arXiv subjects

Tyler Holland-Ashford

Publications and source records attributed to Tyler Holland-Ashford.

16 recordsLinked to original sources

arXiv2026

Galactic Science with Ultra-High Angular Resolution X-ray Imaging

Milli- to micro-arcsecond X-ray imaging will open a new observational regime for Galactic astrophysics by resolving physical scales that are inaccessible to current X-ray observatories. This white paper highlights the science enabled by such capabilities across four broad questions: how particles are accelerated, how stars die, how accretion is fueled, and what populations of X-ray sources inhabit the Galaxy. Ultra-high angular resolution will enable many new studies, such as resolving shocks and jets, measuring proper motions, parallaxes, and binary orbits, and providing secure multiwavelength counterpart identifications in crowded environments such as the Galactic Center and globular clusters. Combined with high-time-resolution observations, these measurements will connect variability and transient events to the physical structures in which they originate, while coordination with gravitational-wave, neutrino, $γ$-ray, radio, optical, and infrared facilities will provide spatial information needed to identify and characterize multi-messenger sources. In addition to defining the science cases, this paper presents a curated list of compelling targets spanning various angular resolutions and outlines the complementary specifications necessary to maximize the scientific outcome. Accomplishing these science goals will require an instrument with high angular resolution, precise astrometry, substantial collecting area, sufficient spectral and timing resolution, and high dynamic range imaging capabilities.

astro-ph.HE↗

arXiv2026

XRISM Observation of the Supernova Remnant N103B: Velocity Structure and Thermal Properties

We present the first analysis of the X-ray Imaging and Spectroscopy Mission (XRISM) observation of the supernova remnant (SNR) N103B. We fit the X-ray spectrum taken with the Resolve microcalorimeter, which captured emission lines from the predominantly ejecta elements Si, S, Ar, Ca, Cr, Mn, and Fe. Notably, our fits require a previously unidentified high-temperature, highly-ionized, Fe-dominated plasma component with particularly high Cr and Mn abundances, matching a feature also present in the recent XRISM analysis of the SNR N132D. We find that all ejecta in N103B exhibits significant line broadening arising mostly from thermal Doppler broadening: increasing from $σ_{\rm th}\sim1700$ km s$^{-1}$ for intermediate-mass element (IME: Si, S, Ar, and Ca) ejecta to $\sim$2800 km s$^{-1}$ for Fe-rich ejecta. These velocities correspond to reverse shock velocities of $\sim$3500 and $\sim$5900 km s$^{-1}$, respectively, in the ejecta frame of rest. Finally, we find that the IMEs are redshifted with a bulk velocity of $\sim$360 km s$^{-1}$ while the Fe-dominated components are split: one redshifted at $\sim$1560 km s$^{-1}$ and the other blueshifted at $\sim$1020 km s$^{-1}$. Our results provide further support for the double-ring structure of N103B as it expands into the bipolar winds of a non-degenerate companion and highlight the strength of high-resolution spectroscopic observations of SNRs.

astro-ph.HE↗

arXiv2025

Taming the Tarantula: How Stellar Wind Feedback Shapes Gas and Dust in 30 Doradus

Observations of massive star-forming regions show that classical stellar wind models over-predict the luminosity of the X-ray emitting gas, indicating a significant fraction of wind energy is lost. In this paper, we present a multi-wavelength analysis of the giant HII region 30 Doradus and its central star cluster R136 using 2 Ms of Chandra X-ray Observatory data, combined with James Webb Space Telescope and Hubble Space Telescope imaging and Spitzer spectral-energy distributions, to investigate how the hot gas energy is lost through turbulent mixing, radiative cooling, and physical leakage. We compare the spatial and spectral properties of the hot gas with those of the warm ionized gas and dust. We find no significant correlation between the dust and hot gas temperatures, suggesting they are not directly coupled and that the dust resides in the swept-up shells where it is heated radiatively. H$α$ and X-ray surface brightness profiles show that the X-rays peak interior to the H$α$ shells, demonstrating partial confinement of the hot gas. The fragmented shell structure and bright X-ray interior that declines near the H$α$ shell reflect efficient cooling from turbulent mixing at the hot-cold interface. We compare against recent simulations of stellar-feedback driven bubbles which have broad agreement with the morphology of the X-ray and H$α$ emission, but the simulations produce a dip in the interior X-ray surface brightness and a lack of hard X-rays compared to the observations. These differences may suggest thermal conduction is important as mass-loading of the hot bubble could reproduce the X-ray observables.

