arXiv subjects

D. Burrows

Publications and source records attributed to D. Burrows.

22 records · Page 2Linked to original sources

arXiv2006

A unified picture for gamma-ray burst prompt and X-ray afterglow emissions

Data from the Swift satellite has enabled us for the first time to provide a complete picture of the gamma-ray burst emission mechanism and its relationship with the early afterglow emissions. We show that gamma-ray photons for two bursts, 050126 & 050219A, for which we have carried out detailed analysis were produced as a result of the synchrotron self-Compton process in the material ejected in the explosion when it was heated to a mildly relativistic temperature at a distance from the center of explosion of order the deceleration radius. Both of these bursts exhibit rapidly declining early X-ray afterglow lightcurves; this emission is from the same source that produced the gamma-ray burst. The technique we exploit to determine this is very general and makes no assumption about any particular model for gamma-ray generation except that the basic radiation mechanism is some combination of synchrotron and inverse-Compton processes in a relativistic outflow. For GRB 050219A we can rule out the possibility that energy from the explosion is carried outward by magnetic fields, and that the dissipation of this field produced the $γ$-ray burst.

astro-ph↗

arXiv2005

Analysis of the X-ray Emission of Nine Swift Afterglows

The X-ray light-curves of 9 Swift XRT afterglows (050126, 050128, 050219A, 050315, 050318, 050319, 050401, 050408, 050505) display a complex behaviour: a steep t^{-3.0 \pm 0.3} decay until ~400 s, followed by a significantly slower t^{-0.65+/-0.20} fall-off, which at 0.2--2 d after the burst evolves into a t^{-1.7+/-0.5} decay. We consider three possible models for the geometry of relativistic blast-waves (spherical outflows, non-spreading jets, and spreading jets), two possible dynamical regimes for the forward shock (adiabatic and fully radiative), and we take into account a possible angular structure of the outflow and delayed energy injection in the blast-wave, to identify the models which reconcile the X-ray light-curve decay with the slope of the X-ray continuum for each of the above three afterglow phases. By piecing together the various models for each phase in a way that makes physical sense, we identify possible models for the entire X-ray afterglow. The major conclusion of this work is that a long-lived episode of energy injection in the blast-wave, during which the shock energy increases at t^{1.0+/-0.5}, is required for five afterglows and could be at work in the other four as well. Optical observations in conjunction with the X-ray can distinguish among these various models. Our simple tests allow the determination of the location of the cooling frequency relative to the X-ray domain and, thus, of the index of the electron power-law distribution with energy in the blast-wave. The resulting indices are clearly inconsistent with an universal value.

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arXiv2005

XRT Light curves: Morphology, Flares and Energy

Following a brief introduction we show that the observations obtained so far with the Swift satellite begin to shed light over a variety of problems that were left open following the excellent performance and related discoveries of the Italian - Dutch Beppo SAX satellite. The XRT light curves show common characteristics that are reasonably understood within the framework of the fireball model. Unforeseen flares are however detected in a large fraction of the GRB observed and the energy emitted by the brightest ones may be as much as 85% of the total soft X ray emission measured by XRT. These characteristics seems to be common to long and short bursts.

astro-ph↗

arXiv2005

Ultraviolet, Optical, and X-Ray Observations of the Type Ia Supernova 2005am with Swift

We present ultraviolet and optical light curves in six broadband filters and grism spectra obtained by Swift's Ultraviolet/Optical Telescope for the Type Ia supernova SN2005am. The data were collected beginning about four days before the B-band maximum, with excellent coverage of the rapid decline phase and later observations extending out to 69 days after the peak. The optical and near UV light curve match well those of SN1992A. The other UV observations constitute the first set of light curves shorter than 2500 Angstroms and allow us to compare the light curve evolution in three UV bands. The UV behavior of this and other low redshift supernovae can be used to constrain theories of progenitor evolution or to interpret optical light curves of high redshift supernovae. Using Swift's X-Ray Telescope, we also report the upper limit to SN2005am's X-ray luminosity to be 1.77 x 10^40 erg s^-1 in the 0.3--10 keV range from 58,117 s of exposure time.

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