N. N. Chugai

A relativistic type Ibc supernova without a detected γ-ray burst

Long duration γ-ray bursts (GRBs) mark the explosive death of some massive stars and are a rare sub-class of type Ibc supernovae. They are distinguished by the production of an energetic and collimated relativistic outflow powered by a central engine (an accreting black hole or neutron star). Observationally, this outflow is manifested in the pulse of γ-rays and a long-lived radio afterglow. Until now, central-engine-driven supernovae have been discovered exclusively through their γ-ray emission, yet it is expected that a larger population goes undetected because of limited satellite sensitivity or beaming of the collimated emission away from our line of sight. In this framework, the recovery of undetected GRBs may be possible through radio searches for type Ibc supernovae with relativistic outflows. Here we report the discovery of luminous radio emission from the seemingly ordinary type Ibc SN 2009bb, which requires a substantial relativistic outflow powered by a central engine. A comparison with our radio survey of type Ibc supernovae reveals that the fraction harbouring central engines is low, about one per cent, measured independently from, but consistent with, the inferred rate of nearby GRBs. Independently, a second mildly relativistic supernova has been reported.

The Type IIn supernova 1994W: evidence for the explosive ejection of a circumstellar envelope

We present and analyse spectra of the Type IIn supernova (SN) 1994W obtained between 18 and 203d after explosion. During the luminous phase (first 100 d) the line profiles are composed of three major components: (i) narrow P-Cygni lines with the absorption minima at -700 km s -1; (ii) broad emission lines with blue velocity at zero intensity ∼4000km s -1; and (iii) broad, smooth wings extending out to at least ∼5000kms -1, most apparent in Hα. These components are identified with an expanding circumstellar (CS) envelope, shocked cool gas in the forward post-shock region, and multiple Thomson scattering in the CS envelope, respectively. The absence of broad P-Cygni lines from the SN is the result of the formation of an optically thick, cool, dense shell at the interface of the ejecta and the CS envelope. Models of the SN deceleration and Thomson scattering wings are used to recover the density (n ≈ 10 9cm -3), radial extent [∼(4-5) × 10 15cm] and Thomson optical depth (τ T ≳ 2.5) of the CS envelope during the first month. The plateau-like SN light curve is reproduced by a hydrodynamical model and is found to be powered by a combination of internal energy leakage after the explosion of an extended pre-SN (∼10 15 cm) and subsequent luminosity from CS interaction. The pre-explosion kinematics of the CS envelope is recovered, and is close to homologous expansion with outer velocity ∼1100 km s -1 and a kinematic age of ∼1.5 yr. The high mass (∼0.4M⊙) and kinetic energy (∼2 × 10 48 erg) of the CS envelope, combined with low age, strongly suggest that the CS envelope was explosively ejected ∼1.5 yr prior to the SN explosion.

A PANCHROMATIC VIEW OF THE RESTLESS SN 2009ip REVEALS THE EXPLOSIVE EJECTION OF A MASSIVE STAR ENVELOPE

The double explosion of SN 2009ip in 2012 raises questions about our understanding of the late stages of massive star evolution. Here we present a comprehensive study of SN 2009ip during its remarkable rebrightenings. High-cadence photometric and spectroscopic observations from the GeV to the radio band obtained from a variety of ground-based and space facilities (including the Very Large Array, Swift, Fermi, Hubble Space Telescope, and XMM) constrain SN 2009ip to be a low energy (E similar to 1050 erg for an ejecta mass similar to 0.5 M-circle dot) and asymmetric explosion in a complex medium shaped by multiple eruptions of the restless progenitor star. Most of the energy is radiated as a result of the shock breaking out through a dense shell of material located at similar to 5 x 10(14) cm with M similar to 0.1 M-circle dot, ejected by the precursor outburst similar to 40 days before the major explosion. We interpret the NIR excess of emission as signature of material located further out, the origin of which has to be connected with documented mass-loss episodes in the previous years. Our modeling predicts bright neutrino emission associated with the shock break-out if the cosmic-ray energy is comparable to the radiated energy. We connect this phenomenology with the explosive ejection of the outer layers of the massive progenitor star, which later interacted with material deposited in the surroundings by previous eruptions. Future observations will reveal if the massive luminous progenitor star survived. Irrespective of whether the explosion was terminal, SN 2009ip brought to light the existence of new channels for sustained episodic mass loss, the physical origin of which has yet to be identified.

