arXiv subjects

David N. Burrows

Publications and source records attributed to David N. Burrows.

At least 55 records · Page 3Linked to original sources

arXiv2013

Characterization of Si Hybrid CMOS Detectors for use in the Soft X-ray Band

We report on the characterization of four Teledyne Imaging Systems HAWAII Hybrid Si CMOS detectors designed for X-ray detection. Three H1RG detectors were studied along with a specially configured H2RG. Read noise measurements were performed, with the lowest result being 7.1 e- RMS. Interpixel capacitive crosstalk (IPC) was measured for the three H1RGs and for the H2RG. The H1RGs had IPC upper limits of 4.0 - 5.5 % (up & down pixels) and 8.7 - 9.7 % (left & right pixels), indicating a clear asymmetry. Energy resolution is reported for two X-ray lines, 1.5 & 5.9 keV, at multiple temperatures between 150 - 210 K. The best resolution measured at 5.9 keV was 250 eV (4.2 %) at 150 K, with IPC contributing significantly to this measured energy distribution. The H2RG, with a unique configuration designed to decrease the capacitive coupling between ROIC pixels, had an IPC of 1.8 +/- 1.0 % indicating a dramatic improvement in IPC with no measurable asymmetry. We also measured dark current as a function of temperature for each detector. For the detector with the lowest dark current, at 150 K, we measured a dark current of 0.020 +/- 0.001 (e- sec-1 pix-1). There is also a consistent break in the fit to the dark current data for each detector. Above 180 K, all the data can be fit by the product of a power law in temperature and an exponential. Below 180 K the dark current decreases more slowly; a shallow power law or constant must be added to each fit, indicating a different form of dark current is dominant in this temperature regime. Dark current figures of merit at 293 K are estimated from the fit for each detector.

astro-ph.IM↗

arXiv2013

A Super-Solar Metallicity for the Progenitor of Kepler's Supernova

We have performed deep X-ray observations of the remnant of Kepler's supernova (SN 1604) as a Key Project of the Suzaku Observatory. Our main goal is to detect secondary Fe-peak elements in the SN ejecta to gain insights into the Type Ia supernova explosion mechanism and the nature of the progenitor. Here we report our initial results. We made a conclusive detection of X-ray emission lines from highly ionized Mn, Cr, and Ni as well as Fe. The observed Mn-to-Cr line flux ratio is ~0.60, ~30% larger than that measured in Tycho's remnant. We estimate a Mn-to-Cr mass ratio of ~0.77, which is strongly suggestive of a large neutron excess in the progenitor star before the onset of the thermonuclear runaway. The observed Ni-to-Fe line flux ratio (~0.03) corresponds to a mass ratio of ~0.06, which is generally consistent with the products of explosive Si-burning regime in Type Ia explosion models, and rules out contamination from the products of neutron-rich nuclear statistical equilibrium in the shocked ejecta. Together with the previously suggested luminous nature of the explosion, these mass ratios provide strong evidence for a super-solar metallicity in the SN progenitor (~3 Z_sun). Kepler's supernova was likely the thermonuclear explosion of a white dwarf formed in the recent past that must have exploded through a relatively prompt channel.

astro-ph.HE↗

arXiv2012

Characterization of an x-ray hybrid CMOS detector with low interpixel capacitive crosstalk

We present the results of x-ray measurements on a hybrid CMOS detector that uses a H2RG ROIC and a unique bonding structure. The silicon absorber array has a 36μm pixel size, and the readout array has a pitch of 18μm; but only one readout circuit line is bonded to each 36x36μm absorber pixel. This unique bonding structure gives the readout an effective pitch of 36μm. We find the increased pitch between readout bonds significantly reduces the interpixel capacitance of the CMOS detector reported by Bongiorno et al. 2010 and Kenter et al. 2005.

astro-ph.IM↗

arXiv2012

Recent Progress on Developments and Characterization of Hybrid CMOS X-ray Detectors

Future space-based X-ray telescope missions are likely to have significantly increased demands on detector read out rates due to increased collection area, and there will be a desire to minimize radiation damage in the interests of maintaining spectral resolution. While CCDs have met the requirements of past missions, active pixel sensors are likely to be a standard choice for some future missions due to their inherent radiation hardness and fast, flexible read-out architecture. One form of active pixel sensor is the hybrid CMOS sensor. In a joint program of Penn State University and Teledyne Imaging Sensors, hybrid CMOS sensors have been developed for use as X-ray detectors. Results of this development effort and tests of fabricated detectors will be presented, along with potential applications for future missions.

