819 research outputs found
The identification of a novel, high frequency variant in the Cytochrome b gene in an isolated population of a rare fish, Spined Loach Cobitis taenia, in England: A population worth protecting?
The spined loach Cobitis taenia, is listed as a protected species under Appendix 3 of the Bern Convention and Annex II of the European Council Directive (92/43/EEC) on the conservation of natural habitats and of wild fauna and flora. It is desirable therefore to understand the genetic diversity within European populations. In a molecular genetic analysis of the cytochrome b gene in Cobitis taenia from three sites in the upper reaches of the River Trent catchment, a novel high frequency variant was identified which has not been previously reported in any European or Non-European population
The host galaxy and late-time evolution of the Super-Luminous Supernova PTF12dam
Super-luminous supernovae of type Ic have a tendency to occur in faint host
galaxies which are likely to have low mass and low metallicity. PTF12dam is one
of the closest and best studied super-luminous explosions that has a broad and
slowly fading lightcurve similar to SN 2007bi. Here we present new photometry
and spectroscopy for PTF12dam from 200-500 days (rest-frame) after peak and a
detailed analysis of the host galaxy (SDSS J142446.21+461348.6 at z = 0.107).
Using deep templates and image subtraction we show that the full lightcurve can
be fit with a magnetar model if escape of high-energy gamma rays is taken into
account. The full bolometric lightcurve from -53 to +399 days (with respect to
peak) cannot be fit satisfactorily with the pair-instability models. An
alternative model of interaction with a dense CSM produces a good fit to the
data although this requires a very large mass (~ 13 M_sun) of hydrogen free
CSM. The host galaxy is a compact dwarf (physical size ~ 1.9 kpc) and with M_g
= -19.33 +/- 0.10, it is the brightest nearby SLSN Ic host discovered so far.
The host is a low mass system (2.8 x 10^8 M_sun) with a star-formation rate
(5.0 M_sun/year), which implies a very high specific star-formation rate (17.9
Gyr^-1). The remarkably strong nebular lines provide detections of the [O III]
\lambda 4363 and [O II] \lambda\lambda 7320,7330 auroral lines and an accurate
oxygen abundance of 12 + log(O/H) = 8.05 +/- 0.09. We show here that they are
at the extreme end of the metallicity distribution of dwarf galaxies and
propose that low metallicity is a requirement to produce these rare and
peculiar supernovae.Comment: 20 pages, 12 figures, 8 tables, accepted for publication to MNRA
The Type I Superluminous Supernova PS16aqv: Lightcurve Complexity and Deep Limits on Radioactive Ejecta in a Fast Event
[Abridged] We present UV/optical observations of PS16aqv (SN 2016ard), a Type
I superluminous supernova (SLSN-I) classified as part of our search for low-
SLSNe. PS16aqv is a fast evolving SLSNe-I that reached a peak absolute
magnitude of . The lightcurves exhibit a significant
undulation at 30 rest-frame days after peak, with a behavior similar to
undulations seen in the slowly fading SLSN-I SN 2015bn. This similarity
strengthens the case that fast and slow SLSNe-I form a continuum with a common
origin. At days after peak, the lightcurves exhibit a transition
to a slow decline, followed by significant subsequent steepening, indicative of
a plateau phase or a second significant undulation. Deep limits at
days after peak imply a tight constraint on the nickel mass, M (lower than for previous SLSNe-I), and indicate that
some SLSNe-I do not produce significantly more nickel than normal Type Ic SNe.
