Early-time Ultraviolet Spectroscopy and Optical Follow-up Observations of the Type IIP Supernova 2021yja

Creators: Vasylyev, Sergiy S.; Filippenko, Alexei V.; Vogl, Christian; Brink, Thomas G.; Brown, Peter J.; de Jaeger, Thomas; Matheson, Thomas; Gal-Yam, Avishay; Mazzali, Paolo A.; Modjaz, Maryam; Patra, Kishore C.; Rowe, Micalyn; Smith, Nathan; Van Dyk, Schuyler D.; Williamson, Marc; Yang, Yi; Zheng, WeiKang; deGraw, Asia; Fox, Ori D.; Gates, Elinor L.; Jennings, Connor; Rich, R. Michael

Abstract

We present three epochs of early-time ultraviolet (UV) and optical HST/STIS spectroscopy of the young, nearby Type IIP supernova (SN) 2021yja. We complement the HST data with two earlier epochs of Swift UVOT spectroscopy. The HST and Swift UVOT spectra are consistent with those of other well-studied Type IIP SNe. The UV spectra exhibit rapid cooling at early times, while less dramatic changes are seen in the optical. We also present Lick/KAIT optical photometry up to the late-time tail phase, showing a very long plateau and shallow decline compared with other SNe IIP. Our modeling of the UV spectrum with the TARDIS radiative transfer code produces a good fit for a high-velocity explosion, a low total extinction E(B − V) = 0.07 mag, and a subsolar metallicity. We do not find a significant contribution to the UV flux from an additional heating source, such as interaction with the circumstellar medium, consistent with the observed flat plateau. Furthermore, the velocity width of the Mg ii λ2798 line is comparable to that of the hydrogen Balmer lines, suggesting that the UV emission is confined to a region close to the photosphere.

Additional Information

© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2022 March 14; revised 2022 May 6; accepted 2022 May 10; published 2022 August 1. This research was funded by HST grants AR-14259 and GO-16178 from the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS5-26555. Additional generous financial support was provided to A.V.F.'s supernova group at UC Berkeley by Steven Nelson, Landon Noll, Sunil Nagaraj, Sandy Otellini, Gary and Cynthia Bengier, Clark and Sharon Winslow, Sanford Robertson, the Christopher R. Redlich Fund, and the Miller Institute for Basic Research in Science (in which A.V.F. was a Miller Senior Fellow). The research of Y.Y. is supported through the Bengier-Winslow-Robertson Postdoctoral Fellowship. A major upgrade of the Kast spectrograph on the Shane 3 m telescope at Lick Observatory, led by Brad Holden, was made possible through gifts from the Heising-Simons Foundation, William and Marina Kast, and the University of California Observatories. KAIT and its ongoing operation were made possible by donations from Sun Microsystems, Inc., the Hewlett-Packard Company, AutoScope Corporation, Lick Observatory, the National Science Foundation, the University of California, the Sylvia & Jim Katzman Foundation, and the TABASGO Foundation. Research at Lick Observatory is partially supported by a generous gift from Google. We thank the staffs at STScI (especially Weston Eck and Svea Hernandez) and Lick Observatory for assistance with the observations. UC Berkeley undergraduates Ivan Altunin, Raphael Baer-Way, Michael May, Vidhi Chander, and Evelyn Liu obtained some of the Lick/Nickel data. M.W. acknowledges support from the NASA Future Investigators in NASA Earth and Space Science and Technology grant (80NSSC21K1849) and support from the Thomas J. Moore Fellowship at New York University. M.M.'s research is supported in part by Swift GI program 1619152 (NASA grant 80NSSC21K0280), TESS GI program G03267 (NASA grant 80NSSC21K0240), and a grant from the New York University Research Challenge Fund Program. This research made use of tardis, a community-developed software package for spectral synthesis in supernovae (Kerzendorf & Sim 2014; Kerzendorf et al. 2022). The development of tardis received support from GitHub, the Google Summer of Code initiative, and ESA's Summer of Code in Space program. tardis is a fiscally sponsored project of NumFOCUS. tardis makes extensive use of Astropy and Pyne. Software: Astropy (Astropy Collaboration et al. 2013, 2018), TARDIS (Kerzendorf & Sim 2014; Vogl et al. 2019), uvotpy (Kuin 2014), DAOPHOT (Stetson 1987), IDL Astronomy user's library (Landsman 1993), SOUSA pipeline (Brown et al. 2014), Pyne (Scopatz et al. 2012).

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