Not Color‐Blind: Using Multiband Photometry to Classify Supernovae

Abstract

ABSTRACT. Large numbers of supernovae (SNe) have been discovered in recent years, and many more will be found in the near future. Once discovered, further study of a SN and its possible use as an astronomical tool (e.g., as a distance estimator) require knowledge of the SN type. Current classification methods rely almost solely on the analysis of SN spectra to determine their type. However, spectroscopy may not be possible or practical when SNe are faint, numerous, or discovered in archival studies. We present a classification method for SNe based on the comparison of their observed colors with synthetic ones, calculated from a large database of multiepoch optical spectra of nearby events. We discuss the capabilities and limitations of this method. For example, Type Ia SNe at redshifts can be distinguished from most other SN types during the first few z ! 0.1 weeks of their evolution, based on VϪR versus RϪI colors. Type II-P SNe have distinct (very red) colors at late ( days) stages. Broadband photometry through standard Johnson-Cousins UBVRI filters can be useful to t 1 100 classify SNe out to . The use of Sloan Digital Sky Survey (SDSS) ugriz filters allows the extension of z ≈ 0.6 our classification method to even higher redshifts ( ), and the use of infrared bands, to . We z p 0.75 z p 2.5 demonstrate the application of this method to a recently discovered SN from the SDSS. Finally, we outline the observational data required to further improve the sensitivity of the method and discuss prospects for its use on future SN samples. Community access to the tools developed is provided by a dedicated Web site. 5

First Results From the Catalina Real-Time Transient Survey

“…Both the DNe system and their outbursts are usually very blue while SNe pass through a range of colors as they age (depending on their type and host galaxy extinction). DNe can also be distinguished from SNe using accurate measurement of source color over time (Poznanski et al 2002). Most CV systems can also be distinguished from variable stars on the giant branch and main-sequence stars in multiband photometry.…”

“…In contrast, the transients we discovered became many magnitudes brighter than their hosts over a period of 2 weeks and were visible for more than a month, consistent with SNe. We carried out photometric follow-up of a number of these candidates and found that their colours and decline rates were indeed consistent with SNe, rather than AGN, CVs, or other variables stars (Poznanski et al 2002). The most likely sources of such transients are SNe in very faint host galaxies or associated with intracluster stars.…”

The Detailed Optical Light Curve of GRB 030329

“…All four models are modifications of the light curve of SN 1998bw, corrected to the redshift of SN 2003dh (z ¼ 0:1685). The transformation was carried out by applying synthetic photometry (using the methods presented in Poznanski et al 2002) to the large collection of SN 1998bw spectra reported by Patat et al (2001) and taking into account the greater luminosity distance of SN 2003dh (810 Mpc, compared with 37 Mpc for SN 1998bw), cosmological redshift, and time dilation effects, as well as the shift in the SN spectrum sampled by each filter (K-corrections). The SN light curve was also corrected for Galactic extinction in the direction of SN 2003dh (E BÀV ¼ 0:025 mag; Schlegel, Finkbeiner, & Davis 1998) but was not corrected for the host galaxy extinction (see below).…”

Dark energy constraints from a space-based supernova survey

“…For example, the rest frame U-band amplitude can be predicted to better than ∼0.04 from B-and V-bands (Astier et al 2006). SNe Ia not only occupy narrow subspaces of multicolour spaces, but also exhibit very reproducible light curve shapes that permit to discriminate against most of the corecollapse events (Poznanski et al 2002;Johnson & Crotts 2006;Rodney & Tonry 2009). Studies of the photometric selection of SNe Ia have been conducted on the SNLS data and their preliminary conclusions are encouraging (Ripoche 2007;Bazin 2008).…”