Multi-Wavelength Properties of the Type IIb SN 2008ax

TL;DR

This paper provides a comprehensive multi-wavelength analysis of supernova SN 2008ax, revealing details about its early UV behavior, spectral features, shock interaction, and progenitor characteristics.

Contribution

It presents the earliest UV observations of a Type IIb supernova and combines multi-wavelength data with models to characterize the progenitor and explosion parameters.

Findings

Early UV observations captured a rapid decline and upturn in light curves.

Spectral analysis identified prominent hydrogen, helium, and calcium lines.

Radio and X-ray data indicated low mass-loss rate and shock interaction with circumstellar material.

Abstract

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. Modeling 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.