arXiv subjects

David N. Burrows

Publications and source records attributed to David N. Burrows.

At least 37 records · Page 2Linked to original sources

arXiv2019

Smoothed Particle Inference Analysis of SNR DEM L71

Supernova remnants (SNRs) are complex, three-dimensional objects; properly accounting for this complexity when modeling the resulting X-ray emission presents quite a challenge and makes it difficult to accurately characterize the properties of the full SNR volume. We apply for the first time a novel analysis method, Smoothed Particle Inference, that can be used to study and characterize the structure, dynamics, morphology, and abundances of the entire remnant with a single analysis. We apply the method to the Type Ia supernova remnant DEM L71. We present histograms and maps showing global properties of the remnant, including temperature, abundances of various elements, abundance ratios, and ionization age. Our analysis confirms the high abundance of Fe within the ejecta of the supernova, which has led to it being typed as a Ia. We demonstrate that the results obtained via this method are consistent with results derived from numerical simulations carried out by us, as well as with previous analyses in the literature. At the same time, we show that despite its regular appearance, the temperature and other parameter maps exhibit highly irregular substructure which is not captured with typical X-ray analysis methods.

astro-ph.HE↗

arXiv2019

Collisionless shock heating of heavy ions in SN 1987A

Astrophysical shocks at all scales, from those in the heliosphere up to the cosmological shock waves, are typically "collisionless", because the thickness of their jump region is much shorter than the collisional mean free path. Across these jumps, electrons, protons, and ions are expected to be heated at different temperatures. Supernova remnants (SNRs) are ideal targets to study collisionless processes because of their bright post-shock emission and fast shocks. Although optical observations of Balmer-dominated shocks in young SNRs showed that the post-shock proton temperature is higher than the electron temperature, the actual dependence of the post-shock temperature on the particle mass is still widely debated. We tackle this longstanding issue through the analysis of deep multi-epoch and high-resolution observations of the youngest nearby supernova remnant, SN 1987A, made with the Chandra X-ray telescope. We introduce a novel data analysis method by studying the observed spectra in close comparison with a dedicated full 3-D hydrodynamic simulation. The simulation is able to reproduce self-consistently the whole broadening of the spectral lines of many ions altogether. We can therefore measure the post shock temperature of protons and selected ions through comparison of the model with observations. We have obtained information about the heating processes in collisional shocks by finding that the ion to proton temperature ratio is always significantly higher than one and increases linearly with the ion mass for a wide range of masses and shock parameters.

astro-ph.HE↗

arXiv2019

Swift spectra of AT2018cow: A White Dwarf Tidal Disruption Event?

The bright transient AT2018cow has been unlike any other known type of transient. Its high brightness, rapid rise and decay and initially nearly featureless spectrum are unprecedented and difficult to explain using models for similar burst sources. We present evidence for faint gamma-ray emission continuing for at least 8 days, and featureless spectra in the ultraviolet bands -- both unusual for eruptive sources. The X-ray variability of the source has a burst-like character. The UV-optical spectrum does not show any CNO line but is well described by a blackbody. We demonstrate that a model invoking the tidal disruption of a 0.1 - 0.4 Msun Helium White Dwarf (WD) by a 100,000 to one million solar mass Black Hole (BH) located in the outskirts of galaxy Z~137-068 could provide an explanation for most of the characteristics shown in the multi-wavelength observations. A blackbody-like emission is emitted from an opaque photosphere, formed by the debris of the WD disruption. Broad features showing up in the optical/infrared spectra in the early stage are probably velocity broadened lines produced in a transient high-velocity outward moving cocoon. The asymmetric optical/infrared lines that appeared at a later stage are emission from an atmospheric layer when it detached from thermal equilibrium with the photosphere, which undergoes more rapid cooling. The photosphere shrinks when its temperature drops, and the subsequent infall of the atmosphere produced asymmetric line profiles. Additionally, a non-thermal jet might be present, emitting X-rays in the 10-150 keV band.

