441 research outputs found
Earliest detection of the optical afterglow of GRB 030329 and its variability
We report the earliest detection of an extremely bright optical afterglow of
the gamma-ray burst (GRB) 030329 using a 30cm-telescope at Tokyo Institute of
Technology (Tokyo, JAPAN). Our observation started 67 minutes after the burst,
and continued for succeeding two nights until the afterglow faded below the
sensitivity limit of the telescope (approximately 18 mag). Combining our data
with those reported in GCN Circulars, we find that the early afterglow light
curve of the first half day is described by a broken power-law (t^{- alpha})
function with indices alpha_{1} = 0.88 +/- 0.01 (0.047 < t < t_{b1} days),
alpha_{2} = 1.18 +/- 0.01 (t_{b1} < t < t_{b2} days), and alpha_{3} = 1.81 +/-
0.04 (t_{b2} < t < 1.2 days), where t_{b1} ~ 0.26 days and t_{b2} ~ 0.54 days,
respectively. The change of the power-law index at the first break at t ~ 0.26
days is consistent with that expected from a ``cooling-break'' when the cooling
frequency crossed the optical band. If the interpretation is correct, the decay
index before the cooling-break implies a uniform ISM environment.Comment: 13 pages, 1 table and 2 figures. Accepted to the Astrophysical
Journal Letter
Dipyridamole plus aspirin versus aspirin alone in the secondary prevention after TIA or stroke: a meta-analysis by risk
Objectives: Our aim was to study the effect of combination therapy with aspirin and dipyridamole (A+D) over aspirin alone (ASA) in secondary prevention after transient
ischemic attack or minor stroke of presumed arterial origin and to perform subgroup analyses to identify patients that might benefit most from secondary prevention with A+D.
Data sources: The previously published meta-analysis of individual patient data was updated with data from ESPRIT (N=2,739); trials without data on the comparison of A+D versus ASA were excluded.
Review methods: A meta-analysis was performed using Cox regression, including several subgroup analyses and following baseline risk stratification.
Results: A total of 7,612 patients (5 trials) were included in the analyses, 3,800 allocated to A+D and 3,812 to ASA alone. The trial-adjusted hazard ratio for the composite event of vascular death, non-fatal myocardial infarction and non-fatal stroke was 0.82 (95% confidence interval 0.72-0.92). Hazard ratios did not differ in subgroup analyses based on age, sex, qualifying event, hypertension, diabetes, previous stroke, ischemic heart disease,
aspirin dose, type of vessel disease and dipyridamole formulation, nor across baseline risk strata as assessed with two different risk scores. A+D were also more effective than ASA alone in preventing recurrent stroke, HR 0.78 (95% CI 0.68 – 0.90).
Conclusion: The combination of aspirin and dipyridamole is more effective than aspirin alone in patients with TIA or ischemic stroke of presumed arterial origin in the secondary
prevention of stroke and other vascular events. This superiority was found in all subgroups and was independent of baseline risk. ---------------------------7dc3521430776
Content-Disposition: form-data; name="c14_creators_1_name_family"
Halke
Discovery of an unidentified Fermi object as a black widow-like millisecond pulsar
The Fermi Gamma-ray Space Telescope has revolutionized our knowledge of the
gamma-ray pulsar population, leading to the discovery of almost 100 gamma-ray
pulsars and dozens of gamma-ray millisecond pulsars (MSPs). Although the
outer-gap model predicts different sites of emission for the radio and
gamma-ray pulsars, until now all of the known gamma-ray MSPs have been visible
in the radio. Here we report the discovery of a "radio-quiet" gamma-ray
emitting MSP candidate by using Fermi, Chandra, Swift, and optical
observations. The X-ray and gamma-ray properties of the source are consistent
with known gamma-ray pulsars. We also found a 4.63-hr orbital period in optical
and X-ray data. We suggest that the source is a black widow-like MSP with a
~0.1 solar-mass late-type companion star. Based on the profile of the optical
and X-ray light-curves, the companion star is believed to be heated by the
pulsar while the X-ray emissions originate from pulsar magnetosphere and/or
from intra-binary shock. No radio detection of the source has been reported yet
and although no gamma-ray/radio pulsation has been found, we estimated that the
spin period of the MSP is ~3-5 ms based on the inferred gamma-ray luminosity.Comment: 6 pages, 2 figures; accepted for publication in ApJ
Spatially resolved XMM-Newton analysis and a model of the nonthermal emission of MSH 15-52
We present an X-ray analysis and a model of the nonthermal emission of the
pulsar wind nebula (PWN) MSH15-52. We analyzed XMM-Newton data to obtain the
spatially resolved spectral parameters around the pulsar PSRB1509-58. A
steepening of the fitted power-law spectra and decrease in the surface
brightness is observed with increasing distance from the pulsar. In the second
part of this paper, we introduce a model for the nonthermal emission, based on
assuming the ideal magnetohydrodynamic limit. This model is used to constrain
the parameters of the termination shock and the bulk velocity of the leptons in
the PWN. Our model is able to reproduce the spatial variation of the X-ray
spectra. The parameter ranges that we found agree well with the parameter
estimates found by other authors with different approaches. In the last part of
this paper, we calculate the inverse Compton emission from our model and
compare it to the emission detected with the H.E.S.S. telescope system. Our
model is able to reproduce the flux level observed with H.E.S.S., but not the
spectral shape of the observed TeV {\gamma}-ray emission.Comment: Accepted for publication in A&A, 9 pages, 15 figure
MITSuME--Multicolor Imaging Telescopes for Survey and Monstrous Explosions
Development of MITSuME is reported. Two 50-cm optical telescopes have been
built at Akeno in Yamanashi prefecture and at Okayama Astrophysical Observatory
(OAO) in Okayama prefecture. Three CCD cameras for simultaneous g'RcIc
photometry are to be mounted on each focal plane, covering a wide FOV of about
30" x 30". The limiting magnitude at V is fainter than 18. In addition to these
two optical telescopes, a 91-cm IR telescope with a 1 deg x 1 deg field of view
is being built at OAO, which performs photometry in YJHK bands. These robotic
telescopes can start the observation of counterparts of a GRB within a minute
from an alert. We aim to obtain photometric redshifts exceeding 10 with these
telescopes. The performance and the current construction status of the
telescopes are presented.Comment: 4 pages, 3 figures, 4th Workshop on Gamma-Ray Burst in the Afterglow
Era, Roma, October 18-22, 200
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