propagation of FRBs in AGN discs and find that the AGN environments lead to the following unique observational properties, which can be verified in future observation. First, the dense material in the disc can cause large dispersion measure (DM) and rotation measure (RM). Secondly, the toroidal magnetic field in the AGN disc can cause Faraday conversion. Thirdly, during the shock breakout, DM and RM show non-power-law evolution patterns over time. Fourthly, for accreting-powered models, higher accretion rates lead to more bright bursts in AGN discs, accounting for up to 1 per cent of total bright repeating FRBs. [ABSTRACT FROM AUTHOR]

Magnetized plasma columns and extended magnetic structures with both footpoints anchored to a surface layer are an important building block of astrophysical dissipation models. Current loops shining in X-rays during the growth of plasma instabilities are observed in the corona of the Sun and are expected to exist in highly magnetized neutron star magnetospheres and accretion disk coronae. For varying twist and system sizes, we investigate the stability of line-tied force-free flux tubes and the dissipation of twist energy during instabilities using linear analysis and time-dependent force-free electrodynamics simulations. Kink modes (m = 1) and efficient magnetic energy dissipation develop for plasma safety factors q ≲ 1, where q is the inverse of the number of magnetic field line windings per column length. Higher-order fluting modes (m > 1) can distort equilibrium flux tubes for q > 1 but induce significantly less dissipation. In our analysis, the characteristic pitch μ ˜ 0 of flux-tube field lines determines the growth rate ( ∝ μ ˜ 0 3 ) and minimum wavelength of the kink instability ( ∝ μ ˜ 0 − 1 ). We use these scalings to determine a minimum flux tube length for the growth of the kink instability for any given μ ˜ 0 . By drawing analogies to idealized magnetar magnetospheres with varying regimes of boundary shearing rates, we discuss the expected impact of the pitch-dependent growth rates for magnetospheric dissipation in magnetar conditions. [ABSTRACT FROM AUTHOR]

SN 2020zbf is a hydrogen-poor superluminous supernova (SLSN) at z = 0.1947 that shows conspicuous C II features at early times, in contrast to the majority of H-poor SLSNe. Its peak magnitude is Mg = −21.2 mag and its rise time (≲26.4 days from first light) places SN 2020zbf among the fastest rising type I SLSNe. We used spectra taken from ultraviolet (UV) to near-infrared wavelengths to identify spectral features. We paid particular attention to the C II lines as they present distinctive characteristics when compared to other events. We also analyzed UV and optical photometric data and modeled the light curves considering three different powering mechanisms: radioactive decay of 56Ni, magnetar spin-down, and circumstellar medium (CSM) interaction. The spectra of SN 2020zbf match the model spectra of a C-rich low-mass magnetar-powered supernova model well. This is consistent with our light curve modeling, which supports a magnetar-powered event with an ejecta mass Mej = 1.5 M⊙. However, we cannot discard the CSM-interaction model as it may also reproduce the observed features. The interaction with H-poor, carbon-oxygen CSM near peak light could explain the presence of C II emission lines. A short plateau in the light curve around 35–45 days after peak, in combination with the presence of an emission line at 6580 Å, can also be interpreted as being due to a late interaction with an extended H-rich CSM. Both the magnetar and CSM-interaction models of SN 2020zbf indicate that the progenitor mass at the time of explosion is between 2 and 5 M⊙. Modeling the spectral energy distribution of the host galaxy reveals a host mass of 108.7M⊙, a star formation rate of 0.24−0.12+0.41M⊙ yr−1, and a metallicity of ∼0.4 Z⊙. [ABSTRACT FROM AUTHOR]

