D. N. Burrows

Pennsylvania State University, University Park, MD, United States

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Publications (893)1257.68 Total impact

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    ABSTRACT: GRB~130925A was an unusual GRB, consisting of 3 distinct episodes of high-energy emission spanning $\sim$20 ks, making it a member of the proposed category of `ultra-long' bursts. It was also unusual in that its late-time X-ray emission observed by \swift\ was very soft, and showed a strong hard-to-soft spectral evolution with time. This evolution, rarely seen in GRB afterglows, can be well modelled as the dust-scattered echo of the prompt emission, with stringent limits on the contribution from the normal afterglow (i.e. external shock) emission. We consider and reject the possibility that GRB~130925A was some form of tidal disruption event, and instead show that if the circumburst density around GRB~130925A is low, the long duration of the burst and faint external shock emission are naturally explained. Indeed, we suggest that the ultra-long GRBs as a class can be explained as those with low circumburst densities, such that the deceleration time (at which point the material ejected from the nascent black hole is decelerated by the circumburst medium) is $\sim$20 ks, as opposed to a few hundred seconds for the normal long GRBs.
    03/2014;
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    ABSTRACT: 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 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 $13-15M_{\odot}$ progenitor. The central 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.
    01/2014;
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    ABSTRACT: A multi-axis, motion controlled test stand has been built in the PSU 47 m X-ray beam-line for the purpose of testing X-ray instrumentation and mirrors using parallel rays. The test stand is capable of translation along two axes and rotation about two axes with motorized fine position control. The translation stages have a range of motion of 200 mm with a movement accuracy of ± 2.5 microns. Rotation is accomplished with a two-axis gimbal which can rotate 360° about one axis and 240° about another; movement with ± 35 arcsecond accuracy are achieved in both axes. The position and status are monitored using a LabView program. An XCalibr source with multiple target materials is used as an X-ray source and can produce multiple lines between 0.8 and 8 keV. Some sample spectra are shown from a Si-PIN diode detector. This system is well suited for testing X-ray mirror segments which are currently being developed.
    01/2014;
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    ABSTRACT: Starting in 2013 February, Swift has been performing short daily monitoring observations of the G2 gas cloud near Sgr A* with the X-Ray Telescope to determine whether the cloud interaction leads to an increase in the flux from the Galactic center. On 2013 April 24 Swift detected an order of magnitude rise in the X-ray flux from the region near Sgr A*. Initially thought to be a flare from Sgr A*, detection of a short hard X-ray burst from the same region by the Burst Alert Telescope suggested that the flare was from an unresolved new Soft Gamma Repeater, SGR J1745-29. Here we present the discovery of SGR J1745-29 by Swift, including analysis of data before, during, and after the burst. We cover the entire light-curve of the SGR outburst so far, from discovery through to the source entering a Swift Sun constraint in November 2013. Thanks to the interest in G2 and it's location near the Galactic Center, SGR J1745-29 has become one of the best monitoring SGRs in outburst yet seen.
    01/2014;
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    ABSTRACT: We report on the results from the preliminary analysis of our 120 ks Chandra HETGS observation of the Galactic core-collapse supernova remnant (SNR) G292.0+1.8. To probe the 3D distribution of the metal-rich ejecta features, we measured Doppler shifts in emission lines from ejecta knots projected at a range of distances from the SNR center using high resolution HETGS spectroscopy. We estimate radial velocities of v ~ -2200 - +1300 km/s. Their overall distribution in the velocity-position space suggests an expanding shell of ejecta. We qualitatively estimate the locations of the reverse shock and contact discontinuity based on this distribution. The reverse shock in G292.0+1.8 appears to be at ~130" from the SNR center, which is close to the outer boundary of the radio pulsar wind nebula.
    01/2014;
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    ABSTRACT: Supergiant Fast X-ray Transients (SFXTs) are HMXBs with OB supergiant companions and are known for hour-long X-ray outbursts characterized by 3-5 orders of magnitude luminosity increases. Our Swift Supergiant Fast X-ray Transients Project, active since 2007, has taken advantage of Swift's flexible scheduling for a systematic investigation on both the SFXT bright flares which triggered the Burst Alert Monitor (BAT) with fast X-Ray Telescope (XRT) follow-up (1-2 min repointing time), and the emission outside the bright outbursts with XRT regular monitoring of several SFXTs and candidates with 2-3 observations per week (1-2 ks) for at least one year per source. This has allowed us to study for the first time broadband spectra of SFXT outbursts, to prove that timescales of source activity during outburts are of the order of weeks, to determine long-term properties of SFXTs, and to obtain an assessment of the fraction of the time these sources spend in each luminosity phase (outbursts, intermediate level, and quiescence) and their duty cycle of inactivity by means of very sensitive and non-serendipitous observations. We summarize the results achieved to date with our observing strategy and focus on the time resolved broadband spectral analysis of the 2011 and 2013 Swift detected outbursts of IGR J08408-4503, carried out with different spectral models, including the COMPMAG model specifically dedicated to the physical framework of accretion at the polar cap of a neutron star with a high magnetic field (>= 1E12 G), expected to be typical of these accreting systems.
