arXiv subjects

Zorawar Wadiasingh

Publications and source records attributed to Zorawar Wadiasingh.

At least 19 recordsLinked to original sources

arXiv2026

The swept-back multipolar magnetic field of neutron stars: Application to NICER MSP J0030+0451

NICER observations of millisecond pulsars (MSPs) suggest that non-dipolar magnetic fields are required to explain their surface X-ray hotspots. C. Kalapotharakos et al. modeled the NICER light curve of MSP J$0030+0451$ (J$0030$) using a static vacuum offset dipole-plus-quadrupole field and corresponding force-free (FF) solutions to jointly reproduce the X-ray and Fermi-LAT $γ$-ray emission. We substitute their static vacuum field model with a more realistic swept-back configuration that accounts for rotational effects. This field more closely resembles the corresponding FF solutions, making it a more physically motivated choice for future multiwavelength modeling. We adopt a centered swept-back vacuum multipolar magnetic field (SVM2F; J. Pétri), expressed as a complete expansion in vector spherical harmonics, enabling flexible descriptions of arbitrary magnetic field geometries. We introduce a metric to quantify the complexity among different field prescriptions, illustrated for the static offset vacuum field. To efficiently explore parameter space, we train a neural network surrogate (G. Olmschenk et al.) on SVM2F light curves including components up to the octupole, accelerating Markov chain Monte Carlo sampling by $\sim 10^3$ compared to direct physical model evaluations. Applying this framework to J$0030$, we constrain the field parameter space and find that a centered swept-back multipolar field including terms up to the octupole adequately reproduces the bolometric thermal X-ray light curve. Our study highlights the importance and inherent complexity of prescribing different multipolar magnetic field models for rotating stars, and can be extended to other MSPs to ultimately constrain the masses and radii of neutron stars, and hence their equation of state.

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arXiv2026

A Proliferated Space Architecture for Time-Domain Astrophysics

Time-Domain and Multi-Messenger Astrophysics (TDAMM) is entering a discovery-rich but follow-up-limited era, creating an urgent need for responsive, multiwavelength space-based capabilities. The Hydra constellation is a concept for a proliferated space architecture for time-domain astrophysics. The constellation would act as a disaggregated observatory composed of coordinated, relatively low-cost spacecraft that collectively provide capabilities traditionally concentrated within a single large mission. The architecture would combine persistent wide-field gamma-ray monitoring, wide-field and focused X-ray observations, and rapid-response ultraviolet, optical, and infrared imaging and spectroscopy. The constellation would both discover high-energy transients and respond to external alerts from gravitational-wave detectors, neutrino observatories, and ground- and space-based surveys, using low-latency communications, automated event prioritization, and community coordination frameworks to rapidly assign observing resources. A proliferated architecture would offer operational advantages over a single larger mission, including simultaneous observations of multiple targets, graceful degradation following individual spacecraft failures, recurring technology refresh, and opportunities for commercial, international, and philanthropic contributed nodes to join the network. The constellation would address fundamental questions concerning cosmic accelerators, the origin and evolution of the elements, the behavior of matter at extreme density, and the nature of dark energy through gravitational-wave standard sirens. This white paper presents the Hydra concept description that was submitted to NASA's ASTRA initiative for consideration by the Cosmic Origins Program Analysis Group (CoPAG) and Physics of the Cosmos Program Analysis Group (PhysPAG).

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arXiv2026

Ad Astra White Paper: A Pitch for the Next 25 Years of NASA's Physics of the Cosmos Program

Astrophysical observations of our universe have been key to our understanding of how the universe works. Shortly after the turn of the millennium, the National Research Council delivered \textit{Connecting Quarks with the Cosmos: Eleven Science Questions for the New Century}. In the subsequent quarter-century, we have made substantial progress in answering each question. These advancements have, in part, arisen because of the success of major US facilities across several domains of physics, guided by long-term planning documents which still largely focus on these questions. This report seeks to provide a status update on each question, and to outline what space-based facilities are crucial for future progress, intended to guide NASA's preparatory work for the Astro2030 Decadal.

