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ASAS-SN and Swift follow-up of PSN J10081059+5150570: An Unusual Type IIn Supernova ?

ATel #3749; J. L. Prieto (Princeton), B. Shappee, K. Z. Stanek, C. S. Kochanek, D. Szczygiel, J. F. Beacom (Ohio State), G. Pojmanski (Warsaw University Observatory), W. Rosing, E. Hawkins, R. Ross, M. Elphick, D. Mullins, Z. Walker (Las Cumbres Observatory)
on 8 Nov 2011; 20:25 UT
Credential Certification: Jose L. Prieto (jose@obs.carnegiescience.edu)

Subjects: Optical, Supernovae, Transient

Referred to by ATel #: 3895, 4062

We have been obtaining V-band photometric observations of the candidate supernova impostor PSN J10081059+5150570 (CBET #2851, ATEL #3690) using the commissioning data from the recently installed 14-cm ASAS-SN telescope in Haleakala, Hawaii. The transient has brightened by ~2.5 mag since the time of discovery (see also ATEL #3690) and by 0.4 mag between Oct. 22 and Oct. 29, 2011. The last V-band magnitude measured was V=14.5 mag on Oct. 29 (consistent with the magnitudes reported by amateur astronomers here), which at a distance of 19.2 Mpc for the host galaxy UGC 5460 (via NED) corresponds to M_V ~ -17. This makes it significantly more luminous than any previous supernova impostor (e.g., Smith et al. 2011, MNRAS, 415, 773) and in the range of type IIn supernovae (e.g., Li et al. 2011, MNRAS, 412, 1441). Indeed, the initial optical spectrum reported by Pastorello et al. (CBET #2851) also shares several properties with spectra of some type IIn supernovae (e.g., Kiewe et al. 2010, arXiv:1010.2689). We note that the strong UV brightening reported in ATEL #3690 is very unusual for any SN impostor or true supernova, although it could be similar to the possible shock breakout from a dense circumstellar wind in the case of PTF 09uj (Ofek et al. 2010, ApJ, 724, 1396). Independent analysis of the Swift/UVOT optical and UV data (PI: P. Roming) obtained from the Swift data archive shows that, assuming no intrinsic reddening, the effective temperature measured from black-body fits to the spectral energy distribution has increased from T=4000 K at 5 days after discovery to 12000 K at 32 days after discovery, while the radius has decreased from R=120 AU to 30 AU. The total estimated radiated energy so far is 3x10^48 ergs.