Massive star supernovae can be divided into four categories, depending on the amount of mass loss from the progenitor star and the star's radius: red supergiant stars with most of the H envelope ...intact (SN IIP), stars with some H but most lost (IIL and IIb), stars with all H lost (Ib and Ic), and blue supergiant stars with a massive H envelope (SN 1987A-like). Various aspects of the immediate aftermath of the supernova are expected to develop in different ways, depending on the supernova category: mixing in the supernova, fallback on the central compact object, expansion of any pulsar wind nebula, interaction with circumstellar matter, and photoionization by shock breakout radiation. The observed properties of young supernova remnants allow many of them to be placed in one of the supernova categories; all the categories are represented except for the SN 1987A-like type. Of the remnants with central pulsars, the pulsar properties do not appear to be related to the supernova category. There is no evidence that the supernova categories form a mass sequence, as would be expected in a single-star scenario for the evolution. Models for young pulsar wind nebulae expanding into supernova ejecta indicate initial pulsar periods of 10-100 ms and approximate equipartition between particle and magnetic energies. Ages are obtained for pulsar nebulae, including an age of 2400 plus or minus 500 yr for 3C 58, which is not consistent with an origin in SN 1181. There is no evidence that mass fallback plays a role in neutron star properties.
Type Ia supernovae are important cosmological distance indicators. Each of these bright supernovae supposedly results from the thermonuclear explosion of a white dwarf star that, after accreting ...material from a companion star, exceeds some mass limit, but the true nature of the progenitor star system remains controversial. Here we report the spectroscopic detection of circumstellar material in a normal type Ia supernova explosion. The expansion velocities, densities, and dimensions of the circumstellar envelope indicate that this material was ejected from the progenitor system. In particular, the relatively low expansion velocities suggest that the white dwarf was accreting material from a companion star that was in the red-giant phase at the time of the explosion.
We present the discovery of two ultraluminous supernovae (SNe) at z 0.9 with the Pan-STARRS1 Medium Deep Survey. These SNe, PS1-10ky and PS1-10awh, are among the most luminous SNe ever discovered, ...comparable to the unusual transients SN 2005ap and SCP 06F6. Like SN 2005ap and SCP 06F6, they show characteristic high luminosities (M bol --22.5 mag), blue spectra with a few broad absorption lines, and no evidence for H or He. We have constructed a full multi-color light curve sensitive to the peak of the spectral energy distribution in the rest-frame ultraviolet, and we have obtained time series spectroscopy for these SNe. Given the similarities between the SNe, we combine their light curves to estimate a total radiated energy over the course of explosion of (0.9-1.4) X 1051 erg. We find photospheric velocities of 12,000-19,000 km s--1 with no evidence for deceleration measured across ~3 rest-frame weeks around light curve peak, consistent with the expansion of an optically thick massive shell of material. We show that, consistent with findings for other ultraluminous SNe in this class, radioactive decay is not sufficient to power PS1-10ky, and we discuss two plausible origins for these events: the initial spin-down of a newborn magnetar in a core-collapse SN, or SN shock breakout from the dense circumstellar wind surrounding a Wolf-Rayet star.
Long-duration gamma-ray bursts (GRBs) are widely believed to be highly collimated explosions (bipolar conical outflows with half-opening angle theta{approx} 1{sup 0}-10{sup 0}). As a result of this ...beaming factor, the true energy release from a GRB is usually several orders of magnitude smaller than the observed isotropic value. Measuring this opening angle, typically inferred from an achromatic steepening in the afterglow light curve (a 'jet' break), has proven exceedingly difficult in the Swift era. Here, we undertake a study of five of the brightest (in terms of the isotropic prompt gamma-ray energy release, E{sub g}amma{sub ,iso}) GRBs in the Swift era to search for jet breaks and hence constrain the collimation-corrected energy release. We present multi-wavelength (radio through X-ray) observations of GRBs 050820A, 060418, and 080319B, and construct afterglow models to extract the opening angle and beaming-corrected energy release for all three events. Together with results from previous analyses of GRBs 050904 and 070125, we find evidence for an achromatic jet break in all five events, strongly supporting the canonical picture of GRBs as collimated explosions. The most natural explanation for the lack of observed jet breaks from most Swift GRBs is therefore selection effects. However, the opening angles for the events in our sample are larger than would be expected if all GRBs had a canonical energy release of {approx}10{sup 51} erg. The total energy release we measure for the 'hyper-energetic' (E{sub tot} {approx}> 10{sup 52} erg) events in our sample is large enough to start challenging models with a magnetar as the compact central remnant.
