THE VERY YOUNG TYPE Ia SUPERNOVA 2012cg: DISCOVERY AND EARLY-TIME FOLLOW-UP OBSERVATIONS

Abstract

On 2012 May 17.2 UT, only 1.5 ± 0.2 d after explosion, we discovered SN 2012cg, a Type Ia supernova (SN Ia) in NGC 4424 (d ≈ 15 Mpc). As a result of the newly modified strategy employed by the Lick Observatory SN Search, a sequence of filtered images was obtained starting 161 s after discovery. Utilizing recent models describing the interaction of SN ejecta with a companion star, we rule out a ∼1 M companion for half of all viewing angles and a red-giant companion for nearly all orientations. SN 2012cg reached a B-band maximum of 12.09 ± 0.02 mag on 2012 June 2.0 and took ∼17.3 d from explosion to reach this, typical for SNe Ia. Our pre-maximum-brightness photometry shows a narrower-than-average B-band light curve for SN 2012cg, though slightly overluminous at maximum brightness and with normal color evolution (including -2some of the earliest SN Ia filtered photometry ever obtained). Spectral fits to SN 2012cg reveal ions typically found in SNe Ia at early times, with expansion velocities 14,000 km s −1 at 2.5 d past explosion. Absorption from C II is detected early, as well as high-velocity components of both Si II λ6355 and Ca II. Our last spectrum (13.5 d past explosion) resembles that of the somewhat peculiar SN Ia 1999aa. This suggests that SN 2012cg will have a slower-than-average declining light curve, which may be surprising given the faster-than-average rising light curve.

LATE-TIME PHOTOMETRY OF TYPE IA SUPERNOVA SN 2012cg REVEALS THE RADIOACTIVE DECAY OF 57Co

“…The Galactic line-of-sight extinction toward SN 2012cg in F350LP, F555W, F814W, and F160W is 0.054, 0.059, 0.032, and 0.011 mag, respectively (Schlafly & Finkbeiner 2011). By using the Cardelli et al (1989) Silverman et al 2012;Marion et al 2015), and assuming R V =3.1, we calculate host-galaxy extinctions of 0.515, 0.582, 0.333, and 0.114 mag in the same filters.…”

“…For more information on SN 2011fe, see, e.g., Li et al 2011;Chomiuk 2013;Kasen & Nugent 2013;Graur et al 2014a), it has a slightly broader light curve. Specifically, by fitting early-time data, Silverman et al (2012) Here, we adopt the value of peak B-band light derived by Munari et al (2013), so that all phases are reported relative to 2012 June 4.5.…”

Constraining the progenitor of the Type Ia Supernova SN 2012cg

“…It was discovered on 2012 May 17 (UT) in the nearby spiral galaxy NGC 4424 (15.2 ± 1.9 Mpc, Cortés, Kenney & Hardy 2006) by the Lick Observatory Supernova Search (Filippenko et al 2001). By fitting early-time data of SN 2012cg, Silverman et al (2012) obtained that it reached the maximum B-band brightness on 2012 June 2.0 ± 0.75, and the peak magnitude in the B-band was m B = 12.09 ± 0.02 mag, which corresponds to an absolute magnitude of M B = −19.73 ± 0.30 mag. However, by measuring the rise and initial decline of the light curve of SN 2012cg in the B, V, R c , and I c filters, Munari et al (2013) found the B-band luminosity of SN 2012cg peaked on 2012 June 4.5 with an absolute magnitude of M B = −19.55 mag (after corrections for a reddening of E(B − V) = 0.18 mag).…”

Type Ia Supernovae Strongly Interacting with Their Circumstellar Medium

“…Extremely nearby SNe Ia which were discovered soon after explosion have recently led to tight constraints on the size and luminosity of the companion star, thus ruling out many plausible SD scenarios for these objects (e.g., Nugent et al 2011;Ganeshalingam et al 2011;Brown et al 2012;Foley et al 2012a;Bloom et al 2012;Silverman et al 2012b). In addition, the so-called super-Chandrasekhar mass SNe Ia are thought to contain >1.4 M of SN ejecta and thus are likely formed from the DD scenario (e.g., Howell et al 2006;Yamanaka et al 2009;Scalzo et al 2010;Silverman et al 2011;Taubenberger et al 2011).…”