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P. Schady (MSSL), C. Gronwall (PSU), K.O. Mason, M.J. Page (MSSL), P.W.A. Roming (PSU), M. Still (GSFC), B. Zhang (University of Nevada), Swift UVOT Team
Swift-UVOT observations of XRF 050406 comprise the earliest detection of an optical counterpart to an X-ray Flash to date, with data starting 88s after the initial prompt emission. The early-time temporal and spectral properties in the optical, together with gamma-ray and simultaneous X-ray data taken with the BAT and XRT telescopes onboard Swift constrains the possible causes of the XRF. The prompt emission had a FRED (fast-rise, exponential decay) profile with a duration of T90=5.7±0.2s, putting it at the short end of the long-burst duration distribution. The absence of photoelectric absorption red-ward of 4000 Åin the UV/optical spectrum provides a firm upper limit of z <= 3.1 on the redshift, therefore excluding a high redshift burst as the sole reason for the soft spectrum. Combining the multiwavelength observations available with Swift we narrow down the origins of the soft spectrum observed in XRF 050406 to an off-axis jet with internal structure.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.