astro-ph.HE↗

arXiv2025

Proper Motion of the Neutron Star in the Supernova Remnant G18.9-1.1

In this paper, we present the first direct measurement of the proper motion of the neutron star (NS) in the supernova remnant (SNR) G18.9-1.1 using a 15-year Chandra baseline. After correcting the observations' astrometric solutions using reference Gaia stars' positions, we measure a total proper motion of 24.7 $\pm$ 6.8 mas yr$^{-1}$ at an angle of $336^\circ \pm$ 16$^\circ$ east of north. Using the distance estimates from literature of 2.1 kpc and 3.8 kpc, this proper motion corresponds to Galactic rotation-corrected transverse velocities of 264d$_{2.1}$ $\pm$ 79 km s$^{-1}$ and 474d$_{3.8}$ $\pm$ 129 km s$^{-1}$, respectively. Our power ratio method analysis of SNR ejecta slightly favors the higher velocity, as multipole moments calculated from the back-evolved center using the farther distance are more consistent with values from other CCSNRs. The NS's motion is directly opposite the motion of bulk ejecta in G18.9$-$1.1, providing yet more evidence that NS kicks are generated via a conservation of momentum-like process between the NS and the ejecta, as has been observed in other SNRs.

astro-ph.HE↗

arXiv2025

Estimating Global Ejecta Mass Ratios in Tycho's SNR

In this work, as a follow-up to our similar analysis of Kepler's supernova remnant (SNR), we estimate total mass ratios of various ejecta elements in Tycho's SNR using Suzaku X-ray data. In our spectral analysis, we account for uncertainties arising from Suzaku's effective area calibration (5%-15%) and from the unknown filling factors of the various plasma components in our spectral model (1%-10%). We compare our calculated ejecta mass ratios to results from previous X-ray analyses of Tycho's SNR and to the nucleosynthesis results from Type Ia supernova simulations. Our estimated ejecta mass ratios for Tycho's SNR are only consistent with simulations that use a $\sim$90% attenuated $^{12}$C$+^{16}$O reaction rate (as for Kepler's SNR), are inconsistent with simulations involving a double detonation of a thick helium layer, and support a Type Ia explosion of normal luminosity where $\sim$85% of the ejecta has been heated by the reverse shock.

astro-ph.HE↗

arXiv2025

Updated Proper Motion of the Neutron Star in the Supernova Remnant Cassiopeia A

In this paper, we present updated estimates of the velocity of the neutron star (NS) in the supernova remnant (SNR) Cassiopeia A using over two decades of Chandra observations. We use two methods: 1.) recording NS positions from dozens of Chandra observations, including the astrometric uncertainty estimates on the data points but not correcting the astrometry of the observations, and 2.) correcting the astrometry of the 13 Chandra observations that have a sufficient number of point sources with identified Gaia counterparts. For method #1, we observe a heliocentric velocity of 275 $\pm$ 121 km/s, with an angle of 177 $\pm$ 22 degrees east of north. For method #2, we observe a heliocentric velocity of 436 $\pm$ 89 km s$^{-1}$ at an angle of 158 $\pm$ 12 degrees. Correcting for galactic rotation and the sun's peculiar motion decreases these estimates to 256 km s$^{-1}$ at 167$^\circ$ and 433 km s$^{-1}$ at 151$^\circ$, respectively. Both of our estimates match with the explosion-center-estimated velocity of $\sim$350 km s$^{-1}$ and the previous 10--year baseline proper motion measurement of 570 $\pm$ 260 km s$^{-1}$, but our use of additional data over a longer baseline has led to a smaller uncertainty by a factor of 2--3. Our estimates rule out velocities $\gtrsim$600 km s$^{-1}$ and better match with simulations of Cassiopeia~A that include NS kick mechanisms.

astro-ph.HE↗

arXiv2024

Comparing the three-dimensional morphological asymmetries in the ejecta of Kepler and Tycho in X-rays

