SN 2007ax : an extremely faint type Ia supernova

Creators: Kasliwal, M. M.; Ofek, E. O.; Gal-Yam, A.; Rau, A.; Brown, P. J.; Cenko, S. B.; Cameron, P. B.; Quimby, R.; Kulkarni, S. R.; Bildsten, L.; Milne, P.; Bryngelson, G.

Abstract

We present multiband photometric and optical spectroscopic observations of SN 2007ax, the faintest and reddest Type Ia supernova (SN Ia) yet observed. With M_B = − 15.9 and (B − V)_(max) = 1.2, this SN is over half a magnitude fainter at maximum light than any other SN Ia. Similar to subluminous SN 2005ke, SN 2007ax also appears to show excess in UV emission at late time. Traditionally, Δ m_(15)(B) has been used to parameterize the decline rate for SNe Ia. However, the B-band transition from fast to slow decline occurs sooner than 15 days for faint SNe Ia. Therefore we suggest that a more physically motivated parameter, the time of intersection of the two slopes, be used instead. Only by explaining the faintest (and the brightest) supernovae can we thoroughly understand the physics of thermonuclear explosions. We suggest that future surveys should carefully design their cadence, depth, pointings, and follow-up to find an unbiased sample of extremely faint members of this subclass of faint SNe Ia.

Additional Information

© 2008 The American Astronomical Society. Received 2008 January 16; accepted 2008 July 3; published 2008 July 23. We thank Nick Scoville, Milan Bogoslavejic, and the Swift team for performing our Target of Opportunity observations flawlessly. We would like to thank Brent Tully for providing his catalog of nearby galaxies. L. B. acknowledges NSF grants PHY 05-51164 and AST 07-07633. Some of the data presented herein 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.

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