astro-ph.HE↗

arXiv2019

X-ray Hybrid CMOS Detectors: Recent Development and Characterization Progress

X-ray Hybrid CMOS Detectors (HCDs) have advantages over X-ray CCDs due to their higher readout rate abilities, flexible readout, inherent radiation hardness, and low power, which make them more suitable for the next generation large area X-ray telescope missions. The Penn State high energy astronomy laboratory has been working on the development and characterization of HCDs in collaboration with Teledyne Imaging Sensors (TIS). We characterized an H2RG detector with a Cryo-SIDECAR readout and controller, and we find an improved energy resolution of ~2.7 % at 5.9 keV and read noise of ~6.5 e-. This detector was successfully flown on NASA's first water recovery sounding rocket flight on April 4th, 2018. We have also been developing several new HCDs with potential applications for future X-ray astronomy missions. We are characterizing the performance of small-pixel HCDs (12.5 μm pitch), which are important for the development of a next-generation high-resolution imager with HCDs. We also characterized a 64 x 64 pixel prototype Speedster-EXD detector that uses comparators in each pixel to read out only those pixels having detectable signal, thereby providing an order of magnitude improvement in the effective readout rate. HCDs can also be utilized as a large FOV instrument to study the prompt and afterglow emissions of GRBs and detect black hole transients. In this context, we are characterizing a Lobster-HCD system for future CubeSat experiments. This paper briefly presents these new developments and experimental results.

astro-ph.IM↗

arXiv2018

Recent X-ray hybrid CMOS detector developments and measurements

The Penn State X-ray detector lab, in collaboration with Teledyne Imaging Sensors (TIS), have progressed their efforts to improve soft X-ray Hybrid CMOS detector (HCD) technology on multiple fronts. Having newly acquired a Teledyne cryogenic SIDECAR ASIC for use with HxRG devices, measurements were performed with an H2RG HCD and the cooled SIDECAR. We report new energy resolution and read noise measurements, which show a significant improvement over room temperature SIDECAR operation. Further, in order to meet the demands of future high-throughput and high spatial resolution X-ray observatories, detectors with fast readout and small pixel sizes are being developed. We report on characteristics of new X-ray HCDs with 12.5 micron pitch that include in-pixel CDS circuitry and crosstalk-eliminating CTIA amplifiers. In addition, PSU and TIS are developing a new large-scale array Speedster-EXD device. The original 64 x 64 pixel Speedster-EXD prototype used comparators in each pixel to enable event driven readout with order of magnitude higher effective readout rates, which will now be implemented in a 550 x 550 pixel device. Finally, the detector lab is involved in a sounding rocket mission that is slated to fly in 2018 with an off-plane reflection grating array and an H2RG X-ray HCD. We report on the planned detector configuration for this mission, which will increase the NASA technology readiness level of X-ray HCDs to TRL 9.

astro-ph.IM↗

arXiv2018

The Athena WFI Science Products Module

The Science Products Module (SPM), a US contribution to the Athena Wide Field Imager, is a highly capable secondary CPU that performs special processing on the science data stream. The SPM will have access to both accepted X-ray events and those that were rejected by the on-board event recognition processing. It will include two software modules. The Transient Analysis Module will perform on-board processing of the science images to identify and characterize variability of the prime target and/or detection of serendipitous transient X-ray sources in the field of view. The Background Analysis Module will perform more sophisticated flagging of potential background events as well as improved background characterization, making use of data that are not telemetered to the ground, to provide improved background maps and spectra. We present the preliminary design of the SPM hardware as well as a brief overview of the software algorithms under development.

astro-ph.IM↗

arXiv2018

Proton Radiation Damage Experiment on a Hybrid CMOS Detector

We report on the initial results of an experiment to determine the effects of proton radiation damage on an X-ray hybrid CMOS detector (HCD). The device was irradiated at the Edwards Accelerator Lab at Ohio University with 8 MeV protons, up to a total absorbed dose of 3 krad(Si) (4.5 $\times$ 10$^9$ protons/cm$^2$). The effects of this radiation on read noise, dark current, gain, and energy resolution are then analyzed. This exposure is the first of several which will be used for characterizing detector performance at absorbed dose levels that are relevant for imaging devices operating in a deep-space environment.

