摘要:

Fifteen KONUS bursts and one HEAO burst showing cyclotron lines have well measured positions. If these are due to strongly magnetized neutron stars then we expect them to be associated with the galactic disk with a scale height of about 500 pc as expected for old neutron stars. The simplest way to test this hypothesis would be to test for a concentration along galactic latitude ∼b‖=1. We got a marginal indication of such a concentration and the probability that the 16 events are isotropically distributed is 0.02. We also show that this result is not in conflict with the present BATSE data set.

ISSN:0094-243X    

DOI:10.1063/1.42836

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

With improved data from BATSE and other instruments, it is important to develop a range of diagnostic tools to link gamma‐ray burst observations with theory. I will review some of the physical processes which may take place to form the spectrum of gamma‐ray burst sources, assuming that the bursts originate on strongly magnetized neutron stars. The important diagnostics that these processes provide to probe the emission region and how they might be used to interpret observed spectra will also be discussed.

ISSN:0094-243X    

DOI:10.1063/1.42838

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

In wind models of &ggr;‐ray bursts, it has been assumed that soft x‐ray photons are scattered only once by relativistic electrons moving away from the star; this assumes that the scattering optical depth is small. Using the observational data from the bursts, we consider three methods for estimating this optical depth: (i) the luminosity of the burst, (ii) the ratio of the &ggr;‐ray flux (≳10 keV) to x‐ray flux (<10 keV), (iii) the presence or lack of cyclotron lines. Within the context of the wind models, we find that multiple scattering is likely to be important in the formation of the spectrum in &ggr;‐ray bursts.

ISSN:0094-243X    

DOI:10.1063/1.42787

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Study of the rapid spectral evolution of gamma ray burst may shed much light on their emission and energization mechanisms. We propose using the peak power energy as a gauge of spectral hardness and introduce the notion of Type I and Type II burst spikes depending on the spectral evolution at the rise phase of the spike. If the recent discovery of temperature‐luminosity correlations is confirmed then an accelerating pair avalanche scenario may be worth pursuing.

ISSN:0094-243X    

DOI:10.1063/1.42788

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Resonant Compton upscattering is commended as a mechanism that produces a hard gamma‐ray spectrum while suppressing x‐rays. This model, however, has severe physical and observational limitations. Effective x‐rays suppression places a lower limit on the electron density; above this limit x‐rays scatter multiple times, so the single‐scattering approximation of this mechanism is invalid. Multiple scattering produces a spectrum that is much harder than the single‐scattering spectrum. As the Thomson optical depth of a power‐law electron beam approaches unity, photon spawning commences at a high rate and physically invalidates the underlying electron distribution. The Compton upscattering model is therefore only valid over a narrow range of electron densities. An observational consequence of this model is the absence of the third cyclotron resonance. Resonant scattering produces gamma‐rays that propagate nearly along the magnetic field. The resonant cross section of the third harmonic, which is strongly angle dependent, falls below the Compton continuum for these gamma rays. The observation of a third cyclotron resonance in a gamma‐ray burst spectrum would eliminate resonant Compton scattering as a gamma‐ray burst process.

ISSN:0094-243X    

DOI:10.1063/1.42789

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

In wind models of &ggr;‐ray bursts, electron‐position pairs stream away from the neutron star surface, upscattering soft x‐ray photons to hard x‐ and &ggr;‐ray energies. For sufficiently high source luminosities, the density of pairs required is high enough that significant pair annihilation occurs before the pairs leave the continuum‐forming region. We examine the effects of annihilation on the outflowing pair distribution using accurate (weak magnetic field) cross‐sections. We compute the annihilation feature produced and conclude it should not be easily observable for source distances ≳100 kpc. We also examine the validity of the single scattering approximation often made in continuum and dynamic cyclotron line‐formation calculations. Even with the inclusion of annihilation which removes pairs from the wind, we find that a photon is likely to scatter several times off the wind if the source is at a distance ≳1 kpc. This can significantly modify the computed spectrum.

ISSN:0094-243X    

DOI:10.1063/1.42790

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Transfer of cyclotron radiation in the electron‐position plasma slab above the polar hot spot of a strongly magnetized neutron star is considered. The interpretation of the cyclotron dips in the spectra of GB870303 and GB880205 is performed. The parameters of the line‐forming region and upper limits for the distance to the source are determined. The results indicate that the bursts considered originate from galactic neutron stars.

ISSN:0094-243X    

DOI:10.1063/1.42791

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Possible secondary signals arising from interactions of primary photons from a gamma‐ray burster with surrounding material are considered. Such signals could result from annihilation of electron‐positron pairs, or from decay of unstable nuclei, such as15O, produced during the burst. A model is assumed in which material surrounds the burster in a thick, uniform, spherical shell. For a wide range of shell parameters, the signal from pair annihilation could be seen with present detectors; its decay half‐life would depend on the temperature and density of the environment in which the pairs were produced. The predicted levels from unstable nuclei would probably not be observable with present detectors. However, given the diagnostic capability provided by their ‘‘afterglow,’’ which would decay with a half‐life characteristics of the nuclei produced, detection by a future generation of detectors could yield useful information.

ISSN:0094-243X    

DOI:10.1063/1.42792

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The synchrotron self‐Compton (SSC) emission model for gamma‐ray bursts is capable of producing narrow line features for a variety of modelled field strengths, primary electron injection distributions and burst luminosities. Multiple resonant scattering with synchrotron continuum photons efficiently traps and cools paris in the ground state to an average energy where the Compton energy loss rate is zero. Annihilation between pairs in these cooled distributions can be very efficient. For isotropic injection of primary electrons, there is an anti‐correlation of the intensity of the angular‐binned emission between the portions of the continuum spectrum below the cyclotron peak and above the annihilation line feature. Small‐angle emission dominates the continuum above the annihilation line feature and is smooth through the line up to the pair production cut‐off, which can be above several MeV for small enough angles. The angle‐averaged annihilation line is made of components which can have peak emission centered at energies away from 511 keV, due to Doppler shifting. For beamed injection, the annihilation line breaks up into relatively narrow components in the angular emission, which sum into a broad feature in the angle‐averaged emission.

ISSN:0094-243X    

DOI:10.1063/1.42793

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We show that scattering atmospheres exist in the magnetospheres of luminous compact objects from considerations of resonance effects in magnetic Compton scattering.1These regions of stable equilibria are formed by a balance between the force of gravity and resonant Compton scattering. We calculate the structure of radiation‐pressure supported atmospheres for neutron stars with different magnetic field strengths and surface temperatures. We propose that the narrow cyclotron absorption lines observed in gamma‐ray burst spectra may be formed by these atmospheres.

ISSN:0094-243X    

DOI:10.1063/1.42794

出版商:AIP    

年代:1991

数据来源: AIP