GCN Circular 18005

M.G. Bernardini, P. D'Avanzo, A. Melandri, S. Campana,
G. Tagliaferri (INAF-OAB), D. Burrows (PSU), K. Page
and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team:

We analyzed the full dataset of Swift-XRT observations of the
Swift trigger 648437 (Bernardini et al., GCN Circ. 18000
Not found
 
 
),
classified as short GRB 150710A (Barthelmy et al., GCN Circ.
18002
Not found
 
 
, Golenetskii et al. GCN Circ. 18003
Not found
 
 
), comprising 11.2 ks in
Photon Counting (PC) mode. One X-ray source has been detected
within the BAT error circle at the following position:

  RA (J2000.0):  194.47045  = 12:57:52.91
  Dec (J2000.0): 14.31807 = +14:19:05.0
  Error: 2.8 arcsec (radius, 90% conf.)

This position is consistent with the location of a ROSAT faint source
1RXS J125754.7+14185. In an initial 0.98 ks observation carried out
between T+57s and T+1056s, the source has an initial count-rate of
(3.22E-02 �� 6.3E-03) ct/s. Then in a subsequent 10 ks observation,
carried out between T+4.9 ks and T+34.5 ks, it is no longer detected
down to a 3sigma UL of 1.3E-3 ct/s. The source is near the edge of
the Virgo cluster, but the non-detection of any host galaxy by RATIR
(Butler et al., GCN Circ. 18001
Not found
 
 
) argues against the possibility of this
being a giant SGR flare from a galaxy in the Virgo cluster. Given the
observed fading, we propose this source as the X-ray counterpart of
GRB 150710A.

We also note the possible presence of a second source at the following 
position:

  RA (J2000.0):  194.4810088073  =  12:57:55.44
  Dec (J2000.0): 14.317574983  =  +14:19:03.3
  Error: 6.0 arcsec (radius, 90% conf.)

also consistent with the location of 1RXS J125754.7+14185. The source
is detected at a low significance, and it is not possible with present data
to assess if is real or not. Further observation can confirm if this second
source is real and if it is possibly related to 1RXS J125754.7+14185.
Otherwise, we cannot exclude that the observed X-ray emission from
Source #1 is due to a brightening from 1RXS J125754.7+14185.

This circular is an official product of the Swift-XRT team.