GCN Circular 15280
Subject
GRB 130925A: continuing Swift/XRT monitoring
Date
2013-10-01T17:52:33Z (11 years ago)
From
Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst <malesani@dark-cosmology.dk>
D. Malesani (DARK/NBI), S. B. Cenko (NASA/GSFC), D. N. Burrows (PSU), A.
Y. Lien (NASA/GSFC/ORAU), P. A. Evans (U. Leicester), and N. Gehrels
(NASA/GSFC) report:
Swift has been continuously monitoring the X-ray counterpart of GRB
130925A (Lien et al., GCN 15246), with data currently extending up to
512 ks after the trigger. The intense X-ray flaring activity reported by
Burrows et al. (GCN 15253) and Evans et al. (GCN 15254) ceased between
12 and 28 ks after the trigger. The X-ray light curve from 27.9 to 512.4
ks can be modelled with an initial power-law decay with an index of
alpha = 0.84 +/- 0.03, followed by a possible break at 310 (+60, -50) ks
to an alpha of 1.38 (+0.47, -0.23). The updated X-ray light curve is
available at the following URL:
http://www.swift.ac.uk/xrt_curves/00571830/
While the duration of the prompt emission and the flaring activity are
extraordinary among GRBs (Suzuki et al., GCN 15248; Fitzpatrick, GCN
15255; Markwardt et al., GCN 15257; Savchenko et al., GCN 15259;
Golenetskii et al., GCN 15260; Jenke, GCN 15261; Hurley et al., GCN
15278), the late-time behaviour is typical of long-duration GRB
afterglows, and quite different from that of the TDE Swift J1644+57,
which showed continuous flares and dips, with no regular power-law decay
(e.g. Burrows et al. 2011, Nat, 476, 421). There is also no prior
detection of the source in BAT before the trigger (Markwardt et al., GCN
15257).
The extremely long-lived high-energy emission coupled with the
relatively steady power-law X-ray decay at t > 20 ks is reminiscent of
the so-called "ultra-long" GRBs (Levan et al. 2013, arXiv:1302.2352),
including GRB 101225A (Thoene et al. 2011, Nat, 480, 72; Campana et al.
2011, Nat, 480, 69), GRB 111209A (Gendre et al. 2013, ApJ, 766, 30), and
GRB 121027A. The origin of these events and their relation to
traditional long-duration GRBs (i.e., the core-collapse of a massive
star) remain controversial, so we encourage continued multi-wavelength
follow-up of this object.