Re-brightening of SN2009ip in the UV

ATel #4425; R. Margutti, A. Soderberg, R. Chornock, R. Foley (Harvard University)
on 26 Sep 2012; 13:56 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Raffaella Margutti (rmargutti@cfa.harvard.edu)

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SN2009ip has been recently suggested to have transitioned from LBV-like eruption episodes to a real type-IIn supernova explosion (Smith, Atel#4412). We performed a Swift/UVOT follow-up observation on Sept 22, and found no clear evidence for a re-brightening (Margutti et al., Atel #4414), in agreement with the results reported by Martin et al., (Atel #4416). Further observations were planned and executed starting from 2012-09-26T05:32:41 UT. We obtained Swift-UVOT observations in the 6 optical/UV filters. SN2009ip is well detected in all the 6 filters with preliminary magnitudes (UVOT photometric system Breeveld et al. 2011, arXiv:1102.4717): v= 14.90 +/- 0.04; b= 14.78 +/- 0.04; u=13.43 +\- 0.04; w1= 13.00 +/- 0.05; m2= 12.82 +\- 0.06; w2= 12.85 +\- 0.07 . The magnitudes listed include possible contamination from the underlying host galaxy and are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.03 in the direction of the transient (Schlegel et al. 1998). These observations indicated that SN2009ip has re-brightened by ~3 mag in ~3.5 days (v-band), in agreement with the findings by Brimacombe in the I-band (Atel # 4423). The re-brightening is even more extreme in the UV, with the w1 flux increasing by ~6 mag in ~3.5 days. This corresponds to a drastic change in the optical to UV colors (w1-v= 1.1 on Sept 22nd; w1-v=-1.9 on Sept. 26th). Contemporaneous Swift-XRT observations revealed no source at the optical position of the transient, with a 3 sigma upper limit of 3.5d-3 cps in the 0.3-10 keV energy band (total exposure of 4.3 ks). The Galactic neutral hydrogen column density in the direction of the event is 1.2d20 /cm2 (Kalberla 2005). Assuming a spectral photon index ~2, this translates into an absorbed flux of ~2d-13 erg/s/cm2 (corresponding to a luminosity of ~1d40 erg/s. A luminosity distance of 24 Mpc has been used). We thank the Swift team for scheduling these ToO observations.