A Continuum of H- to He-Rich Tidal Disruption Candidates With a Preference for E+A Galaxies
We present the results of a Palomar Transient Factory (PTF) archival search for blue transients that lie in the magnitude range between "normal" core-collapse and superluminous supernovae (i.e., with –21 ≤ M_(R (peak)) ≤ – 19). Of the six events found after excluding all interacting Type IIn and Ia-CSM supernovae, three (PTF09ge, 09axc, and 09djl) are coincident with the centers of their hosts, one (10iam) is offset from the center, and a precise offset cannot be determined for two (10nuj and 11glr). All the central events have similar rise times to the He-rich tidal disruption candidate PS1-10jh, and the event with the best-sampled light curve also has similar colors and power-law decay. Spectroscopically, PTF09ge is He-rich, while PTF09axc and 09djl display broad hydrogen features around peak magnitude. All three central events are in low star formation hosts, two of which are E+A galaxies. Our spectrum of the host of PS1-10jh displays similar properties. PTF10iam, the one offset event, is different photometrically and spectroscopically from the central events, and its host displays a higher star formation rate. Finding no obvious evidence for ongoing galactic nuclei activity or recent star formation, we conclude that the three central transients likely arise from the tidal disruption of a star by a supermassive black hole. We compare the spectra of these events to tidal disruption candidates from the literature and find that all of these objects can be unified on a continuous scale of spectral properties. The accumulated evidence of this expanded sample strongly supports a tidal disruption origin for this class of nuclear transients.
Additional Information© 2014 American Astronomical Society. Received 2014 June 9; accepted 2014 July 25; published 2014 September 3. We thank R. Antonucci, L. Bildsten, and C. S. Kochanek for helpful discussions. We appreciate the assistance of V. Bhalerao, A. Cucchiara, D. Levitan, A. Mishra, J. M. Silverman, R. Walters, and O. Yaron in obtaining and reducing observations, and are grateful to the staff at the various observatories where data were obtained. We thank the Swift PI N. Gehrels and the entire Swift team for authorizing, scheduling, and carrying out our requested observations. This paper is based on observations obtained with the Samuel Oschin Telescope as part of the Palomar Transient Factory project. Additional data were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. This research used resources of the National Energy Research Scientific Computing Center, which is supported by the Office of Science of the U.S. Department of Energy under Contract No.DE-AC02-05CH11231. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. This research also made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the U.S. Department of Energy Office of Science. A.G. and I.A. acknowledge support by the Israeli Science Foundation and an EU/FP7/ERC grant. A.G. further acknowledges grants from the BSF, GIF, and Minerva, as well as the "Quantum Universe" I-Core program of the planning and budgeting committee and the ISF, and a Kimmel Investigator award. E.O.O. is incumbent of the Arye Dissentshik career development chair and is grateful for support by a grant from the Israeli Ministry of Science and the I-CORE Program of the Planning and Budgeting Committee and The Israel Science Foundation (grant No. 1829/12). M.M.K. acknowledges generous support from the Hubble Fellowship and Carnegie-Princeton Fellowship. J.S.B. and his group were partially supported by NASA/Swift Guest Investigator grants NNX09AQ66G and NNX10AF93G, and NSF/AST-100991. A.A.M. acknowledges support for this work by NASA from a Hubble Fellowship grant ST-HF-51325.01.
Published - 0004-637X_793_1_38.pdf
Submitted - 1405.1415v2.pdf