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It is possible that MASTER Robotic Net discovered Orphan Optical transient

February 15, 2012

MASTER-Kislovodsk auto-detection system discovered short OT source at (RA, Dec) = 11h 31m 22.95s , -07d 57m 14s.5 on 2012-01-30 00:05:11.145 (ATel #3898 http://www.astronomerstelegram.org/?read=3898).

The OT unfiltered magnitude is 17.6m (the limit is 19.3m). The OT is seen in 2 synchronous images (MASTER-II is the double telescope). The last reference image without OT was at 2012-01-29 23:21:06UT with unfiltered magnitude limit 19.4m.

There are no minor planet or star at this place. There are no GRB events from Swift, Fermi, INTEGRAL, Wind-KONUS at this time.

The discovery and reference images are available at: http://observ.pereplet.ru/images/113122.95-075714.5/MASTER113122.95-075714.jpg

This short optical transient MASTER J113122.95-075714.5 was observed simultaneously in g'r'i'z'JHK with GROND (Atel #3906 http://www.astronomerstelegram.org/?read=3906) mounted at the 2.2 m MPI/ESO telescope at La Silla (Chile) and at SWIFT space observatory . No X-ray source (in fact not a single X-ray photon) is detected at or near the MASTER position, with a conservative upper limit of 1.3E-3 cts/s. And no any source in optical and NIR. But based on the GROND images, J.Greiner et al. noted the existence of a clearly extended (~10" diameter), nearby (z<0.3), blue galaxy just 10" away from the MASTER position.

These observations let suggest that MASTER J113122.95-075714.5 could be an untriggered or orphan afterglow of a gamma-ray burst (Atel #3906). Conservatively assuming the putative GRB to have happened at 30 min before the (few minute duration) MASTER exposure, the GROND limits only imply a decay slope steeper than t^-1.3, well within the range of typical GRBs. The Swift/XRT non-detection at 2.4E+05 sec after the event excludes the majority of Swift X-ray afterglows of long GRBs, but is compatible with the 10-15% faintest afterglows.

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