X-ray detection of the supernova candidate MASTER OT 082752.77+704606.0

ATel #3367; K. V. Sokolovsky (MPIfR/ASC Lebedev/SAI MSU)
on 20 May 2011; 15:22 UT
Credential Certification: Frank Schinzel (schinzel@mpifr-bonn.mpg.de)

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The optical transient MASTER OT 082752.77+704606.0 (ATel #3255, #3265) was observed by Swift on 2011 May 14 for the total exposure time of 4ks. A weak X-ray source has been detected by Swift/XRT at the position 08:27:53.31 +70:46:10.07 (+/-6.2", J2000) only 3.4" from the optical transient (ATel #3265). The source is detected at the 3.5 sigma level with the XRT count rate of 0.005 +/-0.001 counts/sec. Good positional coincidence together with the absence of other detections of comparable significance in the field (apart from the brighter source GALEX 2682502750548263862 reported in ATel #3265) indicate that the X-ray detection of MASTER OT 082752.77+704606.0 is real. No X-ray source was seen at this position during the previous Swift/XRT observations on 2011 April 06 (2.1ks) and 14 (0.6ks).

Simultaneous Swift/UVOT data show only marginal changes in the ultraviolet brightness of the transient compared to previous observations:

 
 
   JD     filter mag. err. 
 
2455696.31  W2  18.26 0.05 
 
2455696.31  M2  18.16 0.07 
 
2455696.30  W1  18.06 0.06 
 
2455696.30  U   18.41 0.08 
 
2455696.30  B   19.58 0.14 
 
2455696.31  V   19.40 0.16 
 
 
 
2455665.82  W2  17.94 0.14 
 
2455665.76  W1  18.11 0.13 
 
2455665.89  U  >19.0 
 
2455665.82  B  >19.0 
 
 
 
2455657.57  W2  18.24 0.13 (ATel #3265) 
 

The optical spectrum of the transient reported in ATel #3255, its ultraviolet brightness and the initial lack of X-ray detection resemble the properties of ROTSE3 J115649.1+542726 = SN 2008es (Miller et al. 2009, ApJ, 690, 1303; Gezari et al. 2009, ApJ, 690, 1313) which was initially classified as an AGN flare (ATel #1515) or possible tidal disruption event (ATel #1524), but has later developed spectral features indicating that it was in fact an extremely luminous Type II supernova at z=0.21 (ATel #1644). The emission feature in the optical spectrum of MASTER OT 082752.77+704606.0 (ATel #3255) may be attributed to the HeII 4686 emission in analogy to SN 2008es (Adam Miller, private communication). MASTER OT 082752.77+704606.0 is likely a luminous Type II supernova at z=0.135. New spectroscopic observations which could trace the expected evolution of the optical spectrum are necessary to confirm this interpretation.