566 research outputs found
Extended GeV-TeV Emission around Gamma-Ray Burst Remnants, and the Case of W49B
We investigate the high-energy photon emission around Gamma-Ray Burst (GRB)
remnants caused by ultrahigh-energy cosmic rays (UHECRs) from the GRBs. We
apply the results to the recent report that the supernova remnant W49B is a GRB
remnant in our Galaxy. If this is correct, and if GRBs are sources of UHECRs, a
natural consequence of this identification would be a detectable TeV photon
emission around the GRB remnant. The imaging of the surrounding emission could
provide new constraints on the jet structure of the GRB.Comment: 12 pages, 2 figures, accepted for publication in ApJ
Microlensing of collimated Gamma-Ray Burst afterglows
We investigate stellar microlensing of the collimated gamma-ray burst
afterglows. A spherical afterglow appears on the sky as a superluminally
expanding thin ring (``ring-like'' image), which is maximally amplified as it
crosses the lens. We find that the image of the collimated afterglow becomes
quite uniform (``disk-like'' image) after the jet break time (after the Lorentz
factor of the jet drops below the inverse of the jet opening angle).
Consequently, the amplification peak in the light curve after the break time is
lower and broader. Therefore detailed monitoring of the amplification history
will be able to test whether the afterglows are jets or not, i.e.,
``disk-like'' or not, if the lensing occurs after the break time. We also show
that some proper motion and polarization is expected, peaking around the
maximum amplification. The simultaneous detection of the proper motion and the
polarization will strengthen that the brightening of the light curve is due to
microlensing.Comment: 16 pages, 6 figures, accepted for publication in Ap
Radiative transfer in ultra-relativistic outflows
Analytical and numerical solutions are obtained for the equation of radiative
transfer in ultra-relativistic opaque jets. The solution describes the initial
trapping of radiation, its adiabatic cooling, and the transition to
transparency. Two opposite regimes are examined: (1) Matter-dominated outflow.
Surprisingly, radiation develops enormous anisotropy in the fluid frame before
decoupling from the fluid. The radiation is strongly polarized. (2)
Radiation-dominated outflow. The transfer occurs as if radiation propagated in
vacuum, preserving the angular distribution and the blackbody shape of the
spectrum. The escaping radiation has a blackbody spectrum if (and only if) the
outflow energy is dominated by radiation up to the photospheric radius.Comment: 12 pages, 8 figures, accepted to Ap
Gravitational Wave Memory of Gamma-Ray Burst Jets
Gamma-Ray Bursts (GRBs) are now considered as relativistic jets. We analyze
the gravitational waves from the acceleration stage of the GRB jets. We show
that (i) the point mass approximation is not appropriate if the opening
half-angle of the jet is larger than the inverse of the Lorentz factor of the
jet, (ii) the gravitational waveform has many step function like jumps, and
(iii) the practical DECIGO and BBO may detect such an event if the GRBs occur
in Local group of galaxy. We found that the light curve of GRBs and the
gravitational waveform are anti-correlated so that the detection of the
gravitational wave is indispensable to determine the structure of GRB jets.Comment: Revtex4, 10 pages, 6 figures, Fig.2 and Fig.3 replaced, minor changes
to text in Sec.I and Sec.V, typos corrected, some reference added, Version to
be published in PR
Cosmic-Ray Electron Excess from Pulsars is Spiky or Smooth?: Continuous and Multiple Electron/Positron injections
We investigate the observed spectrum of cosmic-ray electrons and positrons
from astrophysical sources, especially pulsars, and the physical processes for
making the spectrum spiky or smooth via continuous and multiple
electron/positron injections. We find that (1) the average electron spectrum
predicted from nearby pulsars are consistent with PAMELA, Fermi and H.E.S.S.
