307 research outputs found
Multi-wavelength Observations of the Type IIb Supernova 2009mg
We present Swift UVOT and XRT observations, and visual wavelength
spectroscopy of the Type IIb supernova (SN) 2009mg, discovered in the Sb galaxy
ESO 121-G26. The observational properties of SN 2009mg are compared to the
prototype Type IIb SNe 1993J and 2008ax, with which we find many similarities.
However, minor differences are discernible including SN 2009mg not exhibiting
an initial fast decline or u-band upturn as observed in the comparison objects,
and its rise to maximum is somewhat slower leading to slightly broader light
curves. The late-time temporal index of SN 2009mg, determined from 40 days
post-explosion, is consistent with the decay rate of SN 1993J, but inconsistent
with the decay of 56Co. This suggests leakage of gamma-rays out of the ejecta
and a stellar mass on the small side of the mass distribution. Our XRT
non-detection provides an upper limit on the mass-loss rate of the progenitor
of <1.5x10^-5 Msun per yr. Modelling of the SN light curve indicates a kinetic
energy of 0.15 (+0.02,-0.13) x10^51 erg, an ejecta mass of 0.56(+0.10,-0.26)
Msun and a 56Ni mass of 0.10\pm0.01 Msun.Comment: 10 pages, 8 figures, accepted for publication in MNRA
GRB 081203A: Swift UVOT captures the earliest ultraviolet spectrum of a gamma-ray burst
We present the earliest ultraviolet (UV) spectrum of a gamma-ray burst (GRB) as observed with the Swift Ultra-Violet/Optical Telescope (UVOT). The GRB 081203A spectrum was observed for 50 s with the UV-grism starting 251 s after the Swift-Burst-Alert-Telescope (BAT) trigger. During this time, the GRB was ≈13.4 mag (u filter) and was still rising to its peak optical brightness. In the UV-grism spectrum, we find a damped Lyα line, Lyβ and the Lyman continuum break at a redshift z= 2.05 ± 0.01. A model fit to the Lyman absorption implies a gas column density of log NH i= 22.0 ± 0.1 cm−2, which is typical of GRB host galaxies with damped Lyα absorbers. This observation of GRB 081203A demonstrates that for brighter GRBs (v≈ 14 mag) with moderate redshift (0.5 < z < 3.5) the UVOT is able to provide redshifts, and probe for damped Lyα absorbers within 4–6 min from the time of the Swift-BAT trigger
Accurate early positions for Swift GRBS: enhancing X-ray positions with UVOT astrometry
Here we describe an autonomous way of producing more accurate prompt XRT
positions for Swift-detected GRBs and their afterglows, based on UVOT
astrometry and a detailed mapping between the XRT and UVOT detectors. The
latter significantly reduces the dominant systematic error -- the star-tracker
solution to the World Coordinate System. This technique, which is limited to
times when there is significant overlap between UVOT and XRT PC-mode data,
provides a factor of 2 improvement in the localisation of XRT refined positions
on timescales of less than a few hours. Furthermore, the accuracy achieved is
superior to astrometrically corrected XRT PC mode images at early times (for up
to 24 hours), for the majority of bursts, and is comparable to the accuracy
achieved by astrometrically corrected X-ray positions based on deep XRT PC-mode
imaging at later times (abridged).Comment: 12 pages, 8 figures, 1 table, submitted to Astronomy and
Astrophysics, August 7th 200
Towards optimal 1.5° and 2 °C emission pathways for individual countries: A Finland case study
© 2019 Nationally Determined Contributions (NDCs) submitted so far under the Paris Agreement are not in line with its long-term temperature goal. To bridge this gap, countries are required to provide regular updates and enhancements of their long-term targets and strategies, based on scientific assessments. The goal of this paper is to demonstrate a policy-support approach for evaluating NDCs and guiding enhanced ambition. The approach rests on deriving national targets in line with the Paris Agreement by downscaling regional results of Integrated Assessment Models (IAMs) to the country level. The method of downscaling relies on a reduced complexity IAM: SIAMESE (Simplified Integrated Assessment Model with Energy System Emulator). We apply the approach to an EU28 member state – Finland – with the aim of providing useful insights for policy makers to consider cost-effective mitigation options. Results over the historical period confirm that our approach is valid when national policies are similar to those across the larger IAM region, but must include country-specific circumstances. Strengths and limitations of the approach are discussed. We assess the remaining carbon budget and analyse the different implications of 2 °C and 1.5 °C global warming limits for the emissions pathway and energy mix in Finland over the 21st century
Photometric Calibration of the Swift Ultraviolet/Optical Telescope
We present the photometric calibration of the Swift UltraViolet/Optical
Telescope (UVOT) which includes: optimum photometric and background apertures,
