About

Matthew G. Baring is a professor at Rice University, where he has been a faculty member since 2001. His professional background includes positions at NASA Goddard Space Flight Center, North Carolina State University, and the Max Planck Institut fuer Astrophysik in Garching bei Muenchen, Germany. His research focuses on theoretical high energy astrophysics and cosmic ray physics, with particular attention to modeling X-ray and gamma-ray emission from highly-magnetized pulsars, and exploring the effects of photon splitting and resonant Compton scattering in strong magnetic fields, especially in neutron star systems such as pulsars and magnetars. Dr. Baring's work involves incorporating radiation physics into Monte Carlo modeling of pair cascades in neutron star magnetospheres, aiming to discern the action of exotic predictions of relativistic quantum electrodynamics (QED) in strong magnetic fields, including magnetic birefringence and photon splitting. He has also extensively researched gamma-ray bursts, analyzing relativistic beaming in these sources, and investigates emission from ultra-relativistic plasma particles in the jets of active galaxies, with a focus on diffusive shock acceleration and its implications for emission. His theoretical techniques span mathematical analyses and numerical simulations, employing physics principles from relativistic quantum mechanics, classical electrodynamics, plasma physics, and general relativity.

Research topics

• Astrophysics
• Physics
• Astronomy
• Aerospace engineering
• Medicine
• Engineering
• Optics

Selected publications

• Refined Constraints on the Hard X-ray Polarization of the Crab Pulsar and Nebula Derived from an Extended XL-Calibur Dataset

  arXiv (Cornell University) · 2026-04-16

  preprintOpen access1st authorCorresponding

  We present updated hard X-ray polarization measurements of the Crab pulsar and nebula obtained with the balloon-borne polarimeter XL-Calibur in the ~19-64 keV energy range. During the flight, intermittent GPS-failure resulted in poorly constrained timing for ~38% of the Crab dataset. By implementing a new phase-recovery method that reconstructs timing during extended GPS-off intervals, phase tag data is recovered for ~95% of the GPS-off dataset, increasing the precision of the phase-resolved analysis. Phase-information for the data is recovered by using the Crab pulsar, with its 33 ms period, as an external timing source. Using a Markov-Chain Monte-Carlo framework to jointly fit phase offsets and frequency derivatives, sufficient phase accuracy is achieved, across multiple periods without GPS for a phase-resolved analysis. This enables inclusion of nearly the full dataset in the polarization study. The polarization degree of the nebular emission is found to be (27.7${\pm}$4.9)% at a polarization angle of 127.2°${\pm}$5.1° confirming previous XL-Calibur results and remaining aligned with the Crab's spin axis, consistent with synchrotron emission from the inner nebula. Phase-resolved measurements show that the off-pulse and bridge intervals exhibit a strong polarization, while the pulsar peaks, although weakly constrained, remain in agreement with the softer-energy trends of IXPE. These findings reinforce a scenario in which hard X-ray emission arises primarily in the nebular torus and wind regions. The successful recovery of precise phase tagging from GPS-off data demonstrates the capacity to use the pulsar as an external clock even in the case of sparsely populated data.

  PublisherDOI

• Pulsed, Polarized X-Ray Emission from Neutron Star Surfaces: The Effects of Vacuum Birefringence in the Magnetosphere

  The Astrophysical Journal · 2026-03-12

  articleOpen access

  Abstract Intense magnetic fields in the atmospheres of neutron stars render nontrivial angular dependence of intensity and polarization of soft X-ray emission originating from their surfaces. By tracking the complex electric field vector for each photon during its atmospheric transport and propagation in general relativistic and birefringent magnetospheres, our Monte Carlo simulation, named MAGTHOMSCATT , allows for capturing the complete polarization properties, including the intricate interplay between linearity and circularity. The new inclusion in MAGTHOMSCATT of quantum electrodynamical influences on polarization in the magnetosphere is presented. We simulate the pulsed and polarized X-ray emission from the outer layers of optically thick, fully ionized atmospheres of neutron stars, with a focus on the radiation emitted from extended polar caps of magnetars, which are the most highly magnetized neutron stars. Using the recent intensity pulse profile data for the magnetar 1RXS J1708–4009, we constrain the geometric parameters, namely, the angles between the magnetic axis and the observer’s viewing direction relative to the spin axis, as well as the sizes of emission regions. The distributions of these parameters and the best-fit configuration are provided. In addition, we discuss the important impacts of vacuum birefringence in the magnetosphere on increasing the linear polarization degree. A comparison with the case of a weakly magnetized neutron star, RX J0822.0–4300, is also discussed. Our simulation still needs further development, particularly to incorporate the vacuum resonance effect. Nevertheless, the formalism presented here can be employed to constrain geometric parameters for various types of neutron stars.