astro-ph.IM↗

arXiv2012

GRB 120422A: A Low-luminosity Gamma-ray Burst Driven by Central Engine

GRB 120422A is a low-luminosity Gamma-ray burst (GRB) associated with a bright supernova, which distinguishes itself by its relatively short T90 ~ 5 s and an energetic X-ray tail. We analyze the Swift BAT and XRT data and discuss the physical implications. We show that the early steep decline in the X-ray light curve can be interpreted as the curvature tail of a late emission episode around 58-86 s, with a curved instantaneous spectrum at the end of the emission episode. Together with the main activity in the first ~ 20 s and the weak emission from 40 s to 60 s, the prompt emission is variable, which points towards a central engine origin, in contrast to the shock breakout origin as invoked to interpret some other nearby low-luminosity supernova GRBs. The curvature effect interpretation and interpreting the early shallow decay as the coasting external forward shock emission in a wind medium both give a constraint on the bulk Lorentz factor Γto be around several. Comparing the properties of GRB 120422A and other supernova GRBs, we found that the main criterion to distinguish engine-driven GRBs from the shock breakout GRBs is the time-averaged luminosity, with a separation line of about ~ 10^48 erg s^-1.

astro-ph.HE↗

arXiv2012

An X-Ray Study of Supernova Remnant N49 and Soft Gamma-Ray Repeater 0526-66 in the Large Magellanic Cloud

We report on the results from our deep Chandra observation (120 ks) of the supernova remnant (SNR) N49 and soft Gamma-ray repeater (SGR) 0526-66 in the Large Magellanic Cloud. We firmly establish the detection of an ejecta "bullet" beyond the southwestern boundary of N49. The X-ray spectrum of the bullet is distinguished from that of the main SNR shell, showing significantly enhanced Si and S abundances. We also detect an ejecta feature in the eastern shell, which shows metal overabundances similar to those of the bullet. If N49 was produced by a core-collapse explosion of a massive star, the detected Si-rich ejecta may represent explosive O-burning or incomplete Si-burning products from deep interior of the supernova. On the other hand, the observed Si/S abundance ratio in the ejecta may favor Type Ia origin for N49. We refine the Sedov age of N49, tau_Sed ~ 4800 yr, with the explosion energy E_0 ~ 1.8 x 10^51 erg. Our blackbody (BB) + power law (PL) model for the quiescent X-ray emission from SGR 0526-66 indicates that the PL photon index (Gamma ~ 2.5) is identical to that of PSR 1E1048.1-5937, the well-known candidate transition object between anomalous X-ray pulsars and SGRs. Alternatively, the two-component BB model implies X-ray emission from a small (R ~ 1 km) hot spot(s) (kT ~ 1 keV) in addition to emission from the neutron star's cooler surface (R ~ 10 km, kT ~ 0.4 keV). There is a considerable discrepancy in the estimated column toward 0526-66 between BB+PL and BB+BB model fits. Discriminating these spectral models would be crucial to test the long-debated physical association between N49 and 0526-66.

astro-ph.HE↗

arXiv2011

A New Evolutionary Phase of Supernova Remnant 1987A

We have been monitoring the supernova remnant (SNR) 1987A with {\it Chandra} observations since 1999. Here we report on the latest change in the soft X-ray light curve of SNR 1987A. For the last $\sim$1.5 yr (since day $\sim$8000), the soft X-ray flux has significantly flattened, staying (within uncertainties) at $f_{\rm X}$ $\sim$ 5.7 $\times$ 10$^{-12}$ erg cm$^{-2}$ s$^{-1}$ (corresponding to $L_{\rm X}$ $\sim$ 3.6 $\times$ 10$^{36}$ erg s$^{-1}$) in the 0.5--2 keV band. This remarkable change in the recent soft X-ray light curve suggests that the forward shock is now interacting with a decreasing density structure, after interacting with an increasing density gradient over $\sim$10 yr prior to day $\sim$8000. Possibilities may include the case that the shock is now propagating beyond a density peak of the inner ring. We briefly discuss some possible implications on the nature of the progenitor and the future prospects of our {\it Chandra} monitoring observations.

astro-ph.HE↗

arXiv2011

SNR 0104-72.3: A remnant of Type Ia Supernova in a Star-forming region?

