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

On 2012 May 17.2 UT, only 1.5 +/- 0.2 d after explosion, we discovered SN\n2012cg, a Type Ia supernova (SN Ia) in NGC 4424 (d ~ 15 Mpc). As a result of\nthe newly modified strategy employed by the Lick Observatory SN Search, a\nsequence of filtered images was obtained starting 161 s after discovery.\nUtilizing recent models describing the interaction of SN ejecta with a\ncompanion star, we rule out a ~1 M_Sun companion for half of all viewing angles\nand a red-giant companion for nearly all orientations. SN 2012cg reached a\nB-band maximum of 12.09 +/- 0.02 mag on 2012 June 2.0 and took ~17.3 d from\nexplosion to reach this, typical for SNe Ia. Our pre-maximum brightness\nphotometry shows a narrower-than-average B-band light curve for SN 2012cg,\nthough slightly overluminous at maximum brightness and with normal color\nevolution (including some of the earliest SN Ia filtered photometry ever\nobtained). Spectral fits to SN 2012cg reveal ions typically found in SNe Ia at\nearly times, with expansion velocities >14,000 km/s at 2.5 d past explosion.\nAbsorption from C II is detected early, as well as high-velocity components of\nboth Si II 6355 Ang. and Ca II. Our last spectrum (13.5 d past explosion)\nresembles that of the somewhat peculiar SN Ia 1999aa. This suggests that SN\n2012cg will have a slower-than-average declining light curve, which may be\nsurprising given the faster-than-average rising light curve.\n