共查询到20条相似文献,搜索用时 15 毫秒
1.
The recent detection of very-high-energy (GeV – TeV) γ-ray emission from the Galactic black-hole candidate and microquasar LS 5039 has sparked renewed interest in jet models for
the high-energy emission in those objects. In this work, we have focused on models in which the high-energy emission results
from synchrotron and Compton emission by relativistic electrons in the jet (leptonic jet models). Particular attention has
been paid to a possible orbital modulation of the high-energy emission due to azimuthal asymmetries caused by the presence
of the companion star. Both orbital-phase dependentγγ absorption and Compton scattering of optical/UV photons from the companion star may lead to an orbital modulation of the
gamma-ray emission. We make specific predictions which should be testable with refined data from HESS and the upcoming GLAST
mission. 相似文献
2.
Results are reported from a study of the variability of the x-ray and very high energy (VHE) γ -ray emission from Mrk 421 during a 10-day period of enchanced source activity at the end of 2005. The TeV data were taken
from observations with the Whipple 10-m Cerenkov telescope and the soft x-ray data, from the ASM on board the RXTE orbital
observatory. Light curves for this source indicated an obvious variability in the form of flares in both energy ranges. During
the flares, the flux of VHE γ -rays exceeded that from the Crab nebula and correlated positively with the observed x-ray emission. The flux of VHE γ - rays varied almost linearly with the soft x-ray flux. The statistical characteristics of the variability were independent
of energy and the two emission components were detected quasi-simultaneously. The observed temporal properties of the source
can be interpreted in terms of the rapid acceleration of leptons in a jet using a synchrotron self-Compton model. Our studies
confirm a flare activity intrinsic to this source on the scale of a day found in earlier studies. 相似文献
3.
Li-Sheng Mao 《Astrophysics and Space Science》2012,340(2):331-349
We present the Wide-field Infrared Survey Explorer (WISE) photometric data of 158 Fermi-detected BL Lacs and investigate the nature of their mid-infrared (MIR) continuum emission. In the [3.4]-[4.6]-[12] μm color–color diagram, nearly all their colors lie within the WISE Blazar strip (WBS), which is an effective diagnostic tool to separate sources dominated by non-thermal radiation from those dominated by thermal radiation. This feature indicates that their MIR emission is predominantly non-thermal. This argument is further supported by the strong radio-MIR flux correlation. We derive their MIR spectral indices and compare them with the near-infrared (NIR) spectral indices. We find that there is a prevalent steepening from MIR spectrum to NIR spectrum. The low-frequency-peaked BL Lacs (LBLs) have on average a larger MIR spectral index and a higher MIR luminosity than the high-frequency-peaked BL Lacs (HBLs), and the intermediate-frequency-peaked BL Lacs (IBLs) appear to bridge them. The MIR-γ-ray flux correlation is highly significant. A strong positive correlation is also found between the MIR and γ-ray spectral indices. The γ-ray-MIR loudness is significantly correlated with the synchrotron peak frequency. Finally we propose that the γ-rays are highly associated with the MIR emission from the jet, and the γ-ray emission is likely from the synchrotron self-Compton process for the Fermi-detected BL Lacs in our sample. 相似文献
4.
E × B-drifting jets have been generally ignored for the past 25 years even though they may well describe all the astrophysical
jet sources, both on galactic and stellar scales. Here we present closed-form solutions for their joint field-and-particle
distribution, argue that the observed jets are near equipartition, with extremely relativistic, monoenergetic e±-pairs of bulk Lorentz factor γ ≲ 104, and are first-order stable. We describe plausible mechanisms for the jets’ (i) formation, (ii) propagation, and (iii) termination. Wherever a beam meets with resistance, its frozen-in Poynting flux transforms the delta-shaped energy distribution
of the pairs into an almost white power law,E
2
N
E ∼E
−∫ with ∫ ≳ 0, via single-step falls through the huge convected potential. 相似文献
5.
