ASASSN-18tb: a most unusual Type Ia supernova observed by TESS and SALT

Journal Article · 26 May 2019 · Monthly Notices of the Royal Astronomical Society

DOI: https://doi.org/10.1093/mnras/stz1445 · OSTI ID:1525570

Vallely, P. J.  ^[1]; Fausnaugh, M. ^[2]; Jha, S. W.  ^[3]; Tucker, M. A. ^[4]; Eweis, Y. ^[5]; Shappee, B. J. ^[4]; Kochanek, C. S. ^[6]; Stanek, K. Z. ^[6]; Chen, Ping ^[7]; Dong, Subo ^[7]; Prieto, J. L. ^[8]; Sukhbold, T.  ^[6]; Thompson, Todd A. ^[9]; Brimacombe, J. ^[10]; Stritzinger, M. D. ^[11]; Holoien, T. W-S  ^[12]; Buckley, D. A. H.  ^[13]; Gromadzki, M. ^[14]; Bose, Subhash ^[7]

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1. Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA
2. Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA, Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
3. Department of Physics and Astronomy, Rutgers, the State University of New Jersey, 136 Frelinghuysen Rd., Piscataway, NJ 08854, USA, Center for Computational Astrophysics, Flatiron Institute, 162 5th Avenue, New York, NY 10010, USA
4. Institute for Astronomy, University of Hawai’i, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
5. Department of Physics and Astronomy, Rutgers, the State University of New Jersey, 136 Frelinghuysen Rd., Piscataway, NJ 08854, USA
6. Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA, Center for Cosmology and AstroParticle Physics, The Ohio State University, 191 W. Woodruff Ave., Columbus, OH 43210, USA
7. Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Road 5, Hai Dian District, Beijing 100871, China
8. Núcleo de Astronomía de la Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército 441, Santiago, Chile, Millennium Institute of Astrophysics, Santiago, Chile
9. Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA, Center for Cosmology and AstroParticle Physics, The Ohio State University, 191 W. Woodruff Ave., Columbus, OH 43210, USA, Institute for Advanced Study, 1 Einstein Drive, Princeton, NJ 08540, USA
10. Coral Towers Observatory, Cairns, Queensland 4870, Australia
11. Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark
12. Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101, USA
13. South African Astronomical Observatory, PO Box 9, Observatory 7935, Cape Town, South Africa
14. Warsaw University Astronomical Observatory, Al. Ujazdowskie 4, PL-00-478 Warszawa, Poland

ABSTRACT We present photometric and spectroscopic observations of the unusual Type Ia supernova ASASSN-18tb, including a series of Southern African Large Telescope spectra obtained over the course of nearly six months and the first observations of a supernova by the Transiting Exoplanet Survey Satellite. We confirm a previous observation by Kollmeier et al. showing that ASASSN-18tb is the first relatively normal Type Ia supernova to exhibit clear broad (∼1000 km s−1) H α emission in its nebular-phase spectra. We find that this event is best explained as a sub-Chandrasekhar mass explosion producing $$M_{\mathrm{ Ni}} \approx 0.3\,\, \rm {M}_\odot$$. Despite the strong H α signature at late times, we find that the early rise of the supernova shows no evidence for deviations from a single-component power-law and is best fit with a moderately shallow power law of index 1.69 ± 0.04. We find that the H α luminosity remains approximately constant after its initial detection at phase +37 d, and that the H α velocity evolution does not trace that of the Fe iii λ4660 emission. These suggest that the H α emission arises from a circumstellar medium (CSM) rather than swept-up material from a non-degenerate companion. However, ASASSN-18tb is strikingly different from other known CSM-interacting Type Ia supernovae in a number of significant ways. Those objects typically show an H α luminosity two orders of magnitude higher than what is seen in ASASSN-18tb, pushing them away from the empirical light-curve relations that define ‘normal’ Type Ia supernovae. Conversely, ASASSN-18tb exhibits a fairly typical light curve and luminosity for an underluminous or transitional SN Ia, with MR ≈ −18.1 mag. Moreover, ASASSN-18tb is the only SN Ia showing H α from CSM interaction to be discovered in an early-type galaxy.

• Sponsoring Organization: USDOE
• Grant/Contract Number: SC0019323
• OSTI ID: 1525570
• Alternate ID(s): OSTI ID: 1613173
• Journal Information: Monthly Notices of the Royal Astronomical Society, Journal Name: Monthly Notices of the Royal Astronomical Society Journal Issue: 2 Vol. 487; ISSN 0035-8711
• Publisher: Oxford University PressCopyright Statement
• Country of Publication: United Kingdom
• Language: English