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arXiv2026

Vacuum birefringence and the polarized X-ray emission from a radio magnetar

Magnetars are isolated neutron stars with exceptionally strong surface fields exceeding $10^{14}$ G. Their bright X-ray emission probes physical regimes in which quantum electrodynamic (QED) influences radiation propagation. Strong magnetic fields induce polarization-dependent refractive indices in the vacuum; such vacuum birefringence (VB) remains a long-standing but unconfirmed prediction of QED. Here, we report phase- and energy-resolved polarization measurements of the radio-emitting magnetar 1E 1547.0$-$5408 obtained by coordinating X-ray and radio observations from the Imaging X-ray Polarimetry Explorer (IXPE), the Neutron Star Interior Composition ExploreR (NICER), and the Parkes/Murriyang observatory. We detect large polarization degrees (PD) in the thermally-dominant soft X-ray band, reaching phase-averaged values of $65\%$ at 2 keV before substantially decreasing between 2$-$4 keV. At certain rotational phases, the 2$-$3 keV PD rises to nearly $80\%$ while remaining high ($\gtrsim 40\%$) throughout the radio beam crossing. The phase-dependent X-ray and radio polarization angles are both consistent with the rotating vector model, suggesting that the emission geometries track the star's large-scale magnetic field. Collectively, these characteristics challenge standard surface emission models using non-refractive propagation of light to infinity. VB-governed magnetospheric propagation can naturally explain the X-ray polarization signals. Our results represent a significant advance in probing this hallmark prediction of QED, opening a new cosmic window into superstrong-field quantum physics, thereby motivating further observational and theoretical studies concentrating on this domain.

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arXiv2026

Magnetar Fireballs and Short Bursts: Curved Spacetime Lensing, QED Effects, Spectra, Polarization, and Impulse Responses

Magnetar short bursts (SBs) are hard X-ray transients of durations $0.01-1$ s peaking at $\sim 10-100$ keV, and are prime targets for new high-energy missions and polarimeters. The recent association of SBs with bright radio bursts in SGR 1935+2154 has broadened interest in SB physics. We present new advanced fireball models combining general relativistic light bending, polarized transport in magnetized photospheres, magnetic photon splitting attenuation, and magnetospheric vacuum birefringence. These models also have relevance to trapped fireballs in magnetar giant flare pulsating tails. We adopt confined flux tube geometries consistent with adiabatic fireballs, and anisotropic/polarized emergent intensities to produce spectra and polarizations, and energy-time Stokes impulse responses. We predict that most fireballs are highly linearly polarized, especially when vacuum birefringence is important. There is rich potential for diagnostics: coexisting direct and lensed delayed images, gaps by occultation of the neutron star surface, and Shapiro+Rømer delay with temporal caustics. These effects can imprint spin phase dependence of the spectral and polarization character of bursts. Predicted signatures depend strongly on viewing geometry, fireball configuration, and photon splitting assumptions, yielding large variance in model high-energy spectral shapes and cutoffs, and energy-dependent polarization. The models can reproduce established double-blackbody SB spectral phenomenology, and we find that the unusual April 2020 radio-associated SB from SGR 1935+2154 is broadly consistent with a footpoint close to the magnetic pole, and possibly near pole-on viewing geometry. Our models motivate reverberation-style analyses for SBs and suggest that high-quality data might constrain source geometry, burst crustal footpoints, and, potentially, neutron star masses and radii.

