[vsnet-grb-info 15019] GRB 140516A: further Swift-XRT analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  16313
SUBJECT: GRB 140516A: further Swift-XRT analysis
DATE:    14/05/21 23:42:20 GMT
FROM:    Paolo D'Avanzo at INAF-OAB  <paolo.davanzo at brera.inaf.it>

M. G. Bernardini, P. D'Avanzo, A. Melandri, S. Campana (INAF-OAB), P. A. Evans, K. L. Page (U. Leicester), 
E. Troja (NASA/GSFC/UMCP) report on behalf of the Swift-XRT team:


We have analysed 24.4 ks of XRT data for GRB 140516A (Bernardini et al. GCN Circ. 16285),  
from 92 s to 397.8 ks after the  BAT trigger, in Photon Counting (PC) mode. 

The X-ray counterpart reported by Bernardini et al. (GCN Circ. 16285) and Gompertz 
et al. (GCN Circ. 16291) apparently disappeared in the data collected from t-t0=92.8 ks onwards. 
However, in the same dataset we find evidence for the presence of an unrelated source at 
the position RA, Dec = 252.99269, +39.95659 which is equivalent to:

RA (J2000): 16h 51m 58.25s
Dec (J2000): +39d 57' 23.7"

with an uncertainty of 4.0 arcsec (radius, 90% confidence).

This position is 24" away from the enhanced position for this burst reported by
Osborne et al. (GCN Circ. 16289) while it is consistent with the source
165158.53+395728.9 reported in the Krawczyk et al. (2013; ApJS, 206, 4) QSO
catalogue. 
We therefore caution that this field source is likely contaminating the late-time 
X-ray light curve of GRB 140516A, given the spatial proximity to its transient 
X-ray counterpart.