We report our 110 ks Chandra observations of the supernova remnant (SNR) 0104-72.3 in the Small Magellanic Cloud (SMC). The X-ray morphology shows two prominent lobes along the northwest-southeast direction and a soft faint arc in the east. Previous low resolution X-ray images attributed the unresolved emission from the southeastern lobe to a Be/X-ray star. Our high resolution Chandra data clearly shows that this emission is diffuse, shock-heated plasma, with negligible X-ray emission from the Be star. The eastern arc is positionally coincident with a filament seen in optical and infrared observations. Its X-ray spectrum is well fit by plasma of normal SMC abundances, suggesting that it is from shocked ambient gas. The X-ray spectra of the lobes show overabundant Fe, which is interpreted as emission from the reverse-shocked Fe-rich ejecta. The overall spectral characteristics of the lobes and the arc are similar to those of Type Ia SNRs, and we propose that SNR 0104-72.3 is the first case for a robust candidate Type Ia SNR in the SMC. On the other hand, the remnant appears to be interacting with dense clouds toward the east and to be associated with a nearby star-forming region. These features are unusual for a standard Type Ia SNR. Our results suggest an intriguing possibility that the progenitor of SNR 0104-72.3 might have been a white dwarf of a relatively young population.

astro-ph.GA↗

arXiv2010

Late time observations of GRB080319B: jet break, host galaxy and accompanying supernova

The Swift discovered GRB080319B was by far the most distant source ever observed at naked eye brightness, reaching a peak apparent magnitude of 5.3 at a redshift of z=0.937. We present our late-time optical (HST, Gemini & VLT) and X-ray (Chandra) observations, which confirm that an achromatic break occurred in the power-law afterglow light curve at ~11 days post-burst. This most likely indicates that the gamma-ray burst (GRB) outflow was collimated, which for a uniform jet would imply a total energy in the jet E_{jet} \gsim 10^{52} erg. Our observations also show a late-time excess of red light, which is well explained if the GRB was accompanied by a supernova (SN), similar to those seen in some other long-duration GRBs. The latest observations are dominated by light from the host and show that the GRB took place in a faint dwarf galaxy (r(AB)\approx27.0, rest-frame M_B\approx-17.2). This galaxy is small even by the standards of other GRB hosts, which is suggestive of a low metallicity environment. Intriguingly, the properties of this extreme event - a small host and bright supernova - are entirely typical of the very low-luminosity bursts such as GRB980425 and GRB060218.

astro-ph↗

arXiv2010

Five Years of Mid-Infrared Evolution of the Remnant of SN 1987A: The Encounter Between the Blast Wave and the Dusty Equatorial Ring

We have used the Spitzer satellite to monitor the mid-IR evolution of SN 1987A over a 5 year period spanning the epochs between days 6000 and 8000 since the explosion. The supernova (SN) has evolved into a supernova remnant (SNR) and its radiative output is dominated by the interaction of the SN blast wave with the pre-existing equatorial ring (ER). The mid-IR spectrum is dominated by emission from ~180 K silicate dust, collisionally-heated by the hot X-ray emitting gas with a temperature and density of ~5x10^6 K and 3x10^4 cm-3, respectively. The mass of the radiating dust is ~1.2x10^(-6) Msun on day 7554, and scales linearly with IR flux. The infrared to soft-X-ray flux ratio is roughly constant with a value of 2.5. Gas-grain collisions therefore dominate the cooling of the shocked gas. The constancy of of this ratio suggests that very little grain processing or gas cooling have occurred throughout this epoch. The shape of the dust spectrum remained unchanged during the observations while the total flux increased with a time dependence of t^(0.87), t being the time since the first encounter between the blast wave and the ER. These observations are consistent with the transitioning of the blast wave from free expansion to a Sedov phase as it propagates into the main body of the ER.

astro-ph.CO↗

arXiv2010

Evolution of the Chandra CCD Spectra of SNR 1987A: Probing the Reflected-Shock Picture

We continue to explore the validity of the reflected shock structure (RSS) picture in SNR 1987A that was proposed in our previous analyses of the X-ray emission from this object. We used an improved version of our RSS model in a global analysis of 14 CCD spectra from the monitoring program with Chandra. In the framework of the RSS picture, we are able to match both the expansion velocity curve deduced from the analysis of the X-ray images and light curve. Using a simplified analysis, we also show that the X-rays and the non-thermal radio emission may originate from the same shock structure (the blast wave). We believe that using the RSS model in the analysis of grating data from the Chandra monitoring program of SNR 1987A that cover a long enough time interval, will allow us to build a more realistic physical picture and model of SNR 1987A.