effective area curves, colour transformations, conversion factors for count
rates to flux, and the photometric zero points (which are accurate to better
than 4 per cent) for each of the seven UVOT broadband filters. The calibration
was performed with observations of standard stars and standard star fields that
represent a wide range of spectral star types. The calibration results include
the position dependent uniformity, and instrument response over the 1600-8000A
operational range. Because the UVOT is a photon counting instrument, we also
discuss the effect of coincidence loss on the calibration results. We provide
practical guidelines for using the calibration in UVOT data analysis. The
results presented here supersede previous calibration results.Comment: Minor improvements after referees report. Accepted for publication in
MNRA
Swift-UVOT Observations of the X-Ray Flash 050406
We present Swift-UVOT data on the optical afterglow of the X-ray flash of
2005 April 6 (XRF 050406) from 88s to \sim 10^5s after the initial prompt
gamma-ray emission. Our observations in the V, B and U bands are the earliest
that have been taken of an XRF optical counterpart. Combining the early -time
optical temporal and spectral properties with \gamma- and simultaneous X-ray
data taken with the BAT and XRT telescopes on-board Swift, we are able to
constrain possible origins of the XRF. The prompt emission had a FRED profile
(fast-rise, exponential decay) with a duration of T_90 = 5.7\pm 0.2s, putting
it at the short end of the long-burst duration distribution. The absence of
photoelectric absorption red-ward of 4000 \AA in the UV/optical spectrum
provides a firm upper limit of z\leq 3.1 on the redshift, thus excluding a high
redshift as the sole reason for the soft spectrum. The optical light curve is
consistent with a power-law decay with slope alpha = -0.75\pm 0.26
(F_{\nu}\propto t^{\alpha}), and a maximum occurring in the first 200s after
the initial gamma-ray emission. The softness of the prompt emission is well
described by an off-axis structured jet model, which is able to account for the
early peak flux and shallow decay observed in the optical and X-ray bands.Comment: 14 pages, 4 figures, accepted for publication in ApJ; typos corrected
and upper limits in table 1 changed from background subtracted count rate in
extraction region to the error associated with thi
GRB 081028 and its late-time afterglow re-brightening
‘The definitive version is available at www3.interscience.wiley.com '. Copyright Royal Astronomical SocietySwift captured for the first time a smoothly rising X-ray re-brightening of clear non-flaring origin after the steep decay in a long gamma-ray burst (GRB): GRB 081028. A rising phase is likely present in all GRBs but is usually hidden by the prompt tail emission and constitutes the first manifestation of what is later to give rise to the shallow decay phase. Contemporaneous optical observations reveal a rapid evolution of the injection frequency of a fast cooling synchrotron spectrum through the optical band, which disfavours the afterglow onset (start of the forward shock emission along our line of sight when the outflow is decelerated) as the origin of the observed re-brightening. We investigate alternative scenarios and find that the observations are consistent with the predictions for a narrow jet viewed off-axis. The high on-axis energy budget implied by this interpretation suggests different physical origins of the prompt and (late) afterglow emission. Strong spectral softening takes place from the prompt to the steep decay phase: we track the evolution of the spectral peak energy from the γ-rays to the X-rays and highlight the problems of the high latitude and adiabatic cooling interpretations. Notably, a softening of both the high and low spectral slopes with time is also observed. We discuss the low on-axis radiative efficiency of GRB 081028 comparing its properties against a sample of Swift long GRBs with secure Eγ,iso measurements.Peer reviewe
The First Swift Ultra-Violet/Optical Telescope GRB Afterglow Catalog
We present the first Swift Ultra-Violet/Optical Telescope (UVOT) gamma-ray
burst (GRB) afterglow catalog. The catalog contains data from over 64,000
independent UVOT image observations of 229 GRBs first detected by Swift, the
High Energy Transient Explorer 2 (HETE2), the INTErnational Gamma-Ray
Astrophysics Laboratory (INTEGRAL), and the Interplanetary Network (IPN). The
catalog covers GRBs occurring during the period from 2005 Jan 17 to 2007 Jun 16
and includes ~86% of the bursts detected by the Swift Burst Alert Telescope
(BAT). The catalog provides detailed burst positional, temporal, and
photometric information extracted from each of the UVOT images. Positions for
bursts detected at the 3-sigma-level are provided with a nominal accuracy,
relative to the USNO-B1 catalog, of ~0.25 arcseconds. Photometry for each burst
is given in three UV bands, three optical bands, and a 'white' or open filter.
