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Astron. Astrophys. 330, 1067-1069 (1998)

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Research Note

IR observations of SGR 1806-20
during the November 1996 active period *

A.J. Castro-Tirado 1, J. Gorosabel 1 and P. Hammersley 2

1 Laboratorio de Astrofsica Espacial y Fsica Fundamental (LAEFF-INTA), P.O. Box 50727, E-28080 Madrid, Spain
2 Instituto de Astrofsica de Canarias, E-38200 La Laguna, Tenerife, Spain

Received 25 August 1997 / Accepted 24 October 1997

Abstract

Following the announcement of a new period of activity of the soft gamma-ray repeater SGR 1806-20 in 1996 November, we have performed follow-up observations of the IR counterpart, which has been proposed as a luminous blue variable or B[e] star. We have found that no variability larger than 0.1 mag in the K -band is present in the data. No variation in the K -band flux is found either when comparing our observations (1996 November 6 & 10) with a previous one (1996 July 3), nor any variation larger than 0.1 mag was detected in the K -band on 6 November at the 1-second timescale. Assuming that a faint burst (with fluence S [FORMULA] 10-9 erg cm-2) occurred during our observation, we can set an upper limit to the fluences rate (assuming a 1-s IR burst) as S [FORMULA] /S [FORMULA] 10-2. There is a modest chance that no burst at all could have occurred during our observation. In that case the upper limit quoted here is considerably worse. Photometry revealed that the HK magnitudes are consistent with the values reported by Kulkarni et al. (1995) in 1993 October, but the J value is slightly different by about 0.4 mag.

Key words: stars: neutron – SGR 1806-20 – X-rays: stars

* Based on observations made with the Carlos Sánchez Telescope operated on the island of Tenerife in the Spanish Observatorio del Teide of the Instituto de Astrofsica de Canarias. Additional observations were collected at the 1.2-m Telescope at the German-Spanish Astronomical Center, Calar Alto, Spain, operated jointly by the Max-Planck- Institut fur Astronomie (MPIA), Heidelberg, and the Spanish National Commission for Astronomy.

Send offprint requests to: A.J. Castro-Tirado (ajct@laeff.esa.es)

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© European Southern Observatory (ESO) 1998

Online publication: January 27, 1998
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