The first magnetic field in a star other than the Sun was detected in 1947 in the star 78 Vir. Today, we know that about 10% of these intermediate-mass and high-mass stars have strong, large-scale surface magnetic fields whose origin has remained a mystery till today. It has been suggested that merging of main-sequence and pre-main-sequence stars could produce such strong fields. The massive star τ Sco is a well-known member of the group of magnetic stars and is a blue straggler given its apparently young age compared to that of other members of the Upper Scorpius association. Here, we present 3D magnetohydrodynamic simulations of the coalescence of two massive main-sequence stars and 1D stellar evolution computations of the subsequent evolution of the merger product that can explain τ Sco's magnetic field, apparent youth and other observed characteristics. We argue that field amplification in stellar mergers is a general mechanism to form strongly-magnetised massive stars. Such stars are promising progenitors of magnetars, which may give rise to some of the enigmatic fast radio bursts, and their supernova explosions may be affected by the strong magnetic fields. [ABSTRACT FROM AUTHOR]

We reconsider the escape of high-brightness coherent emission of fast radio bursts (FRBs) from magnetars' magnetospheres, and conclude that there are numerous ways for the powerful FRB pulse to avoid non-linear absorption. Sufficiently strong surface magnetic fields, |$\ge 10{{\ \rm per\ cent}}$| of the quantum field, limit the waves' non-linearity to moderate values. For weaker fields, the electric field experienced by a particle is limited by a combined ponderomotive and parallel-adiabatic forward acceleration of charges by the incoming FRB pulse along the magnetic field lines newly opened during FRB/coronal mass ejection. As a result, particles surf the weaker front part of the pulse, experiencing low radiative losses, and are cleared from the magnetosphere for the bulk of the pulse to propagate. We also find that initial mildly relativistic radial plasma flow further reduces losses. [ABSTRACT FROM AUTHOR]

We present new radio continuum images and a source catalogue from the MeerKAT survey in the direction of the Small Magellanic Cloud. The observations, at a central frequency of 1.3 GHz across a bandwidth of 0.8 GHz, encompass a field of view ∼7° × 7° and result in images with resolution of 8 arcsec. The median broad-band Stokes I image Root Mean Squared noise value is ∼11  μ Jy beam−1. The catalogue produced from these images contains 108 330 point sources and 517 compact extended sources. We also describe a UHF (544–1088 MHz) single pointing observation. We report the detection of a new confirmed Supernova Remnant (SNR; MCSNR J0100–7211) with an X-ray magnetar at its centre and 10 new SNR candidates. This is in addition to the detection of 21 previously confirmed SNRs and two previously noted SNR candidates. Our new SNR candidates have typical surface brightness an order of magnitude below those previously known, and on the whole they are larger. The high sensitivity of the MeerKAT survey also enabled us to detect the bright end of the SMC Planetary Nebulae (PNe) sample – point-like radio emission is associated with 38 of 102 optically known PNe, of which 19 are new detections. Lastly, we present the detection of three foreground radio stars amidst 11 circularly polarized sources, and a few examples of morphologically interesting background radio galaxies from which the radio ring galaxy ESO 029–G034 may represent a new type of radio object. [ABSTRACT FROM AUTHOR]

The development of the latest generation of Imaging Atmospheric Cherenkov Telescopes (IACTs) over recent decades has led to the discovery of new extreme astrophysical phenomena in the very-high-energy (VHE, E > 100 GeV) gamma-ray regime. Time-domain and multi-messenger astronomy are inevitably connected to the physics of transient VHE emitters, which show unexpected (and mostly unpredictable) flaring or exploding episodes at different timescales. These transients often share the physical processes responsible for the production of the gamma-ray emission, through cosmic-ray acceleration, magnetic reconnection, jet production and/or outflows, and shocks interactions. In this review, we present an up-to-date overview of the VHE transients field, spanning from novae to supernovae, neutrino counterparts or fast radio bursts, among others, and we outline the expectations for future facilities. [ABSTRACT FROM AUTHOR]

