TITLE:   GCN CIRCULAR
NUMBER:  12695
SUBJECT: GRB 111215A: TNG K-band observations
DATE:    11/12/16 15:08:56 GMT
FROM:    Stefano Covino at Brera Astronomical Observatory  <stefano.covino@brera.inaf.it>

P. D'Avanzo, A. Melandri, S. Covino (INAF/OABr), L. A. Antonelli, V. D'Elia (INAF/OAR and ASDC/ASI), E. Palazzi (INAF/IASF Bo), D. Fugazza (INAF/OABr), G. Tagliaferri (INAF/OABr), and S. D. Vergani (INAF/OABr), report on behalf of the CIBO collaboration:

We observed the field of GRB 111215A (Oates et al., GCN 12681) with the TNG telescope located in the Canary Islands. We secured 30 min Ks-band imaging with the NICS instrument, with a mean time Dec 15.845 UT (6.30 hr after the GRB trigger).

Within the UVOT-enhanced XRT error circle (Beardmore et al., GCN 12690), we detect no new source down to a limiting magnitude K > 19 (Vega, calibrated against the 2MASS catalog).

Taking the X-ray flux at the time of the TNG observation from the UK X-ray light curve repository (http://www.swift.ac.uk/xrt_curves/00509717/), we compute a broad-band optical-to-X-ray spectral index beta_OX < 0.25, which classifies GRB 111215A as dark according to the widely adopted definition of Jakobsson et al. (2004, ApJ, 617, 21). The non detection in the K band, coupled with the significant absorption in the X-ray spectrum (Beardmore et al., GCN 12692), suggests a highly extinguished, rather than a high redshift, event. Deep observations to look for a host galaxy are encouraged.

We acknowledge excellent support from the observing staff at the TNG, especially Marco Pedani and Giovanni Mainella.