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25 April 2024 |
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Swift XRT Observations of the Afterglow of XRF 050416A | | Vanessa Mangano
; Valentina La Parola
; Giancarlo Cusumano
; Teresa Mineo
; Daniele Malesani
; Jaroslaw Dyks
; Sergio Campana
; Milvia Capalbi
; Guido Chincarini
; Paolo Giommi
; Alberto Moretti
; Matteo Perri
; Patrizia Romano
; Gianpiero Tagliaferri
; David N. Burrows
; Olivier Godet
; Stephen T. Holland
; Jamie A. Kennea
; Kim L. Page
; Judith L. Racusin
; Peter W. A. Roming
; Bing Zhang
; | | Date: |
27 Mar 2006 | | Abstract: | Swift discovered XRF 050416A with the BAT and began observing it with its narrow field instruments only 64.5 s after the burst onset. Its very soft spectrum classifies this event as an X-ray flash. The afterglow X-ray emission was monitored up to 74 days after the burst. The X-ray light curve initially decays very fast, subsequently flattens and eventually steepens again, similar to many X-ray afterglows. The first and second phases end about 172 and 1450 s after the burst onset, respectively. We find evidence of spectral evolution from a softer emission with photon index $Gamma sim 3.0$ during the initial steep decay, to a harder emission with $Gamma sim 2.0$. The spectra show intrinsic absorption in the host galaxy. The consistency of the initial photon index with the high energy BAT photon index suggests that the initial phase of the X-ray afterglow may be the low-energy tail of the prompt emission. This also requires that the spectral peak energy of the burst decreased from the time of the BAT to the time of the XRT observation, becoming as low as $simlt 1$ keV. Hardness ratio evolution during the prompt emission also supports this interpretation. The lack of jet break signatures in the X-ray afterglow light curve is not consistent with the Ghirlanda and Liang relations. The standard uniform jet model can give a possible description of the XRF 050416A X-ray afterglow for an opening angle larger than a few tens degrees, although numerical simulations show that the late time decay is slightly flatter than expected from on-axis viewing of a uniform jet. A structured Gaussian-type jet model with uniform Lorentz factor distribution and viewing angle outside the Gaussian core is another possibility although a full agreement with data is not achieved with the numerical models explored. | | Source: | arXiv, astro-ph/0603738 | | Services: | Forum | Review | PDF | Favorites | |
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