Penn State’s NASA-run Swift satellite sends signals of star bursts

Daily Collegian  

2016-09-23

David Burrows leads the Swift X-ray Telescope team and has been an astronomy and astrophysics professor since the 1980s. Burrows worked with Swift since its first proposal to NASA in the late 1990s...

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NASA discovers slowest-spinning neutron star with unusual bursts of X-rays

Nature World News  

2016-09-20

"Observations with multiple space telescopes have revealed that, while other neutron stars spin multiple times a minute, this object rotates only once about every 6.5 hours -- making it by far the slowest-spinning star in its class discovered to date," stated David Burrows, a professor of astronomy and astrophysics at Penn State. "The data collected by Chandra show that this object has properties of a magnetar -- a type of neutron star with extremely powerful magnetic fields trillions of times as powerful as those of the Sun that can erupt with enormous bursts of energy."...

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More details on the black hole that swallowed a screaming star

Universe Today  

2015-12-24

“Incredibly, this source is still producing X-rays and may remain bright enough for Swift to observe into next year,” said David Burrows, professor of astronomy at Penn State University and lead scientist for Swift’s X-Ray Telescope instrument. “It behaves unlike anything we’ve seen before.”...

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Ultrabright gamma-ray burst "Blinded" NASA telescope

National Geographic  

2010-07-15

Gamma rays are the most energetic forms of light, which means they're capable of penetrating even denser chunks of matter than x-rays, noted Swift lead scientist David Burrows. Because of this, we can see gamma rays that have traveled from sources at very edges of the observable universe...

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Stellar explosion is most distant object visible to naked eye

Space.com  

2008-03-21

"It's amazing ? we've been waiting for a flash this bright from a gamma-ray burst ever since Swift began observing the sky three years ago, and now we've got one that is so bright that it was visible to the naked eye even though its source is half-way across the universe," said David Burrows of Penn State University, who directs the continuing operation of Swift's X-ray telescope and the analysis of the data it collects...

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Chandra observations of SN 1987A: The soft X-ray light curve revisited

2013 We report on the present stage of SN 1987A as observed by the Chandra X-ray Observatory. We reanalyze published Chandra observations and add three more epochs of Chandra data to get a consistent picture of the evolution of the X-ray fluxes in several energy bands. We discuss the implications of several calibration issues for Chandra data. Using the most recent Chandra calibration files, we find that the 0.5-2.0 keV band fluxes of SN 1987A have increased by ~6 x 10 ^-13 erg s^-1 cm^-2 per year since 2009. This is in contrast with our previous result that the 0.5-2.0 keV light curve showed a sudden flattening in 2009. Based on our new analysis, we conclude that the forward shock is still in full interaction with the equatorial ring.

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Relativistic jet activity from the tidal disruption of a star by a massive black hole

2011 Supermassive black holes have powerful gravitational fields with strong gradients that can destroy stars that get too close, producing a bright flare in ultraviolet and X-ray spectral regions from stellar debris that forms an accretion disk around the black hole. The aftermath of this process may have been seen several times over the past two decades in the form of sparsely sampled, slowly fading emission from distant galaxies, but the onset of the stellar disruption event has not hitherto been observed. Here we report observations of a bright X-ray flare from the extragalactic transient Swift J164449.3+573451. This source increased in brightness in the X-ray band by a factor of at least 10,000 since 1990 and by a factor of at least 100 since early 2010. We conclude that we have captured the onset of relativistic jet activity from a supermassive black hole. A companion paper comes to similar conclusions on the basis of radio observations. This event is probably due to the tidal disruption of a star falling into a supermassive black hole, but the detailed behaviour differs from current theoretical models of such events.

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Fermi observations of GRB 090902B: a distinct spectral component in the prompt and delayed emission

2009 We report on the observation of the bright, long gamma-ray burst (GRB), GRB 090902B, by the Gamma-ray Burst Monitor (GBM) and Large Area Telescope (LAT) instruments on-board the Fermi observatory. This was one of the brightest GRBs to have been observed by the LAT, which detected several hundred photons during the prompt phase. With a redshift of z = 1.822, this burst is among the most luminous detected by Fermi. Time-resolved spectral analysis reveals a significant power-law component in the LAT data that is distinct from the usual Band model emission that is seen in the sub-MeV energy range. This power-law component appears to extrapolate from the GeV range to the lowest energies and is more intense than the Band component, both below ~50 keV and above 100 MeV. The Band component undergoes substantial spectral evolution over the entire course of the burst, while the photon index of the power-law component remains constant for most of the prompt phase, then hardens significantly toward the end. After the prompt phase, power-law emission persists in the LAT data as late as 1 ks post-trigger, with its flux declining as t –1.5. The LAT detected a photon with the highest energy so far measured from a GRB, 33.4+2.7 –3.5 GeV. This event arrived 82 s after the GBM trigger and ~50 s after the prompt phase emission had ended in the GBM band. We discuss the implications of these results for models of GRB emission and for constraints on models of the extragalactic background light.

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Physical processes shaping gamma-ray burst X-ray afterglow light curves: theoretical implications from the Swift X-ray telescope observations

2006 With the successful launch of the Swift Gamma-Ray Burst Explorer, a rich trove of early X-ray afterglow data has been collected by its onboard X-Ray Telescope (XRT). Some interesting features are emerging, including a distinct rapidly decaying component preceding the conventional afterglow component in many sources, a shallow decay component before the more "normal" decay component observed in a good fraction of GRBs, and X-ray flares in nearly half of the afterglows. In this paper we systematically analyze the possible physical processes that shape the properties of the early X-ray afterglow light curves and use the data to constrain various models. We suggest that the steep decay component is consistent with the tail emission of the prompt gamma-ray bursts and/or the X-ray flares. This provides strong evidence that the prompt emission and afterglow emission are likely two distinct components, supporting the internal origin of the GRB prompt emission. The shallow decay segment observed in a group of GRBs suggests that very likely the forward shock keeps being refreshed for some time. This might be caused by either a long-lived central engine, or a wide distribution of the shell Lorentz factors, or else possibly the deceleration of a Poynting flux-dominated flow. X-ray flares suggest that the GRB central engine is very likely still active after the prompt gamma-ray emission is over, but with a reduced activity at later times. In some cases, the central engine activity even extends to days after the burst triggers. Analyses of early X-ray afterglow data reveal that GRBs are indeed highly relativistic events and that early afterglow data of many bursts, starting from the beginning of the XRT observations, are consistent with the afterglow emission from an ISM environment.

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The early X-ray emission from GRBs

2006 We present observations of the early X-ray emission for a sample of 40 gamma-ray bursts (GRBs) obtained using the Swift satellite, for which the narrow-field instruments were pointed at the burst within 10 minutes of the trigger. Using data from the Burst Alert Telescope and the X-Ray Telescope, we show that the X-ray light curve can be well described by an exponential that relaxes into a power law, often with flares superimposed. The transition time between the exponential and the power law provides a physically defined timescale for the burst duration. In most bursts, the power law breaks to a shallower decay within the first hour, and a late emission "hump" is observed, which can last for many hours. In other GRBs the hump is weak or absent. The observed variety in the shape of the early X-ray light curve can be explained as a combination of three components: prompt emission from the central engine, afterglow, and the late hump. In this scenario, afterglow emission begins during or soon after the burst, and the observed shape of the X-ray light curve depends on the relative strengths of the emission due to the central engine and that of the afterglow. There is a strong correlation such that those GRBs with stronger afterglow components have brighter early optical emission. The late emission hump can have a total fluence equivalent to that of the prompt phase. GRBs with the strongest late humps have weak or no X-ray flares.

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