Miriam I. Krauss

Panchromatic Observations of SN 2011dh Point to a Compact Progenitor Star

– 3 –the first three weeks after explosion. Combining these observations with earlyoptical photometry, we show that the panchromatic dataset is well-described bynon-thermal synchrotron emission (radio/mm) with inverse Compton scattering(X-ray) of a thermal population of optical photons. We derive the properties ofthe shockwave and the circumstellar environment and find a time-averaged shockvelocity of v ≈ 0.1c and a progenitor mass loss rate of M˙ ≈ 6 × 10

EXPANDED VERY LARGE ARRAY OBSERVATIONS OF THE RADIO EVOLUTION OF SN 2011dh

We report on Expanded Very Large Array observations of the Type IIb supernova 2011dh, performed over the first 100 days of its evolution and spanning 1-40 GHz in frequency. The radio emission is well described by the self-similar propagation of a spherical shockwave, generated as the supernova ejecta interact with the local circumstellar environment. Modeling this emission with a standard synchrotron self-absorption (SSA) model gives an average expansion velocity of v 0.1c, supporting the classification of the progenitor as a compact star (R 1011 cm). We find that the circumstellar density is consistent with a ρr –2 profile. We determine that the progenitor shed mass at a constant rate of 3 × 10–5 M ☉ yr–1, assuming a wind velocity of 1000 km s–1 (values appropriate for a Wolf-Rayet star), or 7 × 10–7 M ☉ yr–1 assuming 20 km s–1 (appropriate for a yellow supergiant [YSG] star). Both values of the mass-loss rate assume a converted fraction of kinetic to magnetic energy density of B = 0.1. Although optical imaging shows the presence of a YSG, the rapid optical evolution and fast expansion argue that the progenitor is a more compact star—perhaps a companion to the YSG. Furthermore, the excellent agreement of the radio properties of SNxa02011dh with the SSA model implies that any YSG companion is likely in a wide, non-interacting orbit.

VLBI OBSERVATIONS OF THE NEARBY TYPE IIb SUPERNOVA 2011dh

We report on phase-referenced very long baseline interferometry radio observations of the Type IIb supernova 2011dh, at times t = 83 days and 179 days after the explosion and at frequencies, respectively, of 22.2 and 8.4 GHz. We detected SN 2011dh at both epochs. At the first epoch only an upper limit on SN 2011dhs angular size was obtained, but at the second epoch, we determine the angular radius of SN 2011dhs radio emission to be 0.25 ± 0.08 mas by fitting a spherical shell model directly to the visibility measurements. At a distance of 8.4 Mpc, this angular radius corresponds to a time-averaged (since t = 0) expansion velocity of the forward shock of 21, 000 ± 7000 km s–1. Our measured values of the radius of the emission region are in excellent agreement with those derived from fitting synchrotron self-absorbed models to the radio spectral energy distribution, providing strong confirmation for the latter method of estimating the radius. We find that SN 2011dhs radius evolves in a power-law fashion, with R∝t 0.92 ± 0.10.

The Radio Light Curve of the Gamma-Ray Nova in V407 CYG: Thermal Emission from the Ionized Symbiotic Envelope, Devoured from within by the Nova Blast

We present multi-frequency radio observations of the 2010 nova event in the symbiotic binary V407 Cygni, obtained with the Karl G. Jansky Very Large Array and spanning 1–45 GHz and 17–770 days following discovery. This nova—the first ever detected in gamma rays—shows a radio light curve dominated by the wind of the Mira giant companion, rather than the nova ejecta themselves. The radio luminosity grew as the wind became increasingly ionized by the nova outburst, and faded as the wind was violently heated from within by the nova shock. This study marks the first time that this physical mechanism has been shown to dominate the radio light curve of an astrophysical transient. We do not observe a thermal signature from the nova ejecta or synchrotron emission from the shock, due to the fact that these components were hidden behind the absorbing screen of the Mira wind. We estimate a mass loss rate for the Mira wind of u Mw ≈ 10 −6 M⊙ yr −1 . We also present the only radio detection of V407 Cyg before the 2010 nova, gleaned from unpublished 1993 archival VLA data, which shows that the radio luminosity of the Mira wind varies by a factor of &20 even in quiescence. Although V407 Cyg likely hosts a massive accreting white dwarf, making it a candidate progenitor system for a Type Ia supernova, the dense and radially continuous circumbinary material surrounding V407 Cyg is inconsistent with observational constraints on the environments of most Type Ia supernovae. Subject headings: Stars: individual (V407 Cygni) — binaries: symbiotic — novae, cataclysmic variables — Radio continuum: stars

