220 research outputs found
Polarimetry of the superluminous supernova LSQ14mo: no evidence for significant deviations from spherical symmetry
We present the first polarimetric observations of a Type I superluminous
supernova (SLSN). LSQ14mo was observed with VLT/FORS2 at five different epochs
in the V band, with the observations starting before maximum light and spanning
26 days in the rest frame (z=0.256). During this period, we do not detect any
statistically significant evolution (< 2) in the Stokes parameters. The
average values we obtain, corrected for interstellar polarisation in the
Galaxy, are Q = -0.01% ( 0.15%) and U = - 0.50% ( 0.14%). This low
polarisation can be entirely due to interstellar polarisation in the SN host
galaxy. We conclude that, at least during the period of observations and at the
optical depths probed, the photosphere of LSQ14mo does not present significant
asymmetries, unlike most lower-luminosity hydrogen-poor SNe Ib/c.
Alternatively, it is possible that we may have observed LSQ14mo from a special
viewing angle. Supporting spectroscopy and photometry confirm that LSQ14mo is a
typical SLSN I. Further studies of the polarisation of Type I SLSNe are
required to determine whether the low levels of polarisation are a
characteristic of the entire class and to also study the implications for the
proposed explosion models.Comment: ApJ Letters, 4 Figures, 3 Tables. The previous version was accepted.
This version contains minor modifications to match proofs (as much as
possible
The interacting nature of dwarf galaxies hosting superluminous supernovae
(Abridged) Type I superluminous supernovae (SLSNe I) are rare, powerful
explosions whose mechanism and progenitors remain elusive. SLSNe I show a
preference for low-metallicity, actively star-forming dwarf galaxies. We
investigate whether the hosts of SLSNe I show increased evidence for
interaction. We use a sample of 42 SLSN I images obtained with
and measure the number of companion galaxies by counting the objects detected
within a given radius from the host. As a comparison, we used two Monte
Carlo-based methods to estimate the expected average number of companion
objects in the same images, as well as a sample of 32 galaxies that have hosted
long gamma-ray bursts (GRBs). About 50% of SLSN I hosts have at least one major
companion (within a flux ratio of 1:4) within 5 kpc. The average number of
major companions per SLSN I host galaxy is . Our Monte
Carlo comparison methods yield a lower number of companions for random objects
of similar brightness in the same image or for the SLSN host after randomly
redistributing the sources in the same image. The Anderson-Darling test shows
that this difference is statistically significant independent of the redshift
range. The same is true for the projected distance distribution of the
companions. The SLSN I hosts are, thus, found in areas of their images, where
the object number density is greater than average. SLSN I hosts have more
companions than GRB hosts ( companions per host
distributed over 25% of the hosts) but the difference is not statistically
significant. The difference between their separations is, however, marginally
significant. The dwarf galaxies hosting SLSNe I are often part of interacting
systems. This suggests that SLSNe I progenitors are formed after a recent burst
of star formation. Low metallicity alone cannot explain this tendency.Comment: Accepted for publication in A&A. In v2 replaced graphs with higher
quality PDF version
Supernova PTF12glz: a possible shock breakout driven through an aspherical wind
We present visible-light and ultraviolet (UV) observations of the supernova
PTF12glz. The SN was discovered and monitored in near-UV and R bands as part of
a joint GALEX and Palomar Transient Factory campaign. It is among the most
energetic Type IIn supernovae observed to date (~10^51erg). If the radiated
energy mainly came from the thermalization of the shock kinetic energy, we show
that PTF12glz was surrounded by ~1 solar mass of circumstellar material (CSM)
prior to its explosive death. PTF12glz shows a puzzling peculiarity: at early
times, while the freely expanding ejecta are presumably masked by the optically
thick CSM, the radius of the blackbody that best fits the observations grows at
~8000km/s. Such a velocity is characteristic of fast moving ejecta rather than
optically thick CSM. This phase of radial expansion takes place before any
spectroscopic signature of expanding ejecta appears in the spectrum and while
both the spectroscopic data and the bolometric luminosity seem to indicate that
the CSM is optically thick. We propose a geometrical solution to this puzzle,
involving an aspherical structure of the CSM around PTF12glz. By modeling
radiative diffusion through a slab of CSM, we show that an aspherical geometry
of the CSM can result in a growing effective radius. This simple model also
allows us to recover the decreasing blackbody temperature of PTF12glz.
SLAB-Diffusion, the code we wrote to model the radiative diffusion of photons
through a slab of CSM and evaluate the observed radius and temperature, is made
available on-line.Comment: Sumbitted to ApJ. Comments are welcom
MiRP1 forms IKr potassium channels with HERG and is associated with cardiac arrhythmia.
A novel potassium channel gene has been cloned, characterized, and associated with cardiac arrhythmia. The gene encodes MinK-related peptide 1 (MiRP1), a small integral membrane subunit that assembles with HERG, a pore-forming protein, to alter its function. Unlike channels formed only with HERG, mixed complexes resemble native cardiac IKr channels in their gating, unitary conductance, regulation by potassium, and distinctive biphasic inhibition by the class III antiarrhythmic E-4031. Three missense mutations associated with long QT syndrome and ventricular fibrillation are identified in the gene for MiRP1. Mutants form channels that open slowly and close rapidly, thereby diminishing potassium currents. One variant, associated with clarithromycin-induced arrhythmia, increases channel blockade by the antibiotic. A mechanism for acquired arrhythmia is revealed: genetically based reduction in potassium currents that remains clinically silent until combined with additional stressors
Early-time spectroscopic modelling of the transitional Type Ia Supernova 2021rhu with TARDIS
An open question in SN Ia research is where the boundary lies between
'normal' Type Ia supernovae (SNe Ia) that are used in cosmological measurements
and those that sit off the Phillips relation. We present the spectroscopic
modelling of one such '86G-like' transitional SN Ia, SN 2021rhu, that has
recently been employed as a local Hubble Constant calibrator using a tip of the
red-giant branch measurement. We detail its modelling from -12 d until maximum
brightness using the radiative-transfer spectral-synthesis code tardis. We base
our modelling on literature delayed-detonation and deflagration models of
Chandrasekhar mass white dwarfs, as well as the double-detonation models of
sub-Chandrasekhar mass white dwarfs. We present a new method for 'projecting'
abundance profiles to different density profiles for ease of computation. Due
to the small velocity extent and low outer densities of the W7 profile, we find
it inadequate to reproduce the evolution of SN 2021rhu as it fails to match the
high-velocity calcium components. The host extinction of SN 2021rhu is
uncertain but we use modelling with and without an extinction correction to set
lower and upper limits on the abundances of individual species. Comparing these
limits to literature models we conclude that the spectral evolution of SN
2021rhu is also incompatible with double-detonation scenarios, lying more in
line with those resulting from the delayed detonation mechanism (although there
are some discrepancies, in particular a larger titanium abundance in SN 2021rhu
compared to the literature). This suggests that SN 2021rhu is likely a lower
luminosity, and hence lower temperature, version of a normal SN Ia.Comment: 25 pages, 22 figures, accepted for publication in MNRA
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