Fast radio bursts (FRBs) are short-duration radio pulses of cosmological origin. Among the most common sources predicted to explain this phenomenon are bright pulses from a class of extremely highly magnetized neutron stars known as magnetars. Motivated by the discovery of an FRB-like pulse from the Galactic magnetar SGR 1935+2154, we searched for similar events in Messier 82 (M82). With a star formation rate 40 times that of the Milky Way, one might expect that the implied rate of events similar to that seen from SGR 1935+2154 from M82 should be 40 times higher than that of the Milky Way. We observed M82 at 1.4 GHz with the 20-m telescope at the Green Bank Observatory for 34.8 d. While we found many candidate events, none had a signal-to-noise ratio greater than 8. We also show that there are insufficient numbers of repeating low-significance events at similar dispersion measures to constitute a statistically significant detection. From these results, we place an upper bound for the rate of radio pulses from M82 to be 30 yr−1 above a fluence limit of 8.5 Jy ms. While this is less than nine times the rate of radio bursts from magnetars in the Milky Way inferred from the previous radio detections of SGR 1935+2154, it is possible that propagation effects from interstellar scattering are currently limiting our ability to detect sources in M82. Further searches of M82 and other nearby galaxies are encouraged to probe this putative FRB population. [ABSTRACT FROM AUTHOR]

After a successful supernova, a proto-neutron star (PNS) cools by emitting neutrinos on ∼1–100 s time-scales. Provided that there are neutrino emission 'hotspots' or 'cold-spots' on the surface of the rotating PNS, we can expect a periodic modulation in the number of neutrinos observable by detectors. We show that Fourier transform techniques can be used to determine the PNS rotation rate from the neutrino arrival times. Provided there is no spin-down, a 1-parameter Discrete Fourier Transform (DFT) is sufficient to determine the spin period of the PNS. If the PNS is born as a magnetar with polar magnetic field strength B 0 ≳ 1015 G and is 'slowly' rotating with an initial spin period ≳100 ms, then it can spin-down to periods of the order of seconds during the cooling phase. We propose a modified DFT technique with three frequency parameters to detect spin-down. Due to lack of neutrino data from a nearby supernova except the ∼20 neutrinos detected from SN1987A, we use toy models and one physically motivated modulating function to generate neutrino arrival times. We use the false alarm rate (FAR) to quantify the significance of the Fourier power spectrum peaks. We show that PNS rotation and spin-down are detected with |$\rm FAR\,\lt\, 2~{{\ \rm per\ cent}}$| (2σ) for periodic signal content |$\rm M\gtrsim 13-15~{{\ \rm per\ cent}}$| if 5 × 103 neutrinos are detected in ∼3 s and with |$\rm FAR\,\lt\, 1{{\ \rm per\ cent}}$| for |$\rm M\,\ge 5{{\ \rm per\ cent}}$| if 5 × 104 neutrinos are detected in ∼3 s. Since we can expect ∼104−105 neutrino detections from a supernova at 10 kpc, detection of PNS rotation and spin-down is possible using the neutrinos from the next Galactic supernova. [ABSTRACT FROM AUTHOR]

The activity of at least one repeating fast radio burst (FRB) source is periodically modulated. If this modulation is the result of precession of the rotation axis and throat of an accretion disc around a black hole, driven by a companion that is also the source of accreted mass, then it may be possible to constrain the mass of the black hole. The dynamics is analogous to that of superorbital periods in ordinary mass-transfer binaries in which the accreting object may be a stellar-mass black hole, a neutron star or a white dwarf, but in the FRB source it may be an intermediate-mass black hole. In a semidetached (mass-transferring) binary, the orbital period is nearly proportional to the −1/2 power of the mean density of the mass-losing star and nearly independent of the mass of the primary, but the ratio of precessional to orbital periods scales approximately as the −2/3 power of the mass ratio for small mass ratios (massive accretors). Assuming a value for the secondary's density and identifying the observed modulation period as a disc precession period would determine the mass ratio and the mass of the black hole. This model and magnetar-SNR (supernova remnant) models make distinguishable predictions of the evolution of the rotation measure that may soon be tested in FRB 121102. [ABSTRACT FROM AUTHOR]

