The Young and Bright Type Ia Supernova ASASSN-14lp: Discovery, Early-Time Observations, First-Light Time, Distance to NGC 4666, and Progenitor Constraints

On 2014 Dec. 9.61, the All-Sky Automated Survey for SuperNovae (ASAS-SN or “Assassin”) discovered ASASSN-14lp just $\sim 2$ days after first light using a global array of 14-cm diameter telescopes. ASASSN-14lp went on to become a bright supernova ($V=11.94$ mag), second only to SN 2014J for the year. We present prediscovery photometry (with a detection less than a day after first light) and ultraviolet through near-infrared photometric and spectroscopic data covering the rise and fall of ASASSN-14lp for more than 100 days. We find that ASASSN-14lp had a broad light curve ($\mathrm{\Delta }{m}_{15}(B)=0.80\pm 0.05$), a $B$-band maximum at $2457015.82\pm 0.03$, a rise time of $16.94^{+ 0.11 }{- 0.10 }$days,andmoderatehost--galaxyextinction($E(B-V){$\text{host}$} = 0.33 \pm 0.06$)\mathrm{.}UsingASASSN-14lpwederiveadistancemodulusforNGC4666of$\mu = 30.8 \pm 0.2$correspondingtoadistanceof$14.7 \pm 1.5$ Mpc. However, adding ASASSN-14lp to the calibrating sample of Type Ia supernovae still requires an independent distance to the host galaxy. Finally, using our early-time photometric and spectroscopic observations, we rule out red giant secondaries and, assuming a favorable viewing angle and explosion time, any non-degenerate companion larger than $0.34R_{\text{sun}}$.