  PublisherDOI

• Refined Constraints on the Hard X-Ray Polarization of the Crab Pulsar and Nebula Derived from an Extended XL-Calibur Dataset

  The Astrophysical Journal · 2026-05-08

  articleOpen access1st authorCorresponding

  Abstract We present updated hard X-ray polarization measurements of the Crab pulsar and nebula obtained with the balloon-borne polarimeter XL-Calibur in the ∼19–64 keV energy range. During the flight, intermittent failure of the Global Positioning System (GPS) receiver resulted in poorly constrained timing for ∼38% of the Crab dataset. By implementing a new phase recovery method that reconstructs timing during extended GPS-off intervals, phase tag data are recovered for ∼95% of the GPS-off dataset, increasing the precision of the phase-resolved analysis. Phase information for the data is recovered by using the Crab pulsar, with its 33 ms period, as an external timing source. Using a Markov Chain Monte Carlo framework to jointly fit phase offsets and frequency derivatives, sufficient phase accuracy is achieved across multiple periods without GPS for a phase-resolved analysis. This enables inclusion of nearly the full dataset in the polarization study. The polarization degree of the nebular emission is found to be (27.7 ± 4.9)% at a polarization angle of 127 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>°</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 2 ± 5 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>°</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 1, confirming previous XL-Calibur results and remaining aligned with the Crab’s spin axis, consistent with synchrotron emission from the inner nebula. Phase-resolved measurements show that the off-pulse and bridge intervals exhibit a strong polarization, while the pulsar peaks, although weakly constrained, remain in agreement with the softer-energy trends of IXPE. These findings reinforce a scenario in which hard X-ray emission arises primarily in the nebular torus and wind regions. The successful recovery of precise phase tagging from GPS-off data demonstrates the capacity to use the pulsar as an external clock even in the case of sparsely populated data.

  PublisherDOI

• NICER Magnetar Burst Catalog

  The Astrophysical Journal Supplement Series · 2026-05-01

  articleOpen access

  Abstract In this paper, we present a comprehensive catalog of short bursts from magnetars based on 8 yr 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 mean of 317 ms, compared to a mean of 23 ms for bursts from other magnetars. Two microsecond-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.

  PublisherDOI

• Searching for quasi-periodicities in short transients: The curious case of GRB 230307A

  Astronomy and Astrophysics · 2025-07-29 · 1 citations

  articleOpen access

  Context. Gamma-ray bursts (GRBs) are the most powerful explosions in the Universe; their energy release reaches us from the end of the re-ionisation era, making them invaluable cosmological probes. GRB 230307A is the second brightest GRB ever observed in the 56 years of observations since the discovery of the phenomenon in 1967. Follow-up observations of the event at longer wavelengths have revealed a lanthanide-rich kilonova with long-lasting X-ray emission immediately following the prompt gamma-rays. Moreover, the gamma-ray light curve of GRB 230307A exhibits high amplitude variability, especially within the first 15 s. Aims. We performed a timing analysis of the prompt emission of GRB 230307A collected with INTEGRAL ’s SPectrometer of INTEGRAL AntiCoincidence Shield (SPI-ACS) and Fermi ’s Gamma-Ray Burst Monitor (GBM). Methods. We used Fourier analysis, wavelets, and Gaussian processes. We critically assessed all three methods in terms of their robustness for detections of quasi-periodic oscillations (QPOs) in fast transients such as GRBs. Results. Our analyses reveal QPOs at a frequency of ∼1.2 Hz (0.82 s period) near the burst’s peak emission phase, consistent across instruments and detection methods. We also identify a second, less significant QPO at ∼2.9 Hz (0.34 s) nearly simultaneously. We hypothesise that the two QPOs originate from the transition epoch at the end of the jet acceleration phase. These QPOs represent plasma circulation periods in vorticity about the jet axis carried outwards to the prompt radiation zone at much larger radii. They are sampled by colliding structures (e.g. shocks) in the spinning jet, possibly marking the evolution of plasma rotation during the final stages of the progenitor neutron star coalescence event.

