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Title: X-ray flare in XRF 050406: evidence for prolonged engine activity
Authors: Romano, Patrizia
Moretti, Alberto
Banat, P.L.
Burrows, David N.
Campana, Sergio
Chincarini, Guido
Covino, S.
Malesani, D.
Tagliaferri, Gianpiero
Kobayashi, Shiho
Zhang, B.
Falcone, Abraham D.
Angelini, Lorella
Barthelmy, Scott D.
Beardmore, Andrew P.
Capalbi, M.
Cusumano, Giancarlo
Giommi, Paolo
Goad, Michael R.
Godet, Olivier
Grupe, Dirk
Hill, Joanne E.
Kennea, Jamie A.
La Parola, V.
Mangano, V.
Mészáros, P.
Morris, David C.
Nousek, John A.
O'Brien, Paul T.
Osborne, Julian P.
Parsons, A.
Perri, M.
Pagani, Claudio
Page, Kim L.
Wells, Alan A.
Gehrels, Neil
First Published: 2006
Publisher: EDP Sciences
Citation: Astronomy and Astrophysics, 2006, 450, pp.59-68.
Abstract: We present observations of XRF 050406, the first burst detected by Swift showing a flare in its X-ray light curve. During this flare, which peaks at tpeak ~ 210 s after the BAT trigger, a flux variation of δF/F ~ 6 in a very short time δt/tpeak << 1 was observed. Its measured fluence in the 0.2−10 keV band was ~∼1.4 × 10−8 erg cm−2, which corresponds to 1−15% of the prompt fluence. We present indications of spectral variations during the flare. We argue that the producing mechanism is late internal shocks, which implies that the central engine is still active at 210 s, though with a reduced power with respect to the prompt emission. The X-ray light curve flattens to a very shallow slope with decay index of ~0.5 after ~4400 s, which also supports continued central engine activity at late times. This burst is classified as an X-ray flash, with a relatively low fluence (~10−7 erg cm−2 in the 15−350 keV band, Eiso ~ 1051 erg), a soft spectrum (photon index 2.65), no significant flux above ~50 keV and a peak energy Ep < 15 keV. XRF 050406 is one of the first examples of a well-studied X-ray light curve of an XRF. We show that the main afterglow characteristics are qualitatively similar to those of normal GRBs. In particular, X-ray flares superimposed on a power-law light curve have now been seen in both XRFs and GRBs. This indicates that a similar mechanism may be at work for both kinds of events.
DOI Link: 10.1051/0004-6361:20054172
ISSN: 0004-6361
eISSN: 1432-0746
Version: Publisher PDF
Status: Peer-reviewed
Type: Article
Rights: © The European Southern Observatory (ESO) 2006. Deposited with permission of the publisher.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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