An early and comprehensive millimetre and centimetre wave and X-ray study of SN 2011dh: a non-equipartition blast wave expanding into a massive stellar wind

Abstract

Only a handful of supernovae (SNe) have been studied in multi-wavelength from radio to X-rays, starting a few days after explosion. The early detection and classification of the nearby type IIb SN 2011dh/PTF 11eon in M51 provides a unique opportunity to conduct such observations. We present detailed data obtained at the youngest phase ever of a core-collapse supernova (days 3 to 12 after explosion) in the radio, millimeter and X-rays; when combined with optical data, this allows us to explore the early evolution of the SN blast wave and its surroundings. Our analysis shows that the expanding supernova shockwave does not exhibit equipartition (ǫ e /ǫ B ∼ 1000), and is expanding into circumstellar material that is consistent with a density profile falling like R −2 . Within modeling uncertainties we find an average velocity of the fast parts of the ejecta of 15,000±1800 km/s, contrary to previous analysis. This velocity places SN 2011dh in an intermediate blast-wave regime between the previously defined compact and extended SN IIb subtypes. Our results highlight the importance of early (∼ 1 day) high-frequency observations of future events. Moreover, we show the importance of combined radio/X-ray observations for determining the microphysics ratio ǫ e /ǫ B .

Spectropolarimetry of SN 2011dh in M51: geometric insights on a Type IIb supernova progenitor and explosion

“…This was considered to be a very likely explanation for the strong continuum polarization detected from SN 1993J (Höflich et al 1996;Tran et al 1997). As mentioned above, early radio and millimeter observations of SN 2011dh provided direct evidence for CSM from the progenitor wind (Horesh et al 2013), while late-time X-ray emission roughly 500 days after explosion indicated the presence of dense CSM at ∼ 8 × 10…”

“…Furthermore, if a SN has more than one component of polarization (for example, Thomson scattering and/or dust scattering by CSM), then this could produce net polarization at the same wavelengths as the strong intrinsically unpolarized emission features (e.g., see Mauerhan et al 2014). The possible existence of extended CSM has been suggested in the case of SN 2011dh, based on detection of broad Hα in late-time nebular spectroscopy at > 200 days (Sahu et al 2013;Shivvers et al 2013) and radio observations (Horesh et al 2013). Whether this CSM component could be influencing the polarization properties of SN 2011dh at the earlier times we are dealing with is not clear, but perhaps unlikely, given the lack of substantial UV excess reported for this object (e.g., see Ben-Ami et al 2015).…”

“…However, Thomson scattering from CSM interaction cannot be ruled for the earliest phases of SN 2011dh, where spectropolarimetric data are not available. Indeed, the very early radio and millimeter detection of SN 2011dh just 3 days post explosion indicates substantial interaction between the SN shock the extended stellar wind of the progenitor (Horesh et al 2013). Recent "flash spectroscopy" of other CC SNe, from just several days to as early as hours after explosion, have indeed exhibited evidence for short-lived CSM interaction and Thomson scattering via Lorentzian emission-line profiles (e.g., Gal-Yam et al 2014;Shivvers et al 2015;Smith et al 2015).…”

A Deep Search for Prompt Radio Emission From Thermonuclear Supernovae With the Very Large Array

“…As discussed by Horesh et al (2012Horesh et al ( , 2013, the most significant uncertainty in converting radio luminosity to a density of the CSM is the efficiency of magnetic field acceleration,  B . In the case of uniform density CSM and optically thin synchrotron emission, the density derived from a given flux density will depend on  B as µ , respectively.…”

Optical and near-infrared observations of SN 2011dh – The first 100 days

“…Optical and NIR photometry and spectroscopy, mainly from the first 50 days, have been published by A11, M11, Tsvetkov et al (2012, hereafter T12), Vinkó et al (2012, hereafter V12), Marion et al (2013, hereafter M13), Van Dyk et al (2013, hereafter D13) and Sahu et al (2013, hereafter S13). Radio and millimeter observations have been published by Martí-Vidal et al (2011), Krauss et al (2012), Bietenholz et al (2012), Soderberg et al (2012) and Horesh et al (2013) and X-ray observations by Soderberg et al (2012), Sasaki & Ducci (2012) and Campana & Immler (2012). The SN has been monitored in the ultraviolet (UV) using Swift, in the mid-infrared (MIR) using Spitzer and at sub-millimeter wavelengths using Herschel.…”