* Astronomy

Blobrana · L

RE: Supernova 2008ax

Blobrana · L

Title: Multi-Wavelength Properties of the Type IIb SN 2008ax
Authors: P.W.A. Roming, T.A. Pritchard, P.J. Brown, S.T. Holland, S. Immler, C.J. Stockdale, K.W. Weiler, N. Panagia, S.D. Van Dyk, E.A. Hoversten, P.A. Milne, S.R. Oates, B. Russell, C. Vandrevala

We present the UV, optical, X-ray, and radio properties of the Type IIb SN 2008ax discovered in NGC 4490. The observations in the UV are one of the earliest of a Type IIb supernova (SN). On approximately day four after the explosion, a dramatic upturn in the u and uvw1 (lambda_c = 2600 Angstroms) light curves occurred after an initial rapid decline which is attributed to adiabatic cooling after the initial shock breakout. This rapid decline and upturn is reminiscent of the Type IIb SN 1993J on day six after the explosion. Optical/near-IR spectra taken around the peak reveal prominent H-alpha, HeI, and CaII absorption lines. A fading X-ray source is also located at the position of SN 2008ax, implying an interaction of the SN shock with the surrounding circumstellar material and a mass-loss rate of the progenitor of M_dot = (9±3)x10^-6 solar masses per year. The unusual time evolution (14 days) of the 6 cm peak radio luminosity provides further evidence that the mass-loss rate is low. Combining the UV, optical, X-ray, and radio data with models of helium exploding stars implies the progenitor of SN 2008ax was an unmixed star in an interacting-binary. Modelling of the SN light curve suggests a kinetic energy (E_k) of 0.5x10^51 ergs, an ejecta mass (M_ej) of 2.9 solar masses, and a nickel mass (M_Ni) of 0.06 solar masses.

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Blobrana · L

Title: The type IIb SN 2008ax: the nature of the progenitor
Authors: R. M. Crockett, J. J. Eldridge, S. J. Smartt, A. Pastorello, A. Gal-Yam, D. B. Fox, D. C. Leonard, M. M. Kasliwal, S. Mattila, J. R. Maund, A. W. Stephens, I. J. Danziger

A source coincident with the position of the type IIb supernova (SN) 2008ax is identified in pre-explosion HST WFPC2 observations in three optical filters. The SN position in these images is pinpointed to within +/-22 mas through alignment with a Gemini-N Altair/NIRI K-band adaptive optics image of the SN. Investigating several scenarios, we identify and constrain two possible progenitor systems: (1) a single massive star that lost most of its hydrogen envelope through radiatively driven mass loss processes, prior to exploding as a helium-rich Wolf-Rayet star with a residual hydrogen envelope, and (2) an interacting binary producing a stripped progenitor. Very late time, high resolution observations along with detailed modelling of the SN will be required to reveal the true nature of this progenitor star.

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Blobrana · L

Title: The type IIb SN 2008ax: spectral and light curve evolution
Authors: A. Pastorello, M. M. Kasliwal, R. M. Crockett, S. Valenti, R. Arbour, K. Itagaki, S. Kaspi, A. Gal-Yam, S. J. Smartt, R. Griffith, K. Maguire, E. O. Ofek, N. Seymour, D. Stern, W. Wiethoff

We present spectroscopy and photometry of the He-rich supernova (SN) 2008ax. The early-time spectra show prominent P-Cygni H lines, which decrease with time and disappear completely about two months after the explosion. In the same period He I lines become the most prominent spectral features. SN 2008ax displays the ordinary spectral evolution of a type IIb supernova. Its light curve, which peaks in the B band about 20 days after the explosion, strongly resembles that of other He-rich core-collapse supernovae. The observed evolution of SN 2008ax is consistent with the explosion of a young Wolf-Rayet (of WNL type) star, which had retained a thin, low-mass shell of its original H envelope.

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