1,241 research outputs found
Exploring the Cosmic Evolution of Habitability with Galaxy Merger Trees
We combine inferred galaxy properties from a semi-analytic galaxy evolution
model incorporating dark matter halo merger trees with new estimates of
supernova and gamma ray burst rates as a function of metallicity from stellar
population synthesis models incorporating binary interactions. We use these to
explore the stellar mass fraction of galaxies irradiated by energetic
astrophysical transients and its evolution over cosmic time, and thus the
fraction which is potentially habitable by life like our own. We find that 18
per cent of the stellar mass in the Universe is likely to have been irradiated
within the last 260 Myr, with GRBs dominating that fraction. We do not see a
strong dependence of irradiated stellar mass fraction on stellar mass or
richness of the galaxy environment. We consider a representative merger tree as
a Local Group analogue, and find that there are galaxies at all masses which
have retained a high habitable fraction (>40 per cent) over the last 6 Gyr, but
also that there are galaxies at all masses where the merger history and
associated star formation have rendered galaxies effectively uninhabitable.
This illustrates the need to consider detailed merger trees when evaluating the
cosmic evolution of habitability.Comment: 11 page, 10 figures. MNRAS accepted 13th Dec 2017. Updated to match
accepted version, with additional discussion of metallicity effect
Thermal Degradation Properties of Wood Reacted With Diethylchlorophosphate or Phenylphosphonic Dichloride as Potential Flame Retardants
Improved thermal degradation properties (an indication of improved flame-retardant properties) were observed when southern pine was reacted with either diethylchlorophosphate (DECP) or phenylphosphonic dichloride (PPDC). These two compounds may prove useful as flame retardants for wood. Thermal degradation was evaluated by thermogravimetric methods; the values were reduced slightly by extraction of the specimens with toluene or ethanol and water. When pyrolyzed in nitrogen, specimens of the reacted wood, extracted or unextracted, showed maximum rates of pyrolysis at lower temperatures and produced more char than control specimens
The Broad Absorption Line Tidal Disruption Event iPTF15af: Optical and Ultraviolet Evolution
We present multi-wavelength observations of the tidal disruption event (TDE)
iPTF15af, discovered by the intermediate Palomar Transient Factory (iPTF)
survey at redshift . The optical and ultraviolet (UV) light curves
of the transient show a slow decay over five months, in agreement with previous
optically discovered TDEs. It also has a comparable black-body peak luminosity
of erg/s. The inferred temperature
from the optical and UV data shows a value of (35) K. The
transient is not detected in X-rays up to erg/s within
the first five months after discovery. The optical spectra exhibit two distinct
broad emission lines in the He II region, and at later times also H
emission. Additionally, emission from [N III] and [O III] is detected, likely
produced by the Bowen fluorescence effect. UV spectra reveal broad emission and
absorption lines associated with high-ionization states of N V, C IV, Si IV,
and possibly P V. These features, analogous to those of broad absorption line
quasars (BAL QSOs), require an absorber with column densities cm. This optically thick gas would also explain the
non-detection in soft X-rays. The profile of the absorption lines with the
highest column density material at the largest velocity is opposite that of BAL
QSOs. We suggest that radiation pressure generated by the TDE flare at early
times could have provided the initial acceleration mechanism for this gas.
Spectral UV line monitoring of future TDEs could test this proposal.Comment: 20 pages, 12 figures, published in Ap
The first Swift X-ray Flash: The faint afterglow of XRF 050215B
We present the discovery of XRF 050215B and its afterglow. The burst was
detected by the Swift BAT during the check-out phase and observations with the
X-ray telescope began approximately 30 minutes after the burst. These
observations found a faint, slowly fading X-ray afterglow near the centre of
the error box as reported by the BAT. Infrared data, obtained at UKIRT after 10
hours also revealed a very faint K-band afterglow. The afterglow appear unusual
since it is very faint, especially in the infrared with K>20 only 9 hours post
burst. The X-ray and infrared lightcurves exhibit a slow, monotonic decay with
alpha=0.8 and no evidence for steepening associated with the jet break to 10
days post burst. We discuss possible explanations for the faintness and slow
decay in the context of present models for the production of X-ray Flashes.Comment: 8 pages, 5 figures, accepted for publication in Ap
Seminal plasma and prostaglandin E2 up-regulate fibroblast growth factor 2 expression in endometrial adenocarcinoma cells via E-series prostanoid-2 receptor-mediated transactivation of the epidermal growth factor receptor and extracellular signal-regulated kinase pathway
We report a multiwavelength (X-ray, ultraviolet/optical/infrared, radio)
analysis of the relativistic tidal disruption event candidate Sw J2058+05 from
3 months to 3 yr post-discovery in order to study its properties and compare
its behavior with that of Sw J1644+57. Our main results are as follows. (1) The
long-term X-ray light curve of Sw J2058+05 shows a remarkably similar trend to
that of Sw J1644+57. After a prolonged power-law decay, the X-ray flux drops
off rapidly by a factor of within a span of /
0.95. Associating this sudden decline with the transition from super-Eddington
to sub-Eddington accretion, we estimate the black hole mass to be in the range
of M. (2) We detect rapid ( s) X-ray
variability before the dropoff, suggesting that, even at late times, the X-rays
originate from close to the black hole (ruling out a forward-shock origin). (3)
We confirm using HST and VLBA astrometry that the location of the source
coincides with the galaxy's center to within pc (in projection).
