GCN Circular 9655: "GRB 090709A: deep optical observations with the Spanish 10.4m GTC"

A. J. Castro-Tirado (IAA-CSIC Granada), A. de Ugarte Postigo (OAB-INAF), J. Gorosabel, S. Guziy, M. Jelinek (IAA-CSIC), P. Kubanek (IAA-CSIC and GACE Valencia), D. Perez-Ramirez (Univ. de Jaen), N. Mirabal (UCM Madrid), A. Llorente, J. M. Castro Ceron (ESAC Villafranca del Castillo), C. Alvarez (IAC/GTC La Palma) and J. Cepa (IAC Tenerife), report:

Following the detection of GRB 090709A by Swift (Morris et al. GCNC 9625), we have conducted follow-up observations with the 10.4-m Gran Telescopio Canarias (GTC) at the Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias, in the island of La Palma. Images in the i'-band filter (7 x 300-s) under 1".0 seeing were gathered with the OSIRIS instrument (Cepa et al. 2009, in prep.) on 11 July 2009, 00:45 UT (i.e. 41 hr after the event).

At the position of the reported nIR-optical afterglow (Aoki et al. GCNC 9634, Morgan et al. GCNC 9635, Cenko et al. GCNC 9646) we detect no single object down to i' = 25.5 (preliminary 3-sigma limit), or i' ~ 25.2 when taking into account the foreground Galactic extinction. We note two nearby faint objects, lie 3".3 south-east and 4" north of the afterglow.

The stacked GTC .jpg image is available at the following link:


Although we cannot exclude that GRB 090709A occurred in a low redshift galaxy (Butler et al. GCNC 9639, Guidorzi et al. GCNC 9648), our non-detection of a host galaxy, together with the reported 8-s quasi-periodic oscillations (Markwardt et al., GCN 9645, Golenetskii et al. 9647, Gotz et al. GCNC 9649, Ohno et al. GCNC 9653) and the fact that the event is at galactic coordinates of about (l = 90, b = 20) cannot rule out that the initial gamma-ray emission arose from a nearby magnetar candidate in the Milky Way, much closer than GRB 070610 / SWIFT J1955+2614 (Castro-Tirado et al. 2008, Nature 455, 506). Multiwavelength observations are encouraged.

We acknowledge the excellent support from the GRANTECAN staff.

This Circular can be quoted.