102 research outputs found
Numerically Modeling the First Peak of the Type IIb SN 2016gkg
Many Type IIb supernovae (SNe) show a prominent additional early peak in
their light curves, which is generally thought to be due to the shock cooling
of extended hydrogen-rich material surrounding the helium core of the exploding
star. The recent SN 2016gkg was a nearby Type IIb SN discovered shortly after
explosion, which makes it an excellent candidate for studying this first peak.
We numerically explode a large grid of extended envelope models and compare
these to SN 2016gkg to investigate what constraints can be derived from its
light curve. This includes exploring density profiles for both a convective
envelope and an optically thick steady-state wind, the latter of which has not
typically been considered for Type IIb SNe models. We find that roughly
of extended material with a radius of
reproduces the photometric light curve data,
consistent with pre-explosion imaging. These values are independent of the
assumed density profile of this material, although a convective profile
provides a somewhat better fit. We infer from our modeling that the explosion
must have occurred within of the first observed data
point, demonstrating that this event was caught very close to the moment of
explosion. Nevertheless, our best-fitting one-dimensional models overpredict
the earliest velocity measurements, which suggests that the hydrogen-rich
material is not distributed in a spherically symmetric manner. We compare this
to the asymmetries seen in the SN IIb remnant Cas A, and we discuss the
implications of this for Type IIb SN progenitors and explosion models.Comment: 8 pages, 8 figures, updated version accepted for publication in The
Astrophysical Journa
An empirical limit on the kilonova rate from the DLT40 one day cadence Supernova Survey
Binary neutron star mergers are important to understand stellar evolution,
the chemical enrichment of the universe via the r-process, the physics of short
gamma-ray bursts, gravitational waves and pulsars. The rates at which these
coalescences happen is uncertain, but it can be constrained in different ways.
One of those is to search for the optical transients produced at the moment of
the merging, called a kilonova, in ongoing SN searches. However, until now,
only theoretical models for kilonovae light curve were available to estimate
their rates. The recent kilonova discovery AT~2017gfo/DLT17ck gives us the
opportunity to constrain the rate of kilonovae using the light curve of a real
event. We constrain the rate of binary neutron star mergers using the DLT40
Supernova search, and the native AT~2017gfo/DLT17ck light curve obtained with
the same telescope and software system. Excluding AT~2017gfo/DLT17ck due to
visibility issues, which was only discovered thanks to the aLIGO/aVirgo
trigger, no other similar transients detected during 13 months of daily cadence
observations of 2200 nearby (40 Mpc) galaxies. We find that the rate
of BNS mergers is lower than 0.47 - 0.55 kilonovae per 100 years per
(depending on the adopted extinction distribution). In volume,
this translates to <0.99\times
10^{-4}\,_{-0.15}^{+0.19},\rm{Mpc^{-3}}\,\rm{yr^{-1}}(SNe Ia-like extinction
distribution), consistent with previous BNS coalescence rates. Based on our
rate limit, and the sensitivity of aLIGO/aVirgo during O2, it is very unlikely
that kilonova events are lurking in old pointed galaxy SN search datasets.Comment: 3 figures, 2 table
The discovery of the electromagnetic counterpart of GW170817: kilonova AT 2017gfo/DLT17ck
During the second observing run of the Laser Interferometer gravitational-
wave Observatory (LIGO) and Virgo Interferometer, a gravitational-wave signal
consistent with a binary neutron star coalescence was detected on 2017 August
17th (GW170817), quickly followed by a coincident short gamma-ray burst trigger
by the Fermi satellite. The Distance Less Than 40 (DLT40) Mpc supernova search
performed pointed follow-up observations of a sample of galaxies regularly
monitored by the survey which fell within the combined LIGO+Virgo localization
region, and the larger Fermi gamma ray burst error box. Here we report the
discovery of a new optical transient (DLT17ck, also known as SSS17a; it has
also been registered as AT 2017gfo) spatially and temporally coincident with
GW170817. The photometric and spectroscopic evolution of DLT17ck are unique,
with an absolute peak magnitude of Mr = -15.8 \pm 0.1 and an r-band decline
rate of 1.1mag/d. This fast evolution is generically consistent with kilonova
models, which have been predicted as the optical counterpart to binary neutron
star coalescences. Analysis of archival DLT40 data do not show any sign of
transient activity at the location of DLT17ck down to r~19 mag in the time
period between 8 months and 21 days prior to GW170817. This discovery
represents the beginning of a new era for multi-messenger astronomy opening a
new path to study and understand binary neutron star coalescences, short
gamma-ray bursts and their optical counterparts.Comment: ApJL in press, 4 figure
Neurophysiological and clinical biomarkers of secondary progressive multiple sclerosis: A cross-sectional study
Timely diagnosis of secondary progressive multiple sclerosis (SPMS) represents a clinical challenge. The Frailty Index, a quantitative frailty measure, and the Neurophysiological Index, a combined measure of sensorimotor cortex inhibitory mechanism parameters, have recently emerged as promising tools to support SPMS diagnosis. The aim of this study was to explore the possible relationship between these two indices in MS. MS participants underwent a clinical evaluation, Frailty Index administration, and neurophysiological assessment. Frailty and Neurophysiological Index scores were found to be higher in SPMS and correlated with each other, thus suggesting that they may capture similar SPMS-related pathophysiological mechanisms