We explore the impact of a magnetar giant flare (GF) on the neutron star (NS) crust, and the associated baryon mass ejection. We consider that sudden magnetic energy dissipation creates a thin high-pressure shell above a portion of the NS surface, which drives a relativistic shockwave into the crust, heating a fraction of these layers sufficiently to become unbound along directions unconfined by the magnetic field. We explore this process using spherically symmetric relativistic hydrodynamical simulations. For an initial shell pressure P GF we find the total unbound ejecta mass roughly obeys the relation |$M_{\rm {ej}}\sim 4\!-\!9\times 10^{24}\, \rm {g}\, (P_{\rm GF}/10^{30}\, \rm {erg}\, \rm {cm}^{-3})^{1.43}$|⁠. For |$P_{\rm {GF}}\sim 10^{30}\!-\!10^{31}\, \rm {erg}\, \rm {cm}^{-3}$| corresponding to the dissipation of a magnetic field of strength |$\sim 10^{15.5}\!-\!10^{16}\, \rm {G}$|⁠ , we find |$M_{\rm {ej}}\sim 10^{25}\!-\!10^{26}\, \rm {g}$| with asymptotic velocities v ej/ c ∼ 0.3–0.6 compatible with the ejecta properties inferred from the afterglow of the 2004 December GF from SGR 1806-20. Because the flare excavates crustal material to a depth characterized by an electron fraction Y e ≈ 0.40–0.46, and is ejected with high entropy and rapid expansion time-scale, the conditions are met for heavy element r -process nucleosynthesis via the alpha-rich freeze-out mechanism. Given an energetic GF rate of roughly once per century in the Milky Way, we find that magnetar GFs could be an appreciable heavy r -process source that tracks star formation. We predict that GFs are accompanied by short ∼minutes long, luminous |$\sim 10^{39}\, \rm {erg}\, \rm {s}^{-1}$| optical transients powered by r -process decay (nova brevis), akin to scaled-down kilonovae. Our findings also have implications for the synchrotron nebulae surrounding some repeating fast radio burst sources. [ABSTRACT FROM AUTHOR]

Time-domain and multimessenger astronomy (TDAMM) involves the study of transient and time-variable phenomena across various wavelengths and messengers. The Astro2020 Decadal Survey has identified TDAMM as the top priority for NASA in this decade, emphasizing its crucial role in advancing our understanding of the universe and driving new discoveries in astrophysics. The TDAMM community has come together to provide further guidance to funding agencies, aiming to define a clear path toward optimizing scientific returns in this research domain. This encompasses not only astronomy but also fundamental physics, offering insights into properties of gravity, the formation of heavy elements, the equation of state of dense matter, and quantum effects associated with extreme magnetic fields. Magnetars, neutron stars with the strongest magnetic fields in the universe, play a critical role in this context. We aim to underscore the significance of magnetars in TDAMM, highlighting the necessity of ensuring observational continuity, addressing current limitations, and outlining essential requirements to expand our knowledge in this field.

Among the more than 60 sources observed in the first two years of operations, IXPE addressed four magnetars, neutron stars believed to host ultra-strong magnetic fields. We report here the main implication coming from IXPE measurements for the physics of magnetars. Polarimetric observations confirmed the expectations of high polarization degrees, up to ≈80%, values which have not been detected in any other source so far, providing further proof (independent from the P-P˙ estimate) that magnetars host indeed ultra-magnetized neutron stars. Polarization measurements also indicate that softer X-rays likely come from surface regions where the overlying atmosphere underwent magnetic condensation. The agreement of the phase-dependent polarization angle with a simple rotating vector model strongly supports the presence of vacuum birefringence around the star.

The shape and polarization properties of the radio pulse profiles of radio-loud magnetars provide a unique opportunity to investigate their magnetospheric properties. Gaussian process regression analysis was used to investigate the variation in the total intensity shape of the radio pulse profiles of the magnetar Swift J1818.0–1607. The observed profile shape was found to evolve through three modes between MJDs 59104 and 59365. The times at which these transitions occurred coincided with changes in the amplitude of modulations in the spin-down rate. The amount of linear and circular polarization was also found to vary significantly with time. Lomb–Scargle periodogram analysis of the spin-down rate revealed three possibly harmonically related frequencies. This could point to the magnetar experiencing seismic activity. However, no profile features exhibited significant periodicity, suggesting no simple correlations between the profile variability and fluctuations of the spin-down on shorter time-scales within the modes. Overall, this implies that the mode changes seen are a result of local magnetospheric changes, with other theories, such as precession, less able to explain these observations. [ABSTRACT FROM AUTHOR]

