Discovery and monitoring of the likely IR counterpart of SGR 1806–20 during the 2004 γ-ray burst-active state

Free access article

Issue		A&A Volume 438, Number 1, July IV 2005


Page(s)		L1 - L4
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:200500138

A&A 438, L1-L4 (2005)
DOI: 10.1051/0004-6361:200500138

Letter

Discovery and monitoring of the likely IR counterpart of SGR 1806-20 during the 2004 $\gamma$ -ray burst-active state

G. Israel¹, S. Covino², R. Mignani³, L. Stella¹, G. Marconi⁴, V. Testa¹, S. Mereghetti⁵, S. Campana², N. Rea^{1, 6}, D. Götz⁵, R. Perna⁷ and G. Lo Curto⁴

¹ INAF - Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone (Roma), Italy
e-mail: gianluca@mporzio.astro.it
² INAF - Osservatorio Astronomico di Brera, via Bianchi 46, 23807 Merate (Lc), Italy
³ European Southern Observatory, Karl-Schwarzschildstr. 2, 85748 Garching, Germany
⁴ European Southern Observatory, Casilla 19001, Santiago, Chile
⁵ INAF - Istituto di Astrofisica Spaziale e Fisica Cosmica "G.Occhialini", via Bassini 15, 20133 Milano, Italy
⁶ SRON - National Institute for Space Research, Sorbonnelaan 2, 3584 CA, Utrecht, The Netherlands
⁷ Department of Astrophysical and Planetary Sciences and JILA, University of Colorado, 440 UCB, Boulder, CO 80309, USA

(Received 7 April 2005 / Accepted 4 June 2005)

Abstract
The sky region including the Chandra position of SGR 1806-20 was monitored in the IR band during 2004, following its increased high energy bursting activity. Observations were performed using NAOS-CONICA, the adaptive optics IR camera mounted on Yepun VLT, which provided images of unprecedented quality (FWHM better than 0 $\farcs$ 1). After the 2004 December 27th giant flare, the source position has been nailed by VLA observations of its radio counterpart, reducing the positional uncertainty to 0 $\farcs$ 04. Using IR data from our monitoring campaign, we discovered the likely IR counterpart to SGR 1806-20 based on positional coincidence with the Chandra and VLA uncertainty regions and flux variability of a factor of about 2 correlated with that at higher energies. We compare our findings with other isolated neutron star classes thought to be related, at some level, with SGRs.

Key words: pulsar: individual: SGR 1806-20 -- stars: neutron -- stars: imaging -- infrared: stars -- X-rays: stars

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Letter

Discovery and monitoring of the likely IR counterpart of SGR 1806-20 during the 2004 -ray burst-active state

Discovery and monitoring of the likely IR counterpart of SGR 1806-20 during the 2004 $\gamma$ -ray burst-active state