Cepheid Calibration of the Peak Brightness of Type Ia Supernovae. X. SN 1991T in NGC 4527

Abstract

Repeated imaging observations have been made of NGC 4527 with the Hubble Space Telescope between April and June 1999, over an interval of 69 days. Images were obtained on 12 epochs in the F 555W band and on five epochs in the F 814W band. The galaxy hosted the type Ia supernova SN1991T, which showed relatively unusual behavior by having both an abnormal spectrum near light maximum, and a slower declining light curve than the proto-typical Branch normal SNe Ia.A total of 86 variables that are putative Cepheids have been found, with periods ranging from 7.4 days to over 70 days. From photometry with the DoPHOT program, the de-reddened distance modulus is determined to be (m − M ) 0 = 30.67 ± 0.12 (internal uncertainty) using a subset of the Cepheid data whose reddening and -2error parameters are secure. A parallel analysis of the Cepheids using photometry with ROMAFOT yields (m − M ) 0 = 30.82 ± 0.11. The final adopted modulus is (m − M ) 0 = 30.74 ± 0.12 ± 0.12 (d = 14.1 ± 0.8 ± 0.8 Mpc).The photometric data for SN1991T are used in combination with the Cepheid distance to NGC 4527 to obtain the absolute magnitude for this supernova of M 0 V (max) = −19.85 ± 0.29. The relatively large uncertainty is a result of the range in estimates of the reddening to the supernova. Thus SN1991T is seen to be only moderately brighter (by ∼ 0.3 mag) than the mean for spectroscopically normal supernovae, although magnitude differences of up to 0.6 mag cannot be ruled out.

The Extremes of Thermonuclear Supernovae

“…A better understanding of the extinction correction in SNe Ia based on their colours (Lira, 1996;Phillips et al, 1999), new Cepheid-based distance estimates for the host galaxy (Saha et al, 2001;Altavilla et al, 2004) and sophisticated modelling of the SN light curves and spectra (Jeffery et al, 1992;Mazzali et al, 1995;Sasdelli et al, 2014) have led to some convergence in the numbers, so that nowadays peak absolute magnitudes ∼ 0.4-0.5 mag above average SNe Ia and 56 Ni masses around 0.8 M are favoured (Sasdelli et al, 2014). This makes SN 1991T at best slightly overluminous with respect to the Phillips relation (Phillips, 1993;Phillips et al, 1999), but consistent within the uncertainties, as can be seen from Fig.…”

Supernova 2008J: early time observations of a heavily reddened SN 2002ic-like transient

“…According to Theureau et al (1998) A&A 545, L7 (2012) (Hamuy et al 2003) and 2005gj (Aldering et al 2006;Prieto et al 2007) are also plotted, assuming distance moduli of 37.32 mag and 37.09 mag respectively. Template optical light curves of SN 1991T (Nugent et al 2002) are plotted and scaled to match the absolute uBVri peak magnitudes of SN 1991T presented by Prieto et al (2007) and Saha et al (2001). Synthetic magnitudes from the spectral decompostion of SN 2008J (see also Fig.…”

Nearby Supernova Factory Observations of SN 2005gj: Another Type Ia Supernova in a Massive Circumstellar Envelope

“…We measure EW( D1) ¼ 0:41 8 and EW( D2) ¼ 0:30 8; the total of 0.7 8 is slightly higher than that measured on December 2, probably due to resolution effects. (Saha et al 2001). In V band, the SN 2005gj points are synthesized photometry from SNIFS observations, as well as values interpolated or extrapolated using NEAT and QUEST data in other bands.…”