Optical and Near‐Infrared Observations of the Highly Reddened, Rapidly Expanding Type Ia Supernova SN 2006X in M100

Abstract

We present extensive optical (U BV RI), near-infrared (JK) light curves and optical spectroscopy of the Type Ia supernova (SN) 2006X in the nearby galaxy NGC 4321 (M100). Our observations suggest that either SN 2006X has an intrinsically peculiar color evolution, or it is highly reddened [E(B − V ) host = 1.42 ± 0.04 mag] with R V = 1.48 ± 0.06, much lower than the canonical value of 3.1 for the average Galactic dust. SN 2006X also has one of the highest expansion velocities ever published for a SN Ia. Compared with the other SNe Ia we analyzed, SN 2006X has a broader light curve in the U band, a more prominent bump/shoulder feature in the V and R bands, a more pronounced secondary maximum in the I and near-infrared bands, and a remarkably smaller late-time decline rate in the B band. The B − V color evolution shows an obvious deviation from the Lira-Phillips relation at 1 to 3 months after maximum brightness. At early times, optical spectra of SN 2006X displayed strong, high-velocity features of both intermediate-mass elements (Si, Ca, and S) and iron-peak elements, while at late times they showed a relatively blue continuum, consistent with the blue U − B and B − V colors at similar epochs. A light echo and/or the interaction of the SN ejecta and its circumstellar material may provide a plausible explanation for its late-time photometric and spectroscopic behavior. Using the Cepheid distance of M100, we derive a Hubble constant of 72.8 ± 8.2 km s −1 Mpc −1 (statistical) from the normalized dereddened luminosity of SN 2006X. We briefly discuss whether abnormal dust is a universal signature for all SNe Ia, and whether the most rapidly expanding objects form a subclass with distinct photometric and spectroscopic properties.

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

“…This limit is R V -dependent and we note that several studies (e.g. Wang et al 2008;Folatelli et al 2010) revealed that R V values for SNe Ia may differ from that of normal interstellar dust, pointing to R V as low as 1.5. We find E(B − V) tot ≤ 0.8 ± 0.2 mag and 1.3 ± 0.3 mag for R V = 3.1 and 1.5 respectively.…”

A reddening-free method to estimate the56Ni mass of Type Ia supernovae

“…They determined a bolometric peak luminosity for SN 2006X of (1.02 ± 0.1) × 10 43 erg s −1 , which compares well with our measurement of (1.14 ± 0.16) × 10 43 erg s −1 . Wang et al (2008) determined M56 Ni = 0.50 ± 0.05 M , which should be compared to M56 Ni = 0.57 ± 0.11 M found from t 2 using the fixed rise time formalism. The measured rise time for SN 2006X is t R (B) = 18.2 ± 0.9 d, which leads to M56 Ni = 0.55 ± 0.10 M .…”

“…Wang et al (2008) have derived a peak luminosity for this SN from multi-band photometry and a correction for dust absorption in the host galaxy. They determined a bolometric peak luminosity for SN 2006X of (1.02 ± 0.1) × 10 43 erg s −1 , which compares well with our measurement of (1.14 ± 0.16) × 10 43 erg s −1 .…”

Extensive HST ultraviolet spectra and multiwavelength observations of SN 2014J in M82 indicate reddening and circumstellar scattering by typical dust

“…It is now understood that at least part of the reason for the low values of RV from large samples is because of poor assumptions about the intrinsic colour distribution of SNe Ia (e.g., Foley & Kasen 2011;Mandel et al 2011); correcting for this effect can increase the best-fitting RV from 1.6 to 2.5 for a large sample of SNe Ia (Foley & Kasen 2011). However, there are several examples of highly reddened SNe Ia, where RV can be measured directly, that still have RV < 2 (e.g., Elias-Rosa et al 2006Krisciunas et al 2006;Wang et al 2008).…”