Swift UVOT and XRT observations of SN2014J in M82

ATel #5809; P. J. Brown (Texas A&M, Mitchell Institute) and P. A. Evans (U. Leicester) report on behalf of the Swift team:
on 24 Jan 2014; 20:10 UT
Credential Certification: Peter J. Brown (grbpeter@yahoo.com)

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The Swift satellite started observing supernova (SN) 2014J in M82 (ATEL#5786, CBET#3792) at 2014-01-22.43 UT. From the Ultraviolet/Optical Telescope (UVOT) observations during that first epoch the following magnitudes were measured: uvw1 = 15.8 +/- 0.1 (315 s), uvm2 = >20.1 (757 s), uvw2 = 17.1 +/- 0.1 (630 s). A later observation beginning 2014-01-24.36 shows a brightening to uvw1 = 15.2 +/- 0.1 (236 s), uvm2 = 19.9 +/- 0.3 (1515 s), uvw2 = 16.5 +/- 0.1 (393 s). These magnitudes are on the updated UVOT Vega photometric system (Breeveld et al. 2011, in AIP Conf. Ser. 1358, p. 373). The photometry has not been corrected for extinction but the underlying galaxy count rates have been subtracted. We note that due to the high reddening (ATEL#5786, ATEL#5797), the effective wavelengths shift compared to their nominal values, and the extinction in a given filter (e.g. A_uvw2) does not scale linearly with the optical depth or color excess (see Figure 4 in Brown et al. 2010, ApJ, 721, 1608). The conversion from observed magnitudes or counts to flux is also highly dependent on the spectral shape.

No X-ray source is found at the position of SN2014J in simultaneous observations with Swift's X-Ray Telescope (XRT). From 17.5 ks of exposure time we derive an upper limit (3 sigma) of 2.1x10^-3 counts/s. Assuming a kt_bb=0.1 keV spectrum and NH=1x10^22/cm^2 (as in ATEL#5798), this corresponds to an upper limit on the 0.3-10 keV flux of 4.2x10^-14 erg/cm^2/s. Prior to the SN, Swift has observed the field in 91 observations, totaling 191 ks of data in PC mode. Combining all of these data, we determine an upper limit of 1.3x10^-4 counts/s, corresponding to a flux of 2.6x10^-15 erg/cm^2/s using the same model as above.

Swift/UVOT light curve of SN2014J