physics.ins-det↗

arXiv2018

Exploring Fine Subpixel Spatial Resolution of Hybrid CMOS Detectors

When an X-ray is incident onto the silicon absorber array of a detector, it liberates a large number of electrons, which tend to diffuse outward into what is referred to as the charge cloud. This number can vary from tens to thousands across the soft X-ray bandpass (0.1 - 10 keV). The charge cloud can then be picked up by several pixels, and forms a specific pattern based on the exact incident location of the X-ray. We present experimental results on subpixel resolution for a custom H2RG with 36 micron pixels, presented in Bray 2018, and compare the data to simulated images . We then apply the model simulation to a prototype small pixel hybrid CMOS detector (HCD) that would be suitable for the Lynx X-ray surveyor. We also discuss the ability of a small pixel detector to obtain subpixel resolution.

astro-ph.IM↗

arXiv2018

BlackCAT CubeSat: A Soft X-ray Sky Monitor, Transient Finder, and Burst Detector for High-energy and Multimessenger Astrophysics

Here we present the conceptual design of a wide field imager onboard a 6U class CubeSat platform for the study of GRB prompt and afterglow emission and detection of electromagnetic counterparts of gravitational waves in soft X-rays. The planned instrument configuration consists of an array of X-ray Hybrid CMOS detectors (HCD), chosen for their soft-X-ray response, flexible and rapid readout rate, and low power, which makes these detectors well suited for detecting bright transients on a CubeSat platform. The wide field imager is realized by a 2D coded mask. We will give an overview of the instrument design and the scientific requirements of the proposed mission.

astro-ph.IM↗

arXiv2016

Chandra Observes the End of an Era SN 1987A

Updated imaging and photometric results from Chandra observations of SN 1987A, covering the last 16 years, are presented. We find that the 0.5-2 keV light curve has remained constant at ~8x10^-12 erg s^-1 cm^-2 since 9500 days, with the 3-8 keV light curve continuing to increase until at least 10000 days. The expansion rate of the ring is found to be energy dependent, such that after day 6000 the ring expands faster in the 2-10 keV band than it does at energies <2 keV. Images show a reversal of the east-west asymmetry between 7000 and 8000 days after the explosion. The latest images suggest the southeastern side of the equatorial ring is beginning to fade. Consistent with the latest optical and infrared results, our Chandra analysis indicates the blast wave is now leaving the dense equatorial ring, which marks the beginning of a major change in the evolutionary phase of the supernova remnant 1987A.

astro-ph.HE↗

arXiv2016

The Speedster-EXD- A New Event-Driven Hybrid CMOS X-ray Detector

The Speedster-EXD is a new 64x64 pixel, 40 $μ$m pixel pitch, 100 $μ$m depletion depth hybrid CMOS X-ray detector (HCD) with the capability of reading out only those pixels containing event charge, thus enabling fast effective frame rates. A global charge threshold can be specified, and pixels containing charge above this threshold are flagged and read out. The Speedster detector has also been designed with other advanced in-pixel features to improve performance, including a low-noise, high-gain CTIA amplifier that eliminates interpixel capacitance crosstalk (IPC), and in-pixel Correlated Double Sampling (CDS) subtraction to reduce reset noise. We measure the best energy resolution on the Speedster-EXD detector to be 206 eV (3.5 %) at 5.89 keV and 172 eV (10.0 %) at 1.49 keV. The average IPC to the four adjacent pixels is measured to be 0.25 $\pm$ 0.2 % (i.e. consistent with zero). The pixel-to-pixel gain variation is measured to be 0.80 $\pm$ 0.03 %, and a Monte Carlo simulation is applied to better characterize the contributions to the energy resolution.

astro-ph.IM↗

arXiv2015

Chandra Observations of SNR RCW 103

We analyze three Chandra observations, with a combined exposure time of 99 ks, of the Galactic supernova remnant RCW 103, a young supernova remnant, previously with no clear detection of metal-rich ejecta. Based on our imaging and spectral analyses of these deep Chandra data, we find evidence for metal-rich ejecta emission scattered throughout the remnant. X-ray emission from the shocked ejecta is generally weak, and the shocked circumstellar medium (CSM) is a largely dominant component across the entire remnant. The CSM component shows abundances of ~0.5 solar, while Ne, Mg, Si, S, and Fe abundances of the ejecta are up to a few times solar. Comparison of these ejecta abundances with yields from supernova nucleosynthesis models suggests, together with the existence of a central neutron star, a progenitor mass of ~18-20 M$_\odot$, though the Fe/Si ratios are larger than predicted. The shocked CSM emission suggests a progenitor with high mass-loss rate and subsolar metallicity.