Optical follow-up of gravitational wave events during the second advanced LIGO/VIRGO observing run with the DLT40 Survey
We describe the GW follow-up strategy and subsequent results of the DLT40
during the second science run (O2) of the LVC. Depending on the information
provided in the GW alert together with the localization map sent by the LVC,
DLT40 would respond promptly to image the corresponding galaxies selected by
our ranking algorithm in order to search for possible EM counterparts in real
time. During the LVC O2 run, DLT40 followed ten GW triggers, observing between
20-100 galaxies within the GW localization area of each event. From this
campaign, we identified two real transient sources within the GW localizations
with an appropriate on-source time -- one was an unrelated type Ia supernova
(SN~2017cbv), and the other was the optical kilonova, AT
2017fgo/SSS17a/DLT17ck, associated with the binary neutron star coalescence
GW170817 (a.k.a gamma-ray burst GRB170817A). We conclude with a discussion of
the DLT40 survey's plans for the upcoming LVC O3 run, which include expanding
our galaxy search fields out to 65 Mpc to match the LVC's planned
three-detector sensitivity for binary neutron star mergers.Comment: 38 pages, 8 figures and 14 tables, Submitted to Ap
Crossover between Equilibrium and Shear-controlled Dynamics in Sheared Liquids
We present a numerical simulation study of a simple monatomic Lennard-Jones
liquid under shear flow, as a function of both temperature and shear rate. By
investigating different observables we find that i) It exists a line in the
(temperature-shear) plane that sharply marks the boarder between an
``equilibrium'' and a ``shear-controlled'' region for both the dynamic and the
thermodynamic quantities; and ii) Along this line the structural relaxation
time, is proportional to the inverse shear rate, i.e. to the typical time-scale
introduced by the shear flow. Above the line the liquid dynamics is unaffected
by the shear flow, while below it both temperature and shear rate control the
particle motion.Comment: 14 pages, 5 figure
Constraints on the Progenitor of SN 2016gkg From Its Shock-Cooling Light Curve
SN 2016gkg is a nearby Type IIb supernova discovered shortly after explosion.
Like several other Type IIb events with early-time data, SN 2016gkg displays a
double-peaked light curve, with the first peak associated with the cooling of a
low-mass extended progenitor envelope. We present unprecedented
intranight-cadence multi-band photometric coverage of the first light-curve
peak of SN 2016gkg obtained from the Las Cumbres Observatory Global Telescope
network, the Asteroid Terrestrial-impact Last Alert System, the Swift satellite
and various amateur-operated telescopes. Fitting these data to analytical
shock-cooling models gives a progenitor radius of ~25-140 solar radii with
~2-30 x 10^-2 solar masses of material in the extended envelope (depending on
the model and the assumed host-galaxy extinction). Our radius estimates are
broadly consistent with values derived independently (in other works) from HST
imaging of the progenitor star. However, the shock-cooling model radii are on
the lower end of the values indicated by pre-explosion imaging. Hydrodynamical
simulations could refine the progenitor parameters deduced from the
shock-cooling emission and test the analytical models.Comment: Accepted by ApJ
Fluctuation-dissipation relations and energy landscape in an out-of-equilibrium strong glass-forming liquid
We study the out-of-equilibrium dynamics following a temperature-jump in a
model for a strong liquid, BKS-silica, and compare it with the well known case
of fragile liquids. We calculate the fluctuation-dissipation relation, from
which it is possible to estimate an effective temperature associated
to the slow out-of-equilibrium structural degrees of freedom. We find the
striking and unexplained result that, differently from the fragile liquid
cases, is smaller than the bath temperature
Short-Lived Circumstellar Interaction in the Low-Luminosity Type IIP SN 2016bkv
While interaction with circumstellar material is known to play an important
role in Type IIn supernovae (SNe), analyses of the more common SNe IIP and IIL
have not traditionally included interaction as a significant power source.
However, recent campaigns to observe SNe within days of explosion have revealed
narrow emission lines of high-ionization species in the earliest spectra of
luminous SNe II of all subclasses. These "flash ionization" features indicate
the presence of a confined shell of material around the progenitor star. Here
we present the first low-luminosity (LL) SN to show flash ionization features,
SN 2016bkv. This SN peaked at mag and has H{\alpha} expansion
velocities under 1350 km/s around maximum light, placing it at the faint/slow
end of the distribution of SNe IIP (similar to SN 2005cs). The light-curve
shape of SN 2016bkv is also extreme among SNe IIP. A very strong initial peak
could indicate additional luminosity from circumstellar interaction. A very
small fall from the plateau to the nickel tail indicates unusually large
production of radioactive nickel compared to other LL SNe IIP. A comparison
between nebular spectra of SN 2016bkv and models raises the possibility that SN
2016bkv is an electron-capture supernova.Comment: Updated to match published version in ApJ. Photometry table and SYN++
input file available at righ
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