    01/2014;
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    ABSTRACT: We report on the development of a new Teledyne Imaging Systems hybrid CMOS x-ray detector called the Speedster-EXD which is capable of event-triggered read-out. Hybrid CMOS detectors currently have many advantages over CCDs including lower susceptibility to radiation damage, lower power consumption, and faster read out time to avoid pile-up. In addition to these advantages, the Speedster-EXD has new in-pixel circuitry which includes CDS subtraction to reduce read noise and a CTIA amplifier to eliminate interpixel capacitance crosstalk. The new circuitry also includes an in-pixel comparator that triggers on x-ray events. The comparator feature allows the detector to only read pixels in which an x-ray is detected. This feature increases the detector array effective frame rate by orders of magnitude. The current advantages of hybrid CMOS x-ray detectors combined with the new in-pixel circuitry makes the Speedster-EXD an ideal candidate for future high throughput x-ray missions requiring large-format silicon imagers.
    01/2014;
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    ABSTRACT: Starting in 2006, the Galactic center has been monitored on a nearly daily basis with the X-ray telescope on-board the Swift satellite. The short pointed observations have offered a unique view of the long-term X-ray behavior of Sgr A*, in particular of its X-ray flaring properties. The Swift campaign also provides an excellent setup to closely monitor the interaction of the supermassive black hole with the gaseous object G2. Because of the unique daily sampling, the Swift program may prove to serve as an important trigger for other observatories at different wavelengths. I will report on the latest results of the Swift X-ray monitoring campaign of the Galactic center.
    01/2014;
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    ABSTRACT: Supernova (SN) explosions are crucial engines driving the evolution of galaxies by shock heating gas, increasing the metallicity, creating dust, and accelerating energetic particles. In 2012 we used the Atacama Large Millimeter/Submillimeter Array to observe SN 1987A, one of the best-observed supernovae since the invention of the telescope. We present spatially resolved images at 450um, 870um, 1.4mm, and 2.8mm, an important transition wavelength range. Longer wavelength emission is dominated by synchrotron radiation from shock-accelerated particles, shorter wavelengths by emission from the largest mass of dust measured in a supernova remnant (>0.2Msun). For the first time we show unambiguously that this dust has formed in the inner ejecta (the cold remnants of the exploded star's core). The dust emission is concentrated to the center of the remnant, so the dust has not yet been affected by the shocks. If a significant fraction survives, and if SN 1987A is typical, supernovae are important cosmological dust producers.
    12/2013; 782(1).
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    ABSTRACT: In this program we propose to use a total of 0.4 hr to obtain 3.6 and 4.5 micron photometry of SNR 1987A at two additional epochs beyond day 9800 after the explosion. The emission in these two IRAC bands arises from a hot dust component residing in the equatorial ring (ER) with a distinctly different spectral shape and temperature from the dominant 180 K silicate dust component in the ER. The dust in the ER is collisionally-heated by the SN blast wave that also gives rise to the soft X-ray emission from the ER. The intensity in the IR emission is generally well correlated with that of the X-ray emission. However, the most recent X-ray observations have showed a difference in the evolution of their respective light curves. These differences could stem from a variety of causes, including the sputtering of the dust or changes in the morphology of the ER. Ongoing X-ray observations of the remnant are taking place. Supplementing these with IR observations is essential for determining the nature and the evolution of this hot dust component. Finally, the observations may reveal the appearance of a new emission component from the SN ejecta which is currently interacting with the reverse shock.
    Spitzer Proposal. 10/2013;
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    ABSTRACT: At 09:13:17 UT, the Swift Burst Alert Telescope (BAT) triggered and located possible GRB 130901A or a Galactic source (trigger=569022). Using partial data covering from T-60 to T+63 sec from the trigger time, we report further analysis. The BAT ground-calculated position is RA, Dec = 263.613, -30.454 deg which is
    The Astronomer's Telegram. 09/2013;
