16123016
A Unified Model of Short and Long Gamma-Ray Bursts, X-Ray Rich Gamma-Ray Bursts, and X-Ray Flashes
Taking into account the recent suggestion that a short gamma-ray burst (GRB) looks like the first 1 s of a long GRB, we propose that the jet of a GRB consists of multiple subjets or subshells (i.e., an inhomogeneous jet model). The multiplicity of the subjets along a line of sight is an important parameter. If is large ( k1) nn ss the event looks like a long GRB, while if is small (∼1) the event looks like a short GRB. If our line of sight ns is off-axis to any subjets, the event looks like an X-ray flash or an X-ray–rich GRB. The lognormal distribution of durations of short and long GRBs are also suggested in the same model.
120122684
Overview of recent experimental works on high energy neutron shielding
Abstract Several experiments on high energy neutron shielding have recently been performed using medium to high energy accelerators of energies above 20 MeV. Below 100 MeV, the benchmark experiments have been done using 25 and 35 MeV p-Li quasi-monoenergetic neutrons at the Cyclotron and Radioisotope Center (CYRIC), Tohoku University, Japan, 43 and 68 MeV p-Li quasi-monoenergetic neutrons at the Azimuthally Varying Field (AVF) cyclotron facility, TIARA of Japan Atomic Energy Research Institute (JAERI). Above 100 MeV, the neutron shielding experiments have been done using 800 MeV protons at ISIS, Rutherford Appleton laboratory (RAL), England, 400 MeV/nucleon carbon ions at the heavy ion medical accelerator facility, HIMAC of National Institute of Radiological Sciences (NIBS), Japan, 500 MeV protons at the spallation neutron source facility, KEK spallation neutron source facility (KENS) of High Energy Accelerator Research Organization (KEK), Japan, 500 MeV protons at the accelerator facility, TRIUMF, Canada, 1.6 to 24 GeV protons at the Alternating Gradient Synchrotron (AGS), Brookhaven National Laboratory (BNL), U.S.A., 28.7 GeV electrons at the Stanford Linear Accelerator Center (SLAG), U.S.A., 800 MeV protons at the Los Alamos Neutron Science Center (LANSCE), Los Alamos National Laboratory (LANL), U.S.A., 120, 205 GeV/c protons and 160 GeV/nucleon lead ions at the European Organization for Nuclear Research (CERN), Switzerland, 230 MeV protons at the Loma Linda University Medical Center, U.S.A., 200 MeV protons at the Orsay Proton Therapy Center, France. In this review paper, the outlines of these deep penetration experiments are summarized together with the neutron detection techniques.
119096961
SOFT X-RAY EXTENDED EMISSIONS OF SHORT GAMMA-RAY BURSTS AS ELECTROMAGNETIC COUNTERPARTS OF COMPACT BINARY MERGERS; POSSIBLE ORIGIN AND DETECTABILITY
We investigate the possible origin of extended emissions (EE) of short gamma-ray bursts (SGRBs) with an isotropic energy of ∼ 10 50-51 erg and a duration of ∼ 100 s, based on the compact binary (neutron star (NS)-NS or NS-black hole (BH)) merger scenario. We analyze the evolution of magnetized neutrino-dominated accretion disks of mass ∼ 0.1 M⊙ around BHs formed after the mergers, and estimate the power of relativistic outflows via the Blandford-Znajek (BZ) process. We show that a rotation energy of the BH up to ∼ 10 53 erg can be extracted with a time scale of ∼ 100 s with a disk viscosity parameter of � ∼ 0.01. Such a BZ power dissipates by clashing with nonrelativistic pre-ejected matter of mass M ∼ 10 −(2-4) M⊙, and form a mildly relativistic fireball. We show that the dissipative photospheric emissions from such fireballs are likely in soft X-ray band (1-10 keV) for M ∼ 10 −2 M⊙ possibly in NS-NS mergers, and in the BAT band (15-150 keV) for M ∼ 10 −4 M⊙ possibly in NS-BH mergers. In the former case, such soft EEs can provide a good chance of ∼ 6 yr −1 (�softEE/4�) (RGW/40 yr −1 ) for simultaneous detections of the gravitational waves with a ∼ 0.1 ◦ angular resolution by soft X-ray survey facilities like Wide-Field MAXI. Here, �softEE is the beaming factor of the soft EEs and RGW is the NS-NS merger rate detectable by advanced LIGO, advanced Virgo, and KAGRA. While in the latter case, the observed EEs, which are associated with ∼ 25% of Swift SGRBs, can be well explained although the simultaneous detection rate with the GWs is expected to be very low . 10 −3 yr −1 . Subject headings: gamma rays: bursts — gamma rays: observations — gamma rays: theory
