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SN 2015bn: A detailed multi-wavelength view of a nearby superluminous supernova

Nicholl, M., Berger, E., Smartt, S. J., Margutti, R., Kamble, A., Alexander, K. D., Chen, T.-W., Inserra, C., Arcavi, I., Blanchard, P. K., Cartier, R., Chambers, K. C., Childress, M. J., Chornock, R., Cowperthwaite, P. S., Drout, M., Flewelling, H. A., Fraser, M., Gal-Yam, A., Galbany, L., Harmanen, J., Holoien, T. W.-S., Hosseinzadeh, G., Howell, D. A., Huber, M. E., Jerkstrand, A., Kankare, E., Kochanek, C. S., Lin, Z.-Y., Lunnan, R., Magnier, E. A., Maguire, K., McCully, C., McDonald, M., Metzger, B. D., Milisavljevic, D., Mitra, A., Reynolds, T., Saario, J., Shappee, B. J., Smith, K. W., Valenti, S., Villar, V. A., Waters, C. and Young, D. R. 2016. SN 2015bn: A detailed multi-wavelength view of a nearby superluminous supernova. Astrophysical Journal 826 (1) , 39. 10.3847/0004-637X/826/1/39

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Abstract

We present observations of SN 2015bn (=PS15ae = CSS141223-113342+004332 = MLS150211-113342+004333), a Type I superluminous supernova (SLSN) at redshift z = 0.1136. As well as being one of the closest SLSNe I yet discovered, it is intrinsically brighter (${M}_{U}\approx -23.1$) and in a fainter galaxy (${M}_{B}\approx -16.0$) than other SLSNe at $z\sim 0.1$. We used this opportunity to collect the most extensive data set for any SLSN I to date, including densely sampled spectroscopy and photometry, from the UV to the NIR, spanning −50 to +250 days from optical maximum. SN 2015bn fades slowly, but exhibits surprising undulations in the light curve on a timescale of 30–50 days, especially in the UV. The spectrum shows extraordinarily slow evolution except for a rapid transformation between +7 and +20–30 days. No narrow emission lines from slow-moving material are observed at any phase. We derive physical properties including the bolometric luminosity, and find slow velocity evolution and non-monotonic temperature and radial evolution. A deep radio limit rules out a healthy off-axis gamma-ray burst, and places constraints on the pre-explosion mass loss. The data can be consistently explained by a $\gtrsim 10$ M ${}_{\odot }$ stripped progenitor exploding with $\sim {10}^{51}$ erg kinetic energy, forming a magnetar with a spin-down timescale of ~20 days (thus avoiding a gamma-ray burst) that reheats the ejecta and drives ionization fronts. The most likely alternative scenario—interaction with ~20 M ${}_{\odot }$ of dense, inhomogeneous circumstellar material—can be tested with continuing radio follow-up.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Publisher: American Astronomical Society
ISSN: 0004-637X
Date of First Compliant Deposit: 23 January 2019
Date of Acceptance: 2 May 2016
Last Modified: 24 May 2019 14:20
URI: http://orca.cf.ac.uk/id/eprint/118713

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