Near-infrared follow-up to the May 2008 activation of SGR 1627-41^*

¹ European Southern Observatory, Casilla 19001, Santiago 19, Chile e-mail: adeugart@eso.org
² Instituto de Astrofísica de Andalucía (IAA-CSIC), Camino Bajo de Huétor, 50, E18008, Granada, Spain
³ INAF - Osservatorio Astronomico di Brera, via Bianchi 46, 23807 Merate, Italy

Received: 20 November 2008
Accepted: 21 January 2009

Abstract

Context. On 28 May 2008, the Swift satellite detected the first reactivation of SGR 1627-41 since its discovery in 1998.

Aims. Following this event, we began an observing campaign at near infrared wavelengths to search for a possible counterpart inside the error circle of this SGR, which is expected to exhibit flaring activity simultaneously with the high energy flares or at least some variability compared to the quiescent state.

Methods. For the follow-up, we used both the 0.6 m REM robotic telescope at La Silla Observatory, which allowed a fast response within 24 h and, through director discretionary time, the 8.2 m Very Large Telescope at Paranal Observatory, where we observed with NACO to produce high angular-resolution imaging with the aid of adaptive optics.

Results. These observations represent the most rapidly acquired near-infrared observations following activation of this SGR and the deepest and highest spatial resolution observations within the Chandra error circle.

Conclusions. Five sources are detected in the immediate vicinity of the most precise X-ray localisation of this source. For 4 of them, we do not detect variability, although the X-ray counterpart exhibited significant decay during our observation period. The 5th source is only detected in one epoch, where we have the highest image quality, so no variability constraints can be imposed and this remains the only plausible counterpart. We can impose a limit of > 21.6 mag on any other counterpart candidate one week after the onset of the activity. Our adaptive optics imaging with a resolution of 0.2″ provides a reference frame for subsequent studies of future periods of activity.