TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  5025
SUBJECT: GRB 051117A: Bright host galaxy not confirmed
DATE:    06/04/28 16:16:33 GMT
FROM:    Alexander Kann at TLS Tautenburg  <kann@tls-tautenburg.de>

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D. A. Kann (TLS Tautenburg), E. Palazzi, N. Masetti & E. Maiorano (INAF/IASF - Bologna) report:

We observed the location of the UVOT afterglow (Holland et al., GCN 4300, Holland, GCN 4301) of GRB 051117A (Band et al., GCN 4280) with the Tautenburg 1.34m Schmidt telescope in the R filter under clear conditions and seeing of 2.8". Observations consisted of 12 x 600 s exposures, total integration time 2 hours, centered at UT 20060406.1, 139.9 days after the burst.

It was suggested by the UVOT observations that an underlying extended source might have been detected at 3.5 days after the burst at a magnitude of V about 21.5 - possibly the host galaxy.

The stacked Tautenburg image reveals no source at the UVOT position. The limiting magnitude at 3 sigma confidence is R = 24.0 measured against the USNOB1.0 R2 magnitudes of several unsaturated and isolated stars. This is not corrected for the very small Galactic extinction of E(B-V) = 0.024.

This field has also been imaged by the fourth release of the Sloan Digital Sky Survey (Adelman-McCarthy et al. 2006, ApJS, in press), and no source is detected at the UVOT location either (our photometry is significantly deeper than the SDSS).

About 2" from the UVOT localization (outside the 3 sigma UVOT localization), there is a group of four pixels slightly above the (subtracted) background. Simply transforming the sum of the counts into a magnitude gives R = 25.3, a "detection" at about one sigma significance. We caution that this is quite probably not a real source. There are no other sources closer than 5" to the UVOT position.

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