GCN Circular 21345

D. A. Kann, A. de Ugarte Postigo, L. Izzo, and C. C. Thoene
(HETH/IAA-CSIC) report:

GRB 170714A (D'Ai et al. GCN #21340) exhibits very variable behavior in
its X-ray light curve beyond what is reported by D'Avanzo et al. (GCN
#21343). We especially point out a very rapid decay at ~ 18ks, from ~5
ct/s to 0.01 ct/s in about 1.3 ks. Even after this steep decay, which is a
typical sign of central-engine turn-off, the XRT light curve shows flaring
activity of a factor of ~5. All this activity is usually the sign of an
active central engine.

This highly variable behavior is reminiscent of two types of sources:
Ultra-long GRBs like GRBs 101225A, 111209A and 130925A (e.g., Thoene et
al., Nature, 480, 72; Gendre et al., ApJ, 766, 30; Levan et al., ApJ, 781,
13; Greiner et al., A&A, 568, A75; Kann et al., A&A, submitted,
arXiv:1706.00601
Not found
 
 
) or relativistic tidal disruption events such as Sw J1644
(e.g., Levan et al., Science, 333, 199).

So far no optical source has been reported, and the X-ray afterglow shows
signs of additional absorption (D'Avanzo et al., GCN #21343), which may be
indicative of a reddened source in the center of its host and therefore a
RTDE. On the other hand, the source is significantly brighter than Sw
J1644, and no obvious host galaxy is seen in SDSS or PanSTARRS
pre-imaging. The hosts of GRBs 101225A and 111209A were also very faint,
and GRB 130925A showed very strong absorption.

If this event is an ULGRB, the flaring activity persists for nearly 40ks
until now, making it significantly longer than even GRB 111209A.

Despite the inclement visibility, observations of this source are strongly
encouraged.