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    ABSTRACT: We present a review of the Supergiant Fast X-ray Transients (SFXT) Project, a systematic investigation of the properties of SFXTs with a strategy that combines Swift monitoring programs with outburst follow-up observations. This strategy has quickly tripled the available sets of broad-band data of SFXT outbursts, and gathered a wealth of out-of-outburst data, which have led us to a broad-band spectral characterization, an assessment of the fraction of the time these sources spend in each phase, and their duty cycle of inactivity. We present some new observational results obtained through our outburst follow-ups, as fitting examples of the exceptional capabilities of Swift in catching bright flares and monitor them panchromatically.
    Advances in Space Research 07/2013; 52(9). · 1.18 Impact Factor
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    ABSTRACT: 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 and 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− s−1 pixel−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.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 07/2013; 717:83–93. · 1.14 Impact Factor
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    ABSTRACT: 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.
    The Astrophysical Journal 05/2013; 772(1). · 6.73 Impact Factor
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    ABSTRACT: Starting in 2013 February, Swift has been performing short daily monitoring observations of the G2 gas cloud near Sgr A* with the X-Ray Telescope to determine whether the cloud interaction leads to an increase in the flux from the Galactic center. On 2013 April 24 Swift detected an order of magnitude rise in the X-ray flux from the region near Sgr A*. Initially thought to be a flare from Sgr A*, detection of a short hard X-ray burst from the same region by the Burst Alert Telescope suggested that the flare was from an unresolved new Soft Gamma Repeater, SGR J1745-29. Here we present the discovery of SGR J1745-29 by Swift, including analysis of data before, during, and after the burst. We find that the spectrum in the 0.3-10 keV range is well fit by an absorbed blackbody model with kTBB ~ 1 keV and absorption consistent with previously measured values from the quiescent emission from Sgr A*, strongly suggesting that this source is at a similar distance. Only one SGR burst has been detected so far from the new source, and the persistent light curve shows little evidence of decay in approximately 2 weeks of monitoring after outburst. We discuss this light curve trend and compare it with those of other well covered SGR outbursts. We suggest that SGR J1745-29 belongs to an emerging subclass of magnetars characterized by low burst rates and prolonged steady X-ray emission 1-2 weeks after outburst onset.
    The Astrophysical Journal Letters 05/2013; 770(2). · 6.35 Impact Factor
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    ABSTRACT: The newly discovered transient source IGR J18245-2452 (Eckert et al, ATel #4925), triggered the Swift Burst Alert Telescope (BAT) on 2013-03-30 at 02:22:21 (image trigger=552336, Barthelmy et al, GCN 14355), and subsequently at 15:10:37 UT (image trigger=552369) and 15:17:33.61 UT (image trigger=552370). The BAT ground-calculated position for trigger 552336 is RA, Dec = 276.111, -24.857 deg which is RA(J2000) = 18h 24m 26.6s Dec(J2000) = -24d 51' 25.6" with an uncertainty of 3.9 arcmin, (radius, sys+stat, 90% c.l.).
    The Astronomer's Telegram. 03/2013;
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    ABSTRACT: Swift is a multi-wavelength observatory specifically designed for gamma-ray burst (GRB) astronomy that is operational since 2004. Swift is also a very flexible multi-purpose facility that supports a wide range of scientific fields such as active galactic nuclei, supernovae, cataclysmic variables, Galactic transients, active stars and comets. The Swift X-ray Telescope (XRT) has collected more than 150 Ms of observations in its first seven years of operations. We present the list of all the X-ray point sources detected in XRT imaging data taken in photon counting mode during the first seven years of Swift operations. All these point-like sources, excluding the Gamma-Ray Bursts (GRB), will be stored in a catalog publicly available (1SWXRT). We consider all XRT observations with exposure time > 500 s taken in the period 2005-2011. Data were reduced and analyzed with standard techniques and a list of detected sources for each observation was produced. A careful visual inspection was performed to remove extended, spurious and piled-up sources. Positions, count rates, fluxes and the corresponding uncertainties were computed. We have analyzed more than 35,000 XRT fields, with exposures ranging between 500 s and 100 ks, for a total exposure time of 140 Ms. The catalog includes ~ 89,000 entries, of which almost 85,000 are not affected by pile-up and are not GRBs. Since many XRT fields were observed several times, we have a total of ~36,000 distinct celestial sources. We computed count rates in three energy bands: 0.3-10 keV (Full, or F), 0.3-3 keV (Soft, or S) and 2-10 keV (Hard, or H). Each entry has a detection in at least one of these bands. In particular, we detect ~ 80,000, ~ 70,000 and ~ 25,500$ in the F, S and H band, respectively. Count rates were converted into fluxes in the 0.5-10, 0.5-2 and 2-10 keV bands. Some possible scientific uses of the catalog are also highlighted.
    Astronomy and Astrophysics 02/2013; · 5.08 Impact Factor
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    ABSTRACT: 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.
    The Astrophysical Journal Letters 02/2013; 767(1). · 6.35 Impact Factor
  • GRB Coordinates Network. 01/2013;
  • GRB Coordinates Network. 01/2013;

