A Wolf-Rayet-like progenitor of SN 2013cu from spectral observations of a stellar wind.
The explosive fate of massive Wolf-Rayet stars (WRSs) is a key open question in stellar physics. An appealing option is that hydrogen-deficient WRSs are the progenitors of some hydrogen-poor supernova explosions of types IIb, Ib and Ic (ref. 2). A blue object, having luminosity and colours consistent with those of some WRSs, has recently been identified in pre-explosion images at the location of a supernova of type Ib (ref. 3), but has not yet been conclusively determined to have been the progenitor. Similar work has so far only resulted in non-detections. Comparison of early photometric observations of type Ic supernovae with theoretical models suggests that the progenitor stars had radii of less than 10(12) centimetres, as expected for some WRSs. The signature of WRSs, their emission line spectra, cannot be probed by such studies. Here we report the detection of strong emission lines in a spectrum of type IIb supernova 2013cu (iPTF13ast) obtained approximately 15.5 hours after explosion (by 'flash spectroscopy', which captures the effects of the supernova explosion shock breakout flash on material surrounding the progenitor star). We identify Wolf-Rayet-like wind signatures, suggesting a progenitor of the WN(h) subclass (those WRSs with winds dominated by helium and nitrogen, with traces of hydrogen). The extent of this dense wind may indicate increased mass loss from the progenitor shortly before its explosion, consistent with recent theoretical predictions.
Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100, Israel.
Avishay
A
Gal-Yam
Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100, Israel.
I
I
Arcavi
Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100, Israel.
E O
EO
Ofek
Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100, Israel.
S
S
Ben-Ami
Astrophysics Science Division, NASA Goddard Space Flight Center, Mail Code 661, Greenbelt, Maryland 20771, USA.
S B
SB
Cenko
Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, California 91101, USA.
M M
MM
Kasliwal
Cahill Center for Astrophysics, California Institute of Technology, Pasadena, California 91125, USA.
Y
Y
Cao
Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100, Israel.
O
O
Yaron
Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100, Israel.
D
D
Tal
Department of Astronomy, University of Texas, Austin, Texas 78712, USA.
J M
JM
Silverman
Cahill Center for Astrophysics, California Institute of Technology, Pasadena, California 91125, USA.
A
A
Horesh
Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100, Israel.
A
A
De Cia
The Oskar Klein Centre, Department of Astronomy, Stockholm University, AlbaNova, 10691 Stockholm, Sweden.
F
F
Taddia
The Oskar Klein Centre, Department of Astronomy, Stockholm University, AlbaNova, 10691 Stockholm, Sweden.
J
J
Sollerman
Cahill Center for Astrophysics, California Institute of Technology, Pasadena, California 91125, USA.
D
D
Perley
Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100, Israel.
P M
PM
Vreeswijk
Cahill Center for Astrophysics, California Institute of Technology, Pasadena, California 91125, USA.
S R
SR
Kulkarni
Physics Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
P E
PE
Nugent
Department of Astronomy, University of California, Berkeley, California 94720-3411, USA.
A V
AV
Filippenko
Department of Astronomy, University of Texas, Austin, Texas 78712, USA.
J C
JC
Wheeler