  PublisherDOI

• GRB 221009A: The B.O.A.T. Burst that Shines in Gamma Rays

  The Astrophysical Journal Supplement Series · 2025-02-28 · 16 citations

  articleOpen access

  Abstract We present a complete analysis of Fermi Large Area Telescope (LAT) data of GRB 221009A, the brightest gamma-ray burst (GRB) ever detected. The burst emission above 30 MeV detected by the LAT preceded, by 1 s, the low-energy (&lt;10 MeV) pulse that triggered the Fermi Gamma-Ray Burst Monitor (GBM), as has been observed in other GRBs. The prompt phase of GRB 221009A lasted a few hundred seconds. It was so bright that we identify a bad time interval of 64 s caused by the extremely high flux of hard X-rays and soft gamma rays, during which the event reconstruction efficiency was poor and the dead time fraction quite high. The late-time emission decayed as a power law, but the extrapolation of the late-time emission during the first 450 s suggests that the afterglow started during the prompt emission. We also found that high-energy events observed by the LAT are incompatible with synchrotron origin, and, during the prompt emission, are more likely related to an extra component identified as synchrotron self-Compton (SSC). A remarkable 400 GeV photon, detected by the LAT 33 ks after the GBM trigger and directionally consistent with the location of GRB 221009A, is hard to explain as a product of SSC or TeV electromagnetic cascades, and the process responsible for its origin is uncertain. Because of its proximity and energetic nature, GRB 221009A is an extremely rare event.

  PublisherDOI

• Magnetic Thomson Transport in High-opacity Domains

  The Astrophysical Journal · 2025-03-24 · 2 citations

  articleOpen access1st authorCorresponding

  Abstract X-ray radiation from neutron stars manifests itself in a variety of settings. Isolated pulsars and magnetars both exhibit quasi-thermal persistent soft X-ray emission from their surfaces. Transient magnetospheric bursts from magnetars and pulsed signals from accreting neutron stars mostly appear in harder X-rays. The emission zones pertinent to these signals are all highly Thomson optically thick, so that their radiation anisotropy and polarization can be modeled using sophisticated simulations of scattering transport from extended emission regions. Validation of such codes and their efficient construction is enhanced by a deep understanding of scattering transport in high-opacity domains. This paper presents a new analysis of the polarized magnetic Thomson radiative transfer in the asymptotic limit of high opacity. The integrodifferential equations for photon scattering transport that result from a phase matrix construction are reduced to a compact pair of equations. This pair is then solved numerically for two key parameters that describe the photon anisotropy and polarization configuration of high Thomson opacity environs. Empirical approximations for these parameters as functions of the ratio of the photon and cyclotron frequencies are presented. Implementation of these semi-analytic transport solutions as interior boundary conditions is shown to speed up scattering simulations. The solutions also enable the specification of the anisotropic radiation pressure. The analysis is directly applicable to the atmospheres of magnetars and moderate-field pulsars, and to the accretion columns of magnetized X-ray binaries, and can be adapted to address other neutron star settings.

  PublisherDOI

• Monte Carlo Simulations of Polarized Radiative Transfer in Neutron Star Atmospheres

  The Astrophysical Journal · 2025-10-15 · 1 citations

  articleOpen access

  Abstract Soft X-ray emission from neutron stars affords powerful diagnostic tools for uncovering their surface and interior properties, as well as their geometric configurations. In the atmospheres of neutron stars, the presence of magnetic fields alters the photon-electron scattering cross sections, resulting in nontrivial angular dependence of intensity and polarization of the emergent signals. This paper presents recent developments of our Monte Carlo simulation, MAGTHOMSCATT, which tracks the complex electric field vector for each photon during its transport. Our analysis encompasses the anisotropy and polarization characteristics of X-ray emission for field strengths ranging from nonmagnetic to extremely magnetized regimes that are germane to magnetars. In the very low field domain, we reproduced the numerical solution to the radiative transfer equation for nonmagnetic Thomson scattering, and provided analytical fits for the angular dependence of the intensity and the polarization degree. These fits can be useful for studies of millisecond pulsars and magnetic white dwarfs. By implementing a refined injection protocol, we show that, in the magnetar regime, the simulated intensity and polarization pulse profiles of emission from extended surface regions becomes invariant with respect to the ratio of photon ( ω ) and electron cyclotron ( ω B ) frequencies once ω / ω B ≲ 0.01. This circumvents the need for simulations pertinent to really high magnetic field strengths, which are inherently slower. Our approach will be employed elsewhere to model observational data to constrain neutron star geometric parameters and properties of emitting hot spots on their surfaces.