L. G. Kocharov G. A. Kovaltsov G. E. Kocharov E. I. Chuikin I. G. Usoskin M. A. Shea D. F. Smart V. F. Melnikov T. S. Podstrigach T. P. Armstrong H. Zirin 《Solar physics》1994,150(1-2):267-283
Data on X-,γ-ray, optical and radio emission from the 1991 June 15 solar flare are considered. We have calculated the spectrum of protons
that producesγ-rays during the gradual phase of the flare. The primary proton spectrum can be described as a Bessel-function-type up to
0.8 GeV and a power law with the spectral index ≈3 from 0.8 up to 10 GeV or above. We have also analyzed data on energetic
particles near the Earth. Their spectrum differed from that of primary protons producingγ-ray line emission. In the gradual phase of the flare additional pulses of energy release occurred and the time profiles of
cm-radio emission andγ-rays in the 0.8–10 MeV energy band and above 50 MeV coincided. A continuous and simultaneous stochastic acceleration of the
protons and relativistic electrons at the gradual phase of the flare is considered as a natural explanation of the data. 相似文献
6.
K. I. Kellermann Y. Y. Kovalev M. L. Lister D. C. Homan M. Kadler M. H. Cohen E. Ros J. A. Zensus R. C. Vermeulen M. F. Aller H. D. Aller 《Astrophysics and Space Science》2007,311(1-3):231-239
We discuss results from a decade long program to study the fine-scale structure and the kinematics of relativistic AGN jets
with the aim of better understanding the acceleration and collimation of the relativistic plasma forming AGN jets. From the
observed distribution of brightness temperature, apparent velocity, flux density, time variability, and apparent luminosity,
the intrinsic properties of the jets including Lorentz factor, luminosity, orientation, and brightness temperature are discussed.
Special attention is given to the jet in M87, which has been studied over a wide range of wavelengths and which, due to its
proximity, is observed with excellent spatial resolution.
Most radio jets appear quite linear, but we also observe curved non-linear jets and non-radial motions. Sometimes, different
features in a given jet appear to follow the same curved path but there is evidence for ballistic trajectories as well. The
data are best fit with a distribution of Lorentz factors extending up to γ∼30 and intrinsic luminosity up to ∼1026 W Hz−1. In general, gamma-ray quasars may have somewhat larger Lorentz factors than non gamma-ray quasars. Initially the observed
brightness temperature near the base of the jet extend up to ∼5×1013 K which is well in excess of the inverse Compton limit and corresponds to a large excess of particle energy over magnetic
energy. However, more typically, the observed brightness temperatures are ∼2×1011 K, i.e., closer to equipartition. 相似文献
7.
S. D. Katore K. S. Adhav A. Y. Shaikh M. M. Sancheti 《Astrophysics and Space Science》2011,333(1):333-341
We consider a self-consistent system of Plane symmetric cosmology and binary mixture of perfect fluid and dark energy. The
perfect fluid is taken to be one obeying the usual equation of state p=γρ with γ∈[0,1]. The dark energy is considered to be either the quintessence or Chaplygin gas. Exact solutions to the corresponding
Einstein’s field equations are obtained as a quadrature. The cases of Zeldovich Universe, Dust Universe and Radiation Universe
and models with power-law and exponential expansion have discussed in detail. For large t, the models tend to be isotropic. 相似文献
8.
We discuss the implications of the recent X-ray and TeV γ-ray observations of the PSR B1259–63 system (a young rotation powered pulsar orbiting a Be star) for the theoretical models
of interaction of pulsar and stellar winds. We show that previously considered models have problems to account for the observed
behaviour of the system. We develop a model in which the broad band emission from the binary system is produced in result
of collisions of GeV–TeV energy protons accelerated by the pulsar wind and interacting with the stellar disk. In this model
the high energy γ-rays are produced in the decays of secondary neutral pions, while radio and X-ray emission are synchrotron and inverse Compton
emission produced by low-energy (≤100 MeV) electrons from the decays of secondary charged π
± mesons. This model can explain not only the observed energy spectra, but also the correlations between TeV, X-ray and radio
emission components.
相似文献
9.
We consider a self consistent system of Bianchi Type-I cosmology and Binary Mixture of perfect fluid and dark energy. The
perfect fluid is taken to be obeying equations of state p
PF
=γρ
PF
with γ∈[0,1]. The dark energy is considered to be obeying a quintessence-like equation of state where the dark energy obeys equation
of state p
DE
=ωρ
DE
where ω∈[−1,0]. Exact solutions to the corresponding Einstein field equations are obtained. Some special cases are discussed and
studied. Further more power law models and exponential models are investigated. 相似文献
10.
Nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova remnants (SNRs) is used to investigate the properties
of Kepler’s SNR and, in particular, to predict the γ-eay spectrum expected from this SNR. Observations of the nonthermal radio and X-ray emission spectra as well as theoretical
constraints for the total supernova (SN) explosion energy E
sn are used to constrain the astronomical and particle acceleration parameters of the system. Under the assumption that Kepler’s
SN is a type Ia SN we determine for any given explosion energy E
sn and source distance d the mass density of the ambient interstellar medium (ISM) from a fit to the observed SNR size and expansion speed. This makes
it possible to make predictions for the expected γ-eay flux. Exploring the expected distance range we find that for a typical explosion energy E
sn=1051 erg the expected energy flux of TeV γ-rays varies from 2×10−11 to 10−13 erg/(cm2 s) when the distance changes from d=3.4 kpc to 7 kpc. In all cases the γ-eay emission is dominated by π
0-decay γ-rays due to nuclear CRs. Therefore Kepler’s SNR represents a very promising target for instruments like H.E.S.S., CANGAROO
and GLAST. A non-detection of γ-rays would mean that the actual source distance is larger than 7 kpc. 相似文献
11.
P. Goldoni M. Ribó T. Di Salvo J. M. Paredes V. Bosch-Ramon M. Rupen 《Astrophysics and Space Science》2007,309(1-4):293-297
LS 5039 is the only X-ray binary persistently detected at TeV energies by the Cherenkov HESS telescope. It is moreover a γ-ray emitter in the GeV and possibly MeV energy ranges. To understand important aspects of jet physics, like the magnetic
field content or particle acceleration, and emission processes, such as synchrotron and inverse Compton (IC), a complete modeling
of the multiwavelength data is necessary. LS 5039 has been detected along almost all the electromagnetic spectrum thanks to
several radio, infrared, optical and soft X-ray detections. However, hard X-ray detections above 20 keV have been so far elusive
and/or doubtful, partly due to source confusion for the poor spatial resolution of hard X-ray instruments. We report here
on deep (∼300 ks) serendipitous INTEGRAL hard X-ray observations of LS 5039, coupled with simultaneous VLA radio observations. We obtain a 20–40 keV flux of 1.1±0.3 mCrab
(5.9 (±1.6) ×10−12 erg cm−2 s−1), a 40–100 keV upper limit of 1.5 mCrab (9.5×10−12 erg cm−2 s−1), and typical radio flux densities of ∼25 mJy at 5 GHz. These hard X-ray fluxes are significantly lower than previous estimates
obtained with BATSE in the same energy range but, in the lower interval, agree with extrapolation of previous RXTE measurements. The INTEGRAL observations also hint to a break in the spectral behavior at hard X-rays. A more sensitive characterization of the hard
X-ray spectrum of LS 5039 from 20 to 100 keV could therefore constrain key aspects of the jet physics, like the relativistic
particle spectrum and the magnetic field strength. Future multiwavelength observations would allow to establish whether such
hard X-ray synchrotron emission is produced by the same population of relativistic electrons as those presumably producing
TeV emission through IC. 相似文献
12.
We have used a simple method to estimate the prompt emission radii of 27 Swift and 37 pre-Swift long gamma-ray bursts with
known redshift and jet break time. The prompt γ-rays are found to emit mainly from a beamed jet with dynamic open angle narrower than its geometric open angle, suggesting
an obviously dynamic evolution from prompt to follow-up phases for the jetted outflow. Under condition of the external shock
scenario, we confirm that long gamma-ray bursts are produced at a larger radius of ∼1016 cm, which puts a strict constraint on the currently theoretical models. 相似文献
13.