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arXiv2026

4th TDAMM Workshop White Paper

Time-Domain and Multi-Messenger Astrophysics (TDAMM) is entering a new era in which the rate and diversity of transient discoveries will grow rapidly across electromagnetic, gravitational-wave, neutrino, and cosmic-ray facilities. The scientific return from these investments will increasingly depend not on discovery alone, but on the ability to identify, prioritize, and coordinate follow-up observations across a heterogeneous and globally distributed network of observatories. This white paper summarizes the outcomes of the Fourth TDAMM Workshop and assesses the near-term discovery landscape, the infrastructure and tools that support coordinated observations, and the technical, policy, and capability gaps that may limit future progress. The workshop identified three principal challenges: insufficiently scalable and interoperable alert and coordination infrastructure, policies that impede rapid multi-facility observations and rare-event science, and the potential loss of critical high-energy, rapid-response, and spectroscopic capabilities. The white paper identifies the need for sustained support for alert distribution, brokers, standardized observatory metadata, cross-facility coordination platforms, and unified follow-up repositories; expanded joint observing opportunities and funding mechanisms for coordinated analysis; and strategic investment in future TDAMM facilities. The white paper also present a framework for community observing plans that would establish pre-coordinated responses to rare, high-impact events, supported by transparent governance, immediate public data release, and regular community revision. Science overviews and detailed observing strategies are provided for gamma-ray bursts, tidal disruption events, X-ray binaries, novae, supernovae, magnetars, compact binary mergers, and high-energy neutrino sources.

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arXiv2026

Multipolar Magnetic-Field Inference for PSR J0740+6620 with Neural-Network-Accelerated NICER Pulse-Profile Modeling

We investigate the multipolar surface magnetic-field structure of the high-mass millisecond pulsar PSR J0740+6620 using the 32-bin bolometric NICER pulse profile of Dittmann et al. (2024). Building on the neural-network surrogate framework of Olmschenk et al. (2025), we model the emitting regions as open-field-line footpoints of an offset dipole plus axisymmetric quadrupole static vacuum field, rather than as prescribed geometric hotspots. We fix the stellar mass, radius, observer inclination, and hotspot temperature ratio to the Dittmann et al. (2024) maximum-likelihood values and explore the resulting 11-dimensional magnetic-field space. To make this feasible, we train convolutional neural-network surrogates on $5.12\times10^7$ synthetic bolometric light curves and use them in a parallel ensemble Markov Chain Monte Carlo calculation on 4000 CPU cores, accelerating likelihood evaluations by a factor of $\gtrsim 400$. We perform independent inferences for two calibrated temperature-weight prescriptions, Tw=1.31 and Tw=1.41, encoding the relative bolometric weight associated with the hotspot temperature difference. The posteriors, posterior-predictive light curves, and maximum-likelihood values are very similar, indicating weak sensitivity to this choice. The offset model reproduces the observed double-peaked profile and yields broad, multimodal posteriors, reflecting both the background-dominated data and degeneracies of the multipolar parameterization. The hotspot-density map shows that pulse phases constrain the approximate azimuthal placement of the emission, while latitude, surface extent, and morphology remain weakly constrained. A restricted zero offset run is disfavored within the adopted field basis. This work extends neural-network-accelerated magnetic-field inference to PSR J0740+6620 and motivates future energy-dependent, force-free, and joint X-ray/$γ$-ray extensions.

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arXiv2026

Detailed Timing, Spectral, and Polarimetric Analysis of Magnetar 1RXS J170849.0-400910