astro-ph.HE↗

arXiv2015

An Analysis of Chandra Deep Follow-up GRBs: Implications for Off-Axis Jets

We present a sample of 27 GRBs with detailed Swift light curves supplemented by late time Chandra observations. To answer the missing jet-break problem in general, we develop a numerical simulation based model which can be directly fit to the data using Monte Carlo methods. Our numerical model takes into account all the factors that can shape a jet-break: (i) lateral expansion (ii) edge effects and (iii) off-axis effects. Our results provide improved fits to the light curves and constraints on physical parameters. More importantly, our results suggest that off-axis effects are important and must be included in interpretations of GRB jet breaks.

astro-ph.HE↗

arXiv2015

Mapping High-velocity H-alpha and Lyman-alpha Emission from Supernova 1987A

We present new {\it Hubble Space Telescope} images of high-velocity H-$α$ and Lyman-$α$ emission in the outer debris of SN~1987A. The H-$α$ images are dominated by emission from hydrogen atoms crossing the reverse shock. For the first time we observe emission from the reverse shock surface well above and below the equatorial ring, suggesting a bipolar or conical structure perpendicular to the ring plane. Using the H$α$ imaging, we measure the mass flux of hydrogen atoms crossing the reverse shock front, in the velocity intervals ($-$7,500~$<$~$V_{obs}$~$<$~$-$2,800 km s$^{-1}$) and (1,000~$<$~$V_{obs}$~$<$~7,500 km s$^{-1}$), $\dot{M_{H}}$ = 1.2~$\times$~10$^{-3}$ M$_{\odot}$ yr$^{-1}$. We also present the first Lyman-$α$ imaging of the whole remnant and new $Chandra$ X-ray observations. Comparing the spatial distribution of the Lyman-$α$ and X-ray emission, we observe that the majority of the high-velocity Lyman-$α$ emission originates interior to the equatorial ring. The observed Lyman-$α$/H-$α$ photon ratio, $\langle$$R(Lα/ Hα)$$\rangle$ $\approx$~17, is significantly higher than the theoretically predicted ratio of $\approx$ 5 for neutral atoms crossing the reverse shock front. We attribute this excess to Lyman-$α$ emission produced by X-ray heating of the outer debris. The spatial orientation of the Lyman-$α$ and X-ray emission suggests that X-ray heating of the outer debris is the dominant Lyman-$α$ production mechanism in SN 1987A at this phase in its evolution.

astro-ph.SR↗

arXiv2014

The speedster-EXD - A new event-triggered hybrid CMOS x-ray detector

We present preliminary characterization of the Speedster-EXD, a new event driven hybrid CMOS detector (HCD) developed in collaboration with Penn State University and Teledyne Imaging Systems. HCDs have advantages over CCDs including lower susceptibility to radiation damage, lower power consumption, and faster read-out time to avoid pile-up. They are deeply depleted and able to detect x-rays down to approximately 0.1 keV. The Speedster-EXD has additional in-pixel features compared to previously published HCDs including: (1) an in-pixel comparator that enables read out of only the pixels with signal from an x-ray event, (2) four different gain modes to optimize either full well capacity or energy resolution, (3) in-pixel CDS subtraction to reduce read noise, and (4) a low-noise, high-gain CTIA amplifier to eliminate interpixel capacitance crosstalk. When using the comparator feature, the user can set a comparator threshold and only pixels above the threshold will be read out. This feature can be run in two modes including single pixel readout in which only pixels above the threshold are read out and 3x3 readout where a 3x3 region centered on the central pixel of the x-ray event is read out. The comparator feature of the Speedster-EXD increases the detector array effective frame rate by orders of magnitude. The new features of the Speedster-EXD hybrid CMOS x-ray detector are particularly relevant to future high throughput x-ray missions requiring large-format silicon imagers.