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

Progenitor mass of the type IIP supernova 2005cs

Context. The progenitor mass of type IIP supernova can be determined from either hydrodynamic modeling of the event or pre-explosion observations. Aims. To compare these approaches, we determine parameters of the sub-luminous supernova 2005cs and estimate its progenitor mass. Methods. We compute the hydrodynamic models of the supernova to describe its light curves and expansion velocity data. Results. We estimate a presupernova mass of 17.3± 1 M⊙, an explosion energy of (4.1± 0.3)× 10 50 erg, a presupernova radius of 600± 140 R⊙, and a radioactive 56 Ni mass of 0.0082± 0.0016 M⊙. The derived progenitor mass of SN 2005cs is 18.2± 1 M⊙, which is in-between those of low-luminosity and normal type IIP supernovae. Conclusions. The obtained progenitor mass of SN 2005cs is higher than derived from pre-explosion images. The masses of four type IIP supernovae estimated by means of hydrodynamic modeling are systematically higher than the average progenitor mass for the 9− 25 M⊙ mass range. This result, if confirmed for a larger sample, would im ply that a serious revision of the present-day view on the pro genitors of type IIP supernovae is required.

Light curves and H

The possibility is investigated that the Hit luminosity at the nebular epoch may be an additional indicator of 5 6 Ni mass in type II supernovae with plateau (SNe IIP), on the basis of available photometry and spectra. Wefirst derive the 5 6 Ni mass from the M V magnitude on the radioactive tail using a standard approach. A confirmation of the correlation between 5 6 Ni mass and plateau M V magnitude found recently by Hamuy (2003) is evident. There is strong evidence of a correlation between steepness of the V light curve slope at the inflection time and the 5 6 Ni mass. If confirmed, this relation may provide distance and extinction independent estimates of the amount of 5 6 Ni in SNe IIP. We then apply upgraded radioactive models of Hα luminosity at the nebular epoch and claim that it may he a good indicator of 5 6 Ni, if mass, energy and mixing properties vary moderately (within factor ∼ 1.4) among SNe IIP. This method of the 5 6 Ni mass determination from Hα luminosities yields results which are consistent with the photometric mass of 5 6 Ni mass to within 20%. This result also implies that the parameters of SNe IIP events (mass, energy and mixing properties) are rather similar among the majority of SNe IIP, except for rare cases of SN II intermediate between IIP and IIL (linear), of which SN 1970G is an example.

\alpha

Context. Previous studies of type IIP supernovae have inferred that progenitor masses recovered from hydrodynamic models are higher than 15 M� . Aims. To verify the progenitor mass of this supernova category, we attempt a parameter determination of the well-observed luminous type IIP supernova 2004et. Methods. We model the bolometric light curve and the photospheric velocities of SN 2004et by means of hydrodynamic simulations in an extended parameter space. Results. From hydrodynamic simulations and observational data, we infer a presupernova radius of 1500 ± 140 R� , an ejecta mass of 24.5 ± 1 M� , an explosion energy of (2.3 ± 0.3) × 10 51 erg, and a radioactive 56 Ni mass of 0.068 ± 0.009 M� . The estimated progenitor mass on the main sequence is in the range of 25−29 M� . In addition, we find clear signatures of the explosion asymmetry in the nebular spectra of SN 2004et. Conclusions. The measured progenitor mass of SN 2004et is significantly higher than the progenitor mass suggested by the preexplosion images. We speculate that the mass inferred from hydrodynamic modeling is overestimated and crucial missing factors are multi-dimensional effects.

