X-ray flare in XRF 050406: evidence for prolonged engine activity
/ Authors
P. Romano, A. Moretti, P. Banat, D. Burrows, S. Campana, G. Chincarini, S. Covino, D. Malesani, G. Tagliaferri, S. Kobayashi
and 29 more authors
Bing Zhang, A. Falcone, L. Angelini, L. Angelini, S. Barthelmy, A. Beardmore, M. Capalbi, G. Cusumano, P. Giommi, M. Goad, O. Godet, D. Grupe, J. Hill, J. Hill, J. Kennea, V. Parola, V. Mangano, P. Mészáros, D. Morris, J. Nousek, P. O’Brien, J. Osborne, A. Parsons, M. Perri, C. Pagani, C. Pagani, K. Page, A. Wells, N. Gehrels
/ Abstract
We present observations of XRF 050406, an X‐ray flash with a relatively low fluence (∼ 10−7 erg cm−2 in the 15–350 keV band), a soft spectrum (photon index Γγ = 2.65), no significant flux above ∼ 50 keV and a peak energy Ep < 15 keV. XRF 050406 is the first burst detected by Swift clearly showing a flare in its X‐ray light curve. The flare peaks 210 s after the BAT trigger, presents a flux variation δF/F ∼ 6 in a timescale δt/tpeak ≪ 1 and a measured fluence of 1–15% of the prompt one. 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 more shallow slope with a decay index of ∼ 0.5 after ∼ 4400 s, also supporting continued central engine activity.