Publication Stats

3k Citations
1,257.68 Total Impact Points

Institutions

  • 1991–2013
    • Pennsylvania State University
      • Department of Astronomy and Astrophysics
      University Park, MD, United States
  • 2012
    • Guilin University of Technology
      Ling-ch’uan, Guangxi Zhuangzu Zizhiqu, China
    • Liverpool John Moores University
      • Astrophysics Research Institute
      Liverpool, England, United Kingdom
  • 2010
    • University of Ferrara
      Ferrare, Emilia-Romagna, Italy
  • 2009
    • Massachusetts Institute of Technology
      • Kavli Institute for Astrophysics and Space Research
      Cambridge, Massachusetts, United States
    • Università degli Studi dell'Insubria
      Varese, Lombardy, Italy
  • 2006–2009
    • Universities Space Research Association
      Houston, Texas, United States
    • Ioffe Physical Technical Institute
      Sankt-Peterburg, St.-Petersburg, Russia
  • 2008
    • Guangxi University
      Yung-ning, Guangxi Zhuangzu Zizhiqu, China
    • Osaka University
      • Department of Earth and Space Science
      Suika, Ōsaka, Japan
  • 2007–2008
    • The Astronomical Observatory of Brera
      Merate, Lombardy, Italy
    • Harvard-Smithsonian Center for Astrophysics
      • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States
    • National Institute of Astrophysics
      • Institute of Space Astrophysics and Cosmic Physics IASF - Rome
      Roma, Latium, Italy
    • Stanford University
      • Department of Physics
      Palo Alto, California, United States
    • University of Nevada, Las Vegas
      • Department of Physics and Astronomy
      Las Vegas, Nevada, United States
  • 2004–2007
    • University of Leicester
      • Department of Physics and Astronomy
      Leiscester, England, United Kingdom
  • 1995–2007
    • William Penn University
      Penn Hills, Pennsylvania, United States
  • 2005–2006
    • University College London
      • Department of Space and Climate Physics
      Londinium, England, United Kingdom
    • Park University
      Parkville, Missouri, United States
    • North Carolina State University
      • Department of Physics
      Raleigh, North Carolina, United States
  • 2001
    • Honolulu University
      Honolulu, Hawaii, United States