IR counterpart candidates to the transient Swift J174535.5-285921

ATel #3481; M. Servillat, J. Grindlay, P. Zhao, J. Hong, B. Allen (CfA), M. van den Berg (U. Utrecht), S. Laycock (UMass Lowell)
on 11 Jul 2011; 01:46 UT
Credential Certification: Mathieu Servillat (mservillat@cfa.harvard.edu)

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Following the recent detection of the new Galactic Center X-ray transient Swift J174535.5-285921 (ATEL #3472) and the search for potential near-infrared counterparts leading to magnitudes limits (ATEL #3476), we searched our catalog of Ks-band sources and long term variables in the 10'x10' field centered on Sgr A* (Servillat et al. in prep). We obtained yearly images of the field with ISPI at CTIO 4m from 2005 to 2009, and 3 images with PANIC at Magellan 6.5m (seeing 0.4-0.6") in 2004-06, 2007-08 and 2010-07 (the 2004 dataset is described in more details by Laycock et al. 2005, ApJL, 634, L53).

We found no long-term variables in the Swift XRT-UVOT enhanced position error circle and no ISPI counterpart (similarly to ATEL #3476), but we found 3 counterpart candidates in our PANIC images to the 2 matching Chandra sources, CXOGC174535.5-285920 and CXOGC174535.4-285925 (Muno et al. 2009, ApJS, 181, 110).

IR CXOGC RA Dec K04 K07 K10
-- --------------- ----------- ----------- ----- ----- -----
A 174535.5-285920 17:45:35.54 -28:59:19.9 16.80 16.93 17.01
B 174535.5-285920 17:45:35.53 -28:59:20.3 16.89
C 174535.4-285925 17:45:35.44 -28:59:25.4 15.49 15.66 15.61

Magnitudes are in the 2MASS system with an rms of ~0.2 mag, the astrometry error is lower than 0.2". We give 3 K-band magnitudes corresponding to the 3 PANIC observation epochs. Source B magnitudes K07 and K10 are not available due to a slightly worse seeing at those epochs and confusion with source A, but the source seems to be present and constant in the images shown below.

We provide finding charts with PANIC and ISPI images at the following link:
http://hea-www.harvard.edu/ChaMPlane/rapid_release.html

Observations are needed in the next week to test if one of these 3 sources, or any of the other IR sources in the Swift error circle, has brightened. Crowding in this region makes the use of large telescopes with an infrared camera required.