Upper limits for magnitudes are reported for sources detected below 3-sigma.
General properties of the burst sample and light curves, including the
filter-dependent temporal slopes, are also provided. The majority of the UVOT
light curves, for bursts detected at the 3-sigma-level, can be fit by a single
power-law, with a median temporal slope (alpha) of 0.96, beginning several
hundred seconds after the burst trigger and ending at ~1x10^5 s. The median
UVOT v-band (~5500 Angstroms) magnitude at 2000 s for a sample of "well"
detected bursts is 18.02. The UVOT flux interpolated to 2000 s after the burst,
shows relatively strong correlations with both the prompt Swift BAT fluence,
and the Swift X-ray flux at 11 hours after the trigger.Comment: 60 pages, 17 figures, 8 tables, accepted for publication by the
Astrophysical Journa
The 26 year-long X-ray light curve and the X-ray spectrum of the BL Lac Object 1E 1207.9+3945 in its brightest state
We studied the temporal and spectral evolution of the synchrotron emission
from the high energy peaked BL Lac object 1E 1207.9+3945. Two recent
observations have been performed by the XMM-Newton and Swift satellites; we
carried out X-ray spectral analysis for both of them, and photometry in
optical-ultraviolet filters for the Swift one. Combining the results thus
obtained with archival data we built the long-term X-ray light curve, spanning
a time interval of 26 years, and the Spectral Energy Distribution (SED) of this
source. The light curve shows a large flux increasing, about a factor of six,
in a time interval of a few years. After reaching its maximum in coincidence
with the XMM-Newton pointing in December 2000 the flux decreased in later
years, as revealed by Swift. The very good statistics available in the 0.5-10
keV XMM-Newton X-ray spectrum points out a highly significant deviation from a
single power law. A log-parabolic model with a best fit curvature parameter of
0.25 and a peak energy at ~1 keV describes well the spectral shape of the
synchrotron emission. The simultaneous fit of Swift UVOT and XRT data provides
a milder curvature (b~0.1) and a peak at higher energies (~15 keV), suggesting
a different state of source activity. In both cases UVOT data support the
scenario of a single synchrotron emission component extending from the
optical/UV to the X-ray band. New X-ray observations are important to monitor
the temporal and spectral evolution of the source; new generation gamma-ray
telescopes like AGILE and GLAST could for the first time detect its inverse
Compton emission.Comment: 7 pages, 6 figures, accepted for publication in A&
Paper II: Calibration of the Swift ultraviolet/optical telescope
The Ultraviolet/Optical Telescope (UVOT) is one of three instruments onboard
the Swift observatory. The photometric calibration has been published, and this
paper follows up with details on other aspects of the calibration including a
measurement of the point spread function with an assessment of the orbital
variation and the effect on photometry. A correction for large scale variations
in sensitivity over the field of view is described, as well as a model of the
coincidence loss which is used to assess the coincidence correction in extended
regions. We have provided a correction for the detector distortion and measured
the resulting internal astrometric accuracy of the UVOT, also giving the
absolute accuracy with respect to the International Celestial Reference System.
We have compiled statistics on the background count rates, and discuss the
sources of the background, including instrumental scattered light. In each case
we describe any impact on UVOT measurements, whether any correction is applied
in the standard pipeline data processing or whether further steps are
recommended.Comment: Accepted for publication in MNRAS. 15 pages, 21 figures, 4 table
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