A long-lived magnetar, potentially originating from a binary neutron star system, has been proposed to explain the extended emission observed in certain short-duration gamma-ray bursts (sGRBs), and is posited as a potential central engine to power the engine-fed kilonovae. Previously, the process by which energy is injected into the surrounding ejecta/jet was widely believed to be nearly isotropic. In this study, we employ special relativity magnetohydrodynamic (SRMHD) simulations to investigate the wind injection process from a magnetar central engine. We explore the dynamics and energy distribution within the system and found that the parameter α = u A/ u MWN can be used to indicate the collimation of the magnetar wind energy injection, where u A is the local Alfven four-speed and u MWN is the four-speed of the magnetar wind nebular (MWN) formed from wind-ejecta collision. A significant portion of the injected energy from the magnetar spin-down wind will be channeled to the jet axis due to collimation within the MWN. Achieving isotropic energy injection requires a significantly small α that necessitates either an ultra-relativistic expanding MWN or an extremely low magnetization MWN, both of which are challenging to attain in sGRBs. Consequently, a considerably reduced energy budget (i.e. energy per solid angle reduced by a factor of up to 10 with respect to the value under isotropic assumption) is anticipated to be injected into the ejecta for engine-fed kilonovae. Engine-fed kilonovae would appear fainter than originally anticipated. [ABSTRACT FROM AUTHOR]

GW190425 is the second of two binary neutron star (BNS) merger events to be significantly detected by the Laser Interferometer Gravitational Wave (GW) Observatory (LIGO), Virgo and the Kamioka Gravitational Wave (KAGRA) detector network. With a detection only in LIGO Livingston, the skymap containing the source was large and no plausible electromagnetic counterpart was found in real-time searching in 2019. Here, we summarize Asteroid Terrestrial-Impact Last Alert System (ATLAS) and Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) wide-field optical coverage of the skymap beginning within 1 and 3 h, respectively, of the GW190425 merger time. More recently, a potential coincidence between GW190425 and a fast radio burst FRB 20190425A has been suggested, given their spatial and temporal coincidences. The smaller sky localization area of FRB 20190425A and its dispersion measure led to the identification of a likely host galaxy, UGC 10667 at a distance of 141 ± 10 Mpc. Our optical imaging covered the galaxy 6.0 h after GW190425 was detected and 3.5 h after the FRB 20190425A. No optical emission was detected and further imaging at +1.2 and +13.2 d also revealed no emission. If the FRB 20190425A and GW190425 association were real, we highlight our limits on kilonova emission from a BNS merger in UGC 10667. The model for producing FRB 20190425A from a BNS merger involves a supramassive magnetized neutron star spinning down by dipole emission on the time-scale of hours. We show that magnetar-enhanced kilonova emission is ruled out by optical upper limits. The lack of detected optical emission from a kilonova in UGC 10667 disfavours, but does not disprove, the FRB–GW link for this source. [ABSTRACT FROM AUTHOR]

Emission in many astrophysical transients originates from a shocked fluid. A central engine typically produces an outflow with varying speeds, leading to internal collisions within the outflow at finite distances from the source. Each such collision produces a pair of forward and reverse shocks with the two shocked regions separated by a contact discontinuity (CD). As a useful approximation, we consider the head-on collision between two cold and uniform shells (a slower leading shell and a faster trailing shell) of finite radial width, and study the dynamics of shock propagation in planar geometry. We find significant differences between the forward and reverse shocks, in terms of their strength, internal energy production efficiency, and the time it takes for the shocks to sweep through the respective shells. We consider the subsequent propagation of rarefaction waves in the shocked regions and explore the cases where these waves can catch up with the shock fronts and thereby limit the internal energy dissipation. We demonstrate the importance of energy transfer from the trailing to leading shell through p d V work across the CD. We outline the parameter space regions relevant for models of different transients,e.g. Gamma-ray burst internal shock model, fast radio burst blast wave model, Giant flare due to magnetars, and superluminous supernovae ejecta. We find that the reverse shock likely dominates the internal energy production for many astrophysical transients. [ABSTRACT FROM AUTHOR]

