TY - JOUR
T1 - Swift XRT observations of the afterglow of XRF 050416A
AU - Mangano, Vanessa
AU - La Parola, Valentina
AU - Cusumano, Giancarlo
AU - Mineo, Teresa
AU - Malesani, Daniele
AU - Dyks, Jaroslaw
AU - Campana, Sergio
AU - Capalbi, Milvia
AU - Chincarini, Guido
AU - Giommi, Paolo
AU - Moretti, Alberto
AU - Perri, Matteo
AU - Romano, Patrizia
AU - Tagliaferri, Gianpiero
AU - Burrows, David N.
AU - Gehrels, Neil
AU - Godet, Olivier
AU - Holland, Stephen T.
AU - Kennea, Jamie A.
AU - Page, Kim L.
AU - Racusin, Judith L.
AU - Roming, Peter W.A.
AU - Zhang, Bing
PY - 2007/1/1
Y1 - 2007/1/1
N2 - Swift discovered XRF 050416A with the Burst Alert Telescope 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 (decay slope α ∼ 2.4), subsequently flattens (α ∼ 0.44), and eventually steepens again (α ∼ 0.88), similar to many X-ray afterglows. The first and second phases end ∼ 172 and ∼ 1450 s after the burst onset, respectively. We find evidence of spectral evolution from a softer emission with photon index Γ ∼ 3.0 during the initial steep decay, to a harder emission with Γ ∼ 2.0 during the following evolutionary phases. The spectra show intrinsic absorption in the host galaxy with column density of ∼6.8 × 1021 cm-2. The consistency of the initial photon index with the high-energy BAT photon index suggests that the initial fast decaying phase of the X-ray light curve may be the low-energy tail of die prompt emission. The lack of jet break signatures in the X-ray afterglow light curve is not consistent with empirical relations between the source rest-frame peak energy and the collimation-corrected energy of the burst. 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 of 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.
AB - Swift discovered XRF 050416A with the Burst Alert Telescope 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 (decay slope α ∼ 2.4), subsequently flattens (α ∼ 0.44), and eventually steepens again (α ∼ 0.88), similar to many X-ray afterglows. The first and second phases end ∼ 172 and ∼ 1450 s after the burst onset, respectively. We find evidence of spectral evolution from a softer emission with photon index Γ ∼ 3.0 during the initial steep decay, to a harder emission with Γ ∼ 2.0 during the following evolutionary phases. The spectra show intrinsic absorption in the host galaxy with column density of ∼6.8 × 1021 cm-2. The consistency of the initial photon index with the high-energy BAT photon index suggests that the initial fast decaying phase of the X-ray light curve may be the low-energy tail of die prompt emission. The lack of jet break signatures in the X-ray afterglow light curve is not consistent with empirical relations between the source rest-frame peak energy and the collimation-corrected energy of the burst. 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 of 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.
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U2 - 10.1086/509100
DO - 10.1086/509100
M3 - Article
AN - SCOPUS:33846487947
VL - 654
SP - 403
EP - 412
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 1 I
ER -