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Swift observation of OGLE17jei = SN 2017jei

ATel #11143; K. Sokolovsky (IAASARS NOA/ASC Lebedev/SAI MSU), M. Gromadzki, L. Wyrzykowski (Warsaw Observatory), A. Udalski, I. Soszynski, K. Ulaczyk, J. Skowron (Warsaw Observatory, on behalf of the OGLE team), R. Roy (IUCAA)
on 9 Jan 2018; 17:05 UT
Credential Certification: Kirill Sokolovsky (kirx@scan.sai.msu.ru)

Subjects: Optical, Ultra-Violet, X-ray, AGN, Black Hole, Supernovae, Transient, Tidal Disruption Event

The optical transient OGLE17jei = SN 2017jei was detected on 2017-11-15 in a face-on galaxy MRSS 054-118874. OGLE-IV deep stack image shows the host galaxy has an extended central feature (bulge or/and bar) and the position of the transient coincides with S-E part of this structure. It could not be ruled out that the transient is associated with the central black hole. The OGLE-IV photometry suggests the transient was slowly rising from below the detection limit around I=21.5 for the past 60 days (latest non-detection on 2017-11-11), about a week ago it suddenly increased its rate of brightening reaching a peak at I=17.1 on 2018-01-06. Spectroscopic observations with the NTT (ePESSTO, ATel #11114) were inconclusive suggesting this may be a Type IIn SN, TDE or an AGN flare at z=0.058.

Swift observed OGLE17jei for 1.0ks on 2018-01-07. Swift/XRT detected no X-ray source at the position of the transient with an upper limit of 0.005 +/-0.002 cts/s. Assuming power law emission with the photon index of 2 and HI column density of 4.16x10^20 cm^-2 this translates to the unabsorbed 0.3-10 keV flux limit of 2x10^-13 ergs/cm^2/s.

An ultraviolet source is detected at the position of the transient with the following UVOT magnitudes (Vega system):

 Band   Mag.  Err. 
 UVW2  16.78  0.06 
 UVM2  16.55  0.09 
 UVW1  16.49  0.07 
   U   16.52  0.07 
   B   17.57  0.09 
   V   17.39  0.14 

We also use the UVOT images to measure the position of OGLE17jei: 03:14:11.94 -71:12:25.5 +/-0.1" J2000 which is 1.1" from the reported position of the host galaxy. Taking into account the Galactic reddening of E(B-V)=0.033 (Schlafly et al. 2011 ApJ, 737, 103) the ultraviolet magnitudes correspond to the color temperature of about 14000 K, consistent with OGLE17jei being a peculiar Type IIn supernova.

We thank the Swift team for rapid execution of this observation. We acknowledge the OGLE-IV Transient Detection System presented in ATel #4495; Kozlowski et al. 2013, AcA, 63, 1, 1; Wyrzykowski et al. 2014, AcA, 64, 197

OGLE17jei = SN 2017jei at the Transient Name Server