123083834
Can Current Detectors Detect Gravitational Radiation from Newborn Pulsars
16735826
GRB 980425 in the Off‐Axis Jet Model of the Standard GRBs
Using a simple off‐axis jet model of GRBs, we can reproduce the observed unusual properties of the prompt emission of GRB 980425, such as the extremely low isotropic equivalent γ‐ray energy, the low peak energy, the high fluence ratio, and the long spectral lag when the jet with the standard energy of ∼ 1051 ergs and the opening half‐angle of 10°⩽Δθ⩽30° is seen from the off‐axis viewing angle θv ∼ Δθ + 10γ−1, where γ is a Lorentz factor of the jet. For our adopted fiducial parameters, if the jet that caused GRB 980425 is viewed from the on‐axis direction, the intrinsic peak energy Ep(1 + z) is ∼2.0–4.0 MeV, which corresponds to those of GRB 990123 and GRB 021004. Our model might be able to explain the other unusual properties of this event. We also discuss the connection of GRB 980425 in our model with the X‐ray flash, and the origin of a class of GRBs with small Eγ such as GRB 030329.
120027595
Gravitational radiation from an extreme Kerr black hole
We analytically investigate gravitational radiation induced by a test particle falling into an extreme Kerr black hole. Assuming the radiation is dominated by the infinite sequence of quasi-normal modes which has the limiting frequencym/(2M), wherem is an azimuthal eigenvalue andM is the mass of the black hole. we find the radiated energy diverges logarithmically in time. Then we evaluate the back reaction to the black hole by appealing to the energy and angular momentum conservation laws. We find the radiation has a tendency to increase the ratio of the angular momentum to mass of the black hole, which is completely different from the non-extreme case, while the contribution of the test particle is to decrease it.
17494376
Hydrodynamic time scales and temporal structure of GRBs
We calculate the hydrodynamic time scales for a spherical ultra-relativistic shell that is decelerated by the ISM and discuss the possible relations between these time scales and the observed temporal structure in γ-ray bursts. We suggest that the bursts’ durations are related to the deceleration time, the variations are related to the ISM inhomogeneities and precursors are related to internal shocks within the shell. Good agreement can be achieved for these quantities with reasonable, not fined tuned, astrophysical parameters. The difference between Newtonian and relativistic reverse shocks may lead to the observed bimodal distribution of bursts’ durations.
14610341
A Method for Weak-Lensing Flexion Analysis by the HOLICs Moment Approach*
We have developed a method for measuring higher order weak-lensing distortions of faint background galaxies, namely, the weak gravitational flexion, by fully extending the Kaiser, Squires, and Broadhurst method to include higher order lensing image characteristics (HOLICs) introduced by Okura, Umetsu, and Futamase. We take into account explicitly the weight function in calculations of noisy shape moments and the effect of higher order point-spread function (PSF) anisotropy, as well as isotropic PSF smearing. Our HOLICs formalism allows accurate measurements of flexion from practical observational data in the presence of a noncircular, anisotropic PSF. We test our method using mock observations of simulated galaxy images and actual, ground-based Subaru observations of the massive galaxy cluster A1689 (z = 0.183). From the high-precision measurements of the spin-1 first flexion, we obtain a high-resolution mass map in the central region of A1689. The reconstructed mass map shows a bimodal feature in the central 4' × 4' region of the cluster. The major, pronounced peak is associated with the brightest cluster galaxy and central cluster members, while the secondary mass peak is associated with a local concentration of bright galaxies. The refined, high-resolution mass map of A1689 demonstrates the power of the generalized weak-lensing analysis techniques for quantitative and accurate measurements of the weak gravitational lensing signal.
