We present the early UV and optical light curve of Type IIP supernova ( SN ) 2010aq at z = 0.0862 , and compare it to analytical models for thermal emission following SN shock breakout in a red supergiant star .
SN 2010aq was discovered in joint monitoring between the Galaxy Evolution Explorer ( GALEX ) Time Domain Survey ( TDS ) in the NUV and the Pan-STARRS1 Medium Deep Survey ( PS1 MDS ) in the g , r , i , and z bands .
The GALEX and Pan-STARRS1 observations detect the SN less than 1 day after shock breakout , measure a diluted blackbody temperature of 31 , 000 \pm 6 , 000 K 1 day later , and follow the rise in the UV/optical light curve over the next 2 days caused by the expansion and cooling of the SN ejecta .
The high signal-to-noise ratio of the simultaneous UV and optical photometry allows us to fit for a progenitor star radius of 700 \pm 200 R _ { \odot } , the size of a red supergiant star .
An excess in UV emission two weeks after shock breakout compared to SNe well fitted by model atmosphere-code synthetic spectra with solar metallicity , is best explained by suppressed line blanketing due to a lower metallicity progenitor star in SN 2010aq .
Continued monitoring of PS1 MDS fields by the GALEX TDS will increase the sample of early UV detections of Type II SNe by an order of magnitude , and probe the diversity of SN progenitor star properties .