Recent simulations have shown that asymmetries in the ejecta distribution of supernova remnants (SNRs) may be a reflection of asymmetries left over from the initial supernova explosion. Thus, SNR studies provide a vital means for testing and constraining model predictions in relation to the distribution of heavy elements, which are key to improving our understanding of the explosion mechanisms in Type Ia supernovae. The use of a novel blind source separation method applied to the megasecond X-ray observations of the historic Kepler and Tycho supernova remnants has revealed maps of the ejecta distribution. These maps are endowed with an unprecedented level of detail and clear separations from the continuum emission. Our method also provides a three-dimensional (3D) view of the ejecta by individually disentangling red- and blueshifted spectral components associated with images of the Si, S, Ar, Ca, and Fe emission. This approach provides insights into the morphology of the ejecta distribution in those two remnants. Those mappings have allowed us to thoroughly investigate the asymmetries in the intermediate-mass elements and Fe distribution in two Type Ia supernova remnants. We also compared the results with the core-collapse Cassiopeia A remnant, which we had studied previously. The images obtained confirm, as expected for Type Ia SNRs, that the Fe distribution is mostly closer to the core than that of intermediate-mass elements. They also highlight peculiar features in the ejecta distribution, such as the Fe-rich southeastern knot in Tycho.

astro-ph.HE↗

arXiv2023

Estimating Ejecta Mass Ratios in Kepler's SNR: Global X-Ray Spectral Analysis Including Suzaku Systematics and Emitting Volume Uncertainties

The exact origins of many Type Ia supernovae$\unicode{x2013}$progenitor scenarios and explosive mechanisms$\unicode{x2013}$remain uncertain. In this work, we analyze the global Suzaku X-Ray spectrum of Kepler's supernova remnant in order to constrain mass ratios of various ejecta species synthesized during explosion. Critically, we account for the Suzaku telescope effective area calibration uncertainties of 5$\unicode{x2013}$20% by generating 100 mock effective area curves and using Markov Chain Monte Carlo based spectral fitting to produce 100 sets of best-fit parameter values. Additionally, we characterize the uncertainties from assumptions made about the emitting volumes of each model plasma component: finding that these uncertainties can be the dominant source of error. We then compare our calculated mass ratios to previous observational studies of Kepler's SNR and to the predictions of SN Ia simulations. Our mass ratio estimates require a $\sim$90% attenuated $^{12}$C$+^{16}$O reaction rate and are potentially consistent with both near- and sub-M$_{\rm Ch}$ progenitors, but are inconsistent with the dynamically stable double detonation origin scenario and only marginally consistent with the dynamically unstable dynamically-driven double-degenerate double detonation (D$^6$) scenario.

astro-ph.HE↗

arXiv2021

Local Environments of Low-Redshift Supernovae

We characterize the local (2-kpc sized) environments of Type Ia, II, and Ib/c supernovae (SNe) that have recently occurred in nearby ($d\lesssim50$ Mpc) galaxies. Using ultraviolet (UV, from GALEX) and infrared (IR, from WISE) maps of 359 galaxies and a sample of 472 SNe, we measure the star formation rate surface density ($Σ_{\rm SFR}$) and stellar mass surface density ($Σ_\star$) in a 2-kpc beam centered on each SN site. We show that core-collapse SNe are preferentially located along the resolved galactic star-forming main sequence, whereas Type Ia SNe are extended to lower values of $Σ_{\rm SFR}$ at fixed $Σ_\star$, indicative of locations inside quiescent galaxies or quiescent regions of galaxies. We also test how well the radial distribution of each SN type matches the radial distributions of UV and IR light in each host galaxy. We find that, to first order, the distributions of all types of SNe mirror that of both near-IR light (3.4 and 4.5 microns, tracing the stellar mass distribution) and mid-IR light (12 and 22 microns, tracing emission from hot, small grains), and also resemble our best-estimate $Σ_{\rm SFR}$. All types of SNe appear more radially concentrated than the UV emission of their host galaxies. In more detail, the distributions of Type II SNe show small statistical differences from that of near-IR light. We attribute this overall structural uniformity to the fact that within any individual galaxy, $Σ_{\rm SFR}$ and $Σ_\star$ track one another well, with variations in $Σ_{\rm SFR}/Σ_\star$ most visible when comparing between galaxies.

