亮暗暴的早期X射线研究

研究亮暴和暗暴的X射线余辉,发现它们的X射线和γ流量的分布基本上相同。即:从统计学的角度上讲,亮暴和暗暴没有本质不同,它们的中心机制应该是相同的,暗暴的形成应该是由环境原因引起的。     

Outflow Propagation in Collapsars: Collimated Jets and Expanding Outflows

We investigate the outflow propagation in the collapsar in the context of gamma-ray bursts (GRBs) with 2D relativistic hydrodynamic simulations. We vary the specific internal energy and bulk Lorentz factor of the injected outflow from non-relativistic regime to relativistic one, fixing the power of the outflow to be 10⁵¹erg s⁻¹. We observed the collimated outflow, when the Lorentz factor of the injected outflow is roughly greater than 2. To the contrary, when the velocity of the injected outflow is slower, the expanding outflow is observed. The transition from collimated jet to expanding outflow continuously occurs by decreasing the injected velocity. Different features of the dynamics of the outflows would cause the difference between the GRBs and similar phenomena, such as, X-ray flashes.     

Search for GRB counterparts: non-optical

The present status of the search for counterparts of gamma-ray bursts is given. Particular emphasis will be put on the search for flaring counterparts, i.e. emission during or shortly after the gamma-ray emission. In view of a separate review on optical counterparts I will concentrate on GeV/TeV, X-ray, radio and neutrino searches.     

On the use of COBE results

The aim of this brief report is to find a lower limit of the Hubble parameter using the COBE's detected fluctuations in the temperature of the CMBR.     

Optical counterparts of cosmological GRBs

The possibility of observing of optical counterparts of cosmological GRBs has been considered assuming that the counterparts are due to the -radiation interaction with the interstellar medium.     

Status of the Transient Gamma-Ray Spectrometer

The Transient Gamma-Ray Spectrometer (TGRS) was launched aboard the GGS/WIND spacecraft on November 1, 1994. After several deep space orbits (2 yrs) WIND will eventually be injected into a halo orbit around the Sun-EarthL ₁ point. TGRS consists of a 215 cm³ high purityn-type Ge crystal which is kept at cryogenic temperatures by a passive radiative cooler. The energy range covered by the instrument is 25–8000 keV with an energy resolution of 2–3 keV. The primary task of TGRS is to perform high resolution spectroscopy of gamma-ray bursts and solar flares. Additional objectives are the study of transient x-ray pulsars and, using an on-board passive occulter, the long-term monitoring of sources such as the Crab and the Galactic Center. Since launch, TGRS has been performing exceedingly well, and all the important experiment parameters such as background levels, gain, and resolution have proven to be very stable. To date, TGRS has detected 27 GRBs and three solar flares. Preliminary analysis of our data also indicates that TGRS is indeed sensitive to sources such as the Crab and the Galactic Center.     

Observations of soft gamma-ray or hard X-ray bursts in the GRIF experiment on the <Emphasis Type="Italic">Mir</Emphasis> orbiting station

During the GRIF experiment onboard the Mir orbiting station, the sky was monitored with a PX-2 wide-field (～1 sr) scintillation X-ray spectrometer to detect bursts in the photon energy range 10–300 keV. Because of the comprehensive instrumentation, which, apart from the X-ray and gamma-ray instruments, also included charged-particle detectors, the imitations of astrophysical bursts by magnetospheric electron precipitations and strongly ionizing nuclei were effectively filtered out. It was also possible to separate solar and atmospheric events. Several tens of bursts interpreted as being astrophysical were detected in the experiment at sensitivity levels S～10^?7 erg cm^?2 (for bursts whose spectra were characterized by effective temperatures kT～100 keV) and S～3×10^?8 erg cm^?2 (for bursts with kT～25 keV). Some of the soft gamma-ray or hard X-ray bursts with kT～10–50 keV were identified with the bursting pulsar GRO J1744-28. Our estimate of the detection rate for cosmological soft gamma-ray or hard X-ray bursts from the entire sky suggests that the distributions of long-duration (>1 s) gamma-ray bursts (GRBs) in characteristic energy kT and duration are inconsistent with the steady-state cosmological model in which the evolution of burst sources is disregarded. Based on GRIF and BATSE/CGRO data, we conclude that most of the GRB sources originate at redshifts 1<z<5.     

First results from the TGRS high-resolution GRB Spectrometer

The Transient Gamma Ray Spectrometer (TGRS) is a 215 cm³ passivelycooled germanium detector designed primarily to study spectral features of gamma ray bursts. Since shortly after its launch on 1994 Nov. 1 it has been producing high-resolution spectra of GRBs and solar flares. Some of these spectra are presented here.Although it has not yet detected any line features in GRBs-none were expected so early in the mission-several bursts have been seen simultaneously by TGRS, the Konus instruments on the same spacecraft, and the BATSE instrument on Compton GRO. A comparison of the spectra obtained by these various instruments, as presented here, may resolve the question of whether line features actually exist, and if so provide detailed spectroscopy to determine their physical origin.