Swift J1822.3-1606: Optical/NIR counterpart candidate

ATel #3496; J. Gorosabel (IAA-CSIC), A. de Ugarte Postigo (DARK/NBI), S. Mottola (DLR, Berlin), S. Hellmich (DLR, Berlin), P. Ferrero (IAC & U. La Laguna), R. Sanchez-Ramirez (IAA-CSIC), J. C. Tello (IAA-CSIC), V. Casanova (OSN, IAA-CSIC), R. Marti (IAC), A. J. Castro-Tirado (IAA-CSIC)
on 18 Jul 2011; 16:14 UT
Credential Certification: Antonio de Ugarte Postigo (adeugartepostigo@gmail.com)

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Optical and near-IR observations were carried out with the 0.82mIAC80, 1.23m CAHA, 1.5m OSN and 3.5m CAHA telescopes as follows:

Telescope	Date 2011 July (UT)	Filter	Exp.Time. (s)
1.5m OSN	15.88761 - 15.94373	I	3x45 + 73x50
1.23m CAHA	15.90429 - 16.03722	I	34x30
1.5m OSN	16.90002 - 16.96309	I	81x50
3.5m CAHA	17.95737 - 18.03200	Ks	10x60 + 2210x1.6
0.82m IAC80	18.07277 - 18.08534	B,V,R,I	5x45,5x30,5x20,5x30

Three objects are detected consistent with, or close to the XRT error circle (Pagani et al. ATel #3493), as shown in http://www.dark-cosmology.dk/~deugarte/Swift1822/swift1822.png

For S1, S2 and S3 we measure I-band magnitudes of 18.2, 19.8 and 19.8 respectively, as compared to stars of the USNOB-1.0 catalogue. We note that S1 (the only one clearly inside the XRT error box and the most probable counterpart) is already detected in the 2MASS catalogue (Source ID 18221794-16044259, RA,Dec: 18:22:17.946,-16:04:25.90) with a K-band magnitude of 11.6, consistent with what we measure in a preliminary analysis of the Ks band data of the 3.5m CAHA telescope.

The presence of S1 in the error box supports the hypothesis of Gogus et al. (ATel #3491) of this object being similar to Swift J1626.6-5156, where the companion star of the Be/X system was detected with comparable brightness.

A search for optical and near-IR variability/periodicity is undergoing.