On the observational behaviour of the highly polarized Type IIn supernova SN 2017hcc

Abstract

We present the results based on photometric (Swift UVOT), broad-band polarimetric (V and Rbands) and optical spectroscopic observations of the Type IIn supernova (SN) 2017hcc. Our study is supplemented with spectropolarimetric data available in literature for this event. The post-peak light-curve evolution is slow (∼0.2 mag 100 d−1 in b band). The spectrum of ∼+27 d shows a blue continuum with narrow emission lines, typical of a Type IIn SN. Archival polarization data along with the Gaia DR2 distances have been utilized to evaluate the interstellar polarization (ISP) towards the SN direction which is found to be PISP = 0.17 ± 0.02 per cent and θISP = 140° ± 3°. To extract the intrinsic polarization of SN 2017hcc, both the observed and the literature polarization measurements were corrected for ISP. We noticed a significant decline of ∼3.5 per cent (V band) in the intrinsic level of polarization spanning a period of ∼2 months. In contrast, the intrinsic polarization angles remain nearly constant at all epochs. Our study indicates a substantial variation in the degree of asymmetry in either the ejecta and/or the surrounding medium of SN 2017hcc. We also estimate a mass-loss rate of M˙ = 0.12 M⊙ yr−1 (for vw = 20 km s−1) which suggests that the progenitor of SN 2017hcc is most likely a luminous blue variable.