astro-ph.GA↗

arXiv2021

Three-dimensional morphological asymmetries in the ejecta of Cassiopeia A using a component separation method in X-rays

Recent simulations have shown that asymmetries in the ejecta distribution of supernova remnants (SNR) can still reflect asymmetries from the initial supernova explosion. Thus, their study provides a great means to test and constrain model predictions in relation to the distributions of heavy elements or the neutron star kicks, both of which are key to better understanding the explosion mechanisms in core-collapse supernovae. The use of a novel blind source separation method applied to the megasecond X-ray observations of the well-known Cassiopeia A SNR has revealed maps of the distribution of the ejecta endowed with an unprecedented level of detail and clearly separated from continuum emission. Our method also provides a three-dimensional view of the ejecta by disentangling the red- and blue-shifted spectral components and associated images of the Si, S, Ar, Ca and Fe, providing insights into the morphology of the ejecta distribution in Cassiopeia A. These mappings allow us to thoroughly investigate the asymmetries in the heavy elements distribution and probe simulation predictions about the neutron star kicks and the relative asymmetries between the different elements. We find in our study that most of the ejecta X-ray flux stems from the red-shifted component, suggesting an asymmetry in the explosion. In addition, the red-shifted ejecta can physically be described as a broad, relatively symmetric plume, whereas the blue-shifted ejecta is more similar to a dense knot. The neutron star also moves directly opposite to the red-shifted parts of the ejecta similar to what is seen with 44Ti. Regarding the morphological asymmetries, it appears that heavier elements have more asymmetrical distributions, which confirms predictions made by simulations. This study is a showcase of the capacities of new analysis methods to revisit archival observations to fully exploit their scientific content.

astro-ph.HE↗

arXiv2020

Spatially-Resolved Study of Recombining Plasma in W49B Using XMM-Newton

W49B is the youngest SNR to date that exhibits recombining plasma. The two prevailing theories of this overionization are rapid cooling via adiabatic expansion or through thermal conduction with an adjacent cooler medium. To constrain the origin of the recombining plasma in W49B, we perform a spatially-resolved spectroscopic study of deep XMM-Newton data across 46 regions. We adopt a 3-component model (with one ISM and two ejecta components), and we find that recombining plasma is present throughout the entire SNR, with increasing overionization from east to west. The latter result is consistent with previous studies, and we attribute the overionization in the west to adiabatic expansion. However, our findings contrast these prior works as we find evidence of overionization in the east as well. As the SNR is interacting with molecular material there, we investigate the plausibility of thermal conduction as the origin of the rapid cooling. We show that based on the estimated timescales, it is possible that small-scale thermal conduction through evaporation of clumpy, dense clouds with a scale of 0.1-1.0 pc can explain the observed overionization in the east.

astro-ph.HE↗

arXiv2020

Evidence of a Type Ia Progenitor for Supernova Remnant 3C 397

The explosive origin of the young supernova remnant (SNR) 3C 397 (G41.1-0.3) is debated. Its elongated morphology and proximity to a molecular cloud are suggestive of a core-collapse (CC) SN origin, yet recent X-ray studies of heavy metals show chemical yields and line centroid energies consistent with a Type Ia SN. In this paper, we analyze the full X-ray spectrum from 0.7-10 keV of 3C 397 observed with Suzaku and compare the line centroid energies, fluxes, and elemental abundances of intermediate-mass and heavy metals (Mg to Ni) to Type Ia and CC hydrodynamical model predictions. Based on the results, we conclude that 3C 397 likely arises from an energetic Type Ia explosion in a high-density ambient medium, and we show that the progenitor was a near Chandrasekhar mass white dwarf.

astro-ph.HE↗

arXiv2020

Asymmetries of Heavy Elements in the Young Supernova Remnant Cassiopeia A

Supernova remnants (SNRs) offer the means to study supernovae (SNe) long after the original explosion and can provide a unique insight into the mechanism that governs these energetic events. In this work, we examine the morphologies of X-ray emission from different elements found in the youngest known core-collapse (CC) SNR in the Milky Way, Cassiopeia A. The heaviest elements exhibit the highest levels of asymmetry, which we relate to the burning process that created the elements and their proximity to the center of explosion. Our findings support recent model predictions that the material closest to the source of explosion will reflect the asymmetries inherent to the SN mechanism. Additionally, we find that the heaviest elements are moving more directly opposed to the neutron star (NS) than the lighter elements. This result is consistent with NS kicks arising from ejecta asymmetries.

