Estimating the First-Light Time of the Type Ia Supernova 2014J in M82

The Type Ia supernova (SN Ia) 2014J in M82 (d~3.5 Mpc) was serendipitously discovered by S. Fossey's group on 2014 Jan. 21 UT and has been confirmed to be the nearest known SN Ia since at least SN 1986G. Although SN 2014J was not discovered until ~7 days after first light, both the Katzman Automatic Imaging Telescope at Lick Observatory and K. Itagaki obtained several prediscovery observations of SN 2014J. With these data, we are able to constrain the object's time of first light to be Jan. 14.75 UT, only 0.82+/-0.21 d before our first detection. Interestingly, we find that the light curve is well described by a varying power law, much like SN 2013dy, which makes SN 2014J the second example of a changing power law in early-time SN Ia light curves. A low-resolution spectrum taken on Jan. 23.388 UT, ~8.70 after first light, shows that SN 2014J is a heavily reddened but otherwise spectroscopically normal SN Ia.
Comment: Accepted for publication in ApJ Letters