astro-ph.IM↗

arXiv2014

Asymmetry in The Observed Metal-Rich Ejecta of Galactic Type Ia Supernova Remnant G299.2-2.9

We have performed a deep Chandra observation of Galactic Type Ia supernova remnant G299.2-2.9. Here we report the initial results from our imaging and spectral analysis. The observed abundance ratios of the central ejecta are in good agreement with those predicted by delayed-detonation Type Ia supernovae models. We reveal inhomogeneous spatial and spectral structures of metal-rich ejecta in G299.2-2.9. The Fe/Si abundance ratio in the northern part of the central ejecta is higher than that in the southern part. An elongation of ejecta material extends out to the western outermost boundary of the remnant. In this western elongation, both the Si and Fe are enriched with a similar abundance ratio to that in the southern part of the central nebula. These structured distributions of metal-rich ejecta material suggest that this Type Ia supernova might have undergone a significantly asymmetric explosion and/or has been expanding into a structured medium.

astro-ph.HE↗

arXiv2014

A Deep Chandra Observation of Oxygen-Rich Supernova Remnant B0049-73.6 in the Small Magellanic Cloud

We report on the initial results from our deep Chandra observation (450 ks) of O-rich supernova remnant (SNR) B0049-73.6 in the Small Magellanic Cloud. We detect small metal-rich ejecta features extending out to the outermost boundary of B0049-73.6, which were not seen in the previous data with a shorter exposure. The central nebula is dominated by emission from reverse-shocked ejecta material enriched in O, Ne, Mg, and Si. O-rich ejecta distribution is relatively smooth throughout the central nebula. In contrast the Si-rich material is highly structured. These results suggest that B0049-73.6 was produced by an asymmetric core-collapse explosion of a massive star. The estimated abundance ratios among these ejecta elements are in plausible agreement with the nucleosynthesis products from the explosion of a 13-15$M_{\odot}$ progenitor. The central ring-like (in projection) ejecta nebula extends to $\sim$9 pc from the SNR center. This suggests that the contact discontinuity may be located at a further distance from the SNR center than the previous estimate. We estimate the Sedov age of $\sim$17000 yr and an explosion energy of $E_0$ $\sim1.7 \times~10^{51}$ erg for B0049-73.6. We place a stringent upper limit on the 2-7 keV band luminosity of $L_{X}\sim$ 8.5 $\times 10^{31}$ erg s$^{-1}$ for the embedded compact stellar remnant at the center of B0049-73.6.

astro-ph.HE↗

arXiv2013

The Burst Cluster: Dark Matter in a Cluster Merger Associated with the Short Gamma Ray Burst, GRB 050509B

We have identified a merging galaxy cluster with evidence of two distinct sub-clusters. The X-ray and optical data suggest that the subclusters are moving away from each other after closest approach. This cluster merger was discovered from observations of the well localized short-duration gamma-ray burst (GRB), GRB 050509B. The Swift/Burst Alert Telescope (BAT) source position is coincident with a cluster of galaxies ZwCl 1234.0+02916. The subsequent Swift/X-Ray Telescope (XRT) localization of the X-ray afterglow found the GRB coincident with 2MASX J12361286+2858580, a giant red elliptical galaxy in the cluster. Deep multi-epoch optical images were obtained to constrain the evolution of the GRB afterglow, including a 27480s exposure in the F814W band with Hubble Space Telescope Advanced Camera for Surveys (ACS), among the deepest imaging ever obtained towards a known galaxy cluster in a single passband. We perform a weak gravitational lensing analysis, including mapping the total mass distribution of the merger system. Combined with Chandra X-ray Observatory and Swift/XRT observations, we investigate the dynamical state of the merger to probe the nature of the dark matter component. Our weak gravitational lensing measurements reveal a separation of the X-ray centroid of the western subcluster from the center of the mass and galaxy light distributions, similar to that of the famous "Bullet cluster". We conclude that the "Burst cluster" is another candidate merger system for determining the nature of dark matter and for studying the environment of short GRBs. We discuss connections between the cluster dynamical state and/or matter composition and compact object mergers, the leading model for the origin of short GRBs. Finally, we present results from a weak lensing survey based on archival Very Large Telescope (VLT) images in the areas of 5 other short GRBs.

astro-ph.CO↗