Radio detection in 2003 of IGR J17091-3624

ATel #3232; Michael F. Bietenholz (Hartebeesthoek Radio Observatory, South Africa and York University, Canada), Michael P. Rupen (NRAO), Vivek Dhawan (NRAO) and Amy J. Mioduszewski (NRAO)
on 24 Mar 2011; 07:42 UT
Credential Certification: Michael Bietenholz (mbieten@yorku.ca)

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The X-ray transient IGR J27091-3624 recently showed an increase in the X-ray flux (Atel #3144, #3148 and #3159). It was also recently detected in the radio with ATCA (Corbel et al; ATEL #3167; 9 Feb 2011). This object had been observed with the NRAO VLA in 2003, and a radio source detected (Rupen et al., ATEL #152). That radio source, however, was at a position inconsistent with the subsequent localization of the X-ray transient by Swift-XRT (Kennea & Capitanio 2007; Atel #1140). Prompted by the recent ATCA detection, we re-examined the 2003 VLA data and find a second, weaker radio source in the same field, whose position is consistent with both the Swift-XRT and the new ATCA radio position.

We measure the following flux densities for IGR J27091-3624:
2003 Apr 26, 8.46 GHz: 0.69 +- 0.12 mJy
2003 May 06, 8.46 GHz: 0.68 +- 0.09 mJy
2003 May 06, 4.98 GHz: 0.67 +- 0.13 mJy
2003 May 09, 8.46 GHz: 0.89 +- 0.13 mJy

The corresponding four peak-brightness positions are consistent within the uncertainties with each other, and with both the Swift XRT X-ray position of Kennea & Capitanio 2007 (Atel #1140) and the 2011 ATCA radio position. The average radio position from these 2003 data was RA = 17h 09m 7.6s +- 0.3s, decl = -36d 24' 23.3" +- 3.1" .

The 8.4-GHz flux densities measured in 2003 are significantly below the 9.0-GHz value of 1.3 mJy observed by ATCA in 2011, suggesting that the radio flux density is significantly variable, perhaps correlated with the X-ray flux which is also presently higher than it was in 2003.