504 research outputs found
Detailed Classification of Swift's Gamma-Ray Bursts
Earlier classification analyses found three types of gamma-ray bursts (short,
long and intermediate in duration) in the BATSE sample. Recent works have shown
that these three groups are also present in the RHESSI and the BeppoSAX
databases. The duration distribution analysis of the bursts observed by the
Swift satellite also favors the three-component model. In this paper, we extend
the analysis of the Swift data with spectral information. We show, using the
spectral hardness and the duration simultaneously, that the maximum likelihood
method favors the three-component against the two-component model. The
likelihood also shows that a fourth component is not needed.Comment: Accepted for publication in The Astrophysical Journa
Time-resolved spectral correlations of long-duration Gamma-Ray Bursts
For a sample of long GRBs with known redshift, we study the distribution of
the evolutionary tracks on the rest-frame luminosity-peak energy Liso-Ep'
diagram. We are interested in exploring the extension of the `Yonetoku'
correlation to any phase of the prompt light curve, and in verifying how the
high-signal prompt duration time, Tf, in the rest frame correlates with the
residuals of such correlation (Firmani et al. 2006). For our purpose, we
analyse separately two samples of time-resolved spectra corresponding to 32
GRBs with peak fluxes >1.8 phot cm^-2 s^-1 from the Swift-BAT detector, and 7
bright GRBs from the CGRO-BATSE detector previously processed by Kaneko et al.
(2006). After constructing the Liso-Ep' diagram, we discuss the relevance of
selection effects, finding that they could affect significantly the
correlation. However, we find that these effects are much less significant in
the Liso x Tf-Ep' diagram, where the intrinsic scatter reduces significantly.
We apply further corrections for reducing the intrinsic scatter even more. For
the sub-samples of GRBs (7 from Swift and 5 from CGRO) with measured jet break
time, we analyse the effects of correcting Liso by jet collimation. We find
that (i) the scatter around the correlation is reduced, and (ii) this scatter
is dominated by the internal scatter of the individual evolutionary tracks.
These results suggest that the time, integrated `Amati' and `Ghirlanda'
correlations are consequences of the time resolved features, not of selection
effects, and therefore call for a physical origin. We finally remark the
relevance of looking inside the nature of the evolutionary tracks.Comment: 11 pages, 6 figures, 4 tables. Submitted to MNRAS (Sept 8th), after
referee comment
Searching for differences in Swift's intermediate GRBs
Gamma-ray bursts are usually classified through their high-energy emission
into short-duration and long-duration bursts, which presumably reflect two
different types of progenitors. However, it has been shown on statistical
grounds that a third, intermediate population is needed in this classification
scheme, although an extensive study of the properties of this class has so far
not been done. The large amount of follow-up studies generated during the Swift
era allows us to have a suficient sample to attempt a study of this third
population through the properties of their prompt emission and their
afterglows. Our study is focused on a sample of GRBs observed by Swift during
its first four years of operation. The sample contains those bursts with
measured redshift since this allows us to derive intrinsic properties.
Intermediate bursts are less energetic and have dimmer afterglows than long
GRBs, especially when considering the X-ray light curves, which are on average
one order of magnitude fainter than long bursts. There is a less significant
trend in the redshift distribution that places intermediate bursts closer than
long bursts. Except for this, intermediate bursts show similar properties to
long bursts. In particular, they follow the Epeak vs. Eiso correlation and
have, on average, positive spectral lags with a distribution similar to that of
long bursts. Like long GRBs, they normally have an associated supernova,
although some intermediate bursts have shown no supernova component. This study
shows that intermediate bursts are different from short bursts and, in spite of
sharing many properties with long bursts, there are some differences between
them as well. We suggest that the physical difference between intermediate and
long bursts could be that for the first the ejecta are thin shells while for
the latter they are thick shells.Comment: Accepted for publication in Astronomy and Astrophysics. 16 pages, 17
figures, 5 table
A faint optical flash in dust-obscured GRB 080603A - implications for GRB prompt emission mechanisms
We report the detection of a faint optical flash by the 2-m Faulkes Telescope
North simultaneously with the second of two prompt gamma-ray pulses in INTEGRAL
gamma-ray burst (GRB) 080603A, beginning at t_rest = 37 s after the onset of
the GRB. This optical flash appears to be distinct from the subsequent emerging
afterglow emission, for which we present comprehensive broadband radio to X-ray
light curves to 13 days post-burst and rigorously test the standard fireball
model. The intrinsic extinction toward GRB 080603A is high (A_V,z = 0.8 mag),
and the well-sampled X-ray-to-near-infrared spectral energy distribution is
interesting in requiring an LMC2 extinction profile, in contrast to the
majority of GRBs. Comparison of the gamma-ray and extinction-corrected optical
