To understand the dynamics of infectious diseases, genomic epidemiology is increasingly advocated, with a need for rapid generation of genetic sequences during outbreaks for public health decision ...making. Here, we explore the use of metagenomic sequencing compared to specific amplicon- and capture-based sequencing, both on the Nanopore and the Illumina platform for generation of whole genomes of Usutu virus, Zika virus, West Nile virus, and Yellow Fever virus. We show that amplicon-based Nanopore sequencing can be used to rapidly obtain whole genome sequences in samples with a viral load up to Ct 33 and capture-based Illumina is the most sensitive method for initial virus determination. The choice of sequencing approach and platform is important for laboratories wishing to start whole genome sequencing. Depending on the purpose of genome sequencing the best choice can differ. The insights presented in this work and the shown differences in data characteristics can guide labs to make a well informed choice.
‘High-velocity features’ (HVFs) are spectral features in Type Ia supernovae (SNe Ia) that have minima indicating significantly higher (by greater than about 6000 km s−1) velocities than typical ...‘photospheric-velocity features’ (PVFs). The PVFs are absorption features with minima indicating typical photospheric (i.e. bulk ejecta) velocities (usually ∼9000–15 000 km s−1 near B-band maximum brightness). In this work, we undertake the most in-depth study of HVFs ever performed. The data set used herein consists of 445 low-resolution optical and near-infrared (NIR) spectra (at epochs up to 5 d past maximum brightness) of 210 low-redshift SNe Ia that follow the ‘Phillips relation’. A series of Gaussian functions is fit to the data in order to characterize possible HVFs of Ca ii H&K, Si ii λ6355, and the Ca ii
NIR triplet. The temporal evolution of the velocities and strengths of the PVFs and HVFs of these three spectral features is investigated, as are possible correlations with other SN Ia observables. We find that while HVFs of Ca ii are regularly observed (except in underluminous SNe Ia, where they are never found), HVFs of Si ii λ6355 are significantly rarer, and they tend to exist at the earliest epochs and mostly in objects with large photospheric velocities. It is also shown that stronger HVFs of Si ii λ6355 are found in objects that lack C ii absorption at early times and that have red ultraviolet/optical colours near maximum brightness. These results lead to a self-consistent connection between the presence and strength of HVFs of Si ii λ6355 and many other mutually correlated SN Ia observables, including photospheric velocity.
SN 2014J in M82 is the closest detected Type Ia supernova (SN Ia) in at least 28 yr and perhaps in 410 yr. Despite its small distance of 3.3 Mpc, SN 2014J is surprisingly faint, peaking at ...V = 10.6 mag, and assuming a typical SN Ia luminosity, we infer an observed visual extinction of A
V
= 2.0 ± 0.1 mag. But this picture, with R
V
= 1.6 ± 0.2, is too simple to account for all observations. We combine 10 epochs (spanning a month) of HST/Space Telescope Imaging Spectrograph (STIS) ultraviolet through near-infrared spectroscopy with HST/Wide Field Camera 3 (WFC3), Katzman Automatic Imaging Telescope, and FanCam photometry from the optical to the infrared and nine epochs of high-resolution TRES (Tillinghast Reflection Echelle Spectrograph) spectroscopy to investigate the sources of extinction and reddening for SN 2014J. We argue that the wide range of observed properties for SN 2014J is caused by a combination of dust reddening, likely originating in the interstellar medium of M82, and scattering off circumstellar material. For this model, roughly half of the extinction is caused by reddening from typical dust (E(B − V) = 0.45 mag and R
V
= 2.6) and roughly half by scattering off Large Magellanic Cloud-like dust in the circumstellar environment of SN 2014J.