Using MOSFiT, we model the lightcurve with a magnetar central engine model and
find ms, G, and
M. The implied rapid spin-down time and large
reservoir of available energy coupled with the high ejecta mass may account for
the fast evolving lightcurve and slow spectroscopic evolution. We also study
the location of PS16aqv in its host galaxy and find that it occurred at an
offset of kpc from the central star-forming region. We find the
host galaxy exhibits low metallicity and spatially varying extinction and star
formation rate, with the explosion site exhibiting lower values than the
central region. The complexity seen in the lightcurves of PS16aqv and other
events highlights the importance of obtaining well-sampled lightcurves for
exploring deviations from a uniform decline.Comment: 16 pages, 10 figures, submitted to Ap
A Decline in the X-ray through Radio Emission from GW170817 Continues to Support an Off-Axis Structured Jet
We present new observations of the binary neutron star merger GW170817 at
days post-merger, at radio (Karl G. Jansky Very Large
Array; VLA), X-ray (Chandra X-ray Observatory) and optical (Hubble Space
Telescope; HST) wavelengths. These observations provide the first evidence for
a turnover in the X-ray light curve, mirroring a decline in the radio emission
at significance. The radio-to-X-ray spectral energy
distribution exhibits no evolution into the declining phase. Our full
multi-wavelength dataset is consistent with the predicted behavior of our
previously published models of a successful structured jet expanding into a
low-density circumbinary medium, but pure cocoon models with a choked jet
cannot be ruled out. If future observations continue to track our predictions,
we expect that the radio and X-ray emission will remain detectable until days post-merger.Comment: Accepted to ApJL. Updated version includes new VLA observations
extending through 2018 June
Improved constraints on H0 from a combined analysis of gravitational-wave and electromagnetic emission from GW170817
The luminosity distance measurement of GW170817 derived from GW analysis in
Abbott et al. 2017 (here, A17:H0) is highly correlated with the measured
inclination of the NS-NS system. To improve the precision of the distance
measurement, we attempt to constrain the inclination by modeling the broad-band
X-ray-to-radio emission from GW170817, which is dominated by the interaction of
the jet with the environment. We update our previous analysis and we consider
the radio and X-ray data obtained at days since merger. We find that the
afterglow emission from GW170817 is consistent with an off-axis relativistic
jet with energy
propagating into an environment with density , with preference for wider jets (opening angle
deg). For these jets, our modeling indicates an off-axis angle deg. We combine our constraints on with the
joint distance-inclination constraint from LIGO. Using the same
km/sec peculiar velocity uncertainty assumed in A17:H0 but with an inclination
constraint from the afterglow data, we get a value of \mbox{km/s/Mpc}, which is higher than the value of
\mbox{km/s/Mpc} found in A17:H0. Further,
using a more realistic peculiar velocity uncertainty of 250 km/sec derived from
previous work, we find km/s/Mpc for H0 from
this system. We note that this is in modestly better agreement with the local
distance ladder than the Planck CMB, though a significant such discrimination
will require such events. Future measurements at days of the
X-ray and radio emission will lead to tighter constraints.Comment: Submitted to ApJL. Comments Welcome. Revised uncertainties in v
The Binary Neutron Star event LIGO/VIRGO GW170817 a hundred and sixty days after merger: synchrotron emission across the electromagnetic spectrum
We report deep Chandra, HST and VLA observations of the binary neutron star
event GW170817 at d after merger. These observations show that GW170817
has been steadily brightening with time and might have now reached its peak,
and constrain the emission process as non-thermal synchrotron emission where
the cooling frequency is above the X-ray band and the synchrotron
frequency is below the radio band. The very simple power-law spectrum
extending for eight orders of magnitude in frequency enables the most precise
measurement of the index of the distribution of non-thermal relativistic
electrons accelerated by a shock launched by a
NS-NS merger to date. We find , which indicates that radiation
from ejecta with dominates the observed emission. While
constraining the nature of the emission process, these observations do
\emph{not} constrain the nature of the relativistic ejecta. We employ
simulations of explosive outflows launched in NS ejecta clouds to show that the
spectral and temporal evolution of the non-thermal emission from GW170817 is
consistent with both emission from radially stratified quasi-spherical ejecta
traveling at mildly relativistic speeds, \emph{and} emission from off-axis
collimated ejecta characterized by a narrow cone of ultra-relativistic material
with slower wings extending to larger angles. In the latter scenario, GW170817
harbored a normal SGRB directed away from our line of sight. Observations at
days are unlikely to settle the debate as in both scenarios the
observed emission is effectively dominated by radiation from mildly
relativistic material.Comment: Updated with the latest VLA and Chandra dat
The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. VI. Radio Constraints on a Relativistic Jet and Predictions for Late-Time Emission from the Kilonova Ejecta
We present Very Large Array (VLA) and Atacama Large Millimeter/sub-millimeter
Array ALMA radio observations of GW\,170817, the first Laser Interferometer
Gravitational-wave Observatory (LIGO)/Virgo gravitational wave (GW) event from
a binary neutron star merger and the first GW event with an electromagnetic
(EM) counterpart. Our data include the first observations following the
discovery of the optical transient at both the centimeter ( hours post
merger) and millimeter ( days post merger) bands. We detect faint
emission at 6 GHz at 19.47 and 39.23 days after the merger, but not in an
earlier observation at 2.46 d. We do not detect cm/mm emission at the position
of the optical counterpart at frequencies of 10-97.5 GHz at times ranging from
0.6 to 30 days post merger, ruling out an on-axis short gamma-ray burst (SGRB)
for energies erg. For fiducial SGRB parameters, our limits
require an observer viewer angle of . The radio and X-ray
data can be jointly explained as the afterglow emission from an SGRB with a jet
energy of erg that exploded in a uniform density
environment with cm, viewed at an angle of from the jet axis. Using the results of our light curve
and spectral modeling, in conjunction with the inference of the circumbinary
density, we predict the emergence of late-time radio emission from the
deceleration of the kilonova (KN) ejecta on a timescale of years
that will remain detectable for decades with next-generation radio facilities,
making GW\,170817 a compelling target for long-term radio monitoring.Comment: 8 pages, 4 figures, 1 table. ApJL, in press. Keywords: GW170817, LV
The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. VII. Properties of the Host Galaxy and Constraints on the Merger Timescale
We present the properties of NGC 4993, the host galaxy of GW170817, the first
gravitational wave (GW) event from the merger of a binary neutron star (BNS)
system and the first with an electromagnetic (EM) counterpart. We use both
archival photometry and new optical/near-IR imaging and spectroscopy, together
with stellar population synthesis models to infer the global properties of the
host galaxy. We infer a star formation history peaked at Gyr ago,
with subsequent exponential decline leading to a low current star formation
rate of 0.01 M yr, which we convert into a binary merger
timescale probability distribution. We find a median merger timescale of
Gyr, with a 90% confidence range of Gyr. This
in turn indicates an initial binary separation of R,
comparable to the inferred values for Galactic BNS systems. We also use new and
archival images to measure a projected offset of
the optical counterpart of kpc (0.64) from the center of NGC 4993
and to place a limit of mag on any pre-existing emission,
which rules out the brighter half of the globular cluster luminosity function.