We present a broadband timing, spectral, and polarimetric study of the magnetar 1RXS~J170849.0-400910 using XMM-Newton, NuSTAR, and IXPE. The pulse morphology evolves strongly across 0.5-70 keV. Below 3 keV, the emission is dominated by a broad soft pulse with a leading shoulder that develops into a faint interpulse near 3 keV, while the pulse fraction remains $\approx$25%. The profile becomes increasingly double-peaked between 3 and 20 keV and returns to a single peak at higher energies. The pulse fraction dips to $\sim$20% near 4 keV and rises to $\sim$42% above 25 keV. The phase-averaged spectrum is well described by an absorbed blackbody plus two power-laws, with $kT=0.468\pm0.003$ keV, $Γ_{\rm soft}=2.63\pm0.04$, and $Γ_{\rm hard}=0.5\pm0.1$. Phase-resolved spectroscopy reveals distinct soft and hard pulse components. The thermal modulation is driven primarily by a factor of $\sim$5 variation in projected emitting area, whereas the soft power-law exhibits two peaks with different phase and energy evolution, suggesting distinct emission regions or mechanisms. The 10-70 keV flux is strongly anticorrelated with the soft power-law photon index, linking spectral hardening to the hard pulse. The polarization degree also varies strongly with phase and energy. In the 2-3 keV band, it is anticorrelated with the intensity profile, consistent with magnetized-atmosphere emission, whereas in the 4-8 keV band it reaches $64\pm10$% during the nonthermal power-law-dominated peak. This high polarization can be reproduced by magnetospheric quantum pair-synchrotron emission. Together, these results reveal an intricate, phase-dependent superposition of emitting regions and radiative processes whose complexity emerges only through broadband, phase-resolved spectropolarimetry.

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arXiv2026

Estimation of neutron star mass and radius of FRB 20240114A by identification of crustal oscillations

By identifying quasi-periodic oscillations (QPOs) reported in FRB 20240114A (from the Five-hundred-meter Aperture Spherical Telescope) with neutron star crustal torsional oscillations, together with experimental constraints on the incompressibility $K_0$ of symmetric nuclear matter at saturation density, we constrain the mass and radius of an extragalactic neutron star at redshift $z\approx0.13$. Identifying the low-order QPO frequencies as fundamental oscillations, and frequencies of $567.7\,\mathrm{Hz}$ or $655.5\,\mathrm{Hz}$ (rest frame) as first overtone candidates, implies neutron star mass ranges of $1.00$--$1.55\,M_\odot$ or $1.17$--$1.76\,M_\odot$, respectively. The radius is also constrained, with a self-consistent value around $13$~km, consistent with the calculation of the NS structure within the low-mass/low-central density regime. Simultaneously, we also constrain another nuclear saturation parameter, namely the density dependence of the nuclear symmetry energy at saturation density (i.e., the slope parameter), $L$, and determine it to be $L=59.5-96.8$ MeV with $\sim 10\%$ systematic uncertainty, which is broadly consistent with previous constraints on $L$ obtained from experiments and astronomical observations. Thus, a mapping of FRB QPOs to crustal torsional modes seems reasonable. This interpretation will be tested with the discovery of additional QPOs in upcoming FRB surveys.

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arXiv2026

NICER Magnetar Burst Catalog

In this paper, we present a comprehensive catalog of short bursts from magnetars based on eight years of NICER observations. A total of 1130 bursts were identified from 14 sources, with the sample dominated by SGR 1935+2154, which accounts for 76% of all detected bursts. We analyzed burst durations, spectral properties, and their correlations across multiple sources. Bursts from SGR 1935+2154 exhibit significantly longer durations, with a distribution peak at 316 ms, compared to a peak of 23 ms for bursts from other magnetars. Two μs-scale bursts were detected for the first time, originating from 1E 1048.1-5937 and CXOU J010043.1-721134. Spectral analysis in the 0.5-8 keV range using both blackbody and power-law models shows that bursts with higher fluences have harder spectra. In contrast, correlations between burst duration and spectral parameters are weak or absent. This catalog provides a valuable dataset for studying magnetar short bursts, enabling future modeling efforts and improving our understanding of the diversity and physical mechanisms of magnetar bursts.

