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Type IIn supernovae (SNe IIn) are rare events, constituting only a few percent of all core-collapse SNe, and the current sample of well-observed SNe IIn is small. Here, we study the four SNe IIn observed by the Caltech Core- Collapse Project (CCCP). The CCCP SN sample is unbiased to the extent that object selection was not influenced by target SN properties. Therefore, these events are representative of the observed population of SNe IIn. We find that a narrow P-Cygni profile in the hydrogen Balmer lines appears to be a ubiquitous feature of SNe IIn. Our light curves show a relatively long rise time (>20 days) followed by a slow decline stage (0.01-0.15 mag day-1), and a typical V-band peak magnitude of Mv = - 18.4 ± 1.0 mag. We measure the progenitor star wind velocities (600-1400 km s-1) for the SNe in our sample and derive pre-explosion mass-loss rates (0.026-0.12 M⊙ yr-1). We compile similar data for SNe IIn from the literature and discuss our results in the context of this larger sample. Our results indicate that typical SNe IIn arise from progenitor stars that undergo luminous-blue-variable-like mass loss shortly before they explode. [ABSTRACT FROM AUTHOR]

The recent long-duration GRB 100316D, associated with supernova SN 2010bh and detected by Swift, is one of the nearest gamma-ray burst (GRB)-supernovae (SNe) ever observed (z = 0.059). This provides us with a unique opportunity to study the explosion environment on ~kpc scale in relation to the host galaxy complex. Here we present spatially resolved spectrophotometry of the host galaxy, focusing on both the explosion site and the brightest star-forming regions. Using these data, we extract the spatial profiles of the relevant emission features (Hα, Hβ, [O III])λ5007, and [N II]λ6584) and use these profiles to examine variations in metallicity and star formation rate (SFR) as a function of position in the host galaxy. We conclude that GRB 100316D/SN2010bh occurred in a low-metallicity host galaxy, and that the GRB-SN explosion site corresponds to the region with the lowest metallicity and highest SFR sampled by our observations. [ABSTRACT FROM AUTHOR]

The specific incidence of radio flares appears to be significantly larger than that of the prompt optical emission. This abundance, coupled with the reverse shock interpretation, suggests that radio flares add a unique probe on the physics of gamma-ray burst (GRB) shocks. Motivated thus, we estimate the strength of the reverse shock expected for bursts in which multiwavelength observations have allowed the physical parameters of the forward shock to be determined. We use all six bursts (980519, 990123, 990510, 991208, 991216, 000418) which are found to be adiabatic and thus are predicted to have a strong reverse shock. We aim to constrain the hydrodynamic evolution of the reverse shock and the initial bulk Lorentz factor – which we found to be between 102 and 103 and well above the lower limits derived from the requirement that GRBs be optically thin to high-energy photons. In half of the cases we improve the description of the early afterglow light curves by adding a contribution from the reverse shock. Modelling of this early emission provides the opportunity to investigate the immediate surroundings of the burst. For 991216 and 991208, the expected density structure for a stellar wind is not compatible with the early afterglow light curves. Considering the radial range relevant to these GRBs, we discuss the conditions under which the inclusion of a wind termination shock may resolve the absence of a density profile. [ABSTRACT FROM AUTHOR]

GRB 990123 was a long, complex gamma-ray burst accompanied by an extremely bright optical flash. We find different constraints on the bulk Lorentz of this burst to be consistent with the speculation that the optical light is emission from the reverse shock component of the external shock. Motivated by this currently favoured idea, we compute the prompt reverse shock emission to be expected for bursts in which multiwavelength observations allow the physical parameters to be constrained. We find that for reasonable assumptions about the velocity of source expansion, a strong optical flash mv ≈ 9 was expected from the reverse shocks, which were usually found to be mildly relativistic. The best observational prospects for detecting these prompt flashes are highlighted, along with the possible reasons for the absence of optical prompt detections in ongoing observations. [ABSTRACT FROM AUTHOR]

We present theGALEXdetection of a UV burst at the time of explosion of an optically normal supernova (SN) IIP (PS1-13arp) from the Pan-STARRS1 survey atz= 0.1665. The temperature and luminosity of the UV burst match the theoretical predictions for shock breakout in a red supergiant (RSG), but with a duration a factor of ~50 longer than expected. We compare the NUV light curve of PS1-13arp to previousGALEXdetections of SNe IIP and find clear distinctions that indicate that the UV emission is powered by shock breakout, and not by the subsequent cooling envelope emission previously detected in these systems. We interpret the ~1 day duration of the UV signal with a shock breakout in the wind of an RSG with a pre-explosion mass-loss rate ofyr−1. This mass-loss rate is enough to prolong the duration of the shock breakout signal, but not enough to produce an excess in the optical plateau light curve or narrow emission lines powered by circumstellar interaction. This detection of non-standard, potentially episodic high mass loss in an RSG SN progenitor has favorable consequences for the prospects of future wide-field UV surveys to detect shock breakout directly in these systems, and provide a sensitive probe of the pre-explosion conditions of SN progenitors., Astronomy

