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Register a new userThe early and late-time spectral and temporal evolution of GRB 050716
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E. Rol
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We report on a comprehensive set of observations of Gamma Ray Burst 050716, detected by the Swift satellite and subsequently followed-up rapidly in X-ray, optical and near infra-red wavebands. The prompt emission is typical of long-duration bursts, with two peaks in a time interval of T90 = 68 seconds (15 - 350 keV). The prompt emission continues at lower flux levels in the X-ray band, where several smaller flares can be seen, on top of a decaying light curve that exhibits an apparent break around 220 seconds post trigger. This temporal break is roughly coincident with a spectral break. The latter can be related to the extrapolated evolution of the break energy in the prompt gamma-ray emission, and is possibly the manifestation of the peak flux break frequency of the internal shock passing through the observing band. A possible 3 sigma change in the X-ray absorption column is also seen during this time. The late-time afterglow behaviour is relatively standard, with an electron distribution power-law index of p = 2 there is no noticable temporal break out to at least 10 days. The broad-band optical/nIR to X-ray spectrum indicates a redshift of z ~> 2 for this burst, with a host-galaxy extinction value of E(B-V) ~ 0.7 that prefers an SMC-like extinction curve.
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We present the second Swift Ultra-Violet/Optical Telescope (UVOT) gamma-ray burst (GRB) afterglow catalog, greatly expanding on the first Swift UVOT GRB afterglow catalog. The second catalog is constructed from a database containing over 120,000 independent UVOT observations of 538 GRBs first detected by Swift, the High Energy Transient Explorer 2 (HETE2), the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL), the Interplanetary Network (IPN), Fermi, and Astro-rivelatore Gamma a Immagini Leggero (AGILE). The catalog covers GRBs discovered from 2005 Jan 17 to 2010 Dec 25. Using photometric information in three UV bands, three optical bands, and a `white or open filter, the data are optimally co-added to maximize the number of detections and normalized to one band to provide a detailed light curve. The catalog provides positional, temporal, and photometric information for each burst, as well as Swift Burst Alert Telescope (BAT) and X-Ray Telescope (XRT) GRB parameters. Temporal slopes are provided for each UVOT filter. The temporal slope per filter of almost half the GRBs are fit with a single power-law, but one to three breaks are required in the remaining bursts. Morphological comparisons with the X-ray reveal that approximately 75% of the UVOT light curves are similar to one of the four morphologies identified by Evans et al. (2009). The remaining approximately 25% have a newly identified morphology. For many bursts, redshift and extinction corrected UV/optical spectral slopes are also provided at 2000, 20,000, and 200,000 seconds.
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We present observations with VLT and HST of the broad emission lines from the inner ejecta and reverse shock of SN 1987A from 1999 until 2012 (days 4381 -- 9100 after explosion). We detect broad lines from H-alpha, H-beta, Mg I], Na I, [O I], [Ca II] and a feature at 9220 A. We identify the latter line with Mg II 9218, 9244,most likely pumped by Ly-alpha fluorescence. H-alpha, and H-beta both have a centrally peaked component, extending to 4500 km/s and a very broad component extending to 11,000 km/s, while the other lines have only the central component. The low velocity component comes from unshocked ejecta, heated mainly by X-rays from the circumstellar ring collision, whereas the broad component comes from faster ejecta passing through the reverse shock. The reverse shock flux in H-alpha has increased by a factor of 4-6 from 2000 to 2007. After that there is a tendency of flattening of the light curve, similar to what may be seen in soft X-rays and in the optical lines from the shocked ring. The core component seen in H-alpha, [Ca II] and Mg II has experienced a similar increase, consistent with that found from HST photometry. The ring-like morphology of the ejecta is explained as a result of the X-ray illumination, depositing energy outside of the core of the ejecta. The energy deposition in the ejecta of the external X-rays illumination is calculated using explosion models for SN 1987A and we predict that the outer parts of the unshocked ejecta will continue to brighten because of this. We finally discuss evidence for dust in the ejecta from line asymmetries.
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