We present extensive radio observations of SN 2003L, the most luminous and energetic Type Ibc radio supernova with the exception of SN 1998bw (associated with GRB 980425). Observations from the Very ...Large Array are well described by fitting a synchrotron self-absorption model to the emission spectrum. This model implies a subrelativistic ejecta velocity, u - 0.2c, and a size of r - 4.3 x 10 super(15) cm at t - 10 days. The circumstellar density is suitably fitted with a stellar wind profile, n sub(e) 8 r super(-2) cm super(-3) and a constant mass-loss rate of M - 7.5 x 10 super(-6) M sub( )yr super(-1). Moreover, the magnetic field follows B 8 r super(-1) and the kinetic energy of the radio-bright ejecta is roughly E - 10 super(48) ergs assuming equipartition of energy between relativistic electrons and magnetic fields. Furthermore, we show that free-free absorption does not contribute significantly to the radio spectrum, since it implies ejecta velocities that are inconsistent with size constraints derived from Very Long Baseline Array observations. In conclusion, we find that although SN 2003L has a radio luminosity comparable to that seen in SN 1998bw, it shows no evidence for a significant amount of energy coupled to relativistic ejecta. Using SN 2003L as an example, we comment briefly on the coupling of ejecta velocity and energy in Type Ibc supernovae.
We present extensive radio and X-ray observations of the nearby Type Ic SN 2007gr in NGC 1058 obtained with the Very Large Array (VLA) and the Chandra X-ray Observatory and spanning 5 to 150 days ...after explosion. Through our detailed modeling of these data, we estimate the properties of the blast wave and the circumstellar environment. We find evidence for a freely expanding and non-relativistic explosion with an average blast wave velocity, , and a total internal energy for the radio emitting material of E 2 X 1046 erg assuming equipartition of energy between electrons and magnetic fields ( e = B = 0.1). The temporal and spectral evolution of the radio emission points to a stellar wind-blown environment shaped by a steady progenitor mass loss rate of (wind velocity, vw = 103 km s--1). These parameters are fully consistent with those inferred for other SNe Ibc and are in line with the expectations for an ordinary, homologous SN explosion. Our results are at odds with those of Paragi et al. who recently reported evidence for a relativistic blast wave in SN 2007gr based on their claim that the radio emission was resolved away in a low signal-to-noise Very Long Baseline Interferometry (VLBI) observation. Here we show that the exotic physical scenarios required to explain the claimed relativistic velocity--extreme departures from equipartition and/or a highly collimated outflow--are excluded by our detailed VLA radio observations. Moreover, we present an independent analysis of the VLBI data and propose that a modest loss of phase coherence provides a more natural explanation for the apparent flux density loss which is evident on both short and long baselines. We conclude that SN 2007gr is an ordinary Type Ibc supernova.
We present multi-epoch high-resolution optical spectroscopy, UV/radio/X-ray imaging, and archival Hubble and Spitzer observations of an intermediate luminosity optical transient recently discovered ...in the nearby galaxy NGC 300. We find that the transient (NGC 300 OT2008-1) has a peak absolute magnitude of M bol ≈ -11.8 mag, intermediate between novae and supernovae, and similar to the recent events M85 OT2006-1 and SN 2008S. Our high-resolution spectra, the first for this event, are dominated by intermediate velocity (~200-1000 km s-1) hydrogen Balmer lines and Ca II emission and absorption lines that point to a complex circumstellar environment, reminiscent of the yellow hypergiant IRC+10420. In particular, we detect asymmetric Ca II H&K absorption with a broad red wing extending to ~103 km s-1, indicative of gas inflow at high velocity (possibly the wind of a massive binary companion). The low luminosity, intermediate velocities, and overall similarity to a known eruptive star indicate that the event did not result in a complete disruption of the progenitor. We identify the progenitor in archival Spitzer observations, with deep upper limits from Hubble data. The spectral energy distribution points to a dust-enshrouded star with a luminosity of about 6 × 104 L sun, indicative of a ~10-20 M sun progenitor (or binary system). This conclusion is in good agreement with our interpretation of the outburst and circumstellar properties. The lack of significant extinction in the transient spectrum indicates that the dust surrounding the progenitor was cleared by the outburst. We thus predict that the progenitor should be eventually visible with Hubble if the transient event marks an evolutionary transition to a dust-free state, or with Spitzer if the event marks a cyclical process of dust formation.
•Consistency between two MPS approaches and between MPS and qPCR.•Greater detection of Bacillus at the Canberra Airport with MPS compared to qPCR.•Selected MPS target(s) generated metagenomic ...fingerprint of bacterial community.•Selected MPS target(s) could not resolve Bacillus beyond the B. cereus group.•Choice of target(s) is key to differentiate pathogenic from non-pathogenic species.
Anthrax, caused by the Gram-positive, spore forming bacterium Bacillus anthracis, is a disease with naturally occurring outbreaks in many parts of the world, primarily in domestic and wild herbivores. Due to the movement of people and stock, B. anthracis could, however, be at transportation hubs including airports. The continuous threat to national and international security from a biological agent release, or hoax attack, is a very real concern. Sensitive, robust and rapid (hours-day) methods to identify biological agents, including B. anthracis, and distinguish pathogenic from non-pathogenic species, is an essential cornerstone to national security. The aim of this project was to determine the presence of Bacillus species at the Canberra Airport using two massively parallel sequencing (MPS) approaches and compare with previous results using real-time polymerase chain reaction (qPCR).
