Classification of AT 2021sew as a Type-II Superluminous Supernova
ATel #14934; B. P. Thomas, J. C. Wheeler (UT Austin), J. Vinko (Konkoly)
on 23 Sep 2021; 22:49 UT
Credential Certification: Jozsef Vinko (vinko@astro.as.utexas.edu)
Subjects: Optical, Supernovae
AT2021sew (ZTF21abjaeco) was observed on the 26th August 2021 with the blue arm, and on 20th September 2021 with the red arm of the Low Resolution Spectrograph-2 (LRS2-B and LRS2-R), mounted on the Hobby-Eberly Telescope (HET) at McDonald Observatory, Texas. The spectra were integrated for 2700s and had an observed-frame wavelength coverage of 3700-7000 AA and 6500-10500 AA for LRS2-B and LRS2-R respectively.
We detect narrow- and intermediate-width components to the H-alpha and H-beta emission profiles that imply interaction with circumstellar hydrogen. The intermediate H-alpha and H-beta components appear red-shifted relative to the narrow components, with an implied velocity of ~1500 km/s. We also detect an emission profile in the blue that we identify as C III/N III (4640 AA) and He II (4686 AA), common to Type II SNe in the photospheric phase (Leonard et al. 2000). We determine a redshift from narrow host galaxy emission lines of z = 0.1524, which implies an uncorrected absolute peak magnitude M_r = -20.2. We note that this object is close to the MW galactic plane (b = -7.11). Given the bright absolute magnitude and slow light curve evolution, we suggest that this object is a Type II superluminous supernova.