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arXiv2026

On the Expected Orbitally-modulated TeV Signatures of Spider Binaries: The Effect of Intrabinary Shock Geometry

'Spider' binary systems - black widow and redback compact binaries differentiated by their companion's mass and nature - are an important type of pulsar system exhibiting a rich empirical phenomenology, including radio eclipses, optical light curves from a heated companion, as well as non-thermal X-ray and GeV orbital light curves and spectra. Multi-wavelength observations have now resulted in the detection of >~50 of these systems in which a millisecond pulsar heats and ablates its low-mass companion via its intense pulsar wind. Broadband observations have established the presence of relativistic leptons that have been accelerated in the pulsar magnetosphere and near the intrabinary shock, as well as a hot companion, presenting an ideal environment for the creation of orbitally-modulated inverse Compton fluxes that should be within reach of current and future Cherenkov telescopes. We have included an updated synchrotron kernel, different parametric injection spectral shapes, and several intrabinary shock geometries in our emission code to improve our predictions of the expected TeV signatures from spider binaries. Our updated phase-dependent spectral and energy-dependent light curve outputs may aid in constraining particle energetics, wind properties, shock geometry, and system inclination of several spider binaries.

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arXiv2026

Testing Magnetic Field Configurations in Spider Pulsar PSR J1723-2837 with IXPE

We present the first X-ray polarimetry observations of a redback millisecond pulsar binary, PSR J1723-2837, with the Imaging X-ray Polarimetry Explorer (IXPE). We conduct a spectro-polarimetric analysis combining IXPE data with archival Chandra, XMM-Newton, NuSTAR, and Swift observations. We explore two limiting magnetic field configurations, parallel and perpendicular to the bulk flow, and simulate their expected polarization signatures using the 3DPol radiative transport code. To account for the rapid rotation of the polarization angle predicted by these models, we implement a phase-dependent Stokes alignment procedure that preserves the polarization degree while correcting for a phase-rotating PA. We also devise a new maximum-likelihood fitting strategy to determine the phase-dependence of the polarization angle by minimizing the polarization degree uncertainty. This technique hints that the binary may be rotating clockwise relative to the celestial north pole. We find no significant detection of polarization in the IXPE data, with PD<~50% at 99% confidence level. Our results excludes the high-polarization degree scenario predicted by the perpendicular field model during the brightest orbital phase bin. Simulations show that doubling the current exposure would make the parallel configuration detectable. The new PA rotation technique is also applicable to IXPE data of many sources whose intrinsic PA variation is a priori not known but is strictly periodic.

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arXiv2026

A Comprehensive Interpretation of Fermi-LAT Pulsars: Fundamental-Plane Death Border, Visibility Thresholds, and GeV-TeV Unification

We present a framework that links equatorial-current-sheet (ECS) physics to catalog-level, phase-averaged gamma-ray pulsar properties. Guided by analytic scalings and particle-in-cell (PIC) simulations, we show that the pulsar ``Fundamental Plane'' (relating gamma-ray luminosity, spectral cutoff energy, spin-down power $\dot{\cal{E}}$, and surface magnetic field) is bounded by two regimes: a radiation-reaction-limited branch and a potential-drop-limited branch. Their intersection defines a transition in $\dot{\cal{E}}$ that maps to a gamma-ray visibility threshold on the $P-\dot{P}$ diagram, above which detectability is set by distance and beaming, and below which both cutoff energy and efficiency decline rapidly. Placing ATNF pulsars and McGill magnetars onto these planes reproduces the observed Fermi occupancy, with millisecond pulsars (MSPs) on the observable side, young pulsars (YPs) straddling the threshold, and magnetars clustering at or just below it. At higher $\dot{\cal{E}}$, both MSPs and YPs depart from the maximal radiation-reaction-limited envelope at similar cutoff energies, suggesting that enhanced pair creation screens the accelerating electric field in the ECS. We interpret this behavior with a compactness-based criterion for optically thin $γγ$ pair feedback in or near the ECS and briefly note an extension to $γγ\rightarrowμ^\pm$ that could yield pulsed multi-TeV neutrinos in the most energetic systems. The framework predicts a MeV-bright, GeV-faint corridor below Fermi sensitivity, a target for next-generation MeV missions. Finally, motivated by the recent HESSII detection of pulsed multi-TeV emission from Vela, we use PIC particle distributions with a seed-photon model to reproduce a multi-TeV inverse-Compton component alongside the GeV curvature emission, supporting a unified ECS-based GeV-TeV origin.

