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Optical Spectroscopy of the Transient ROTSE3 J115649.1+542726

ATel #1593; A. A. Miller, R. Chornock, J. S. Bloom, M. Modjaz, A. V. Filippenko, W. Li, R. J. Foley, N. R. Butler, D. A. Perley (UC Berkeley)
on 28 Jun 2008; 00:40 UT
Credential Certification: Weidong Li (weidong@astron.berkeley.edu)

Subjects: Optical, Supernovae, Transient

Referred to by ATel #: 1644

We have continued follow-up of the UV/optical transient ROTSE3 J115649.1+542726 (Yuan et al. 2008; ATel #1515) using the RC spectrograph on the 4-m Mayall Telescope at Kitt Peak. Following the approval of our request for Director's Discretionary time, on 2008 June 21 and 2008 June 23 UT we obtained 30 minute spectra of the transient covering a spectral range of 410-900 nm.

ROTSE3 J115649.1+542726 continues to evolve slowly, with spectral features that remain very similar to those present in our Keck spectrum taken on 2008 June 7 UT (Miller et al. 2008; ATel #1576). The continuum continues to dominate the spectrum and remains very blue now 59 days post discovery. The features we previously identified as possibly being Halpha, Hbeta, and Hgamma at a redshift z ~ 0.08, are only marginally stronger in the combined spectra from June 21 and June 23 UT relative to the Keck spectrum. The slow evolution of these lines gives us pause that this transient is in fact a type II supernova, as was previously suggested by us (ATel #1576) and later by Gezari et al. 2008 (ATel #1578). We note, however, that at z ~ 0.08 and M_R ~ -20 this would not be a typical SN, and the SN hypothesis cannot be excluded at this time. The classification of ROTSE3 J115649.1+542726 remains elusive, and further observations are encouraged.

We wish to thank Buell Jannuzi, for approving our request for DD time, and the support staff at Kitt Peak, especially Di Harmer and Dave Summers, for their support in obtaining these observations.