data. However, the ATIC/PPB-BETS peak around 500GeV is hard to produce by the
sum of multiple pulsar contributions and requires a single (or a few) energetic
pulsar(s). (2) A continuous injection produces a broad peak and a high energy
tail above the peak, which can constrain the source duration (yr
with the current data). (3) The H.E.S.S. data in the TeV range suggest that
young sources with age less than yr are less energetic than
. (4) We also expect a large dispersion in the TeV
spectrum due to the small number of sources, that may cause the high energy
cutoff inferred by H.E.S.S. and potentially provide a smoking-gun for the
astrophysical origin. These spectral diagnostics can be refined in the near
future by the CALET experiments to discriminate different astrophysical and
dark matter origins.Comment: 5 pages, 3 figures, revised to reflect referee's comments, added
Fermi/HESS result
Influence of general convective motions on the exterior of isolated rotating bodies in equilibrium
The problem of describing isolated rotating bodies in equilibrium in General
Relativity has so far been treated under the assumption of the circularity
condition in the interior of the body. For a fluid without energy flux, this
condition implies that the fluid flow moves only along the angular direction,
i.e. there is no convection. Using this simplification, some recent studies
have provided us with uniqueness and existence results for asymptotically flat
vacuum exterior fields given the interior sources. Here, the generalisation of
the problem to include general sources is studied. It is proven that the
convective motions have no direct influence on the exterior field, and hence,
that the aforementioned results on uniqueness and existence of exterior fields
apply equally in the general case.Comment: 8 pages, LaTex, uses iopart style files. To appear in Class. Quatum
Gra
Risk factors for intrahepatic cholangiocarcinoma: a possible role of hepatitis B virus
There are several established risk factors for intrahepatic cholangiocarcinoma (ICC), namely primary sclerosing cholangitis, fibropolycystic liver disease, parasitic infection, intrahepatic biliary stones and chemical carcinogen exposure. However, the majority of patients with ICC do not have any of these risk factors. Therefore, identification of other risk factors is warranted for the prevention and early detection of ICC. We evaluated the risk factors for ICC in a large-scale cohort study in the province of Osaka, Japan. This retrospective cohort study included 154,814 apparently healthy individual blood donors, aged 40â64 years at the time of blood donation in the period 1991â1993. The average observation period was 7.6 years, resulting in 1.25 million person-years of observation. Incident ICC cases were identified by linking the blood-donor database to the records in the population-based cancer registry for the province. There were 11 incident ICC cases during follow-up, with an incidence rate of 0.88 per 100 000 person-years. Compared with subjects aged 40â49 years, the subjects aged 50â54 years and 55â59 years had a significantly higher risk for ICC (hazard ratio [HR] = 5.90; 95%CI:1.08â32.31 and 11.07; 95%CI:1.98â61.79, respectively). Compared with those with ALT level of 19 Karmen Units (KU) or less, subjects with ALT level of 40 KU or higher had a significantly higher risk for ICC (HR: 8.30; 95%CI:1.47â46.83). Compared with those who tested negative for both HBsAg and anti-HCV, those who tested HBsAg-positive had a significantly higher risk for ICC (HR: 8.56; 95%CI: 1.33â55.20). Our results suggest that HBV infection and liver inflammation are independently associated with ICC development. These findings need to be verified by further large cohort studies
Observations of GRB 060526 Optical Afterglow with Russian-Turkish 1.5-m Telescope
We present the results of the photometric multicolor observations of GRB
060526 optical afterglow obtained with Russian-Turkish 1.5-m Telescope (RTT150,
Mt. Bakirlitepe, Turkey). The detailed measurements of afterglow light curve,
starting from about 5 hours after the GRB and during 5 consecutive nights were
done. In addition, upper limits on the fast variability of the afterglow during
the first night of observations were obtained and the history of afterglow
color variations was measured in detail. In the time interval from 6 to 16
hours after the burst, there is a gradual flux decay, which can be described
approximately as a power law with an index of -1.14+-0.02. After that the
variability on the time scale \delta t < t is observed and the afterglow
started to decay faster. The color of the afterglow, V-R=~0.5, is approximately
the same during all our observations. The variability is detected on time
scales up to \delta t/t =~ 0.0055 at \Delta F_\nu/F_\nu =~ 0.3, which violates
some constraints on the variability of the observed emission from
ultrarelativistic jet obtained by Ioka et al. (2005). We suggest to explain
this variability by the fact that the motion of the emitting shell is no longer
ultrarelativistic at this time.Comment: 6 pages, 7 figures, Astronomy Letters, 2007, 33, 797, The on-line
data tables and the original text in Russian can be found at
http://hea.iki.rssi.ru/grb/060526/indexeng.htm
Algebraic approach to time-delay data analysis for LISA
Cancellation of laser frequency noise in interferometers is crucial for
attaining the requisite sensitivity of the triangular 3-spacecraft LISA
configuration. Raw laser noise is several orders of magnitude above the other
noises and thus it is essential to bring it down to the level of other noises
such as shot, acceleration, etc. Since it is impossible to maintain equal
distances between spacecrafts, laser noise cancellation must be achieved by
appropriately combining the six beams with appropriate time-delays. It has been
shown in several recent papers that such combinations are possible. In this
paper, we present a rigorous and systematic formalism based on algebraic
geometrical methods involving computational commutative algebra, which
generates in principle {\it all} the data combinations cancelling the laser
frequency noise. The relevant data combinations form the first module of
syzygies, as it is called in the literature of algebraic geometry. The module
is over a polynomial ring in three variables, the three variables corresponding
to the three time-delays around the LISA triangle. Specifically, we list
several sets of generators for the module whose linear combinations with
polynomial coefficients generate the entire module. We find that this formalism
can also be extended in a straight forward way to cancel Doppler shifts due to
optical bench motions. The two modules are infact isomorphic.
We use our formalism to obtain the transfer functions for the six beams and
for the generators. We specifically investigate monochromatic gravitational
wave sources in the LISA band and carry out the maximisiation over linear
combinations of the generators of the signal-to-noise ratios with the frequency
and source direction angles as parameters.Comment: 27 Pages, 6 figure
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