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Optical counterpart to IGR J17098-3628

ATel #494; D. Steeghs (CfA), M. A.P. Torres (CfA), P. G.Jonker (SRON/CfA), H. Chen (MIT), P. Green (CfA), J. Miller (CfA), M. R.Garcia (CfA)
on 16 May 2005; 00:27 UT
Credential Certification: Danny Steeghs (dsteeghs@cfa.harvard.edu)

Subjects: Radio, Infra-Red, Optical, X-ray, Black Hole, Neutron Star, Transient

Referred to by ATel #: 3150

Following the recent report of a possible radio counterpart to the X-ray transient IGR J17098-3628 (ATEL #490), we re-investigated our Magellan I-band exposures obtained on 2005 April 9 UT (see ATEL #478). The frames show a point source located at R.A.(J2000)=17:09:45.93, DEC(J2000)= -36:27:58.2 in the 2MASS reference frame (0.2" uncertainty). This optical position is consistent within 2 sigma with that derived from the radio observations (ATEL #490).

We acquired additional I-band images with the 6.5m Magellan-Baade telescope during 2005 May 13 9:19-9:27 UT. The instrumental setup and exposure times were similar to those used in our previous observation (ATEL #478). The seeing was also comparable at 0.6 arcsec. Differential photometry with respect to 6 nearby stars indicates that the optical source close to the radio position has faded by 0.12 +/- 0.02 mag in the I band since 2005 April 9. The positional coincidence with the SWIFT and VLA detections and its photometric variability strongly suggest that this source is indeed the optical counterpart to IGR J17098-3628.

Follow-up photometric observations and the acquisition of a spectrum to characterise the optical counterpart are encouraged.

IMACS image including SWIFT and VLA error circles