摘要:

Recently we have shown that the unshocked winds of pulsars could be directly observed through its inverse Compton (IC) &ggr;-ray emission caused by illumination of the wind by low-frequency photons emitted by the surface of the neutron star or by the pulsar’s magnetosphere [1]. Limitations imposed by present &ggr;-ray observations of the Crab Nebula on the wind acceleration mechanisms are discussed. In particular, the comparison of the upper limits on pulsed TeV &ggr;-ray emission from the Crab with the calculated IC &ggr;-ray fluxes excludes the possibility of formation of the kinetic-energy-dominated wind with Lorentz factor&ggr;W⩾106within 30 light-cylinder radii of the pulsar, provided that the soft nonthermal emission is produced inside the light cylinder. At the same time, the acceleration of the wind on the light cylinder is allowed under a radical assumption that the production of the soft nonthermal emission and the acceleration of the wind occur in the same place. If so, the remarkable IC signatures of the pulsar winds could be revealed, under certain conditions, by current and planned space- and satellite-based high energy &ggr;-ray detectors. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1370786

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Rotation powered pulsars with main sequence star companions may provide a new class of sources of hard &ggr;-rays. Relativistic electrons and positrons in the pulsar wind can inverse Compton scatter target photons from the companion star to energies as high as a few TeV. The best candidate binary pulsar system is PSR B1259−63/SS2883 in which the energy density of target photons at the pulsar reaches a maximum which is∼1012times that of background targets encountered at isolated pulsars. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1370787

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

A brief review of the status of &ggr;-ray observations of plerions with their theoretical interpretations are given. This review concentrates further on the Crab Nebula, with special emphasis on the inner region near the pulsar wind shock. Two independent approaches are used to test MHD flow solutions (phenomological and a particle-in-cell approach), using the tails of the synchrotron and inverse Compton spectra, as well as information on the synchrotron surface brightness distribution: the frequency dependent underluminous inner region of the torus, as well as the terminating outer radius of this structure requires a MHD post shock flow solution where the magnetic field strength increases with radius in the torus, whereas the flow speed decreases correspondingly. We find that the solution of Kennel & Coroniti (1984) for&sgr;=0.003fits this constraint, and simultaneously predicts the observed multi-TeV spectrum of the Crab Nebula correctly—without any free parameters! Any MHD flow solution which predicts a constant field and flow speed inside the torus (e.g.,&sgr;∼1) will fail to predict the hollow inner structure of the X-ray torusbeyondthe pulsar wind shock. Whereas the Kennel & Coroniti solution appears to be successful for the toroidal component (atr<0.5&hthinsp;pc), the same solution fails to describe the observed inverse Compton emission outside this radius, which hints at the need to develop a 2-D MHD flow solution. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1370788

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

AGILE and GLAST are the next high-energy gamma-ray telescopes to be flown in space. These instruments will have angular resolution about 5 times better than EGRET above 10 GeV and much larger field of view. The on-axis effective area of AGILE will be about half that of EGRET, whereas GLAST will have about 6 times greater effective area than EGRET. The capabilities of ground based very high-energy telescopes are also improving, e.g. Whipple, and new telescopes, e.g. STACEE, CELESTE, and MAGIC are expected to have low-energy thresholds and sensitivities that will overlap the GLAST sensitivity above ∼10 GeV. In anticipation of the results from these new telescopes, our current understanding of the galactic diffuse gamma-ray emission, including the matter and cosmic ray distributions is reviewed. The outstanding questions are discussed and the potential of future observations with these new instruments to resolve these questions is examined. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1370789

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Star-formation regions are the most active sites in our Galaxy. The combined activity of their stellar population is in a position to produce detectable amount of gamma rays, but the observational evidence for high-energy emission from specific early-type stars has remained rather elusive till now. After having summarized the lessons from large-scale studies relevant to the production of gamma rays in star-formation regions, the paper discusses the contribution of young stellar objects in the framework of their protoscalar activity as well as the high-energy emission from massive early-type mass-losing stars. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1370790

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

The origin of the unidentified EGRET sources remains one of the great puzzles to solve in &ggr;-ray astronomy. It is increasingly apparent from population studies of their combined spatial, spectral, and temporal characteristics that various kinds of objects are involved. Evidence exists for an important correlation between the positions of the stable sources and active star-forming regions, both in the Galactic disc and locally, in the Gould Belt. Different options as to their nature in these young environments are discussed. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1370791

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Statistical arguments show that the volume- and time-averaged kinetic power of GRBs and fireball transients (FTs) into an L*galaxy like the Milky Way is at the level of1040&hthinsp;ergs&hthinsp;s−1.This number, though with wide uncertainties related to the internal or external shock efficiency, is sufficient to power hadronic cosmic rays observed locally. The release of energy by the high-mass progenitor stars of GRBs and FTs is sufficient to power the ultrahigh energy cosmic rays, as already shown by Waxman and Vietri in 1995. It is sufficient to power the cosmic rays above the knee of the cosmic-ray spectrum. Indeed, all hadronic cosmic rays could originate from the high-mass(≳100 M⊙)stars that collapse to black holes, in the process forming GRBs and FTs. This source class represents a new solution to the problem of cosmic-ray origin. The∼104–107black holes made by these stars could make their presence known by radiating as they accrete from the ISM, by microlensing background radiations, and by forming luminous binary systems. Some unidentified EGRET sources could be isolated black holes that accrete from the ISM. Better imaging and sensitivity with GLAST and TeV observatories will test this model for the unidentified &ggr;-ray sources, and this theory for cosmic-ray origin. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1370792

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

I review some of the basic observational details of jets from X-ray binaries, or ‘micro-quasars.’ It is shown that in both (Z and Atoll) NS and BHC systems radio emission, and therefore jet formation, is correlated with the presence of hard (30–500 keV) X-ray emission. At &ggr;-ray (>500 keV) energies, the relation is not so clear. Possible physical connections between the presence of a jet, with a population of relativistic electrons, and the emission of hard X-rays, are briefly discussed. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1370793

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Based on the results of detailed modelling of the powerful radio flare of the microquasar GRS1915+105in March/April 1994, here we discuss &ggr;-ray fluxes which can be expected from this class of objects. We discuss also perspectives and possible strategy for detection of microquasars in high and very high energy gamma-rays. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1370794

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Jets and outflows must be produced directly from accretion disks and in-flows, especially when the central gravitating objects are compact, such as neutron stars and black holes, and themselves arenotmass losing. Here, we review the formation of jets from advective inflows. We show that the centrifugal pressure supported boundary layer (CENBOL) of the black holes may play crucial role in producing outflows. CENBOL is not present in Keplerian disks. Thus energetic jet formation is directly connected to sub-Keplerian flows close to compact objects. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1370795

出版商:AIP    

年代:1901

数据来源: AIP