摘要:

The Compton Gamma Ray Observatory was de-orbited on 4 June 2000 after 9 highly successful years in orbit. Major discoveries were made every year withCompton. We present a retrospective overview of the mission from launch to deorbit, highlighting some seminal scientific findings. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419362

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Positron annihilation radiation from the Galaxy has been observed by the OSSE, SMM and TGRS instruments. Improved spectral modeling of OSSE observations has allowed studies of the distribution of both positron annihilation radiation components, the narrow line emission at 511 keV and the positronium continuum emission. The results derived for each individual annihilation component are then compared with each other. These comparisons reveal approximate agreement between the distribution of these two emissions. In certain regions of the sky (notably in the vicinity of the previously reported positive latitude enhancement), the distribution of the emissions differ. We discuss these differences and the methods currently being employed to understand whether the differences are physical or a systematic error in the present analysis. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419363

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

One of the interesting prospects raised by CGRO but never properly investigated due to the lack of instrumental sensitivity and resolution is the gamma-ray line emission from giant molecular clouds. In this paper, we study the 0.511 MeV annihilation line that is emitted when cosmic rays (CRs) bombarding a cloud produce radioisotopes that decay and produce positrons, which subsequently annihilate either directly or after the formation of Positronium. Several interesting factors come into play to decide whether the flux of this emission is strong enough to be detected by INTEGRAL, among them the intensity of the cosmic rays and their nuclear composition, as well as the mass, distance, and other characteristics of the molecular cloud. We have computed both the flux and the line width of the radiation for four nearby clouds. It is found that the line width can be very small (0.1 keV or less) in the case of a partially ionized cold core. This preliminary result, however, does not take into account Doppler shifts due to various motions of the cloud, as well as field-view effects, which may lead to a modification of the overall measured spectrum. We compare our preliminary results to INTEGRAL’s capabilities and conclude with the prospects for a successful detection of such a radiation. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419364

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

During the CGRO mission, the Galactic center region was well exposed by COMPTEL. There is evidence for a distinct excess near the Galactic center direction in the COMPTEL energy range 1–30 MeV. The analysis for point sources is however complicated by the intense emission from the Galactic ridge. We use data from the full mission to investigate this source, present a multiwavelength spectrum and discuss various possible counterparts, including the microquasar source 1E1740.7-2942. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419365

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

We consider the cascade initiated by high energy electrons or &ggr;-rays in the radiation field of the massive star in Cen X-3. The spectra of cascade &ggr;-rays, which escape from the system and collide with a surface of the massive star, are computed for different viewing angles. They have different shapes and intensities. We predict the &ggr;-ray light curves at energies above 100 MeV and 300 GeV from the Cen X-3 system. Photons falling onto the massive star should excite &ggr;-ray lines. However we show that the phase distribution of the &ggr;-ray line and the continuum &ggr;-ray emission is different. This feature can be used as a good test of our model by future &ggr;-ray observations in the MeV, GeV and TeV energy ranges. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419366

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

EXO2030+375is a 42-second X-ray pulsar orbiting a Be star every 46 days. Previous work using epoch-folded frequency searches over 1-day intervals of BATSE data [1] indicated that EXO2030+375underwent a 2.5 year period of quiescence from 1993 September-1996 March. Improvements in the search method that reduced systematic errors due to (1) aperiodic noise from the nearby black hole candidate Cyg X-1 and (2) sources undergoing Earth occultation, have allowed longer time intervals to be searched, hence increasing BATSE’s sensitivity. Using the improved method with 4-day intervals, we detect EXO2030+375near most of its periastron passages during 1993 September-1996 March and for most periastron passages during BATSE’s 9 years in orbit. Earth occultation measurements in the 20-100 keV band, selected when Cyg X-1 was below the Earth’s horizon and epoch-folded at EXO2030+375’sorbital period of 46 days, also indicate that EXO2030+375was active for most of the mission. We will present histories of EXO2030+375’spulse frequency and pulsed flux. In addition, we will present results of a pulse timing analysis and evidence that EXO2030+375’soutbursts shift in orbital phase. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419367

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

We discuss the results of coupled Monte-Carlo/Fokker-Planck simulations of the thermal/nonthermal radiation and electron acceleration and cooling in the case of accretion onto a magnetized neutron star. Most of the energy release into thermal/nonthermal electrons is assumed to happen in a thin shell near the Alfve´n radius, where the radiation from the neutron star surface is reprocessed into thermal/nonthermal high-energy (hard X-ray—&ggr;-ray) emission. We explore the parameter space defined by the accretion rate, stellar surface field and the level of wave turbulence in the shell. Our results are relevant to the emission from atoll sources, transient X-ray binaries containing weakly magnetized neutron stars, and to recently suggested models of accretion-powered emission from anomalous X-ray pulsars. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419368

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

We reportRXTEresults of spectral analyses of three (Sco X-1, GX349+2,and Cyg X-2) out of the 6 known Z sources. No hard X-ray tails were found for Cyg X-2 (<8.4×10−5 photons cm−2 s−1,50–100 keV, 3&sgr;) and for GX349+2(<7.9×10−5photons cm−2 s−1,50–100 keV, 3&sgr;). For Sco X-1 a variable hard X-ray tail (with an average flux of2.0×10−3 photons cm−2 s−1,50–100 keV) has already been reported. We compare our results to reported detections of a hard component in the spectrum of Cyg X-2 and GX349+2.We argue that, taking into account all the results on detections of hard X-ray tails in Sco X-1 and GX349+2,the appearance of such a component is correlated with the brightness of the thermal component. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419369

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

RecentRXTEobservations of the SMC have revealed two previously unknown transient X-ray pulsars with pulse periods of 95s and 4.78s. The sources are proposed as Be/neutron star systems on the basis of their pulsations, transient nature and characteristically hard spectra. Optical observations indicate an H&agr; emission-line star as a candidate optical counterpart. These results add to the emerging picture of the SMC as containing an extremely dense population of transient HMXBs, only a fraction of which are active at any one time. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419370

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

We present analytical and numerical solutions which describe a hot, viscous, two-temperature accretion flow onto a rotating neutron star or any other rotating compact star with a surface. We assume Coulomb coupling between the protons and electrons, and free-free cooling from the electrons. Outside a thin boundary layer, where the accretion flow meets the star, we show that there is an extended settling region which is well-described by two self-similar solutions: (i) a two-temperature solution which is valid in an inner zoner⩽102.5(ris in Schwarzchild units), and (ii) a one-temperature solution at larger radii. In both zones,&rgr;∝r−2,&OHgr;∝r−3/2,v∝r0,Tp∝r−1;in the two-temperature zone,Te∝r−1/2.The luminosity of the settling zone arises from the rotational energy of the star as the star is braked by viscosity. Hence the luminosity and the flow parameters (density, temperature, angular velocity) are independent ofM. The settling solution described here is not advection-dominated, and is thus different from the self-similar ADAF found around black holes. When the spin of the star is small enough, however, the present solution transforms smoothly to a (settling) ADAF. We carried out a stability analysis of the settling flow. The flow is convectively and viscously stable and is unlikely to have strong winds or outflows. Unlike another cooling-dominated system—the SLE disk,—the settling flow is thermally stable provided that thermal conduction is taken into account. This strong saturated-like thermoconduction does not change the structure of the flow. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1419371

出版商:AIP    

年代:1901

数据来源: AIP