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arXiv2025

Future Space-based Gamma-ray Pulsar Timing Arrays

Radio pulsar timing array (PTA) experiments using millisecond pulsars (MSPs) are beginning to detect nHz gravitational waves (GWs). MSPs are bright GeV gamma-ray emitters, and all-sky monitoring of about 100 MSPs with the Fermi Large Area Telescope (LAT) has enabled a gamma-ray Pulsar Timing Array. The GPTA provides a complementary view of nHz GWs because its MSP sample is different, and because the gamma-ray data are immune to plasma propagation effects, have minimal data gaps, and rely on homogeneous instrumentation. To assess GPTA performance for future gamma-ray observatories, we simulated the population of Galactic MSPs and developed a high-fidelity method to predict their gamma-ray spectra. This combination reproduces the properties of the LAT MSP sample, validating it for future population studies. We determined the expected signal from the simulated gamma-ray MSPs for instrument concepts with a wide range of capabilities. We found that the optimal GPTA energy range runs about 0.1 to 5 GeV, but we also examined Compton/MeV instruments. With the caveat that the MSP spectra models are extrapolated beyond observational constraints, we found low signal-to-background ratios, yielding few MSP detections. GeV-band concepts would detect 10$^3$ to 10$^4$ MSPs and achieve GW sensitivity on par with and surpassing the current generation of radio PTAs, reaching the GW self-noise regime. When considering two possible scenarios for the formation of MSPs in the Galactic bulge, the collective signal from which is a potential source of an excess GeV signal observed towards the Galactic center, we find that most of the concepts can both detect this bulge population and distinguish the production channel. In summary, the high discovery potential, strong GW performance, and tremendous synergy with radio PTAs all argue for the pursuit of next-generation gamma-ray pulsar timing.

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arXiv2025

Searching for Long-Period Radio Transients in ASKAP EMU Data with 10-Second Imaging

Long-period radio transients (LPTs) are a recently identified phenomenon that challenge our current understanding of compact objects and coherent radio emission mechanisms. These objects emit radio pulses similar to those of pulsars, but at much longer periods -- on the order of minutes to hours. With duty cycles of only a few percent, individual pulses have been observed to last between 10 and 1000 seconds. This places LPTs in a timescale gap between the two main techniques used in transient radio searches: time-series analysis at millisecond to second timescales, and image-plane searches sensitive to variability on the scale of days. As a result, LPTs remained undetected until recently, and only a handful are currently known. To increase the sample of known LPTs, we conducted a dedicated search using 200 hours of archival data from the ASKAP Evolutionary Map of the Universe survey, covering 750 deg$^2$ of sky at the shortest possible imaging time step of 10-seconds. This represents the first large-scale search using ASKAP data at second-scale resolution. Although no LPTs were detected, we identified flares from six stars, at least one had never been detected in the radio regime before. We placed a lower limit on the transient surface density of $2.21\times10^{-6}$ deg$^{-2}$ at a 10-second timescale, with a sensitivity of 16.9 mJy. Our findings evaluate the feasibility of detecting radio transients using 10-second imaging with ASKAP and provide insights into improving detection pipelines and observation strategies for LPTs.

