GCN Circular 16451

V. D'Elia (ASDC), F. E. Marshall (NASA/GSFC), L. Izzo (URoma/ICRA) &  
D. Malesani (DARK/NBI) report on behalf of the Swift team:

Following the report of a potential optical afterglow iPTF14cyb  
(Bhalerao et al., GCN Circ. 16442
Not found
 
 
) to the Fermi/GBM-detected burst GRB  
140623A (von Kienlin, GCN Circ. 16450
Not found
 
 
), Swift began a follow-up  
observation of the iPTF field.

We have analyzed all the 3.0 ks of XRT data for GRB 140623A,  from  
38.7 ks to 49.6 ks after the Fermi/GBM trigger. The data are entirely  
in Photon Counting (PC) mode. An X-ray source is detected at a  
position consistent with the candidate optical afterglow (Bhalerao et  
al., GCN Circ. 16442
Not found
 
 
) within the Fermi/GBM error circle.

Using 1153 s of PC mode data and 1 UVOT images, we find an enhanced  
XRT position (using the XRT-UVOT alignment and matching UVOT field  
sources to the USNO-B1 catalogue): RA, Dec = 225.47927, +81.19049  
which is equivalent to:

RA (J2000): 15h 01m 55.02s
Dec(J2000): +81d 11' 25.7"

with an uncertainty of 5.8 arcsec (radius, 90% confidence). This  
position is 5.0 arcsec from the the optical counterpart iPTF14cyb, and  
consistent with it. We cannot determine at the present time whether  
the source is fading.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00020388.

The Swift/UVOT began settled observations of the field of GRB 140423A  
38708 s after the GBM trigger. No optical afterglow consistent with  
the optical position (Bhalerao et al. GCN Circ. 16442
Not found
 
 
) is detected in  
the initial UVOT exposures. Preliminary 3-sigma upper limits using the  
UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358,  
373) are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

u                38708        44173          925         >22.0
white            38926        44863          851         >21.9

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.037 in the direction of the burst
(Schlegel et al. 1998).

This circular is an official product of the Swift team.