40 research outputs found
Gamma-ray Burst host galaxy gas and dust
We report on the results of a study to obtain limits on the absorbing columns
to wards an initial sample of 10 long Gamma-Ray Bursts observed with BeppoSAX,
using a new approach to SED fitting to nIR, optical and X-ray afterglow data,
in count space and including the effects of metallicity. When testing MW, LMC
and SMC extinction laws we find that SMC-like extinction provides the best fit
in most cases. A MW-like ext inction curve is not preferred for any of these
sources, largely since the 2175A bump, in principle detectable in all these
afterglows, is not present in the data. We rule out an SMC-like gas-to-dust
ratio or lower value for 4 of the hosts analysed here (assuming SMC metallicity
and extinction law) whilst the remainder of the sample have too large an error
to discriminate. We provide an accurate estimate of the line-of-sight
extinction, improving upon the uncertainties for the majority of the extinction
measurements made in previous studies of this sample.Comment: 3 pages, 1 figure, MG11 proceeding
Optical Polarimetry of the May 2022 Lunar Eclipse
The sunlight reflected from the Moon during a total lunar eclipse has been
transmitted through the Earth's atmosphere on the way to the Moon. The
combination of multiple scattering and inhomogeneous atmospheric
characteristics during that transmission can potentially polarize that light. A
similar (although much smaller) effect should also be observable from the
atmosphere of a transiting exoplanet. We present the results of polarization
observations during the first 15 minutes of totality of the lunar eclipse of
2022 May 16. We find degrees of polarization of 2.1 +/- 0.4 per cent in B, 1.2
+/- 0.3 per cent in V, 0.5 +/- 0.2 per cent in R and 0.2 +/- 0.2 per cent in I.
Our polarization values lie in the middle of the range of those reported for
previous eclipses, providing further evidence that the induced polarization can
change from event to event. We found no significant polarization difference
(<0.02 per cent) between a region of dark Mare and nearby bright uplands or
between the lunar limb and regions closer to the disk centre due to the
different angle of incidence. This further strengthens the interpretation of
the polarization's origin being due to scattering in the Earth's atmosphere
rather than by the lunar regolith.Comment: Accepted for publication in MNRA
Optical Polarimetry of the May 2022 Lunar Eclipse
The sunlight reflected from the Moon during a total lunar eclipse has been
transmitted through the Earth's atmosphere on the way to the Moon. The
combination of multiple scattering and inhomogeneous atmospheric
characteristics during that transmission can potentially polarize that light. A
similar (although much smaller) effect should also be observable from the
atmosphere of a transiting exoplanet. We present the results of polarization
observations during the first 15 minutes of totality of the lunar eclipse of
2022 May 16. We find degrees of polarization of 2.1 +/- 0.4 per cent in B, 1.2
+/- 0.3 per cent in V, 0.5 +/- 0.2 per cent in R and 0.2 +/- 0.2 per cent in I.
Our polarization values lie in the middle of the range of those reported for
previous eclipses, providing further evidence that the induced polarization can
change from event to event. We found no significant polarization difference
(<0.02 per cent) between a region of dark Mare and nearby bright uplands or
between the lunar limb and regions closer to the disk centre due to the
different angle of incidence. This further strengthens the interpretation of
the polarization's origin being due to scattering in the Earth's atmosphere
rather than by the lunar regolith.Comment: Accepted for publication in MNRA
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 host-galaxy response to the afterglow of GRB 100901A
For Gamma-Ray Burst 100901A, we have obtained Gemini-North and Very Large
Telescope optical afterglow spectra at four epochs: one hour, one day, three
days and one week after the burst, thanks to the afterglow remaining unusually
bright at late times. Apart from a wealth of metal resonance lines, we also
detect lines arising from fine-structure levels of the ground state of Fe II,
and from metastable levels of Fe II and Ni II at the host redshift (z =
1.4084). These lines are found to vary significantly in time. The combination
of the data and modelling results shows that we detect the fall of the Ni II 4
F9/2 metastable level population, which to date has not been observed. Assuming
that the population of the excited states is due to the UV-radiation of the
afterglow, we estimate an absorber distance of a few hundred pc. This appears
to be a typical value when compared to similar studies. We detect two
intervening absorbers (z = 1.3147, 1.3179). Despite the wide temporal range of
the data, we do not see significant variation in the absorption lines of these
two intervening systems.Comment: 17 pages, 9 figures. Accepted by Monthly Notices of the Royal
Astronomical Society on Jan 11th 201
SPLOT : a Snapshot survey for polarised light in optical transients