Finally, the age and offset of the system indicates it experienced a modest
natal kick with an upper limit of km s. Future GWEM
observations of BNS mergers will enable measurement of their population delay
time distribution, which will directly inform their viability as the dominant
source of -process enrichment in the Universe.Comment: 9 Pages, 3 Figures, 2 Tables, ApJL, In Press. Keywords: GW170817, LV
The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. V. Rising X-ray Emission from an Off-Axis Jet
We report the discovery of rising X-ray emission from the binary neutron star
(BNS) merger event GW170817. This is the first detection of X-ray emission from
a gravitational-wave source. Observations acquired with the Chandra X-ray
Observatory (CXO) at t~2.3 days post merger reveal no significant emission,
with L_x<=3.2x10^38 erg/s (isotropic-equivalent). Continued monitoring revealed
the presence of an X-ray source that brightened with time, reaching L_x\sim
9x10^39 erg/s at ~15.1 days post merger. We interpret these findings in the
context of isotropic and collimated relativistic outflows (both on- and
off-axis). We find that the broad-band X-ray to radio observations are
consistent with emission from a relativistic jet with kinetic energy
E_k~10^49-10^50 erg, viewed off-axis with theta_obs~ 20-40 deg. Our models
favor a circumbinary density n~ 0.0001-0.01 cm-3, depending on the value of the
microphysical parameter epsilon_B=10^{-4}-10^{-2}. A central-engine origin of
the X-ray emission is unlikely. Future X-ray observations at
days, when the target will be observable again with the CXO, will provide
additional constraints to solve the model degeneracies and test our
predictions. Our inferences on theta_obs are testable with gravitational wave
information on GW170817 from Advanced LIGO/Virgo on the binary inclination.Comment: 7 Pages, 4 Figures, ApJL, In Press. Keywords: GW170817, LV
Hydrogen-poor Superluminous Supernovae with Late-time H alpha Emission: Three Events From the Intermediate Palomar Transient Factory
We present observations of two new hydrogen-poor superluminous supernovae (SLSN-I), iPTF15esb and iPTF16bad, showing late-time Hα emission with line luminosities of (1\mbox{--}3)\times {10}^{41} erg s−1 and velocity widths of (4000–6000) km s−1. Including the previously published iPTF13ehe, this makes up a total of three such events to date. iPTF13ehe is one of the most luminous and the slowest evolving SLSNe-I, whereas the other two are less luminous and fast decliners. We interpret this as a result of the ejecta running into a neutral H-shell located at a radius of ~1016 cm. This implies that violent mass loss must have occurred several decades before the supernova explosion. Such a short time interval suggests that eruptive mass loss could be common shortly before core collapse, and more importantly helium is unlikely to be completely stripped off the progenitor and could be present in the ejecta. It is a mystery why helium features are not detected, even though nonthermal energy sources, capable of ionizing He, may exist as suggested by the O ii absorption series in the early-time spectra. Our late-time spectra (+240 days) appear to have intrinsically lower [O i] 6300 Å luminosities than that of SN2015bn and SN2007bi, which is possibly an indication of less oxygen (<10 M ⊙). The blueshifted Hα emission relative to the hosts for all three events may be in tension with the binary model proposed for iPTF13ehe. Finally, iPTF15esb has a peculiar light curve (LC) with three peaks separated from one another by ~22 days. The LC undulation is stronger in bluer bands. One possible explanation is ejecta-circumstellar medium interaction
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