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VVV near-infrared observations of the IGR J17494-3030 field

ATel #4006; A. F. Rojas (PUC, Santiago), S. Greiss (Warwick), N. Masetti (INAF/IASF, Bologna), D. Steeghs (Warwick/CfA) and D. Minniti (PUC, Santiago)
on 28 Mar 2012; 16:01 UT
Credential Certification: Nicola Masetti (masetti@iasfbo.inaf.it)

Subjects: Infra-Red, X-ray, Transient

As a near-infrared (NIR) follow-up of the arcsec-sized soft X-ray (ATel #3989) error box of the X-ray transient source IGR J17494-3030 (ATel #3984) and to look for a possible quiescent counterpart, we searched the archival frames of the NIR VVV survey (vvvsurvey.org; Minniti et al. 2010, New Astron., 15, 433) of the Galactic Bulge and inner arms, which is being obtained with the 4.1m VISTA telescope at Cerro Paranal (Chile).

JHKs images were acquired on 9 July 2010 between 06:20 and 06:33 UT under an average seeing of 1.0 arcsec and on 11 July 2010 between 04:41 and 04:52 UT with an average seeing of 0.67 arcsec; further Ks images were secured on 13 October 2011 at 01:07 UT with a seeing of 1.1 arcsec.

Exposure times were 6 s for the J-band images, and 4 s for the H and Ks ones. The image scale is 0.34 arcsec/pixel for all frames.

Within the Swift/XRT X-ray error circle of IGR J17494-3030 (ATel #3989) we find five sources. Their coordinates, distance from the best XRT position, and NIR magnitudes at the 11 July 2010 epoch are:

 
 
#    RA(J2000)    Dec(J2000)  d(")      J            H            Ks 
------------------------------------------------------------------------ 
1   17 49 23.76  -30 29 59.2  0.3  17.08+-0.05  16.12+-0.10  15.73+-0.10  
2   17 49 23.85  -30 29 58.6  1.1  18.85+-0.14  17.84+-0.16   17.2+-0.2 
3   17 49 23.89  -30 29 59.3  1.4  18.52+-0.14  17.56+-0.15   17.3+-0.3 
4   17 49 23.66  -30 29 58.5  1.8  16.17+-0.04  15.47+-0.09  15.15+-0.08  
5   17 49 23.71  -30 30 00.9  1.8  14.69+-0.04  13.73+-0.08  13.26+-0.03  
 

Coordinate errors are 0.1 arcsec at 1 sigma confidence level on both directions for all sources.

The worse seeing in the other two epochs prevented us from detecting the fainter sources #2 and #3; comparison among the magnitudes of the three brighter objects across the observation dates does not show significant variability for any of them.

At this stage we cannot tell which of these five sources (if any) is the quiescent NIR counterpart of IGR J17494-3030. Comparison with NIR imaging acquired during the present outburst of this transient or availability of an X-ray position with a subarcsecond uncertainty are therefore needed to pinpoint the correct counterpart.