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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