IGR J17497-2821: Additional Optical Counterpart Identifications.

ATel #895; S. Laycock, P. Zhao, M. van den Berg, J. Grindlay, J. Hong., (CfA)
on 22 Sep 2006; 02:50 UT
Credential Certification: Silas Laycock (silas@head.cfa.harvard.edu)

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We looked for counterparts for the new Integral/Swift transient IGR J17497-2821 toward the Galactic Bulge on a set of very deep (limiting Vmag~24) optical images taken in 2003 with the CTIO 4m + MOSAIC imager, as part of the ChaMPlane survey. There are 7 stars within the Swift error circle: co-ordinates 17:49:37.8,-28:21:18, radius 5 arcsec, reported in ATEL #889. Champlane and 2MASS photometry is summarized below, and may be used for comparing against new observations to look for optical transients in the error circle. We have provided an image of the field at: hea-www.harvard.edu/ChaMPlane/rapid_release.html. ID RA Dec V Verr R Rerr I Ierr Halpha Halpha_err ------ ----------- ---------- ------ ------ ------ ----- ----- ----- ------ ------ 219913 17 49 37.51 -28 21 15.6 22.649 0.097 21.568 0.053 20.068 0.047 21.485 0.066 220000 17 49 37.55 -28 21 19.0 23.263 0.185 21.960 0.055 20.164 0.049 21.778 0.067 220215 17 49 37.67 -28 21 13.4 22.432 0.070 21.043 0.027 19.692 0.020 21.115 0.033 220350 17 49 37.72 -28 21 16.9 16.722 0.004 15.850 0.010 15.135 0.010 15.946 0.009 220729 17 49 37.92 -28 21 14.8 22.223 0.069 21.121 0.041 19.775 0.030 21.088 0.032 220793 17 49 37.98 -28 21 17.5 23.085 0.110 22.182 0.064 -- -- 22.053 0.065 221118 17 49 38.11 -28 21 17.2 -- -- 22.375 0.070 21.308 0.088 22.952 0.133 ------------------------------------------------------------------------------------- Star 220350 is the brightest and also the closest match - 1.2" off the Swift position. All of the Champlane stars appear to be foreground objects and do not lie in the galactic bulge. None show evidence for Ha emission by our established criteria (Zhao et al 2005). Magnitudes have DAO fit errors, not including any systematic calibration errors, which could be in the order of 0.1mag. New observations can definitively rule out any of these stars as the ID, as suspected, by limiting any change in magnitude. 2MASS_ID RA Dec J H K ---------------- ---------- ---------- ----- ----- ----- 17493774-2821173 267.407266 -28.354818 14.03 13.42 12.41 17493780-2821181 267.407450 -28.355030 14.02 13.17 12.88 --------------------------------------------------------------------- 2MASS 17493780-2821181 has H-K=0.3 which is also consistent with a foreground star. 2MASS 17493774-2821173 is reddened, having H-K approx 1 magnitude. Stars in the Bulge typically exhibit E(H-K) ~ 1.8mag while the range of intrinsic H-K runs from 0 for early spectral types to 0.4 at late M. Hence this star also lies in front of the bulge. We note the reported X-ray properties of IGR J17497-2821 appear inconsistent with stellar coronal emission, and the spectral index is too soft for most Be transients (typically around 1), added to which there is no evidence for any of the candidate counterparts being a Be star. The most likely explanation for IGR J17497-2821 based on X-ray properties is a Black-Hole or Neutron star binary at the distance of the Galactic bulge. The presumed low mass companion would not be visible at any wavelength due to crowding and extinction. New observations taken during the current outburst may be successful in spotting an accompanying nova or brightening in one of the above stars.

ChaMPlane image of the field.