D. A. Schwartz D. E. Harris H. Landt A. Siemiginowska H. L. Marshall J. M. Gelbord E. S. Perlman M. Georganopoulos M. Birkinshaw D. M. Worrall C. C. Cheung L. Stawarz S. G. Jorstad A. P. Marscher Y. Uchiyama C. M. Urry 《Astrophysics and Space Science》2007,311(1-3):341-345
We present a Chandra image of the quasar, jet, and lobes of PKS 1354+195 (=4C 19.44). The radio jet is 18 arcsec long, and appears to be very
straight. The length gives many independent spatial resolution elements in the Chandra image while the straightness implies that the geometrical factors are constant along the jet although their values are uncertain.
We also have 4 frequency radio images with half to one arcsecond angular resolution, and use HST and Spitzer data to study
the broad band spectral energy distributions. The X-ray and radio spectra are both consistent with a spectrum f
ν
∝
ν
−0.7 for the integrated jet. Using that spectral index, the model of inverse Compton scattering of electrons on the cosmic microwave
background (IC/CMB) gives magnetic field strengths and Doppler factors that are relatively constant along the jet. Extended
X-ray emission is evident in the direction of the otherwise unseen counter-jet. X-ray emission continues past the radio jet
to the South, and is detected within both the southern and northern radio lobes. 相似文献
14.
Abhas Mitra 《Journal of Astrophysics and Astronomy》1994,15(2):179-186
Recent accelerator data based parameterization of the inclusive cross section (c −s) forπ0 production in hadronic collisions and an explicit incorporation of the finiteness of the relevant projectile hadron spectrum
suggest a significant steepening in the spectrum (by as much as 0.4 in the spectral index) of the secondaryγ-ray towards the end of the spectrum. We emphasize here that this spectral steepening in conjunction with the possibility
that in the bright X-ray binaries the maximum energy to which theγ-ray producing progenitor protons may be accelerated is only ∼ l0 PeV, may imply an effective efficiency forγ-ray production,ε, as reckoned by the PeV arrays, one or two orders smaller than the previous estimates. To explain the genesis of a given
PeV photon flux from an X-ray binary, one, therefore, has to. accordingly consider a much higher value of the progenitor proton
beam luminosity,L
p
. This requirement may raise further questions regarding the actual genesis of PeVγ-rays in X-ray binaries, or alternatively, on the veracity of the high values of the PeV photon fluxes reported by earlier
experiments. 相似文献
15.
Share G.H. Murphy R.J. Tylka A.J. Schwartz R.A. Yoshimori M. Suga K. Nakayama S. Takeda H. 《Solar physics》2001,204(1-2):41-53
The HXS and GRS detectors on Yohkoh observed the 14 July 2000, X5.7 flare, beginning at ∼ 10:20 UT, ∼ 4 min before the peak in soft X-rays. The hard X-rays and
γ-rays peaked ∼ 3 min later at ∼ 10:27 UT. Solar γ-ray emission lasted until ∼ 10:40 UT. Impact of high-energy ions at the
Sun is revealed by the γ-ray lines from neutron capture, annihilation radiation and de-excitation that are visible above the
bremsstrahlung continuum. From measurement of these lines we find that the flare-averaged spectrum of accelerated protons
is consistent with a power law ge10 MeV with index 3.14±0.15 and flux 1.1×1032 protons MeV−1 at 10 MeV. We estimate that there were ∼1.5×1030 erg in accelerated ions if the power law extended without a break down to 1 MeV; this is about 1% of the energy in electrons
> 20 keV from measurements of the hard X-rays. We find no evidence for spectral hardening in the hard X-rays that has been
suggested as a predictor for the occurrence of solar energetic particle (SEP) events. This was the third largest proton event
above 10 MeV since 1976. The GRS and HXS also observed γ-ray lines and continuum produced by the impact of SEP on the Earth's
atmosphere beginning about 13 UT on 14 July. These measurements show that the SEP spectrum softened considerably over the
next 24 hours. We compare these measurements with proton measurements in space. 相似文献
16.
《Experimental Astronomy》2009,23(1):91-120
The primary scientific goal of the GRIPS mission is to revolutionize our understanding of the early universe using γ-ray bursts. We propose a new generation gamma-ray observatory capable of unprecedented spectroscopy over a wide range of
γ-ray energies (200 keV–50 MeV) and of polarimetry (200–1000 keV). The γ-ray sensitivity to nuclear absorption features enables the measurement of column densities as high as 1028cm − 2. Secondary goals achievable by this mission include direct measurements of all types of supernova interiors through γ-rays from radioactive decays, nuclear astrophysics with massive stars and novae, and studies of particle acceleration near
compact stars, interstellar shocks, and clusters of galaxies.