(4) We modeled Sw J2058+05's ultraviolet/optical/infrared spectral energy
distribution with a single-temperature blackbody and find that while the radius
remains more or less constant at a value of AU (
cm) at all times during the outburst, the blackbody temperature drops
significantly from 30,000 K at early times to a value of 15,000 K
at late times (before the X-ray dropoff). Our results strengthen Sw J2058+05's
interpretation as a tidal disruption event similar to Sw J1644+57.Comment: Replaced with the published version of the manuscrip
The early and late-time spectral and temporal evolution of GRB 050716
We report on a comprehensive set of observations of Gamma Ray Burst 050716,
detected by the Swift satellite and subsequently followed-up rapidly in X-ray,
optical and near infra-red wavebands. The prompt emission is typical of
long-duration bursts, with two peaks in a time interval of T90 = 68 seconds (15
- 350 keV). The prompt emission continues at lower flux levels in the X-ray
band, where several smaller flares can be seen, on top of a decaying light
curve that exhibits an apparent break around 220 seconds post trigger. This
temporal break is roughly coincident with a spectral break. The latter can be
related to the extrapolated evolution of the break energy in the prompt
gamma-ray emission, and is possibly the manifestation of the peak flux break
frequency of the internal shock passing through the observing band. A possible
3 sigma change in the X-ray absorption column is also seen during this time.
The late-time afterglow behaviour is relatively standard, with an electron
distribution power-law index of p = 2 there is no noticable temporal break out
to at least 10 days. The broad-band optical/nIR to X-ray spectrum indicates a
redshift of z ~> 2 for this burst, with a host-galaxy extinction value of
E(B-V) ~ 0.7 that prefers an SMC-like extinction curve.Comment: Accepted to MNRAS. 8 pages, 5 figure
GRB 050911: a black hole - neutron star merger or a naked GRB
GRB 050911, discovered by the Swift Burst Alert Telescope, was not seen 4.6
hr later by the Swift X-ray Telescope, making it one of the very few X-ray
non-detections of a Gamma-Ray Burst (GRB) afterglow at early times. The
gamma-ray light-curve shows at least three peaks, the first two of which (~T_0
- 0.8 and T_0 + 0.2 s, where T_0 is the trigger time) were short, each lasting
0.5 s. This was followed by later emission 10-20 s post-burst. The upper limit
on the unabsorbed X-ray flux was 1.7 x 10^-14 erg cm^-2 s^-1 (integrating 46 ks
of data taken between 11 and 18 September), indicating that the decay must have
been rapid. All but one of the long bursts detected by Swift were above this
limit at ~4.6 hr, whereas the afterglows of short bursts became undetectable
more rapidly. Deep observations with Gemini also revealed no optical afterglow
12 hr after the burst, down to r=24.0 (5-sigma limit). We speculate that GRB
050911 may have been formed through a compact object (black hole-neutron star)
merger, with the later outbursts due to a longer disc lifetime linked to a
large mass ratio between the merging objects. Alternatively, the burst may have
occured in a low density environment, leading to a weak, or non-existent,
forward shock - the so-called 'naked GRB' model.Comment: 4 pages using emulateapj; 2 figures. Accepted for publication in ApJ
Letter
Light from the Cosmic Frontier: Gamma-Ray Bursts
Gamma-Ray Bursts (GRBs) are the most powerful cosmic explosions since the Big
Bang, and thus act as signposts throughout the distant Universe. Over the last
2 decades, these ultra-luminous cosmological explosions have been transformed
from a mere curiosity to essential tools for the study of high-redshift stars
and galaxies, early structure formation and the evolution of chemical elements.
In the future, GRBs will likely provide a powerful probe of the epoch of
reionisation of the Universe, constrain the properties of the first generation
of stars, and play an important role in the revolution of multi-messenger
astronomy by associating neutrinos or gravitational wave (GW) signals with
GRBs. Here, we describe the next steps needed to advance the GRB field, as well
as the potential of GRBs for studying the Early Universe and their role in the
up-coming multi-messenger revolution.Comment: White paper submitted to ESA as a contribution to the deliberations
on the science themes for the L2 and L3 mission opportunitie
The dark GRB080207 in an extremely red host and the implications for GRBs in highly obscured environments
[Abridged] We present comprehensive X-ray, optical, near- and mid-infrared,
and sub-mm observations of GRB 080207 and its host galaxy. The afterglow was
undetected in the optical and near-IR, implying an optical to X-ray index <0.3,
identifying GRB 080207 as a dark burst. Swift X-ray observations show extreme
absorption in the host, which is confirmed by the unusually large optical
extinction found by modelling the X-ray to nIR afterglow spectral energy
distribution. Our Chandra observations obtained 8 days post-burst allow us to
place the afterglow on the sky to sub-arcsec accuracy, enabling us to pinpoint
an extremely red galaxy (ERO). Follow-up host observations with HST, Spitzer,
Gemini, Keck and the James Clerk Maxwell Telescope (JCMT) provide a photometric
redshift solution of z ~1.74 (+0.05,-0.06) (1 sigma), 1.56 < z < 2.08 at 2
sigma) for the ERO host, and suggest that it is a massive and morphologically
disturbed ultra-luminous infrared galaxy (ULIRG) system, with L_FIR ~ 2.4 x
10^12 L_solar. These results add to the growing evidence that GRBs originating
in very red hosts always show some evidence of dust extinction in their
afterglows (though the converse is not true -- some extinguished afterglows are
found in blue hosts). This indicates that a poorly constrained fraction of GRBs
occur in very dusty environments. By comparing the inferred stellar masses, and
estimates of the gas phase metallicity in both GRB hosts and sub-mm galaxies we
suggest that many GRB hosts, even at z>2 are at lower metallicity than the
sub-mm galaxy population, offering a likely explanation for the dearth of
sub-mm detected GRB hosts. However, we also show that the dark GRB hosts are
systematically more massive than those hosting optically bright events, perhaps
implying that previous host samples are severely biased by the exclusion of
dark events.Comment: 13 pages, 6 figures, accepted for publication in MNRA
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