5492160
Low-Luminosity GRB 060218: A Collapsar Jet from a Neutron Star, Leaving a Magnetar as a Remnant?
The gamma-ray burst (GRB) 060218 has a luminosity ~105 times lower than that of typical long GRBs and is associated with a supernova (SN). The radio afterglow displays no jet break, so this burst might arise from a mildly relativistic spherical outflow produced by the SN shock sweeping the stellar surface. Since this model is energetically difficult, we propose that the radio afterglow is produced by a nonrelativistic phase of an initially collimated outflow (jet). Our jet model is supported by the detection of optical linear polarization in the SN component. We also show analytically that the jet can penetrate a progenitor star. We analyzed the observational data of the prompt emission of this burst and obtained a smooth power-law light curve which might last longer than 106 s. This behavior contrasts with the long intermittent activities of the X-ray flares of typical GRBs, implying that the central engine of this burst is different from those of typical GRBs. This argument is consistent with the analysis of the SN component of this burst, which suggests that the progenitor star was less massive and collapsed to a neutron star instead of a black hole. The collimation-corrected event rate of such low-luminosity GRBs is estimated to be ~10 times higher than that of typical long GRBs, and they might form a different GRB population: low-luminosity GRBs are produced by mildly relativistic jets from neutron stars at the collapses of massive stars, while typical long GRBs are produced by highly relativistic jets from black holes. We suggest that the central engine of GRB 060218 is a pulsar (or a magnetar) with initial rotation period P0 ~ 10 ms and magnetic field B ~ 1016 G. A giant flare from the magnetar might be observed in future.
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
96043155
Measurements of Activation Cross Sections on Spallation Reactions for 59Co and natCu at Incident Neutron Energies of 40 to 120 MeV
In our previous work, we have measured the neutron spallation cross sections of 12C and 209Bi in the 20-to 150-MeV energy range. Here in this succeeding study, the neutron activation cross sections on spallation reactions for 59Co and natCu have been measured in the quasi-monoenergetic p-7Li neutron fields in the 40-to 120-MeV energy range which have been established at two cyclotron facilities of Takasaki Research Establishment of Japan Atomic Energy Research institute (TIARA) and the Institute of Physical and Chemical Research (RIKEN). The neutron spectrum has been measured with the TOF (Time of Flight) method using an organic liquid scintillator, and the absolute value of peak neutron fluence has been determined from the proton recoil counter telescope at TIARA and the activation method of lithium target at RIKEN. In this study, the following seventeen neutron activation cross section data are reported which produce 56Mn, 54Mn, 52Mn, 58Co, 57Co, 56Co, 55Co, 59Fe from 59Co reactions and 56Mn, 59Fe, 60Co...
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.
973744
Wave Effects in the Gravitational Lensing of Gravitational Waves from Chirping Binaries
In the gravitational lensing of gravitational waves, wave optics should be used instead of geometrical optics when the wavelength λ of the gravitational waves is longer than the Schwarzschild radius of the lens mass ML. For gravitational lensing of chirp signals from the coalescence of supermassive black holes at redshift zS ~ 1 relative to the Laser Interferometer Space Antenna, the wave effects become important for a lens mass smaller than ~108 M☉. For such cases, we compute how accurately we can extract the mass of the lens and the source position from the lensed signal. We consider two simple lens models: the point-mass lens and the SIS (singular isothermal sphere). We find that the lens mass and the source position can be determined to within ~0.1% of [(S/N)/103]-1 for a lens mass larger than 108 M☉ and 10% of [(S/N)/103]-1 for a lens mass smaller than 107 M☉ because of the diffraction effect, where S/N is the signal-to-noise ratio of the unlensed chirp signals. For the SIS model, if the source position is outside the Einstein radius, only a single image exists in the geometrical optics approximation, so that the lens parameters cannot be determined, while in the wave optics cases we find that the lens mass can be determined even for ML < 108 M☉. For the point-mass lens, one can extract the lens parameters even if the source position is far outside the Einstein radius. As a result, the lensing cross section is an order of magnitude larger than that for the usual strong lensing of light.
15956163
Factor Two Discrepancy of Hawking Radiation Temperature
The possibility of an alternative way to formulate the Hawking radiation in a static Schwarzschild spacetime has been explored. To calculate the Hawking radiation, there can be two possible choices of the spacetime wedge pairs in the Krucal-Szekeres coordinates. One is the wedge pair consists of exterior spacetime of a black hole and the exterior spacetime of a white hole, and the other is that of exterior and interior spacetimes of one black hole. The radiation from the former is the Hawking's original one. Though the the latter has been often regarded as the same phenomena as the former, the result here suggests it is not; its radiation has a temperature twice as high as the Hawking temperature.