摘要:

Centrifugal acceleration of charged test particles at the base of a rotating jet magnetosphere is considered. Based on an analysis of forces we derive the equation for the radial accelerated motion and present an analytical solution. It is shown that for particles moving outwards along rotating magnetic field lines, the energy gain is in particular limited by the breakdown of the bead-on-the-wire approximation which occurs in the vicinity of the light cylinderrL.The corresponding upper limit for the maximum Lorentz factor&ggr;maxfor electrons scales∝B2/3rL2/3,withBthe magnetic field strength atrL,and is at most of the order of a102–103for the conditions regarded to be typical for BL Lac objects. Such values suggest that this mechanism may provide pre-accelerated seed particles which are required for efficient Fermi-type particle acceleration at larger scales in radio jets. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1370886

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

We show that outflow rates in jets directly depend on the spectral states of black holes. In particular, in soft states, when the Comptonized electrons are cold, outflow rate is close to zero. In hard states, outflow could be steady, but the rate may be very small—only a few percent of the inflow. In the intermediate states, on the other hand, the outflow rate is the highest—roughly thirty percent of the inflow. In this case, piled up matter below the sonic surface of the outflow could become optically thick and radiative processes could periodically cool the outflow and produce very interesting effects including transitions between burst (high-count or On) and quiescence (low-count or Off) states such as those observed inGRS&hthinsp;1915+105.©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1370887

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Jets and outflows are known to form out of advective accretion flows around black holes. Hard photons from the centrifugal barrier directly hit the electrons and deposit momentum on them. For optically thick flows such deposition is not efficient, but for optically thin flows matter could be accelerated to relativistic speed. In fact, even bound matter could be made free through successive deposition. We discuss these possibilities. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1370888

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

The observed total energies of GRBs show a wide dispersion by a factor of102–3,and the most energetic GRBs emitE&ggr;,iso∼3×1054&hthinsp;ergas the isotropic energy. Therefore the true kinetic energy must exceedEiso∼1055&hthinsp;erg,and may reachEiso∼1056&hthinsp;ergif the efficiency of internal shocks is not so high. (Of course, the actual energy can be much smaller if GRBs are strongly beamed.) We propose a unified picture for the energetics of GRBs, in which all GRBs emit a true kinetic energy ofEiso∼1055–56&hthinsp;ergper 4&pgr; steradian with a strong beaming implicitly assumed. Difference of the observed total energies in soft gamma-rays is attributed to different efficiency of energy transfer from protons into electrons. This model predicts that, for GRBs weak in the sub-MeV emission, energy emission in very high energy (VHE) photons (≳TeV) is even larger than the ordinary emission in the sub-MeV range. We try to interpret the suggestion for VHE emission from GRB970417a reported by the Milagro project in this conference in the context of this model. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1370889

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

We searched for multi-TeV counterparts to the gamma–ray bursts (GRBs) at keV energies detected by BATSE during the period from October 2, 1995 to March 18, 1999 using the data of the Tibet Air Shower Array. In the field of view of the array there were 70 GRBs detected by BATSE in this period. The search was done based on the sky survey within error circles of BATSE bursts and with time scales during 10 to several hundred seconds. No significant signals of counterparts were detected. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1370890

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Universal observational feature of microscopic primordial black holes is the Hawking emission which is believed to occur in the regime of noninteracting quark-gluon jets and their products. Then, stringent upper limit on the number density of primordial black holes seems to rule out the possibility of their discovery in the near future. Contrary to this widely accepted opinion, we show that, when the black-hole temperature exceeds 10 GeV, the charged particle outflow from a black hole becomes plasma and the magnetohydrodynamical regime of expansion can be realized. In this case, the kinetic energy of ejected particles can be converted into the 0.1–1 MeV &ggr;-rays due to the synchrotron radiation and electromagnetic cascade in the close-to-equipartition turbulent magnetic field. Also, the cascade leads to the significant increase of photon flux in the sub-GeV range. As a result, a black hole with mass below1012&hthinsp;gbecomes a transient &ggr;-ray source with luminosity growing according to the explosive-type law. We show that up to several per cent of the gamma-ray bursts detected by BATSE can be associated with evaporating black holes with temperature exceeding ∼1 TeV and masses below1010&hthinsp;g,located at distances within ∼1 pc from the Earth. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1370891