flux densities of the flash rules out an inverse-Compton origin for the prompt
gamma-rays; instead, we suggest that the optical flash could originate from the
inhomogeneity of the relativistic flow. In this scenario, a large velocity
irregularity in the flow produces the prompt gamma-rays, followed by a milder
internal shock at a larger radius that would cause the optical flash. Flat
gamma-ray spectra, roughly F propto nu^-0.1, are observed in many GRBs. If the
flat spectrum extends down to the optical band in GRB 080603A, the optical
flare could be explained as the low-energy tail of the gamma-ray emission. If
this is indeed the case, it provides an important clue to understanding the
nature of the emission process in the prompt phase of GRBs and highlights the
importance of deep (R> 20 mag), rapid follow-up observations capable of
detecting faint, prompt optical emission.Comment: 22 pages, 11 figures, accepted to MNRA
Ruthenium-catalyzed azide alkyne cycloaddition reaction: scope, mechanism and applications
The ruthenium-catalyzed azide alkyne cycloaddition (RuAAC) affords 1,5-disubstituted 1,2,3-triazoles in one step and complements the more established copper-catalyzed reaction providing the 1,4-isomer. The RuAAC reaction has quickly found its way into the organic chemistry toolbox and found applications in many different areas, such as medicinal chemistry, polymer synthesis, organocatalysis, supramolecular chemistry, and the construction of electronic devices. This Review discusses the mechanism, scope, and applications of the RuAAC reaction, covering the literature from the last 10 years
GRB 021004: Tomography of a gamma-ray burst progenitor and its host galaxy
We analyse the distribution of matter around the progenitor star of gamma-ray
burst GRB 021004 as well as the properties of its host galaxy with
high-resolution echelle as well as near-infrared spectroscopy. Observations
were taken by the 8.2m Very Large Telescope with the Ultraviolet and Visual
Echelle spectrograph (UVES) and the Infrared Spectrometer And Array Camera
(ISAAC) between 10 and 14 hours after the onset of the event. We report the
first detection of emission lines from a GRB host galaxy in the near-infrared,
detecting H-alpha and the [O III] doublet. These allow an independent
measurement of the systemic redshift (z = 2.3304 +/- 0.0005) which is not
contaminated by absorption as the Ly-alpha line is, and the deduction of
properties of the host galaxy. From the visual echelle spectroscopy, we find
several absorption line groups spanning a range of about 3,000 km/s in velocity
relative to the redshift of the host galaxy. The absorption profiles are very
complex with both velocity-broadened components extending over several 100 km/s
and narrow lines with velocity widths of only 20 km/s. By analogy with QSO
absorption line studies, the relative velocities,widths, and degrees of
ionization of the lines ("line-locking", "ionization--velocity correlation")
show that the progenitor had both an extremely strong radiation field and
several distinct mass loss phases (winds). These results are consistent with
GRB progenitors being massive stars, such as Luminous Blue Variables (LBVs) or
Wolf--Rayet stars, providing a detailed picture of the spatial and velocity
structure of the GRB progenitor star at the time of explosion. The host galaxy
is a prolific star-forming galaxy with a SFR of about 40 solar masses per year.Comment: 11 pages, 5 figures. Accepted for publication in Astronomy and
Astrophysics
Scheduling Games with Machine-Dependent Priority Lists
We consider a scheduling game in which jobs try to minimize their completion
time by choosing a machine to be processed on. Each machine uses an individual
priority list to decide on the order according to which the jobs on the machine
are processed. We characterize four classes of instances in which a pure Nash
equilibrium (NE) is guaranteed to exist, and show, by means of an example, that
none of these characterizations can be relaxed. We then bound the performance
of Nash equilibria for each of these classes with respect to the makespan of
the schedule and the sum of completion times. We also analyze the computational
complexity of several problems arising in this model. For instance, we prove
that it is NP-hard to decide whether a NE exists, and that even for instances
with identical machines, for which a NE is guaranteed to exist, it is NP-hard
to approximate the best NE within a factor of for all
. In addition, we study a generalized model in which players'
strategies are subsets of resources, each having its own priority list over the
players. We show that in this general model, even unweighted symmetric games
may not have a pure NE, and we bound the price of anarchy with respect to the
total players' costs.Comment: 19 pages, 2 figure
The optical identifcation of events with poorly defined locations: The case of the Fermi GBM GRB140801A
We report the early discovery of the optical afterglow of gamma-ray burst
(GRB) 140801A in the 137 deg 3- error-box of the Fermi Gamma-ray
Burst Monitor (GBM). MASTER is the only observatory that automatically react to
all Fermi alerts. GRB 140801A is one of the few GRBs whose optical counterpart
was discovered solely from its GBM localization. The optical afterglow of GRB
140801A was found by MASTER Global Robotic Net 53 sec after receiving the
alert, making it the fastest optical detection of a GRB from a GBM error-box.