  PublisherDOI

• Pulsed, Polarized X-ray Emission from Neutron Star Surfaces: the Effects of Vacuum Birefringence in the Magnetosphere

  Maryland Shared Open Access Repository (USMAI Consortium) · 2025-12-28

  articleOpen access

  Intense magnetic fields in the atmospheres of neutron stars render non-trivial angular dependence of intensity and polarization of soft X-ray emission originating from their surfaces. By tracking the complex electric field vector for each photon during its atmospheric transport and propagation in general relativistic and birefringent magnetospheres, our Monte Carlo simulation, named MAGTHOMSCATT, allows for capturing the complete polarization properties, including the intricate interplay between linearity and circularity. The new inclusion in MAGTHOMSCATT of quantum electrodynamical influences on polarization in the magnetosphere is presented. We simulate the pulsed and polarized X-ray emission from the outer layers of optically thick, fully ionized atmospheres of neutron stars, with a focus on the radiation emitted from extended polar caps of magnetars, which are the most highly magnetized neutron stars. Using the recent intensity pulse profile data for the magnetar 1RXS J11708-4009, we constrain the geometric parameters, namely the angles between the magnetic axis and the observer's viewing direction relative to the spin axis, as well as the sizes of emission regions. The distributions of these parameters and the best-fit configuration are provided. In addition, we discuss the important impacts of vacuum birefringence in the magnetosphere on increasing the linear polarization degree. A comparison with the case of a weakly magnetized neutron star, RX J0822.0-4300, is also discussed. Our simulation still needs further development, particularly to incorporate the vacuum resonance effect. Nevertheless, the formalism presented here can be employed to constrain geometric parameters for various types of neutron stars.

  PublisherDOI

• Pair Cascades in Magnetar Magnetospheres

  The Astrophysical Journal · 2025-09-26 · 1 citations

  articleOpen accessSenior author

  Abstract Resonant inverse Compton scattering (RICS) of soft thermal photons by relativistic particles on closed magnetic field loops has been proposed to explain the hard emission observed up to and beyond 200 keV from magnetars. If particles injected at the base of the loops have Lorentz factors ≳10 2 , the RICS spectra will be attenuated by both one-photon pair production and photon splitting in the ultrastrong magnetar fields, producing additional spectral components from pair synchrotron radiation and split photons that produce further generations of pairs and split photons. We investigate such cascades initiated by the primary injected electrons through a Monte Carlo simulation, and study the cascade spectra and pair distributions. For most observer angles, the pair synchrotron and split-photon spectra dominate the RICS primary spectra and produce complex polarization signals. In particular, the synchrotron spectra are highly polarized with degree 40%–80%, are softer than the RICS spectra, and may account for the high polarization of some magnetar spectra observed by the Imaging X-ray Polarimetry Explorer above 3 keV.

  PublisherDOI

Recent grants

• Collaborative Research: Radio, X-ray and Gamma-Ray Emission from Neutron Stars

  NSF · $199k · 2010–2014

• Modeling Emission and Particle Acceleration in Magnetars

  NSF · $273k · 2006–2011

• Cosmic Ray Ion and Electron Production at Relativistic Shocks in Gamma-Ray Bursts

  NSF · $75k · 2008–2012

• Modeling Comptonized Soft Gamma-Ray Flare Emission in Magnetars

  NSF · $304k · 2015–2019

• Collaborative Research: Theoretical Studies of the Atmospheres of Highly Magnetized Neutron Stars

  NSF · $327k · 2018–2023

Frequent coauthors

• I. A. Grenier

  Centre National de la Recherche Scientifique

  307 shared

• F. Piron

  Laboratoire Univers et Particules de Montpellier

  247 shared

• N. Omodei

  Stanford University

  246 shared

• A. K. Harding

  234 shared

• J. M. Casandjian

  Université Paris Cité

  227 shared

• L. Tibaldo

  Université de Toulouse

  219 shared

• J. Cohen-Tanugi

  Université Clermont Auvergne

  185 shared

• S. Razzaque

  182 shared