See for the authors’ affiliations. 相似文献
17.
Compressible homogeneous spheres with constant adiabatic index γ were studied for their dynamical stability by Chandrasekhar
and he found that for each value of u (≡ mass to size ratio), there is a value of γ = γc, such that for γ < γc, the configuration is dynamically unstable. On examining the properties of the Chandrasekhar's spheres (homogeneous spheres
with constant γ) it is found that these spheres are non-isentropic, and the speed of sound within these spheres is finite.
The authors find that (i) for the causality condition to be fulfilled throughout the configuration, the value of γ ≤ [2/(surface
redshift)], (ii) for a given value of u, the binding coefficient, αr = (Mr -M)/M, vanishes for some value of γ = γb and for all the values of γ < γb the configurations are unbound, and (iii) for u≤ (1/3), one can find configurations which are bound, dynamically stable, and the speed of sound is less than that of light
throughout the configuration, whereas, for u >(1/3), the physically viable models of homogeneous density distribution are not possible. If the configuration is considered
to be isentropic, then both γ and the speed of sound become infinite throughout the configuration.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
Philip Hardee Yosuke Mizuno Ken-Ichi Nishikawa 《Astrophysics and Space Science》2007,311(1-3):281-286
A new general relativistic magnetohydrodynamics (GRMHD) code “RAISHIN” used to simulate jet generation by rotating and non-rotating
black holes with a geometrically thin Keplarian accretion disk finds that the jet develops a spine-sheath structure in the
rotating black hole case. Spine-sheath structure and strong magnetic fields significantly modify the Kelvin-Helmholtz (KH)
velocity shear driven instability. The RAISHIN code has been used in its relativistic magnetohydrodynamic (RMHD) configuration
to study the effects of strong magnetic fields and weakly relativistic sheath motion, c/2, on the KH instability associated with a relativistic, γ=2.5, jet spine-sheath interaction. In the simulations sound speeds up to
and Alfvén wave speeds up to ∼0.56c are considered. Numerical simulation results are compared to theoretical predictions from a new normal mode analysis of the
RMHD equations. Increased stability of a weakly magnetized system resulting from c/2 sheath speeds and stabilization of a strongly magnetized system resulting from c/2 sheath speeds is found. 相似文献
19.
Mathieu de Naurois 《Astrophysics and Space Science》2007,309(1-4):277-284
Recent observations of the binary system LS 5039 with the High Energy Stereoscopic System (H.E.S.S.) revealed that its Very
High Energy (VHE) γ-ray emission is modulated at the 3.9 days orbital period of the system. The bulk of the emission is largely confined to half
of the orbit, peaking around the inferior conjunction epoch of the compact object. The flux modulation provides the first
indication of γ-ray absorption by pair production on the intense stellar photon field. This implies that the production region size must
be not significantly greater than the gamma-gamma photosphere size (∼1 AU), thus excluding the large scale collimated outflows
or jets (extending out to ∼1000 AU). A hardening of the spectrum is also observed at the same epoch between 0.2 and a few
TeV which is unexpected under a pure absorption scenario and could rather arise from variation with phase in the maximum electron
energy and/or the dominant VHE γ-ray production mechanism. This first-time observation of modulated γ-ray emission allows precise tests of the acceleration and emission models in binary systems.
Mathieu de Naurois for the H.E.S.S. Collaboration. 相似文献
20.
A. V. Morozhenko 《Kinematics and Physics of Celestial Bodies》2009,25(4):182-188
Spectral values (with 1 nm spectral resolution) of the product of γk
ν and γ′k
ν (where k
ν is the monochromatic coefficient of ammonia absorption and γ and γ′ are the relative (with respect to 0.85/0.15 hydrogen-helium
mixture and methane, respectively)) concentrations of ammonia for the absorption bands at λλ = 552, 604, 645, 787, and 932
nm in thermal conditions of Jupiter’s and Saturn’s atmospheres are determined (). 相似文献