摘要:

We briefly report preliminary results of observations of strong (≳10&sgr;) variable MeV emission from the Taurus region, possibly the Crab nebula, in 1980 by the HEAO 3 Gamma‐Ray Spectroscopy experiment. The ∼50‐day time‐averaged spectrum of the Crab shows a new component, which consists of a hard spectral ‘‘knee’’ in the 0.4–1 MeV range followed by a higher energy component extending to ≳3 MeV, superposed on the canonical Crab power law spectrum with a spectral index of 2.2. This new spectral component was not observed 4 months earlier in the fall of 1979, when the spectrum was consistent with a single power law with the index of 2.2, the same as that observed in 1980. There is no indication that the &ggr;‐ray emission was pulsed. Such variable emission could be interpreted as Comptonization of soft photons by relativistic electrons in the magnetic field surrounding the neutron star.

ISSN:0094-243X    

DOI:10.1063/1.40907

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The region containing the galactic source Sco X‐1 has been observed on May 17, 1989 in the energy range 15–160 keV. The measurement was performed with the balloon borne experiment ‘‘POKER’’ based on an array of three high pressure Multiwire Proportional Counters (MWPC) with energy resolution of 10% at 120 keV. The total sensitive area was 8,000 cm2and the experiment was passively collimated with a copper hexagonal collimator with 1.9 degree FWHM field of view. The preliminary data analysis confirmed the detection of the source at energies up to 60 keV.

ISSN:0094-243X    

DOI:10.1063/1.40908

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We report a ‘‘super‐low’’ state observation of the black hole candidate Cygnus X‐1 in the energy range 15‐120 keV. The data were obtained with the ‘‘POKER’’ experiment, designed to perform high sensitivity observations of cosmic sources in the hard X‐Ray range (15‐120 keV). The telescope consisted of an array of three high pressure Xenon Multiwire Proportional Counters (MWPC) with a total sensitive area of 7,500 cm2. The detectors were filled at a pressure of 2.6 bar with a mixture of Xe/Argon/Isobutane to provide an efficiency greater than 20% for photon energies from 15 keV to 110 keV. The MWPC spectral resolution was 13% at 60 keV. The fields of view of the three MWPCs were coaligned and limited by means of hexagonal copper collimators with an aperture of 5.0 degree FWHM. In order to provide imaging capability to the telescope one of the MWPC was equipped with two co‐rotating Rotation Modulation Collimators, developed at AIT, and modulating a geometrical area of 1,600 cm2of the detector. The telescope was launched from the Milo Base, Sicily (Italy), on 1985 August 5, and scanning and pointed observations were carried out on the Crab Nebula, A0535+26, MCG 8‐11‐11, NGC 4151, Cygnus X‐1 and Her X‐1. The Cygnus X‐1 and Crab photon spectra are well described by single power laws, with photon indeces of &agr;=1.87 and &agr;=2.17 and intensities of 2.57×10−3and 2.32×10−3ph cm−2s−1keV−1at 50 keV, respectively. The low hard X‐ray emission from Cyg X‐1 confirms that during the POKER observation the source was in a ‘‘low’’ state as also supported by EXOSAT data collected at lower energies on August 12.

ISSN:0094-243X    

DOI:10.1063/1.40909

出版商:AIP    

年代:1991

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.40910

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We review the theoretical framework of both line and continuum spectra formation in gamma ray bursts. These include the cyclotron features at 10’s of keV, redshifted annihilation features at ∼400 keV, as well as other potentially detectable nuclear transition lines, atomic x‐ray lines, proton cyclotron lines and plasma oscillation lines. By combining the parameters derived from line and continuum modeling we can try to reconstruct the location, geometry and physical conditions of the burst emission region, thereby constraining and discriminating the astrophysical models. Hence spectroscopy with current and future generations of detectors should provide powerful diagnostic tools for gamma ray bursters.

ISSN:0094-243X    

DOI:10.1063/1.40911

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The presence of cyclotron lines in a significant fraction of &ggr;‐ray burst spectra suggests a source association with strongly magnetized neutron stars. The burster distance scale is not known but constrained by their angular‐ and brightness distribution. Using pulsar data we calculate the corresponding age distribution of Galactic neutron stars and apply an exponential field decay model to test whether the observed incidence rate of cyclotro lines is consistent with decay time scales derived for radio pulsars. We find that the statistical properties of &ggr;‐ray bursts are inconsistent with the idea of events originating at arbitrary times on neutron stars whose fields decay on time scales shorter than ∼109yrs. Possible interpretations of this inconsistency with radio pulsar field decay models are discussed.

ISSN:0094-243X    

DOI:10.1063/1.40955

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The current generation of &ggr;‐ray telescopes (SIGMA, GRO) provides a new opportunity for observing red‐shifted &ggr;‐ray lines from the atmospheres of accreting neutron stars. A successful observation would provide important information about how the accretion stream settles onto the neutron star and might allow limits to be placed on the nuclear equation of state. Thus, we have undertaken a theoretical re‐analysis of different &ggr;‐ray emission mechanisms. This paper describe our results on the 4.438 MeV &ggr;‐ray line emission from12C and16O and outlines the ongoing calculation of the 2.2 MeV D‐recombination line flux expected from the spallation of incident Helium. We show that a neutron star accreting material of solar abundances will produce a 4.438 MeV &ggr;‐ray line flux that is below the current observational limits.

ISSN:0094-243X    

DOI:10.1063/1.40913

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Strong continuum gamma‐ray emission at ∼1 MeV possibly correlated with a narrow annihilation line at 511 keV has been observed from both Cygnus X‐1 and the Galactic Center. Such correlated emission has been interpreted as a unique gamma‐ray signature for theoretically predicted relativistic, positron‐electron pair‐dominated plasma in regions surrounding the black holes. In this paper, I review primarily the Cygnus X‐1 results, which have provided important new insights about the source. Cygnus X‐1 may be considered a canonical reference stellar black hole whose spectral and temporal characteristics can be used for comparison with those of other black‐hole candidates including the Galactic Center and AGN.

ISSN:0094-243X    

DOI:10.1063/1.40914

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

In this paper we present the use of the theoretical spectra derived in the most recent studies on the electron‐proton beam interactions with the matter and/or radiation to fit the experimental data of Cyg X‐1, Geminga, and 3C 273.

ISSN:0094-243X    

DOI:10.1063/1.40915

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The observation of gamma‐ray lines during solar flares is the most convincing evidence that nuclear reactions take place between high energy particles and the solar atmosphere. The application of data from the measurements of these lines is very wide spread. It ranges from information about the acceleration of charged particles to elemental composition determination of the various solar atmospheric layers. After a brief review of the production of the nuclear lines it is shown, how their measurements can be applied in different ares of the solar flare phenomenon.

ISSN:0094-243X    

DOI:10.1063/1.40916

出版商:AIP    

年代:1991

数据来源: AIP