We present SPLOT, a small scale pilot survey to test the potential of snapshot (single epoch) linear imaging polarimetry as a supplementary tool to traditional transient follow-up. Transients exist in a vast volume of observational parameter space and polarimetry has the potential to highlight sources of scienti c interest and add value to near real-time transient survey streams. We observed a sample of 50 randomly selected optical transients with the EFOSC2 and SofI instruments, on the 3.6m New Technology Telescope (NTT) to test the feasibility of the survey. Our sample contained a number of interesting individual sources: a variety of supernovae, X-ray binaries, a tidal disruption event, blazar outbursts, and, by design, numerous transients of unknown nature. We discuss the results, both for the individual sources and the survey in detail. We provide an overview on the success and limitations of SPLOT and also describe a novel calibration method for removing instrumental polarisation e ects from Nasymth-mounted telescopes. We nd that a SPLOT-like survey would be a bene t to the large scale future transient survey streams such as LSST. The polarimetric measurements have added scienti c value to a signi cant number of the sources and, most importantly, has shown the potential to highlight unclassi ed transient sources of scienti c interest for further study
The January 2015 outburst of a red nova in M31
M31N 2015-01a (or M31LRN 2015) is a red nova that erupted in January 2015 --
the first event of this kind observed in M31 since 1988. Very few similar
events have been confirmed as of 2015. Most of them are considered to be
products of stellar mergers. Results of an extensive optical monitoring of the
transient in the period January-March 2015 are presented. Eight optical
telescopes were used for imaging. Spectra were obtained on BTA, GTC and the
Rozhen 2m telescope. We present a highly accurate 70 d lightcurve and
astrometry with a 0.05" uncertainty. The color indices reached a minimum 2-3 d
before peak brightness and rapidly increased afterwards. The spectral type
changed from F5I to F0I in 6 d before the maximum and then to K3I in the next
30 d. The luminosity of the transient was estimated to
during the optical maximum. Both the
photometric and the spectroscopic results confirm that the object is a red
nova, similar to V838 Monocerotis.Comment: 5 pages, 4 figures, 4 tables, accepted for publication in Astronomy
and Astrophysics as a Letter to the Editor; page 5 is online material onl
The diversity of kilonova emission in short gamma-ray bursts
The historic first joint detection of both gravitational-wave and electromagnetic emission from a binary neutron star merger cemented the association between short gamma-ray bursts (SGRBs) and compact object mergers, as well as providing a well-sampled multi-wavelength light curve of a radioactive kilonova (KN) for the first time. Here, we compare the optical and near-infrared light curves of this KN, AT 2017gfo, to the counterparts of a sample of nearby (z < 0.5) SGRBs to characterize their diversity in terms of their brightness distribution. Although at similar epochs AT 2017gfo appears fainter than every SGRB-associated KN claimed so far, we find three bursts (GRBs 050509B, 061201, and 080905A) where, if the reported redshifts are correct, deep upper limits rule out the presence of a KN similar to AT 2017gfo by several magnitudes. Combined with the properties of previously claimed KNe in SGRBs this suggests considerable diversity in the properties of KN drawn from compact object mergers, despite the similar physical conditions that are expected in many NS–NS mergers. We find that observer angle alone is not able to explain this diversity, which is likely a product of the merger type (NS–NS versus NS–BH) and the detailed properties of the binary (mass ratio, spins etc.). Ultimately disentangling these properties should be possible through observations of SGRBs and gravitational-wave sources, providing direct measurements of heavy element enrichment throughout the universe
The most luminous, merger-free AGN show only marginal correlation with bar presence
The role of large-scale bars in the fuelling of active galactic nuclei (AGN)
is still debated, even as evidence mounts that black hole growth in the absence
of galaxy mergers cumulatively dominated and may substantially influence disc
(i.e., merger-free) galaxy evolution. We investigate whether large-scale
galactic bars are a good candidate for merger-free AGN fuelling. Specifically,
we combine slit spectroscopy and Hubble Space Telescope imagery to characterise
star formation rates (SFRs) and stellar masses of the unambiguously
disc-dominated host galaxies of a sample of luminous, Type-1 AGN with 0.02 < z
0.024. After carefully correcting for AGN signal, we find no clear difference
in SFR between AGN hosts and a stellar mass-matched sample of galaxies lacking
an AGN (0.013 < z < 0.19), although this could be due to a small sample size
(n_AGN = 34). We correct for SFR and stellar mass to minimise selection biases,
and compare the bar fraction in the two samples. We find that AGN are
marginally (1.7) more likely to host a bar than inactive galaxies, with
AGN hosts having a bar fraction, fbar = 0.59^{+0.08}_{-0.09} and inactive
galaxies having a bar fraction fbar = 0.44^{+0.08}_{-0.09}. However, we find no
further differences between SFR- and mass-matched AGN and inactive samples.
While bars could potentially trigger AGN activity, they appear to have no
further, unique effect on a galaxy's stellar mass or SFR.Comment: 15 pages (9 figures). Accepted for publication in MNRA