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Swift observations of SN2011ei (PSN J20342262-3158236)

ATel #3528; R. Margutti (Harvard Univ.), P. Brown (U. of Utah), A. M. Soderberg (Harvard Univ.) P. Roming (SwRI)
on 3 Aug 2011; 15:54 UT
Credential Certification: Raffaella Margutti (rmargutti@cfa.harvard.edu)

Subjects: Optical, Ultra-Violet, X-ray, Supernovae

The spectral properties of 2011ei (PSN J20342262-3158236) have been recently demonstrated to show a good match to the energetic type-IIb 'hypernova' 2003bg approximately 7 days before maximum light (Milisavljevic, ATel #3526). A Swift-ToO was executed to observe the field of 2011ei starting from 2011-08-03T04:47:14 UT. No X-ray source is detected at the optical position of the transient (RA=20:34:22.62 dec=-31:58:23.6) with a 3 sigma upper limit of 4.6d-3 c/s in the 0.3-10 keV energy band (total exposure= 9.6 ks). The Galactic neutral hydrogen column density in the direction of the event is 4.76d20 1/cm2 (Kalberla et al., 2005). Assuming a spectral photon index ~2, this translates into an absorbed flux of ~2.3d-13 erg/s/cm2. This implies that 2011ei is intrinsically fainter than the recently detected type IIb SN2011dh at comparable epoch (Soderberg et al., ArXiv:1107.1876 ). Contemporary Swift-UVOT observations have been obtained in the 6 optical/UV filters. A source is clearly detected at the transient position in the U, B and V band. Including possible contamination from the host galaxy, we measure the following preliminary magnitudes (UVOT photometric system Breeveld et al. 2011, arXiv:1102.4717): filter MJD Mag err U 5776.81 16.66 0.10 B 5776.81 17.54 0.10 V 5776.82 17.27 0.10 The source is seen faintly in the uvw1 filter but not clearly in the uvm2 or uvw2 filters. Reliable magnitudes/limits in the UV would require subtraction of the underlying galaxy. The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) =0.059 in the direction of the transient. (Schlegel et al. 1998). We thank the Swift team for scheduling these ToO observations.