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arXiv2025

Fast X-ray Transient Detection with AXIS: application to Magnetar Giant Flares

Magnetar giant flares (MGFs) are among the most luminous high-energy transients in the local universe, consisting of a short, intense MeV gamma-ray spike followed by a softer, pulsating X-ray tail and possibly delayed radioactive emission. While only three Galactic events have been firmly detected, several extragalactic candidates have recently been reported, motivating the need for sensitive, rapid-response gamma- and X-ray facilities to constrain their rates and energetics. We present a feasibility study of detecting MGFs with the Advanced X-ray Imaging Satellite (AXIS), focusing on two complementary pathways: (i) serendipitous discovery of the prompt gamma-ray spike within the field of view, and (ii) rapid follow-up of MGF tails in nearby galaxies. Using sensitivity rescaling and volumetric rate estimates, we find that serendipitous detection of prompt spikes during the mission lifetime is possible but unlikely, primarily because of their short duration and primarily because of their short duration and hard spectrum, in the assumption that the hard gamma-ray spectrum can be reliably extrapolated to the instrument's energy range. In contrast, AXIS's superior sensitivity, if accompanied by fast repointing capabilities, offer an extraordinary opportunity to detect pulsating X-ray tails out to about 20 Mpc, enabling the first extragalactic measurements of periodic modulations from a magnetar and potentially constraining emission geometry and fireball physics. Finally, we evaluate the detectability of soft X-ray line emission from r-process nucleosynthesis in MGFs, finding that such signals are extremely faint and confining the detection to Galactic distances. Our study offer a general framework for assessing the detectability of short transients with future missions.

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arXiv2025

Magnetosphere Evolution and Precursor-Driven Electromagnetic Signals in Merging Binary Neutron Stars

We detail new force-free simulations to investigate magnetosphere evolution and precursor electromagnetic (EM) signals from binary neutron stars. Our simulations fully follow a representative inspiral motion, capturing the intricate magnetospheric dynamics and their impact on EM outflows. We explore a range of stellar magnetic moment orientations and relative strengths, finding that the magnetospheres and Poynting flux evolution are strongly configuration-dependent. The Poynting flux exhibits pulsations at twice the orbital frequency, $2Ω$, and is highly anisotropic, following a power-law dependence on orbital frequency. The index ranges from 1 to 6, shaped by the intricate dynamics of the magnetospheres. Furthermore, we present the first computation of: (1) The EM forces acting on the star surfaces, revealing the presence of torques that, for highly-magnetized stars, could influence the orbital dynamics or break the crust. (2) The high-energy emission signals from these systems by adopting the established isolated pulsar theory. Assuming curvature radiation in the radiation reaction limit, we find that photons could reach TeV--PeV energies in the last $\sim$~ms for magnetic field strengths $10^{10}-10^{15}$~G. However, our analysis of single photon magnetic pair production suggests that these photons are unlikely to escape, with the MeV band emerging as a promising observational window for precursor high-energy emission. In this framework, we construct high-energy emission skymaps and light curves, exploring observational implications. Finally, we propose potential precursor radio emission and delayed afterglow echoes from magnetized outflows, which may contribute to late-time re-brightening in short gamma-ray bursts or to orphan afterglows.

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arXiv2025

Pioneering High-Speed Pulsar Parameter Estimation Using Convolutional Neural Networks

Accurate thermal emission models of neutron stars are essential for constraining the dense matter equation of state. However, incorporating realistic magnetic field structures is computationally prohibitive, severely constraining feasible parameter space exploration. In this work, we develop a neural network (NN) emulator to generate model thermal bolometric X-ray light curves of millisecond pulsars with multipolar magnetic fields. We assess the NN's predictive and computational performance across a broad parameter space. We find that for a static vacuum field model, the NN provides a >400 times speedup. We integrate this NN emulator into a Monte Carlo Markov Chain (MCMC) framework to replace the computationally expensive physical model during parameter exploration. Applied to PSR J0030+0451, this approach allows the MCMC to reach equilibrium in ~1 day on 4000 cores, where with the original physical model alone it would have taken more than a year on the same hardware. We compare posterior distributions by running equivalent MCMC iterations with both the NN and the physical model, evaluate differences in distributions when continuing the physical model MCMC from the NN MCMC equilibrium state, and assess variations in posterior distributions resulting from NNs trained on datasets of different sizes. Our NN architecture is agnostic to the underlying physics of the physical model and can be trained for any other physical model, opening many previously intractable avenues of analysis. The NN speed remains the same regardless of the complexity of the physical model it was trained to emulate, allowing greater speedups for more complex physical models.

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