Spectroscopy obtained with the 10.4-m Gran Telescopio Canarias and the 6-m BTA
of SAO RAS reveals a redshift of . We performed optical and
near-infrared photometry of GRB 140801A using different telescopes with
apertures ranging from 0.4-m to 10.4-m. GRB 140801A is a typical burst in many
ways. The rest-frame bolometric isotropic energy release and peak energy of the
burst is erg and
keV, respectively, which is consistent with the
Amati relation. The absence of a jet break in the optical light curve provides
a lower limit on the half-opening angle of the jet deg. The
observed is consistent with the limit derived from the
Ghirlanda relation. The joint Fermi GBM and Konus-Wind analysis shows that GRB
140801A could belong to the class of intermediate duration. The rapid detection
of the optical counterpart of GRB 140801A is especially important regarding the
upcoming experiments with large coordinate error-box areas.Comment: in press MNRAS, 201
Identifying the Location in the Host Galaxy of the Short GRB 111117A with the Chandra Sub-arcsecond Position
We present our successful Chandra program designed to identify, with
sub-arcsecond accuracy, the X-ray afterglow of the short GRB 111117A, which was
discovered by Swift and Fermi. Thanks to our rapid target of opportunity
request, Chandra clearly detected the X-ray afterglow, though no optical
afterglow was found in deep optical observations. The host galaxy was clearly
detected in the optical and near-infrared band, with the best photometric
redshift of z=1.31_{-0.23}^{+0.46} (90% confidence), making it one of the
highest known short GRB redshifts. Furthermore, we see an offset of 1.0 +- 0.2
arcseconds, which corresponds to 8.4 +- 1.7 kpc, between the host and the
afterglow position. We discuss the importance of using Chandra for obtaining
sub-arcsecond X-ray localizations of short GRB afterglows to study GRB
environments.Comment: 17 pages, 11 figures, accepted for publication in Ap
Does an activity based remuneration system attract young doctors to general practice?
<p>Abstract</p> <p>Background</p> <p>The use of increasingly complex payment schemes in primary care may represent a barrier to recruiting general practitioners (GP). The existing Norwegian remuneration system is fully activity based - 2/3 fee-for-service and 1/3 capitation. Given that the system has been designed and revised in close collaborations with the medical association, it is likely to correspond - at least to some degree - with the preferences of <it>current </it>GPs (men in majority). The objective of this paper was to study which preferences that young doctors (women in majority), who are the <it>potential entrants </it>to general practice have for activity based vs. salary based payment systems.</p> <p>Methods</p> <p>In November-December 2010 all last year medical students and all interns in Norway (n = 1.562) were invited to participate in an online survey. The respondents were asked their opinion on systems of remuneration for GPs; inclination to work as a GP; risk attitude; income preferences; work pace tolerance. The data was analysed using one-way ANOVA and multinomial logistic regression analysis.</p> <p>Results</p> <p>A total of 831 (53%) responded. Nearly half the sample (47%) did not consider the remuneration system to be important for their inclination to work as GP; 36% considered the current system to make general practice <it>more </it>attractive, while 17% considered it to make general practice <it>less </it>attractive. Those who are attracted by the existing system were men and those who think high income is important, while those who are deterred by the system are risk averse and less happy with a high work pace. On the question of preferred remuneration system, half the sample preferred a mix of salary and activity based remuneration (the median respondent would prefer a 50/50 mix). Only 20% preferred a fully activity based system like the existing one. A salary system was preferred by women, and those less concerned with high income, while a fully activity based system was preferred by men, and those happy with a high work pace.</p> <p>Conclusions</p> <p>Given a concern about low recruitment to general practice in Norway, and the fact that an increasing share of medical students is women, we were interested in the extent to which the current Norwegian remuneration system correspond with the preferences of potential GPs. This study suggests that an existing remuneration mechanism has a selection effect on who would like to become a GP. Those most attracted are income motivated men. Those deterred are risk averse, and less happy with a high work pace. More research is needed on the extent to which experienced GPs differ along the questions we asked potential GPs, as well as studying the relative importance of other attributes than payment schemes.</p
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