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Discovery of primordial black holes (PBHs) or more stringent upper limit on their number would have a great impact on the existing cosmological theories and provide better understanding of conditions in the early Universe, including the spectrum of density and metric fluctuations and cold dark matter models. We consider possible strategies of searching for the high-energy Hawking radiation from evaporating PBHs. Specifically, we analyze the capture of cold dark matter species (especially PBHs) during the formation of gravitationally bound objects. Among all the objects considered, large(M⩾105&hthinsp;M⊙),nearby (within ∼5 kpc from the Sun) globular clusters are shown to provide the best prospects for detection of the black holes. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1370892

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Gamma rays withE>10&hthinsp;GeVinteract with optical-UV photons through pair production. Therefore, a large sample of high redshift sources of these gamma rays can be used to probe the extragalactic background light (EBL) by examining the attenuation of the flux above 10 GeV. GLAST will detect thousands of gamma-ray blazars up to redshifts of at leastz=4,with sufficient angular resolution to allow identification of many of their optical counterparts. By combining the gamma-ray blazar luminosity function, models of the high energy gamma-ray opacity due to EBL absorption, and the expected GLAST instrument performance to produce simulated redshifts and fluxes for blazars detected by GLAST, we demonstrate that these blazars have can be a highly effective probe of the EBL. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1370893

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

We present a semi-empirical model for the evolving far-infrared to ultraviolet diffuse background produced by stars in galaxies. The model is designed to reproduce the results of deep galaxy surveys, and therefore may be considered as a cosmology-independent lower limit to the extragalactic background light. Using this model and recent HEGRA data, we infer the intrinsic spectrum at multi-TeV gamma-ray energies for Mkn 501 and find that it is consistent with a power law of spectral index2.49±0.04.In turn, this finding renders it rather unlikely that the present-day infrared background has an intensity as high as claimed by Finkbeiner &etal; [1]. Future 10 GeV to TeV observations could be used to either constrain the ultraviolet-to-infrared background model at high redshifts or cosmological parameters. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1370894

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

The TeV and X-ray data obtained by the imaging Cherenkov telescope CAT and X-ray satellite BeppoSAX during the remarkable flare of Mkn 501 in April 16, 1997 are used to constrain the flux of the Cosmic Infrared Background (CIB) using different CIB models. We show that a non-negligible absorption of &ggr;-rays due to the CIB could take place already in the low-energy (sub-TeV) domain of the spectrum of Mkn 501. The density of the near-infrared background with typical “starlight spectrum” around 1 &mgr;m should be between 5 and 35 nW&hthinsp;m−2&hthinsp;sr−1(99&percent; CL), with the most likely value around 20 nW&hthinsp;m−2&hthinsp;sr−1. We also argue that the CAT &ggr;-ray data alone allow a rather robust upper limits on the CIB,&lgr;F&lgr;⩽60&hthinsp;nW&hthinsp;m−2&hthinsp;sr−1at 1 &mgr;m, based on the belief that, within the conventional models of &ggr;-ray production, the differential source spectrum of &ggr;-rays hardly could be flatter thandN/dE∝E−1.The high flux of CIB at ⩽ few &mgr;m wavelengths,&lgr;F&lgr;⩾10&hthinsp;nW&hthinsp;m−2&hthinsp;sr−1implies significant distortion of the initial (source) sub-TeV spectrum of &ggr;-rays from Mkn 501, therefore has a strong impact in derivation of the jet parameters. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1370895

出版商:AIP    

年代:1901

数据来源: AIP