Riess, Adam G.Filippenko, Alexei V.Li, WeidongTreffers, Richard R.Schmidt, Brian P.Qiu, YuleiHu, JingyaoArmstrong, MarkFaranda, ChuckThouvenot, EricBuil, Christian2018-10-032018-10-030004-6256http://hdl.handle.net/1885/148058We present calibrated photometric measurements of the earliest detections of nearby type Ia supernovae (SNe Ia). The set of ~30 new, unfiltered CCD observations delineate the early rise behavior of SNe Ia > 18 to 10 days before maximum. Using simple empirical models, we demonstrate the strong correlation between the risetime (i.e., the time between explosion and maximum), the post-rise light-curve shape, and the peak luminosity. Using a variety of light-curve shape methods, we find the risetime to B maximum for a SN Ia with Delta m15(B)=1.1 mag and peak M_V=-19.45 mag to be 19.5+/-0.2 days. We find that the peak brightness of SNe Ia is correlated with their risetime; SNe Ia which are 0.10 mag brighter at peak in the B-band require 0.80+/-0.05 days longer to reach maximum light. We determine the effects of several possible sources of systematic errors, but none of these significantly impacts the inferred risetime. Constraints on SN Ia progenitor systems and explosion models are derived from a comparison between the observed and theoretical predictions of the risetime.The work at the University of California, Berkeley, was supported by the Miller Institute for Basic Research in Science, by NSF grant AST 94-17213, and by grant GO-7505 from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.14 pagesapplication/pdf© 1999. The American Astronomical Society. http://www.sherpa.ac.uk/romeo/issn/0004-6256/ Author can archive publisher's version/PDF. Publisher's version/PDF may be used on any website or authors' institutional repository (Sherpa/Romeo as of 3/10/2018).cosmologyobservationssupernovae1999-1210.1086/301143