astro-ph.HE↗

arXiv2010

The Outer Shock of the Oxygen-Rich Supernova Remnant G292.0+1.8: Evidence for the Interaction with the Stellar Winds from its Massive Progenitor

We study the outer-shock structure of the oxygen-rich supernova remnant G292.0+1.8, using a deep observation with the Chandra X-ray Observatory. We measure radial variations of the electron temperature and emission measure that we identify as the outer shock propagating into a medium with a radially decreasing density profile. The inferred ambient density structure is consistent with models for the circumstellar wind of a massive progenitor star rather than for a uniform interstellar medium. The estimated wind density n_H = 0.1 ~ 0.3 cm^-3) at the current outer radius (~7.7 pc) of the remnant is consistent with a slow wind from a red supergiant (RSG) star. The total mass of the wind is estimated to be ~ 15 - 40 solar mass (depending on the estimated density range), assuming that the wind extended down to near the surface of the progenitor. The overall kinematics of G292.0+1.8 are consistent with the remnant expanding through the RSG wind.

astro-ph.GA↗

arXiv2010

Late-time detections of the X-ray afterglow of GRB 060729 with Chandra - the latest detections ever of an X-ray afterglow

We report on 5 Chandra observations of the X-ray afterglow of the Gamma-Ray Burst GRB 060729 performed between 2007 March and 2008 May. In all five observations the afterglow is clearly detected. The last Chandra pointing was performed on 2008-May-04, 642 days after the burst - the latest detection of a GRB X-ray afterglow ever. A reanalysis of the Swift XRT light curve together with the three detections by Chandra in 2007 reveals a break at about 1.0 Ms after the burst with a slight steepening of the decay slope from alpha = 1.32 to 1.61. This break coincides with a significant hardening of the X-ray spectrum, consistent with a cooling break in the wind medium scenario, in which the cooling frequency of the afterglow crosses the X-ray band. The last two Chandra observations in 2007 December and 2008 May provide evidence for another break at about one year after the burst. If interpreted as a jet break, this late-time break implies a jet half opening angle of about 14 degrees for a wind medium. Alternatively, this final break may have a spectral origin, in which case no jet break has been observed and the half-opening angle of the jet of GRB 060729 must be larger than about 15 degrees for a wind medium. We compare the X-ray afterglow of GRB 060729 in a wind environment with other bright X-ray afterglows, in particular GRBs 061121 and 080319B, and discuss why the X-ray afterglow of GRB 060729 is such an exceptionally long-lasting event.

astro-ph.CO↗

arXiv2009

A Deep Chandra Observation of the Oxygen-Rich Supernova Remnant 0540-69.3 in the Large Magellanic Cloud

Using our deep ~120 ks Chandra observation, we report on the results from our spatially-resolved X-ray spectral analysis of the "oxygen-rich" supernova remnant (SNR) 0540-69.3 in the Large Magellanic Cloud. We conclusively establish the nonthermal nature of the "arcs" in the east and west boundaries of the SNR, which confirms the cosmic-ray electron acceleration in the supernova shock (B ~ 20-140 microG). We report tentative evidence for Fe overabundance in the southern region close to the outer boundary of the SNR. While such a detection would be intriguing, the existence of Fe ejecta is not conclusive with the current data because of poor photon statistics and limited plasma models. If it is verified using deeper X-ray observations and improved plasma models, the presence of Fe ejecta, which was produced in the core of the supernova, near the SNR's outer boundary would provide an intriguing opportunity to study the explosive nucleosynthesis and the ejecta mixing in this young core-collapse SNR. There is no evidence of X-ray counterparts for the optical O-rich ejecta in the central regions of the SNR.

