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Early observations of the nearby Type Ia supernova SN 2015F

Early observations of the nearby Type Ia supernova SN 2015F
Early observations of the nearby Type Ia supernova SN 2015F
We present photometry and time series spectroscopy of the nearby Type Ia supernova (SN Ia) SN 2015F over -16 dsys to +80 days relative to maximum light, obtained as part of the Public ESO Spectroscopic Survey of Transient Objects. SN 2015F is a slightly sub-luminous SN Ia with a decline rate of Δm15(B) = 1.35 ± 0.03 mag, placing it in the region between normal and SN 1991bg-like events. Our densely sampled photometric data place tight constraints on the epoch of first light and form of the early-time light curve. The spectra exhibit photospheric CII λ6580 absorption until -4 days, and high-velocity CaII is particularly strong at <-10 days at expansion velocities of ~23000 km s-1. At early times, our spectral modelling with SYN++ shows strong evidence for iron-peak elements (FeII, CrII, TiII, and VII) expanding at velocities >14000 km s-1, suggesting mixing in the outermost layers of the SN ejecta. Although unusual in SN Ia spectra, including VII in the modelling significantly improves the spectral fits. Intriguingly, we detect an absorption feature at ~6800 Å that persists until maximum light. Our favoured explanation for this line is photospheric AlII, which has never been claimed before in SNe Ia, although detached high-velocity CII material could also be responsible. In both cases, the absorbing material seems to be confined to a relatively narrow region in velocity space. The nucleosynthesis of detectable amounts of AlII would argue against a low-metallicity white dwarf progenitor. We also show that this 6800 Å feature is weakly present in other normal SN Ia events and common in the SN 1991bg-like sub-class.
0035-8711
4476-4494
Cartier Ugarte, R.
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Sullivan, M.
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Firth, R.
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Pignata, G.
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Mazzali, P.
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Maguire, K.
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Childress, M.
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Arcavi, I.
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Ashall, C.
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Bassett, B.
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Crawford, S.M.
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Frohmaier, C.
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Galbany, L.
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Gal-Yam, A.
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Hosseinzadeh, G.
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Howell, D.A.
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Inserra, C.
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Johansson, J.
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Kasai, E.K.
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McCully, C.
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Prajs, S.
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Prentice, S.
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Schulze, S.
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Smartt, S.J.
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Smith, K.W.
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Smith, M.
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Valenti, S.
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Young, D.R.
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Cartier Ugarte, R.
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Sullivan, M.
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Firth, R.
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Pignata, G.
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Mazzali, P.
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Maguire, K.
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Childress, M.
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Arcavi, I.
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Ashall, C.
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Bassett, B.
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Crawford, S.M.
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Frohmaier, C.
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Galbany, L.
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Gal-Yam, A.
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Hosseinzadeh, G.
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Howell, D.A.
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Inserra, C.
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Johansson, J.
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Kasai, E.K.
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McCully, C.
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Prajs, S.
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Prentice, S.
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Schulze, S.
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Smartt, S.J.
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Smith, K.W.
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Smith, M.
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Valenti, S.
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Young, D.R.
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Cartier Ugarte, R., Sullivan, M., Firth, R., Pignata, G., Mazzali, P., Maguire, K., Childress, M., Arcavi, I., Ashall, C., Bassett, B., Crawford, S.M., Frohmaier, C., Galbany, L., Gal-Yam, A., Hosseinzadeh, G., Howell, D.A., Inserra, C., Johansson, J., Kasai, E.K., McCully, C., Prajs, S., Prentice, S., Schulze, S., Smartt, S.J., Smith, K.W., Smith, M., Valenti, S. and Young, D.R. (2017) Early observations of the nearby Type Ia supernova SN 2015F. Monthly Notices of the Royal Astronomical Society, 464 (4), 4476-4494. (doi:10.1093/mnras/stw2678).

Record type: Article

Abstract

We present photometry and time series spectroscopy of the nearby Type Ia supernova (SN Ia) SN 2015F over -16 dsys to +80 days relative to maximum light, obtained as part of the Public ESO Spectroscopic Survey of Transient Objects. SN 2015F is a slightly sub-luminous SN Ia with a decline rate of Δm15(B) = 1.35 ± 0.03 mag, placing it in the region between normal and SN 1991bg-like events. Our densely sampled photometric data place tight constraints on the epoch of first light and form of the early-time light curve. The spectra exhibit photospheric CII λ6580 absorption until -4 days, and high-velocity CaII is particularly strong at <-10 days at expansion velocities of ~23000 km s-1. At early times, our spectral modelling with SYN++ shows strong evidence for iron-peak elements (FeII, CrII, TiII, and VII) expanding at velocities >14000 km s-1, suggesting mixing in the outermost layers of the SN ejecta. Although unusual in SN Ia spectra, including VII in the modelling significantly improves the spectral fits. Intriguingly, we detect an absorption feature at ~6800 Å that persists until maximum light. Our favoured explanation for this line is photospheric AlII, which has never been claimed before in SNe Ia, although detached high-velocity CII material could also be responsible. In both cases, the absorbing material seems to be confined to a relatively narrow region in velocity space. The nucleosynthesis of detectable amounts of AlII would argue against a low-metallicity white dwarf progenitor. We also show that this 6800 Å feature is weakly present in other normal SN Ia events and common in the SN 1991bg-like sub-class.

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Accepted/In Press date: 14 October 2016
e-pub ahead of print date: 19 October 2016
Published date: 1 February 2017
Organisations: Astronomy Group

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Local EPrints ID: 404045
URI: https://eprints.soton.ac.uk/id/eprint/404045
ISSN: 0035-8711
PURE UUID: b11d6908-eb23-43e3-ac11-a53001923566
ORCID for M. Sullivan: ORCID iD orcid.org/0000-0001-9053-4820
ORCID for M. Smith: ORCID iD orcid.org/0000-0002-3321-1432

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Date deposited: 20 Dec 2016 09:20
Last modified: 20 Jul 2019 00:40

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Contributors

Author: R. Cartier Ugarte
Author: M. Sullivan ORCID iD
Author: R. Firth
Author: G. Pignata
Author: P. Mazzali
Author: K. Maguire
Author: M. Childress
Author: I. Arcavi
Author: C. Ashall
Author: B. Bassett
Author: S.M. Crawford
Author: C. Frohmaier
Author: L. Galbany
Author: A. Gal-Yam
Author: G. Hosseinzadeh
Author: D.A. Howell
Author: C. Inserra
Author: J. Johansson
Author: E.K. Kasai
Author: C. McCully
Author: S. Prajs
Author: S. Prentice
Author: S. Schulze
Author: S.J. Smartt
Author: K.W. Smith
Author: M. Smith ORCID iD
Author: S. Valenti
Author: D.R. Young

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