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Possible identification of the IR counterpart of SGR 1806-20

ATel #378; G. L. Israel (INAF AO Roma), S. Covino (INAF AO Milano), S. Mereghetti (INAF IASF Milano), R. Mignani (ESO), L. Stella (AO Roma), V. Testa (AO Roma), G. Marconi (ESO), on behalf of a larger team
on 5 Jan 2005; 18:27 UT
Credential Certification: GianLuca Israel (gianluca@mporzio.astro.it)

Subjects: Infra-Red, Gamma Ray, Soft Gamma-ray Repeater

Referred to by ATel #: 439

Following the recent radio detection of SGR 1806-20 (Gaensler et al. 2005, GCN 2929) which provided an unprecedented positional accuracy (at the level of 0.1"), we re-analysed all the VLT NACO images of the field (in J, H and Ks bands) we collected in 2004 after the X-ray burst activity from the source detected during March, June, August and October 2004 (Mereghetti et al. 2004, GCN 2541, Golenetskii et al. 2004, GCN 2693 and 2823).

We have detected several sources (Israel et al. 2004, GCN 2609) within the Chandra error circle (radius of 0.3") reported in Eikenberry et al. 2001 (ApJ 563, L133) and Kaplan et al. 2002 (ApJ, 564, 935). However, only one faint object (Ks=21.6+\-1.0) is consistent with the VLA radio position (Kouveliotou et al. 2005, GCN 2929) and within the Chandra error circle. The source was detected in the June and September 2004 images, during which the sky conditions were exceptionally good (on-axis PSF of about 0.09") and with a long exposure time (about 6000s in the Ks band; Ks limiting magnitude of about 23). No flux variability has been detected from the source within the relatively large magnitude uncertainties. Candidate C, proposed by Eikenberry et al. 2001, is about 0.5" away form the radio position and resolved in at least 2 point-like objects within the VLT NACO images.

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