The study of quasi-periodic oscillations (QPOs) and power density spectra (PDSs) continuum properties can help shed light on the still elusive emission physics of magnetars and as a window into the interiors of neutron stars using asteroseismology. In this work, we employ a PDS method to search for the QPOs in the hundreds of X-ray bursts from SGR J1935+2154 observed by Insight - HXMT, GECAM , and Fermi/ GBM from 2014 July to 2022 January. Although no definitive QPO signal (significance >3 σ) is detected in individual bursts or the averaged periodogram of the bursts grouped by duration, we identify several bursts exhibiting features at ∼40 Hz, attributed to the the proximity intervals between adjacent pulses and consistent with that reported in the X-ray burst associated with FRB 200428. We investigate the PDS continuum properties and find that the distribution of the PDS slope in the simple power-law model peaks at ∼2.5, which is consistent with other magnetars but higher than 5/3 commonly seen in gamma-ray bursts. Besides, the distribution of the break frequency in the broken power-law model peaks at ∼60 Hz. Finally, we report that the power-law index of PDS has an anti-correlation and power-law dependence on the burst duration as well as the minimum variation time-scale. [ABSTRACT FROM AUTHOR]

We report on IXPE, NICER, and XMM–Newton observations of the magnetar 1E 2259+586. We find that the source is significantly polarized at about or above 20  per cent for all phases except for the secondary peak where it is more weakly polarized. The polarization degree is strongest during the primary minimum which is also the phase where an absorption feature has been identified previously. The polarization angle of the photons are consistent with a rotating vector model with a mode switch between the primary minimum and the rest of the rotation of the neutron star. We propose a scenario in which the emission at the source is weakly polarized (as in a condensed surface) and, as the radiation passes through a plasma arch, resonant cyclotron scattering off of protons produces the observed polarized radiation. This confirms the magnetar nature of the source with a surface field greater than about 1015 G. [ABSTRACT FROM AUTHOR]

In this study, we explore the dynamical stability of magnetar bursts within the context of the chaos-randomness phase space for the first time, aiming to uncover unique behaviours compared to various astrophysical transients, including fast radio bursts (FRBs). We analyse burst energy time series data from active magnetar sources SGR J1550−5418 and SGR J1935+2154, focusing on burst arrival time and energy differences between consecutive events. We find a distinct separation in the time domain, where magnetar bursts exhibit significantly lower randomness compared to FRBs, solar flares, and earthquakes, with a slightly higher degree of chaos. In the energy domain, magnetar bursts exhibit a broad consistency with other phenomena, primarily due to the wide distribution of chaos-randomness observed across different bursts and sources. Intriguingly, contrary to expectations from the FRB-magnetar connection, the arrival time patterns of magnetar bursts in our analysis do not exhibit significant proximity to repeating FRBs in the chaos-randomness plane. This finding may challenge the hypothesis that FRBs are associated with typical magnetar bursts but indirectly supports the evidence that FRBs may primarily be linked to special magnetar bursts like peculiar X-ray bursts from SGR J1935+2154 observed simultaneously with Galactic FRB 200428. [ABSTRACT FROM AUTHOR]

Magnetars are a type of pulsars powered by magnetic field energy. Part of the X‐ray luminosities of magnetars in quiescence have a thermal origin and can be fitted by a blackbody spectrum with the surface temperature, much higher than the typical values for rotation‐powered pulsars. The persistent thermal emissions and bursts of magnetars indicate the presence of some internal heat sources in their outer crusts. In this work, we have formulated the energy balance equation and applied it to investigate the thermal evolution in the magnetar crust, taking into account the heating mechanisms of Ohmic decay and electron capture processes. This model can explain the changes in the X‐ray luminosity of the magnetars. [ABSTRACT FROM AUTHOR]