* Astronomy

Title: GALEX and Pan-STARRS1 Discovery of SN IIP 2010aq: The First Days After Shock Breakout in a Red Supergiant Star
Authors: S. Gezari, A. Rest, M. E. Huber, G. Narayan, K. Forster, J. D. Neill, D. C. Martin, S. Valenti, S. J. Smartt, R. Chornock, E. Berger, A. M. Soderberg, S. Mattila, E. Kankare, W. S. Burgett, K. C. Chambers, T. Dombeck, T. Grav, J. N. Heasley, K. W. Hodapp, R. Jedicke, N. Kaiser, R. Kudritzki, G. Luppino, R. H. Lupton, E. A. Magnier, D. G. Monet, J. S. Morgan, P. M. Onaka, P. A. Price, P. H. Rhoads, W. A. Siegmund, C. W. Stubbs, J. L. Tonry, R. J. Wainscoat, M. F. Waterson, C. G. Wynn-Williams

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 supernova shock breakout in a red supergiant star. SN 2010aq was discovered in joint monitoring between the GALEX Time Domain Survey in the NUV and the Pan-STARRS1 Medium Deep Survey 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 ±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 ±200 R_sun, 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 Pan-STARRS1 Medium Deep Survey fields by the GALEX Time Domain Survey 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.

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