The Peculiar Transient AT2018cow: A Possible Origin of a Type Ibn/IIn Supernova
Danfeng Xiang, Xiaofeng Wang, Weili Lin, Jun Mo, Han Lin, Jamison Burke, Daichi Hiramatsu, Griffin Hosseinzadeh, D. Andrew Howell, Curtis McCully, Stefan Valenti, József Vinkó, J. Craig Wheeler, Shuhrat A. Ehgamberdiev, Davron Mirzaqulov, Attila Bódi, Zsófia Bognár, Borbála Cseh, Ottó Hanyecz, Bernadett Ignácz, Csilla Kalup, Réka Könyves-Tóth, Levente Kriskovics, András Ordasi, András Pál, Krisztián Sárneczky, Bálint Seli, Róbert Szakáts, T. Arranz-Heras, R. Benavides-Palencia, D. Cejudo-Martínez, P. De la Fuente-Fernández, A. Escartín-Pérez, F. García-De la Cuesta, J. L. González-Carballo, R. González-Farfán, F. Limón-Martínez, A. Mantero, R. Naves-Nogués, M. Morales-Aimar, V. R. Ruíz-Ruíz, F. C. Soldán-Alfaro, J. Valero-Pérez, F. Violat-Bordonau, Tianmeng Zhang, Jujia Zhang, Xue Li, Zhihao Chen, Hanna Sai, Wenxiong Li
Abstract
Abstract We present our photometric and spectroscopic observations of the peculiar transient AT2018cow. The multiband photometry covers from peak to ∼70 days, and the spectroscopy ranges from 5 to ∼50 days. The rapid rise ( t r ≲ 2.9 days), high luminosity ( M V ,peak ∼ −20.8 mag), and fast decline after peak make AT2018cow stand out from any other optical transients, whereas we find that its light curves show a high resemblance to those of Type Ibn supernovae. Moreover, the spectral energy distribution remains at a high temperature of ∼14,000 K at t > 15 days after discovery. The spectra are featureless in the first 10 days, while some broad emission lines due to H, He, C, and O emerge later, with velocity declining from ∼14,000 to ∼3000 km s −1 at the end of our observations. Narrow and weak He I emission lines emerge in the spectra at t > 20 days after discovery. These emission lines are reminiscent of the features seen in interacting supernovae like the Type Ibn and IIn subclasses. We fit the bolometric light curves with a model of circumstellar interaction and radioactive decay of 56 Ni and find a good fit with ejecta mass M ej ∼ 3.16 M ⊙ , circumstellar medium (CSM) mass M CSM ∼ 0.04 M ⊙ , and ejected 56 Ni mass M ⊙ . The CSM shell might be formed in an eruptive mass ejection of the progenitor star. Furthermore, the host environment of AT2018cow implies a connection of AT2018cow with massive stars. Combining observational properties and the light-curve fitting results, we conclude that AT2018cow might be a peculiar interacting supernova that originated from a massive star.