18067084
Statistics of Weak Gravitational Lensing in Cold Dark Matter Models: Magnification Bias on Quasar Luminosity Functions
We compute statistical properties of weak gravitational lensing by large-scale structure in three cold dark matter (CDM) models: two —at models with 0) and (0.3, 0.7) and one open model () 0 , j 0 ) \ (1, with 0), where and are the density parameter and cosmological constant, respec- () 0 , j 0 ) \ (0.3, ) 0 j 0 tively. We use a particle-particle/particle-mesh (P3M) N-body code to simulate the formation and evolu- tion of large-scale structure in the universe. We perform 1.1 ) 107 ray-tracing experiments for each model, by computing the Jacobian matrix along random lines of sight, using the multiple lensplane algorithm. From the results of these experiments, we calculate the probability distribution functions of the convergences, shears, and magni—cations, and their rms values. We —nd that the rms values of the convergence and shear agree with the predictions of a nonlinear analytical model. We also —nd that the probability distribution functions of the magni—cations k have a peak at values slightly smaller than k \ 1 and are strongly skewed toward large magni—cations. In particular, for the high-density () 0 \ 1) model, a power-law tail appears in the distribution function at large magni—cations for sources at red- shifts The rms values of the magni—cations essentially agree with the nonlinear analytical predic- z s ( 2. tions for sources at low redshift but exceed these predictions for high redshift sources, once the power-law tail appears. We study the eUect of magni—cation bias on the luminosity functions of high- redshift quasars, using the calculated probability distribution functions of the magni—cations. We show that the magni—cation bias is moderate in the absence of the power-law tail in the magni—cation dis- tribution but depends strongly on the value of the density parameter In presence of the power-law ) 0 . tail, the bias becomes considerable, especially at the bright end of the luminosity functions where its logarithmic slope steepens. We present a speci—c example that demonstrates that the bias —attens the bright-side logarithmic slope of a double power-law luminosity function. Subject headings: cosmology: observationscosmology: theorydark matter ¨ gravitational lensinglarge-scale structure of universequasars: general
15830405
Cooling Timescales and Temporal Structure of Gamma-Ray Bursts
A leading mechanism for producing cosmological gamma-ray bursts (GRBs) is via ultrarelativistic particles in an expanding fireball. The kinetic energy of the particles is converted into thermal energy in two shocks, a forward shock and a reverse shock, when the outward flowing particles encounter the interstellar medium. The thermal energy is then radiated via synchrotron emission and Comptonization. We estimate the synchrotron cooling timescale of the shocked material in the forward and reverse shocks for electrons of various Lorentz factors, focusing in particular on those electrons whose radiation falls within the energy detection range of the BATSE detectors. We find that in order to produce the rapid variability observed in most bursts, the energy density of the magnetic field in the shocked material must be greater than about 1% of the thermal energy density. In addition, the electrons must be nearly in equipartition with the protons, since otherwise we do not have reasonable radiative efficiencies of GRBs. Inverse Compton scattering can increase the cooling rate of the relevant electrons, but the Comptonized emission itself is never within the BATSE range. These arguments allow us to pinpoint the conditions within the radiating regions in GRBs and to determine the important radiation processes. In addition, they provide a plausible explanation for several observations. The model predicts that the duty cycle of intensity variations in GRB light curves should be nearly independent of burst duration and should scale inversely as the square root of the observed photon energy. Both correlations are in agreement with observations. The model also provides a plausible explanation for the bimodal distribution of burst durations. There is no explanation, however, for the presence of a characteristic break energy in GRB spectra.