astro-ph.HE↗

arXiv2019

The Age Evolution of the Radio Morphology of Supernova Remnants

Recent hydrodynamical models of supernova remnants (SNRs) demonstrate that their evolution depends heavily on the inhomogeneities of the surrounding medium. As SNRs expand, their morphologies are influenced by the non-uniform and turbulent structure of their environments, as reflected in their radio continuum emission. In this paper, we measure the asymmetries of 96 SNRs in radio continuum images from three surveys of the Galactic plane and compare these results to the SNRs' radii, which we use as a proxy for their age. We find that larger (older) SNRs are more elliptical/elongated and more mirror asymmetric than smaller (younger) SNRs, though the latter vary in their degrees of asymmetry. This result suggests that SNR shells become more asymmetric as they sweep up the interstellar medium (ISM), as predicted in hydrodynamical models of SNRs expanding in a multi-phase or turbulent ISM.

astro-ph.HE↗

arXiv2018

Measurement of the core-collapse progenitor mass distribution of the Small Magellanic Cloud

The physics of core-collapse (CC) supernovae (SNe) and how the explosions depend on progenitor properties are central questions in astronomy. For only a handful of SNe, the progenitor star has been identified in pre-explosion images. Supernova remnants (SNRs), which are observed long after the original SN event, provide a unique opportunity to increase the number of progenitor measurements. Here, we systematically examine the stellar populations in the vicinities of 23 known SNRs in the Small Magellanic Cloud (SMC) using the star formation history (SFH) maps of Harris & Zaritsky (2004). We combine the results with constraints on the SNR metal abundances and environment from X-ray and optical observations. We find that 22 SNRs in the SMC have local SFHs and properties consistent with a CC explosion, several of which are likely to have been high-mass progenitors. This result supports recent theoretical findings that high-mass progenitors can produce successful explosions. We estimate the mass distribution of the CC progenitors and find that this distribution is similar to a Salpeter IMF (within the uncertainties), while this result is shallower than the mass distribution found in M31 and M33 by Jennings et al. (2014) and D\'ıaz-Rodr\'ıguez et al. (2018) using a similar approach. Additionally, we find that a number of the SMC SNRs exhibit a burst of star formation between 50-200 Myr ago. As these sources are likely CC, this signature may be indicative of massive stars undergoing delayed CC as a consequence of binary interaction, rapid rotation, or low metallicity. In addition, the lack of Type Ia SNRs in the SMC is possibly a result of the short visibility times of these sources as they may fall below the sensitivity limits of current radio observations.

astro-ph.SR↗

arXiv2017

Comparing Neutron Star Kicks to Supernova Remnant Asymmetries

Supernova explosions are inherently asymmetric and can accelerate new-born neutron stars (NSs) to hundreds of km/s. Two prevailing theories to explain NS kicks are ejecta asymmetries (e.g., conservation of momentum between NS and ejecta) and anisotropic neutrino emission. Observations of supernova remnants (SNRs) can give us insights into the mechanism that generates these NS kicks. In this paper, we investigate the relationship between NS kick velocities and the X-ray morphologies of 18 SNRs observed with the Chandra X-ray Observatory and the Rontgen Satellite (ROSAT). We measure SNR asymmetries using the power-ratio method (a multipole expansion technique), focusing on the dipole, quadrupole, and octupole power-ratios. Our results show no correlation between the magnitude of the power-ratios and NS kick velocities, but we find that for Cas A and G292.0+1.8, whose emission traces the ejecta distribution, their NSs are preferentially moving opposite to the bulk of the X-ray emission. In addition, we find a similar result for PKS 1209-51, CTB 109, and Puppis A; however their emission is dominated by circumstellar/interstellar material, so their asymmetries may not reflect their ejecta distributions. Our results are consistent with the theory that NS kicks are a consequence of ejecta asymmetries as opposed to anisotropic neutrino emission. In the future, additional observations to measure NS proper motions within ejecta-dominated SNRs are necessary to constrain robustly the NS kick mechanism.

astro-ph.HE↗