astro-ph.HE↗

arXiv2009

Measurements of Si Hybrid CMOS X-Ray Detector Characteristics

The development of Hybrid CMOS Detectors (HCDs) for X-Ray telescope focal planes will place them in con- tention with CCDs on future satellite missions due to their faster frame rates, flexible readout scenarios, lower power consumption, and inherent radiation hardness. CCDs have been used with great success on the current generation of X-Ray telescopes (e.g. Chandra, XMM, Suzaku, and Swift). However their bucket-brigade read-out architecture, which transfers charge across the chip with discrete component readout electronics, results in clockrate limited readout speeds that cause pileup (saturation) of bright sources and an inherent susceptibility to radiation induced displacement damage that limits mission lifetime. In contrast, HCDs read pixels with low power, on-chip multiplexer electronics in a random access fashion. Faster frame rates achieved with multi-output readout design will allow the next generation's larger effective area telescopes to observe bright sources free of pileup. Radiation damaged lattice sites effect a single pixel instead of an entire row. Random access, multi-output readout will allow for novel readout modes such as simultaneous bright-source-fast/whole-chip-slow readout. In order for HCDs to be useful as X-Ray detectors, they must show noise and energy resolution performance similar to CCDs while retaining advantages inherent to HCDs. We will report on readnoise, conversion gain, and energy resolution measurements of an X-Ray enhanced Teledyne HAWAII-1RG (H1RG) HCD and describe techniques of H1RG data reduction.

astro-ph.IM↗

arXiv2009

X-ray Evolution of SNR 1987A: The Radial Expansion

We present the evolution of the radial expansion of SNR 1987A as measured using Chandra X-ray observations taken over the last 10 years. To characterize the complex structure of the remnant and isolate the expansion measurement, we fit the images to several empirical models including: a simple circular torus, a torus with bilateral lobes, and a torus with four tangentially extended lobes. We discuss the results of this measure in the context of the overall evolution of the supernova remnant, for which we believe we have measured the end of the free expansion phase and its transition to the adiabatic phase (at least along the equatorial ring). The timing of this event is in agreement with early predictions of the remnant evolution.

astro-ph.HE↗

arXiv2009

Discerning the physical origins of cosmological Gamma-ray bursts based on multiple observational criteria: the cases of z=6.7 GRB 080913, z=8.3 GRB 090423, and some short/hard GRBs

(Abridged) The two high-redshift gamma-ray bursts, GRB 080913 at z=6.7 and GRB 090423 at z=8.3, recently detected by Swift appear as intrinsically short, hard GRBs. They could have been recognized by BATSE as short/hard GRBs should they have occurred at z <= 1. We perform a more thorough investigation on two physically distinct types (Type I/II) of cosmological GRBs and their observational characteristics. We reiterate the definitions of Type I/II GRBs and review the observational criteria and their physical motivations. Contrary to the traditional approach of assigning the physical category based on the gamma-ray properties (duration, hardness, and spectral lag), we take an alternative approach to define the Type I and Type II Gold Samples using several criteria that are more directly related to the GRB progenitors, and study the properties of the two Gold Samples and compare them with the traditional long/soft and short/hard samples. We find that the Type II Gold Sample reasonably tracks the long/soft population, although it includes several intrinsically short (shorter than 1s in the rest frame) GRBs. The Type I Gold Sample only has 5 GRBs, 4 of which are not strictly short but have extended emission. Other short/hard GRBs detected in the Swift era represent the BATSE short/hard sample well, but it is unclear whether all of them belong to Type I. We suggest that some (probably even most) high-luminosity short/hard GRBs instead belong to Type II. We suggest that GRB 080913 and GRB 090423 are more likely Type II events. We re-emphasize the importance of invoking multiple observational criteria, and cautiously propose an operational procedure to infer the physical origin of a given GRB with available multiple observational criteria, with various caveats laid out.

astro-ph.HE↗

arXiv2008

High-Resolution X-ray Spectroscopy of SNR 1987A: Chandra LETG and HETG Observations in 2007

We present an extended analysis of the deep Chandra LETG and HETG observations of the supernova remnant 1987A (SNR 1987A) carried out in 2007. The global fits to the grating spectra show that the temperature of the X-ray emitting plasma in the slower shocks in this system has remained stable for the last three years, while that in the faster shocks has decreased. This temperature evolution is confirmed by the first light curves of strong X-ray emission lines and their ratios. On the other hand, bulk gas velocities inferred from the X-ray line profiles are too low to account for the post-shock plasma temperatures inferred from spectral fits. This suggests that the X-ray emission comes from gas that has been shocked twice, first by the blast wave and again by shocks reflected from the inner ring of SNR 1987A. A new model that takes these considerations into account gives support to this physical picture.

astro-ph↗