Swift XRT and UVOT detection of SN2013ej

ATel #5243; R. Margutti, S. Chakraborti (Harvard University), P. J. Brown (Mitchell Institute, Texas A&M), K. Sokolovsky (ASC Lebedev/SAI MSU)
on 1 Aug 2013; 19:53 UT
Credential Certification: Sayan Chakraborti (schakraborti@fas.harvard.edu)

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SN2013ej (PSN J01364816+1545310, CBET #3606) is a young and nearby type IIP supernova (Atel #5228, #5229, #5230, #5237) that exploded in M74 at a distance of ~9 Mpc (from NED). We obtained Swift (Gehrels et al., 2004 ApJ, 611, 1005) X-ray Telescope (XRT, Burrows et al., 2005 SSRv, 120, 165) observations starting from 2013 July 30 until 2013 July 31, for a total exposure of 15 ks. The X-ray counterpart of SN2013ej is 45" away from an ULX source M74 X-1 which is clearly visible at XRT images and 15" from an X-ray source J013649.2+154527 observed by Chandra (Colbert et al. 2004 ApJ, 602, 231). An X-ray source is detected at a position consistent with SN2013ej, with significance of 5.2 sigma. We measure a 0.3-10 keV count-rate of (2.7 +/- 0.5)d-3 cps. The Galactic absorption in the direction of SN2013ej is 4.6e20 cm-2 (Roming et al. 2005 SSRv, 120, 95). Assuming a simple power-law spectral model with photon index Gamma=2 the measured count-rate translates into an unabsorbed flux of ~1.1d-13 erg/s/cm2 (0.3-10 keV), corresponding to a luminosity L~1.1d39 erg/s. All the reported errors are only statistical. Simultaneous observations were also obtained with the UltraViolet/Optical Telescope (UVOT; Roming et al. 2005). Preliminary analysis shows the brightness in the uvm2 filter [166-268nm] fades from 12.00+/- 0.03 at MJD 56504.0 to 12.23 +/- 0.03 at MJD 56505.0. These magnitudes are on the UVOT Vega photometric system (Breeveld et al. 2011 AIPC, 1358, 373) and have not been corrected for extinction. The other UVOT filters are near or above their saturation limit and this could affect the measurements. Further observations at all wavelengths are encouraged. We thank the Swift team for scheduling these ToO observations.