luminosities as indicators of

We present an optical and near-infrared photometric and spectroscopic study of supernova (SN) 2009kn spanning ˜1.5 yr from the discovery. The optical spectra are dominated by the narrow (full width at half-maximum ˜1000 km s-1) Balmer lines distinctive of a Type IIn SN with P Cygni profiles. Contrarily, the photometric evolution resembles more that of a Type IIP SN with a large drop in luminosity at the end of the plateau phase. These characteristics are similar to those of SN 1994W, whose nature has been explained with two different models with different approaches. The well-sampled data set on SN 2009kn offers the possibility to test these models, in the case of both SN 2009kn and SN 1994W. We associate the narrow P Cygni lines with a swept-up shell composed of circumstellar matter and SN ejecta. The broad emission line wings, seen during the plateau phase, arise from internal electron scattering in this shell. The slope of the light curve after the post-plateau drop is fairly consistent with that expected from the radioactive decay of 56Co, suggesting an SN origin for SN 2009kn. Assuming radioactivity to be the main source powering the light curve of SN 2009kn in the tail phase, we infer an upper limit for 56Ni mass of 0.023 Msun. This is significantly higher than that estimated for SN 1994W, which also showed a much steeper decline of the light curve after the post-plateau drop. We also observe late-time near-infrared emission which most likely arises from newly formed dust produced by SN 2009kn. As with SN 1994W, no broad lines are observed in the spectra of SN 2009kn, not even in the late-time tail phase.

\mathsf{^{56}}

The Type Ib/c supernova SN 2001em was observed to have strong radio, X-ray, and Hα emission at an age of ~2.5 yr. Although the radio and X-ray emission have been attributed to an off-axis gamma-ray burst, we model the emission as the interaction of normal SN Ib/c ejecta with a dense, massive (~3 M☉) circumstellar shell at a distance of ~7 × 1016 cm. We investigate two models, in which the circumstellar shell has or has not been overtaken by the forward shock at the time of the X-ray observation. The circumstellar shell was presumably formed by vigorous mass loss with a rate of ~(2-10) × 10-3 M☉ yr-1 at ~(1-2) × 103 yr prior to the supernova explosion. The hydrogen envelope was completely lost and subsequently was swept up and accelerated by the fast wind of the presupernova star up to a velocity of 30-50 km s-1. Although interaction with the shell can explain most of the late emission properties of SN 2001em, we need to invoke clumping of the gas to explain the low absorption at X-ray and radio wavelengths.

Ni mass in type IIP supernovae

We set sensitive upper limits to the X-ray emission of four Type Ia supernovae (SNe Ia) using the Chandra X-Ray Observatory. SN 2002bo, a normal, although reddened, nearby SN Ia, was observed 9.3 days after explosion. For an absorbed, high-temperature bremsstrahlung model the flux limits are 3.2 × 10-16 ergs cm-2 s-1 (0.5-2 keV band) and 4.1 × 10-15 ergs cm-2 s-1 (2-10 keV band). Using conservative model assumptions and a 10 km s-1 wind speed, we derive a mass-loss rate of ~ 2 × 10-5 M☉ yr-1, which is comparable to limits set by the nondetection of Hα lines from other SNe Ia. Two other objects, SN 2002ic and SN 2005gj, observed 260 and 80 days after explosion, respectively, are the only SNe Ia showing evidence for circumstellar interaction. The SN 2002ic X-ray flux upper limits are ~4 times below predictions of the interaction model currently favored to explain the bright optical emission. To resolve this discrepancy, we invoke the mixing of cool dense ejecta fragments into the forward shock region, which produces increased X-ray absorption. A modest amount of mixing allows us to accommodate the Chandra upper limit. SN 2005gj is less well studied at this time. Assuming the same circumstellar environment as for SN 2002ic, the X-ray flux upper limits for SN 2005gj are ~4 times below the predictions, suggesting that mixing of cool ejecta into the forward shock has also occurred here. Our reanalysis of Swift and Chandra data on SN 2005ke does not confirm a previously reported X-ray detection. The host galaxies NGC 3190 (SN 2002bo) and NGC 1371 (SN 2005ke) each harbor a low-luminosity [LX ~ (3-4) × 1040 ergs s-1] active nucleus in addition to widespread diffuse soft X-ray emission.