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
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.