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PTF11eon/SN2011dh is Possibly a Type IIb Event

ATel #3413; I. Arcavi, A. Gal-Yam, D. Polishook, O. Yaron, D. Xu (Weizmann Institute of Science), W. Li, A. V. Filippenko, J. M. Silverman, S. B. Cenko (University of California, Berkeley), P. E. Nugent, D. Poznanski (LBNL), E. Gorbikov (Tel Aviv University), M. Sullivan (Oxford), M. M. Kasliwal, E. O. Ofek, A. Horesh, R. Quimby (California Institute of Technology), E. S. Walker (Scuola Normale Superiore di Pisa), and S. D. Van Dyk (Spitzer Science Center, California Institute of Technology), on behalf of the Palomar Transient Factory Collaboration.
on 8 Jun 2011; 13:22 UT
Credential Certification: Avishay Gal-Yam (avishay.gal-yam@weizmann.ac.il)

Subjects: Optical, Ultra-Violet, Supernovae

Referred to by ATel #: 3428, 3432, 3433, 3641

We have obtained optical photometry of the Type II SN PTF11eon/SN2011dh (ATEL #3398; CBET #2736) using the Palomar 48" Oschin Telescope and the Wise Observatory 1m and 18" telescopes. In the g band we find that the supernova declined from magnitude 13.18 to magnitude 14.94 between June 1.69 and June 3.85 (UT dates used throughout), and then began to increase in brightness rapidly at ~0.3 mag/day. This behavior is reminiscent of that of the prototypical Type IIb SN 1993J, and may indicate the detection of the shock-breakout tail. However, PTF11eon is fainter by more than two magnitudes (absolute) and is evolving much faster than SN 1993J. We have compared the spectrum reported by Silverman et al. (2011, ATEL #3398) to spectra of many other Type II events. Though there are some subtle differences, the spectrum of this event exhibits striking similarities to a spectrum of SN 1993J taken on 1993 Apr 13 (Filippenko et al. 1993, ApJ, 415, L103) and to a spectrum of the transitional Type IIb SN 2008ax on 2008 Mar 8 (Chornock et al. 2010,http://xxx.lanl.gov/abs/1001.2775; Pastorello et al. 2008, MNRAS, 389, 955). However, clear He I features have not yet appeared. Furthermore, we have analyzed the archival Swift/UVOT data for PTF11eon (ATEL #3402). In the U band, PTF11eon declined from mag 15.07 on Jun 3.51 to mag 15.24 on Jun 5.32, then rebrightened to mag 15.05 on Jun 6.65. In the B and V bands, the SN brightened monotonically within measurement errors, from B = 15.40 mag on Jun 3.51 to B = 14.69 mag on Jun 6.65, and from V = 14.96 on Jun 3.52 to V = 14.15 on Jun 6.59. (This reduction is based on the calibration by Li et al. 2006, PASP, 118, 37.) This photometric behavior of PTF11eon is also reminiscent of that of SN 2008ax (Pastorello et al. 2008, MNRAS, 389, 955; Chornock et al. 2010,http://xxx.lanl.gov/abs/1001.2775). Thus, we suggest that PTF11eon is possibly a Type IIb event, or a SN2008ax-like transitional Type IIb event. It is quite clear this event is not a normal SN IIP (ATEL #3400). However, because of the limited range of the temporal and spectral coverage, future photometric and spectroscopic observations are required to determine an exact classification.