We present extensive radio and X-ray observations of SN 2012au, an energetic, radio-luminous supernova of Type Ib that exhibits multi-wavelength properties bridging subsets of hydrogen-poor superluminous supernovae, hypernovae, and normal core-collapse supernovae. The observations closely follow models of synchrotron emission from a shock-heated circumburst medium that has a wind density profile (ρ∝r–2). We infer a sub-relativistic velocity for the shock wave v ≈ 0.2 c and a radius of r ≈ 1.4 × 1016cm at 25 days after the estimated date of explosion. For a wind velocity of 1000 km s–1, we determine the mass-loss rate of the progenitor to be , consistent with the estimates from X-ray observations. We estimate the total internal energy of the radio-emitting material to be E ≈ 1047 erg, which is intermediate to SN 1998bw and SN 2002ap. The evolution of the radio light curve of SN 2012au is in agreement with its interaction with a smoothly distributed circumburst medium and the absence of stellar shells ejected from previous outbursts out to r ≈ 1017 cm from the supernova site. We conclude that the bright radio emission from SN 2012au was not dissimilar from other core-collapse supernovae despite its extraordinary optical properties, and that the evolution of the SN 2012au progenitor star was relatively quiet, marked with a steady mass loss, during the final years preceding explosion. [ABSTRACT FROM AUTHOR]

GRB 120422A is a nearby (z = 0.283) long-duration gamma-ray burst (LGRB) detected by Swift with Eγ, iso ∼ 4.5 × 1049 erg. It is also associated with the spectroscopically confirmed broad-lined Type Ic SN 2012bz. These properties establish GRB 120422A/SN 2012bz as the sixth and newest member of the class of subluminous GRBs supernovae (SNe). Observations also show that GRB 120422A/SN 2012bz occurred at an unusually large offset (∼8 kpc) from the host galaxy nucleus, setting it apart from other nearby LGRBs and leading to speculation that the host environment may have undergone prior interaction activity. Here, we present spectroscopic observations using the 6.5 m Magellan telescope at Las Campanas. We extract spectra at three specific locations within the GRB/SN host galaxy, including the host nucleus, the explosion site, and the “bridge” of diffuse emission connecting these two regions. We measure a metallicity of log(O/H) + 12 = 8.3 ± 0.1 and a star formation rate (SFR) per unit area of 0.08 M☼ yr–1 kpc–2 at the host nucleus. At the GRB/SN explosion site we measure a comparable metallicity of log(O/H) + 12 = 8.2 ± 0.1 but find a much lower SFR per unit area of 0.01 M☼ yr–1 kpc–2. We also compare the host galaxy of this event to the hosts of other LGRBs, including samples of subluminous LGRBs and cosmological LGRBs, and find no systematic metallicity difference between the environments of these different subtypes. [ABSTRACT FROM AUTHOR]

We report four years of radio and X-ray monitoring of the Type IIn supernova SN 2006jd at radio wavelengths with the Very Large Array, Giant Metrewave Radio Telescope, and Expanded Very Large Array; at X-ray wavelengths with Chandra, XMM-Newton, and Swift-XRT. We assume that the radio and X-ray emitting particles are produced by shock interaction with a dense circumstellar medium. The radio emission shows an initial rise that can be attributed to free-free absorption by cool gas mixed into the nonthermal emitting region; external free-free absorption is disfavored because of the shape of the rising light curves and the low gas column density inferred along the line of sight to the emission region. The X-ray luminosity implies a preshock circumstellar density ∼106 cm–3 at a radius r ∼ 2 × 1016 cm, but the column density inferred from the photoabsorption of X-rays along the line of sight suggests a significantly lower density. The implication may be an asymmetry in the interaction. The X-ray spectrum shows Fe line emission at 6.9 keV that is stronger than is expected for the conditions in the X-ray emitting gas. We suggest that cool gas mixed into the hot gas plays a role in the line emission. Our radio and X-ray data both suggest the density profile is flatter than r–2 because of the slow evolution of the unabsorbed emission. [ABSTRACT FROM AUTHOR]

We present extensive radio observations of the nearby Type Ibc supernovae (SNe Ibc) 2004cc, 2004dk, and 2004gq spanning Δt ≈ 8-1900 days after explosion. Using a dynamical model developed for synchrotron emission from a slightly decelerated shock wave, we estimate the velocity and energy of the fastest ejecta and the density profile of the circumstellar medium. The shock waves of all three supernovae are characterized by non-relativistic velocities of and associated energies of E ≈ (2-10) × 1047 erg, in line with the expectations for a typical homologous explosion. Smooth circumstellar density profiles are indicated by the early radio data and we estimate the progenitor mass-loss rates to be (wind velocity, vw = 103 km s–1). These estimates approach the saturation limit () for line-driven winds from Wolf-Rayet stars, the favored progenitors of SNe Ibc including those associated with long-duration gamma-ray bursts. Intriguingly, at later epochs all three supernovae show evidence for abrupt radio variability that we attribute to large density modulations (factor of ∼3-6) at circumstellar radii of r ≈ (1-50) × 1016 cm. If due to variable mass loss, these modulations are associated with progenitor activity on a timescale of ∼10-100 years before explosion. We consider these results in the context of variable mass-loss mechanisms including wind clumping, metallicity-independent continuum-driven ejections, and binary-induced modulations. It may also be possible that the SN shock waves are dynamically interacting with wind termination shocks; however, this requires the environment to be highly pressurized and/or the progenitor to be rapidly rotating prior to explosion. The proximity of the density modulations to the explosion sites may suggest a synchronization between unusual progenitor mass loss and the SN explosion, reminiscent of Type IIn supernovae. This study underscores the utility of radio observations for tracing the final evolutionary stage(s) of SN progenitor systems. [ABSTRACT FROM AUTHOR]