Search for an IR counterpart to the newly discovered transient Swift J174535.5-285921

ATel #3476; R. M. Bandyopadhyay, C. DeWitt, S. S. Eikenberry (UF)
on 6 Jul 2011; 19:50 UT
Credential Certification: Reba Bandyopadhyay (reba@alum.mit.edu)

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We have searched for potential near-infrared counterparts to the new Galactic Center X-ray transient, Swift J174535.5-285921 (ATEL #3472) using our catalog of JHK_s sources within the 17'x17' field centered on Sgr A* (DeWitt et al. 2010, ApJ 721, 1663), obtained with ISPI on CTIO on 2005 August 10. Within the Swift error circle are two faint X-ray point sources that were previously detected by Chandra, CXOGC174535.5-285920 and CXOGC174535.4-285925 (Muno et al. 2009, ApJS 181, 110), which may represent Swift J174535.5-285921 in quiescence. Both of these Chandra sources are X-ray hard, consistent with a location at the distance of the Galactic Center. In the Muno 2009 X-ray catalog, both sources have a flux of order 10^31 erg/s (for d = 8 kpc); thus if the Swift transient is associated with one of these two previously identified Chandra sources, the X-ray flux has increased by approximately 4 orders of magnitude.

We find that neither CXOGC174535.5-285920 or CXOGC174535.4-285925 had a near-infrared counterpart to 5-sigma limits of J = 18.3 mag, H = 17.2 mag, and K_s = 15.8 mag on the date of our ISPI observations. If Swift J174535.5-285921 is an X-ray binary associated with either of these Chandra sources, assuming a Galactic Center distance of 8 kpc and an extinction of A_Ks = 2.5 mag, our counterpart non-detection limits the nature of Swift J174535.5-285921 to either an HMXB with a donor star spectral type later than B2 V or an LMXB with either a main sequence or subgiant A-M type companion.

Follow-up IR imaging of this transient to search for the counterpart while it is in an X-ray active phase is strongly encouraged.