The Most Slowly Declining Type Ia Supernova 2001ay

Creators: Krisciunas, Kevin; Quimby, Robert

Abstract

We present optical and near-infrared photometry, as well as ground-based optical spectra and Hubble Space Telescope ultraviolet spectra, of the Type Ia supernova (SN) 2001ay. At maximum light the Si II and Mg II lines indicated expansion velocities of 14,000 km s^(–1), while Si III and S II showed velocities of 9000 km s^(–1). There is also evidence for some unburned carbon at 12,000 km s^(–1). SN 2001ay exhibited a decline-rate parameter of Δm_(15)(B) = 0.68 ± 0.05 mag; this and the B-band photometry at t ≳+25 day past maximum make it the most slowly declining Type Ia SN yet discovered. Three of the four super-Chandrasekhar-mass candidates have decline rates almost as slow as this. After correction for Galactic and host-galaxy extinction, SN 2001ay had M_B = –19.19 and M_V = –19.17 mag at maximum light; thus, it was not overluminous in optical bands. In near-infrared bands it was overluminous only at the 2σ level at most. For a rise time of 18 days (explosion to bolometric maximum) the implied ^(56)Ni yield was (0.58 ± 0.15)/α M_☉, with α = L_(max)/E_(Ni) probably in the range 1.0-1.2. The ^(56)Ni yield is comparable to that of many Type Ia SNe. The "normal" 56Ni yield and the typical peak optical brightness suggest that the very broad optical light curve is explained by the trapping of γ rays in the inner regions.

Additional Information

© 2011 The American Astronomical Society. Received 2011 January 6; accepted 2011 June 17; published 2011 August 10. The work presented here is based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555; the Cerro Tololo Inter-American Observatory and the Kitt Peak National Observatory of the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under cooperative agreement with the NSF; the MMT Observatory, a joint facility of the Smithsonian Institution and the University of Arizona; the Fred L. Whipple Observatory; the Lick Observatory of the University of California; the Las Campanas Observatory; the Beijing Astronomical Observatory; and the W.M. Keck Observatory, which was generously funded by the W.M.Keck Foundation and is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA. We thank the staffs at these observatories for their efficient assistance, Don Groom for taking some of the Nickel 1 m images, and Rachel Gibbons, Maryam Modjaz, Isobel Hook, and Saul Perlmutter for other observational assistance. We are grateful to Peter Höflich, Alexei Khokhlov, and Eddie Baron for comments on Section 4.3. The supernova research of A.V.F.'s group at U. C. Berkeley is supported by NSF grant AST-0908886 and by the TABASGO Foundation, as well as by NASA through grants AR-11248 and AR-12126 from the Space Telescope Science Institute, which is operated by Associated Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. KAIT and its ongoing operation were made possible by donations from Sun Microsystems, Inc., the Hewlett-Packard Company, AutoScope Corporation, Lick Observatory, the NSF, the University of California, the Sylvia & Jim Katzman Foundation, and the TABASGO Foundation. J.M.S. is grateful to Marc J. Staley for a Graduate Fellowship. K.K., L.W., and N.B.S. are supported in part by NSF grant AST-0709181. Supernova research at Harvard is supported by NSF grant AST-0907903. This work was also supported by the Director, Office of Science, Office of High Energy Physics, of the U.S. Department of Energy under Contract No.DE-AC02-05CH11231.

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