[vsnet-grb-info 18033] GRB 160530A: Swift follow-up and X-ray afterglow candidate

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19481
SUBJECT: GRB 160530A: Swift follow-up and X-ray afterglow candidate
DATE:    16/06/01 16:58:01 GMT
FROM:    Valerio D'Elia at ASDC  <delia at asdc.asi.it>

V. D’Elia (ASDC), L. Izzo (IAA-CSIC), P. A. Evans (U. Leicester), A.  
A. Breeveld (UCL-MSSL), J.A. Kennea (PSU), D. Malesani (DARK/NBI), C.  
B. Markwardt (NASA/GSFC) report on behalf of the Swift team:

Swift has performed follow-up observations of the COSI-detected burst  
GRB 160530A (Tomsick, GCN Circ. 19473) in a series of observations  
tiled on the sky. The total exposure time is 24 ks, distributed over  
46 tiles; the maximum exposure at a single sky location was 1.4 ks.  
The data were collected between T0+19.0 ks and T0+158 ks, and are  
entirely in Photon Counting (PC) mode.

One uncatalogued X-ray source has been detected by XRT in the  
intersection of the COSI and the IPN error regions (Svinkin et al.,  
GCN Circ. 19476), however, this source is below the RASS limit at its  
location, and we cannot currently determine whether it is fading.  
Therefore, at the present time we cannot state if it is the afterglow.  
The source was imaged and detected in the time interval T0+145 ks to  
T0+158 ks and comprises 920 s of exposure time. More XRT data are  
expected in the forthcoming days. Further details of this source are  
given below:

RA (J2000.0):  118.9741  =  07:55:53.77
Dec (J2000.0): -25.4638  =  -25:27:49.7
Error: 6.6 arcsec (radius, 90% conf.)
Count-rate: 0.0222 +/- 0.0070 ct s^-1
Flux: (6.3 +/- 2.0)e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)

No optical afterglow consistent with the XRT source position is  
detected in the initial UVOT exposures. The preliminary 3-sigma upper  
limit for the summed U-band exposures (926 s) is 20.8 mag.