We present extensive early photometric (ultraviolet through near-infrared) and spectroscopic (optical and near-infrared) data on supernova (SN) 2008D as well as X-ray data analysis on the associated ...Swift X-ray transient (XRT) 080109. Our data span a time range of 5 hr before the detection of the X-ray transient to 150 days after its detection, and a detailed analysis allowed us to derive constraints on the nature of the SN and its progenitor; throughout we draw comparisons with results presented in the literature and find several key aspects that differ. We show that the X-ray spectrum of XRT 080109 can be fit equally well by an absorbed power law or a superposition of about equal parts of both power law and blackbody. Our data first established that SN 2008D is a spectroscopically normal SN Ib (i.e., showing conspicuous He lines) and showed that SN 2008D had a relatively long rise time of 18 days and a modest optical peak luminosity. The early-time light curves of the SN are dominated by a cooling stellar envelope (for Delta *Dt0.1-4 days, most pronounced in the blue bands) followed by 56Ni decay. We construct a reliable measurement of the bolometric output for this stripped-envelope SN, and, combined with estimates of E K and M ej from the literature, estimate the stellar radius R of its probable Wolf-Rayet progenitor. According to the model of Waxman et al. and Chevalier & Fransson, we derive R W07 = 1.2 +/- 0.7R and R CF08 = 12 +/- 7 R, respectively; the latter being more in line with typical WN stars. Spectra obtained at three and four months after maximum light show double-peaked oxygen lines that we associate with departures from spherical symmetry, as has been suggested for the inner ejecta of a number of SN Ib cores.
A growing subset of Type Ia supernovae (SNe Ia) shows evidence via narrow emission lines for unexpected interaction with a dense circumstellar medium (SNe IIn/Ia–CSM). The precise nature of the ...progenitor, however, remains debated owing to spectral ambiguities arising from a strong contribution from the CSM interaction. Late-time spectra offer potential insight if the post-shock cold, dense shell becomes sufficiently thin and/or the ejecta begin to cross the reverse shock. To date, only a few high-quality spectra of this kind exist. Here we report on the late-time optical and infrared spectra of the SNe Ia–CSM 2012ca and 2013dn. These SNe Ia–CSM spectra exhibit low Fe iii/Fe ii ratios and strong Ca ii at late epochs. Such characteristics are reminiscent of the super-Chandrasekhar-mass candidate SN 2009dc, for which these features suggested a low-ionization state due to high densities, although the broad Fe features admittedly show similarities to the blue ‘quasi-continuum’ observed in some core collapse SNe Ibn and IIn. Neither SN 2012ca nor any of the other SNe Ia–CSM in this paper show evidence for broad oxygen, carbon, or magnesium in their spectra. Similar to the interacting Type IIn SN 2005ip, a number of high-ionization lines are identified in SN 2012ca, including S iii, Ar iii, Ar x, Fe viii, Fe x, and possibly Fe xi. The total bolometric energy output does not exceed 1051 erg, but does require a large kinetic-to-radiative conversion efficiency. All of these observations taken together suggest that SNe Ia–CSM are more consistent with a thermonuclear explosion than a core collapse event, although detailed radiative transfer models are certainly necessary to confirm these results.
The flare of radiation from the tidal disruption and accretion of a star can be used as a marker for supermassive black holes that otherwise lie dormant and undetected in the centres of distant ...galaxies. Previous candidate flares have had declining light curves in good agreement with expectations, but with poor constraints on the time of disruption and the type of star disrupted, because the rising emission was not observed. Recently, two 'relativistic' candidate tidal disruption events were discovered, each of whose extreme X-ray luminosity and synchrotron radio emission were interpreted as the onset of emission from a relativistic jet. Here we report a luminous ultraviolet-optical flare from the nuclear region of an inactive galaxy at a redshift of 0.1696. The observed continuum is cooler than expected for a simple accreting debris disk, but the well-sampled rise and decay of the light curve follow the predicted mass accretion rate and can be modelled to determine the time of disruption to an accuracy of two days. The black hole has a mass of about two million solar masses, modulo a factor dependent on the mass and radius of the star disrupted. On the basis of the spectroscopic signature of ionized helium from the unbound debris, we determine that the disrupted star was a helium-rich stellar core.