THE 2011 OUTBURST OF RECURRENT NOVA T PYX: RADIO OBSERVATIONS REVEAL THE EJECTA MASS AND HINT AT COMPLEX MASS LOSS

Despite being the prototype of its class, T Pyx is arguably the most unusual and poorly understood recurrent nova. Here, we use radio observations from the Karl G. Jansky Very Large Array to trace the evolution of the ejecta over the course of the 2011 outburst of T Pyx. The radio emission is broadly consistent with thermal emission from the nova ejecta. However, the radio flux began rising surprisingly late in the outburst, indicating that the bulk of the radio-emitting material was either very cold, or expanding very slowly, for the first ∼50 days of the outburst. Considering a plausible range of volume filling factors and geometries for the ejecta, we find that the high peak flux densities of the radio emission require a massive ejection of (1-30) × 10{sup –5} M {sub ☉}. This ejecta mass is much higher than the values normally associated with recurrent novae, and is more consistent with a nova on a white dwarf well below the Chandrasekhar limit.

A MISSING-LINK IN THE SUPERNOVA–GRB CONNECTION: THE CASE OF SN 2012ap

Gamma-ray bursts (GRBs) are characterized by ultra-relativistic outflows, while supernovae are generally characterized by non-relativistic ejecta. GRB afterglows decelerate rapidly, usually within days, because their low-mass ejecta rapidly sweep up a comparatively larger mass of circumstellar material. However, supernovae with heavy ejecta can be in nearly free expansion for centuries. Supernovae were thought to have non-relativistic outflows except for a few relativistic ones accompanied by GRBs. This clear division was blurred by SN 2009bb, the first supernova with a relativistic outflow without an observed GRB. However, the ejecta from SN 2009bb was baryon loaded and in nearly free expansion for a year, unlike GRBs. We report the first supernova discovered without a GRB but with rapidly decelerating mildly relativistic ejecta, SN 2012ap. We discovered a bright and rapidly evolving radio counterpart driven by the circumstellar interaction of the relativistic ejecta. However, we did not find any coincident GRB with an isotropic fluence of more than one-sixth of the fluence from GRB 980425. This shows for the first time that central engines in SNe Ic, even without an observed GRB, can produce both relativistic and rapidly decelerating outflows like GRBs.

The 2011 outburst of recurrent nova T Pyx: X-ray observations expose the white dwarf mass and ejection dynamics

We are grateful to R. Williams, A. Ederoclite, M. Bode, R. Smith, and U. Munari for useful conversations. We thank the Suzaku mission for the generous allocation of target-of-opportunity time to observe T Pyx. We also thank Neil Gehrels and the Swift mission team for their support of the target-of-opportunity program for this nova. We acknowledge with thanks the variable star observations from the AAVSO International Database contributed by observers worldwide and used in this research. This work made use of the HEASARC archive, data supplied by the UK Swift Science Data Centre at the University of Leicester, and observations obtained with the Suzaku satellite, a collaborative mission between the space agencies of Japan (JAXA) and the USA (NASA). The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. L. Chomiuk is a Jansky Fellow of the National Radio Astronomy Observatory. J. Osborne and K. Page acknowledge the support of the UK Space Agency. J. L. Sokoloski and J. Weston acknowledge support from NSF award AST-1211778.

Non-thermal radio emission from colliding flows in classical nova V1723 Aql

The importance of shocks in nova explosions has been highlighted by Fermis discovery of gamma-ray producing novae. Over three years of multi-band VLA radio observations of the 2010 nova V1723 Aql show that shocks between fast and slow flows within the ejecta led to the acceleration of particles and the production of synchrotron radiation. Soon after the start of the eruption, shocks in the ejecta produced an unexpected radio flare, resulting in a multi-peaked radio light curve. The emission eventually became consistent with an expanding thermal remnant with mass

EXPANDED VERY LARGE ARRAY NOVA PROJECT OBSERVATIONS OF THE CLASSICAL NOVA V1723 AQUILAE

2 times 10^{-4} M_odot

Radio studies of novae: a current status report and highlights of new results

and temperature