Samples were collected daily for seven days each month from August 2011–July 2012 targeting movement of people, luggage and freight into and out of the Canberra Airport. Extracted DNA was analysed using qPCR specific for B. anthracis. A subset of samples was analysed using two MPS approaches. Approach one, using the Ion PGM™ (Thermo Fisher Scientific; TFS) and an in-house assay, targeted the two B. anthracis virulence plasmids (cya and capB genes) and a single conserved region of the 16S rRNA gene. Approach two, using the Ion S5™ (TFS) and the commercial Ion 16S™ Metagenomics Kit (TFS), targeted multiple regions within the bacterial 16S rRNA gene.
Overall there was consistency between the two MPS approaches and between MPS and qPCR, however, MPS was more sensitive, particularly for plasmid detection. Whilst the broad-range 16S genomic target(s) used in both MPS approaches in this study was able to generate a metagenomic fingerprint of the bacterial community at the Canberra Airport, it could not resolve Bacillus species beyond the level of the Bacillus cereus group. The inclusion of B. anthracis virulence plasmid targets in the in-house assay did allow for the potential presumptive identifications of pathogenic species. No plasmid targets were in the Ion 16S™ Metagenomics Kit.
This study shows the choice of target(s) is key in MPS assay development and should be carefully considered to ensure the assay is fit for purpose, whether as an initial screening (presumptive) or a more specific (but not entirely confirmatory) test. Identification approaches may also benefit from a combination of MPS and qPCR as each has benefits and limitations.
We present a generalized analytic formalism for the inverse Compton X-ray emission from hydrogen-poor supernovae and apply this framework to SN 2011fe using Swift X-Ray Telescope (XRT), UVOT, and ...Chandra observations. We characterize the optical properties of SN 2011fe in the Swift bands and find them to be broadly consistent with a "normal" SN Ia, however, no X-ray source is detected by either XRT or Chandra. We constrain the progenitor system mass-loss rate M < 2 x 10 super(-9) M sub(odot) yr super(-1) (3sigma c.l.) for wind velocity v sub(w), = 100km s super(-1). Our result rules out symbiotic binary progenitors for SN 2011fe and argues against Roche lobe overflowing subgiants and main-sequence secondary stars if gap 1% of the transferred mass is lost at the Lagrangian points. Regardless of the density profile, the X-ray non-detections are suggestive of a clean environment (n sub(CSM) < 150 cm super(-3)) for 2 x 10 super(15) lap R lap 5 x 10 super(16) cm around the progenitor site. This is either consistent with the bulk of material being confined within the binary system or with a significant delay between mass loss and supernova explosion. We furthermore combine X-ray and radio limits from Chomiuk et al. to constrain the post-shock energy density in magnetic fields. Finally, we searched for the shock breakout pulse using gamma-ray observations from the Interplanetary Network and find no compelling evidence for a supernova-associated burst. Based on the compact radius of the progenitor star we estimate that the shock breakout pulse was likely not detectable by current satellites.
We present seven epochs between October 1999 and November 2007 of high resolution VLT/UVES echelle spectra of the ejecta-ring collision of SN 1987A. The fluxes of most of the narrow lines from the ...unshocked gas decreased by a factor of $2{-}3$ during this period, consistent with the decay from the initial ionization by the shock break-out. However, O III in particular shows an increase up to day ~6800. This agrees with radiative shock models where the pre-shocked gas is heated by the soft X-rays from the shock. The evolution of the O III line ratio shows a decreasing temperature of the unshocked ring gas, consistent with a transition from a hot, low density component which was heated by the initial flash ionization to the lower temperature in the pre-ionized gas ahead of the shocks. The line emission from the shocked gas increases rapidly as the shock sweeps up more gas. We find that the neutral and high ionization lines follow the evolution of the Balmer lines roughly, while the intermediate ionization lines evolve less rapidly. Up to day ~6800, the optical light curves have a similar evolution to that of the soft X-rays. The break between day 6500 and day 7000 for O III and Ne III is likely due to recombination to lower ionization levels. Nevertheless, the evolution of the Fe XIV line, as well as the lines from the lowest ionization stages, continue to follow that of the soft X-rays, as expected. There is a clear difference in the line profiles between the low and intermediate ionization lines, and those from the coronal lines at the earlier epochs. This shows that these lines arise from regions with different physical conditions, with at least a fraction of the coronal lines coming from adiabatic shocks. At later epochs the line widths of the low ionization lines, however, increase and approach those of the high ionization lines of Fe X-XIV . The Hα line profile can be traced up to ~500 km s-1 at the latest epoch. This is consistent with the cooling time of shocks propagating into a density of (1-4) $\times$ 104 cm-3. This means that these shocks are among the highest velocity radiative shocks observed.
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