VVV near-infrared observations of the GRS 1736-297 field

ATel #8733; N. Masetti (INAF/IASF, Bologna), R. K. Saito (Univ. Federal de Sergipe), A. F. Rojas & D. Minniti (UNAB, Santiago de Chile)
on 25 Feb 2016; 14:38 UT
Credential Certification: Nicola Masetti (masetti@iasfbo.inaf.it)

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After the announcement of the arcsec-sized soft X-ray error box (ATel #8704) of the X-ray source GRS 1736-297 which recently underwent an active phase at high energies (ATel #8698), we searched the archival frames of the near-infrared (NIR) VVV survey (vvvsurvey.org; Minniti et al. 2010, New Astron., 15, 433) of the Galactic Bulge and inner disk, obtained with the 4.1m VISTA telescope at Cerro Paranal (Chile), to look for the presence of NIR objects within the Swift/XRT error circle reported in ATel #8704.

JHKs images were acquired on 8 April 2010 between 06:51 and 06:58 UT under a seeing of 0.9 arcsec. Further Z- and Y-band pointings were performed on 24 August 2011; these images had a seeing of 0.8 arcsec. Exposure times were 24 s in the J band, 8 s in both H and Ks, and 20 s in both Z and Y bands; the image scale is 0.34 arcsec/pixel for all frames.

We do not find any source within the 2.2 arcsec Swift/XRT error circle down to the following (3-sigma) limits:

 
Z  > 19.2 
Y  > 18.3 
J  > 17.2 
H  > 16.2 
Ks > 15.7 

These can thus be considered the lower limits for the magnitudes of the NIR counterpart of GRS 1736-297 during quiescence.

We note that, in the VVV images, the nearest sources are seen at 2.8 arcsec from the coordinates of the centre of the Swift/XRT error circle, in comparison with the 5.8 arcsec distance of the Be star previously proposed to be the counterpart of GRS 1736-297 (see ATel #8704).