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Continued Swift monitoring campaign of SN2011fe

ATel #3642; R. Margutti, A. Soderberg (Harvard University)
on 9 Sep 2011; 20:24 UT
Credential Certification: Raffaella Margutti (rmargutti@cfa.harvard.edu)

Subjects: Ultra-Violet, X-ray, Supernovae

Swift has continued to monitor the evolution of the type Ia SN2011fe since its discovery (Atel #3581) providing the best sampled UV light-curve of a type Ia SN at very early times, ever. Compared to the first epoch of Swift-UVOT observations (Atel #3590) the SN has brightened of ~4.5 mag, ~5 mag and ~6 mag in the uvm2, uvw2 and uvw1 filter, respectively. Assuming August 23rd to be the date of the SN explosion, SN2011fe reached an observed peak magnitude of ~10.9 in the uvw1 band at day 16th. This corresponds to an absolute magnitude M(uvw1)~ -17.8 at a distance of 6.4 Mpc (Shappee & Stanek 2011). A comparison to the average evolution of type Ia supernovae in the uvw1-band as computed by Milne 2010, ApJ, 721, 1627 reveals a good agreement between SN2011fe and the expected behavior of normal type Ia events. A plot can be retrieved from: https://www.cfa.harvard.edu/~rmargutt/ We note that at earlier times (t<6 days) there is a suggestion for a slower rise best seen in the uvm2 and uvw2 filters. No correction for the Galactic extinction in the direction of the SN (E(B-V)=0.009 mag) has been performed; the contribution of the host galaxy has not been subtracted. Both effects are expected to give a negligible contribution around the peak. Using 60.5 ks of Swift-XRT data acquired in PC mode we detect no X-ray source at the optical position with a 3 sigma upper limit on the 0.3-10 keV count-rate of ~1d-3 c/s. Assuming a simple power-law spectrum with spectral photon index Gamma=2 this translates into an absorbed flux limit of ~5d-14 erg/s/cm2 and a luminosity of 2.5d38 erg/s. The Galactic neutral hydrogen column in the direction of the SN is 1.8d20 1/cm2 (Kalberla 2005). This is consistent with our earlier estimates (Atel #3584) and with the deep Chandra limit from Atel #3602. We are grateful to the entire Swift team for making this observations possible. Further observations are ongoing.