[vsnet-grb-info 15035] GRB 140523A: NOT observation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  16329
SUBJECT: GRB 140523A: NOT observation
DATE:    14/05/25 12:03:59 GMT
FROM:    Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst  <malesani at dark-cosmology.dk>

D. Malesani (DARK/NBI), D. Xu (DARK/NBI), A. Somero (NOT), A. de Ugarte 
Postigo (IAA/CSIC and DARK/NBI), Z. Cano (Univ. Iceland), and P. 
Jakobsson (Univ. Iceland), report on behalf of a larger collaboration:

We observed the field of the Fermi GRB 140523A (von Kienlin & 
Connaughton, GCN 16321; Vianello et al., GCN 16322; Golenetskii et al., 
GCN 16327) with the NOT equipped with the AlFOSC camera. Observations 
were started on 2014 May 24 at 21:23 UT (1.76 days after the GRB), using 
an SDSS r filter. Exposure time was 20 or 30 min, depending on the 
pointing. We targeted the XRT sources reported by Evans (GCN 16323; see 
also D'Elia & Izzo, GCN 16324):

http://www.swift.ac.uk/xrt_products/TILED_GRB00026/

XRT source #3 is spatially coincident with the bright star BD+25 2008 
and is likely unrelated to the GRB. XRT source #1 is inconsistent with 
the IPN triangulation annulus (Golenetskii et al., GCN 16327).

Within or close to the positions of XRT sources #1, 2, 4, and 5, several 
objects are visible in our images. Some of them may be responsible for 
the X-ray emission.

A pointlike object consistent with XRT source #3 (at RA = 08:52:25.38, 
Dec = +24:57:27.3) is found to be brighter by about 0.5 mag in the NOT 
image compared to its archival SDSS magnitude r = 19.50 +- 0.02 (AB). 
Given the bright historical counterpart and lack of spatial extension, 
this is unlikely to be related to the GRB.

None of the other objects have significantly varied compared to their 
catalog values. Within the position of XRT source #5, an extended object 
(possibly an interacting galaxy, or a blend of sources) is apparent. 
Consistent with XRT source #2, an extra, dim object is visible (r ~ 24), 
fainter than the SDSS limit. A bright pointlike source (r = 19.8) is 
consistent with the position of XRT source #1.

Our data do not reveal any obvious candidate optical afterglow for this 
GRB. We encourage further Swift/XRT follow-up in order to ascertain 
whether any of the X-ray sources is variable. Our analysis suggests that 
XRT sources #3 and #4 are not related to the GRB, as also indicated in 
the web page by Evans (GCN 16323). Sources #2 and #5 remain viable 
afterglow candidates.