We present a densely sampled, homogeneous set of light curves of 64 low-redshift (z <, ~ 0.05) stripped-envelope supernovae (SNe of Type IIb, Ib, Ic, and Ic-BL). These data were obtained between 2001 ...and 2009 at the Fred L. Whipple Observatory (FLWO) on Mount Hopkins in Arizona, with the optical FLWO 1.2 m and the near-infrared (NIR) Peters Automated Infrared 1.3 m telescopes. Our data set consists of 4543 optical photometric measurements on 61 SNe, including a combination of U B V R I, U BVr'i', and u'B Vr'i', and 1919 JHK sub(s) NIR measurements on 25 SNe. This sample constitutes the most extensive multi-color data set of stripped-envelope SNe to date. Our photometry is based on template-subtracted images to eliminate any potential host-galaxy light contamination. This work presents these photometric data, compares them with data in the literature, and estimates basic statistical quantities: date of maximum, color, and photometric properties. We identify promising color trends that may permit the identification of stripped-envelope SN subtypes from their photometry alone. Many of these SNe were observed spectroscopically by the Harvard-Smithsonian Center for Astrophysics (CfA) SN group, and the spectra are presented in a companion paper. A thorough exploration that combines the CfA photometry and spectroscopy of stripped-envelope core-collapse SNe will be presented in a follow-up paper.
We present nebular phase optical and near-infrared spectroscopy of the Type Ia supernova (SN) 2017cbv. The early light curves of SN 2017cbv showed a prominent blue bump in the U, B, and g bands ...lasting for ∼5 days. One interpretation of the early light curve is that the excess blue light is due to shocking of the SN ejecta against a nondegenerate companion star-a signature of the single degenerate scenario. If this is the correct interpretation, the interaction between the SN ejecta and the companion star could result in significant H (or helium) emission at late times, possibly along with other species, depending on the companion star and its orbital separation. A search for H emission in our +302 d spectrum yields a nondetection, with a LH < 8.0 × 1035 erg s−1 (given an assumed distance of D = 12.3 Mpc), which we verified by implanting simulated H emission into our data. We make a quantitative comparison to models of swept-up material stripped from a nondegenerate companion star and limit the mass of hydrogen that might remain undetected to MH < 1 × 10−4 M . A similar analysis of helium star related lines yields a MHe < 5 × 10−4 M . Taken at face value, these results argue against a nondegenerate H- or He-rich companion in Roche lobe overflow as the progenitor of SN 2017cbv. Alternatively, there could be weaknesses in the envelope-stripping and radiative transfer models necessary to interpret the strong H and He flux limits.
Type Iax supernovae are stellar explosions that are spectroscopically similar to some type Ia supernovae at the time of maximum light emission, except with lower ejecta velocities. They are also ...distinguished by lower luminosities. At late times, their spectroscopic properties diverge from those of other supernovae, but their composition (dominated by iron-group and intermediate-mass elements) suggests a physical connection to normal type Ia supernovae. Supernovae of type Iax are not rare; they occur at a rate between 5 and 30 per cent of the normal type Ia rate. The leading models for type Iax supernovae are thermonuclear explosions of accreting carbon-oxygen white dwarfs that do not completely unbind the star, implying that they are 'less successful' versions of normal type Ia supernovae, where complete stellar disruption is observed. Here we report the detection of the luminous, blue progenitor system of the type Iax SN 2012Z in deep pre-explosion imaging. The progenitor system's luminosity, colours, environment and similarity to the progenitor of the Galactic helium nova V445 Puppis suggest that SN 2012Z was the explosion of a white dwarf accreting material from a helium-star companion. Observations over the next few years, after SN 2012Z has faded, will either confirm this hypothesis or perhaps show that this supernova was actually the explosive death of a massive star.
ABSTRACT We report evidence for excess blue light from the Type Ia supernova (Sn Ia) SN 2012cg at 15 and 16 days before maximum B-band brightness. The emission is consistent with predictions for the ...impact of the supernova on a non-degenerate binary companion. This is the first evidence for emission from a companion to a normal SN Ia. Sixteen days before maximum light, the color of SN 2012cg is 0.2 mag bluer than for other normal SN Ia. At later times, this supernova has a typical SN Ia light curve, with extinction-corrected mag and . Our data set is extensive, with photometry in seven filters from five independent sources. Early spectra also show the effects of blue light, and high-velocity features are observed at early times. Near maximum, the spectra are normal with a silicon velocity vSi = −10,500 km s−1. Comparing the early data with models by Kasen favors a main-sequence companion of about six solar masses. It is possible that many other SN Ia have main-sequence companions that have eluded detection because the emission from the impact is fleeting and faint.
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