SN2007ax : An Extremely Faint Type Ia Supernova

TL;DR

This paper reports detailed observations of SN2007ax, the faintest Type Ia supernova observed, highlighting its unique properties and proposing new methods to analyze such faint supernovae for better understanding of thermonuclear explosion physics.

Contribution

It introduces detailed photometric and spectroscopic data of the faintest SNIa and proposes a new parameter for decline rate analysis tailored for faint supernovae.

Findings

SN2007ax is the faintest and reddest SNIa observed.

Faint SNeIa show earlier transition from fast to slow decline.

A new decline rate parameter based on slope intersection is suggested.

Abstract

We present multi-band photometric and optical spectroscopic observations of SN2007ax, the faintest and reddest Type Ia supernova (SNIa) 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 SNIa. Similar to subluminous SN2005ke, SN2007ax also appears to show excess in UV emission at late time. Traditionally, Delta-m_15(B) has been used to parameterize the decline rate for SNeIa. However, the B-band transition from fast to slow decline occurs sooner than 15 days for faint SNeIa. 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, we can 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 SNeIa.