Broad-band observations of the possible SN in NGC 2770

ATel #7517; S. Campana (OAB/INAF), C. C. Thoene (IAA-CSIC), G. Leloudas (Weizmann, DARK/NBI), F. Aceituno (IAA-CSIC), A. de Ugarte Postigo (IAA-CSIC, DARK/NBI)
on 16 May 2015; 23:46 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Antonio de Ugarte Postigo (adeugartepostigo@gmail.com)

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We continued to monitor the SN impostor/LBV/possible SN in NGC 2770, also known under "iPTF13efv", "SNhunt275" and "PSN J09093496+3307204" (see ATEL#7042, #7409, #7514 and #7515). The object was observed by XRT+UVOT on the Swift satellite starting at 2015-05-16 16:26:09 UT and the 0.9 m and 1.5m telescopes at Observatorio de Sierra Nevada (OSN) with UBVRI filters starting at 20:50 UT.

The XRT data were taken in photon counting mode for 1976 s. At the position of the object there is no source and we put a 3 sigma upper limit of 7.6E-03 cts/s Assuming a power law spectrum (Gamma=2) and the Galactic column density (2e20 cm-2) the upper limit on the 0.3-10 keV luminosity is < 2.8d40 erg/s.

The UVOT observed the field in all its filters and found a very bright source. Magnitudes in the AB system for the transient are

v=16.09+/-0.08 (79 s)
b=16.00+/-0.06 (79 s)
u=15.99+/-0.05 (79 s)
uvw2=17.25+/-0.04 (315 s)
uwm2=16.81+/-0.03 (1210 s)
uvw1=16.48+/-0.04 (157 s)

Together with the observations obtained at OSN in UBVRI offset to a similar epoch, we can roughly fit the optical and UV SED with a black body with a temperature of ~11000 K.