共查询到20条相似文献,搜索用时 437 毫秒
1.
D. Horns F. Aharonian A. I. D. Hoffmann A. Santangelo 《Astrophysics and Space Science》2007,309(1-4):189-195
Observations of the inner radian of the Galactic disk at very high energy (VHE) gamma-rays have revealed at least 16 new sources.
Besides shell type super-nova remnants, pulsar wind nebulae (PWN) appear to be a dominant source population in the catalogue
of VHE gamma-ray sources. Except for the Crab nebula, the newly discovered PWN are resolved at VHE gamma-rays to be spatially
extended (5–20 pc). Currently, at least 3 middle aged (t>10 kyrs) PWN (Vela X, G18.0-0.7, and G313.3+0.6 in the “Kookaburra” region) and 1 young PWN MSH 15-52 (t=1.55 kyrs) have been identified to be VHE emitting PWN (sometimes called “TeV Plerions”). Two more candidate “TeV Plerions”
have been identified and have been reported at this conference (Carrigan, These proceedings, in preparation). In this contribution,
the gamma-ray emission from Vela X is explained by a nucleonic component in the pulsar wind. The measured broad band spectral
energy distribution is compared with the expected X-ray emission from primary and secondary electrons. The observed X-ray
emission and TeV emission from the three middle aged PWN are compared with each other. 相似文献
2.
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
3.
Amongst the sources seen in very high gamma-rays several are associated with Pulsar Wind Nebulae (“TeV plerions”). The study
of hard X-ray/soft gamma-ray emission is providing an important insight into the energetic particle population present in
these objects. The unpulsed emission from pulsar/pulsar wind nebula systems in the energy range accessible to the INTEGRAL satellite is mainly synchrotron emission from energetic and fast cooling electrons close to their acceleration site. Our
analyses of public INTEGRAL data of known TeV plerions detected by ground based Cherenkov telescopes indicate a deeper link between these TeV plerions
and INTEGRAL detected pulsar wind nebulae. The newly discovered TeV plerion in the northern wing of the Kookaburra region (G313.3+0.6
powered by the middle aged PSR J1420-6048) is found to have a previously unknown INTEGRAL counterpart which is besides the Vela pulsar the only middle aged pulsar detected with INTEGRAL. We do not find an INTEGRAL counterpart of the TeV plerion associated with the X-ray PWN “Rabbit” G313.3+0.1 which is possibly powered by a young pulsar. 相似文献
4.
For the case of Tycho’s supernova remnant (SNR) we present the relation between the blast wave and contact discontinuity radii
calculated within the nonlinear kinetic theory of cosmic ray (CR) acceleration in SNRs. It is demonstrated that these radii
are confirmed by recently published Chandra measurements which show that the observed contact discontinuity radius is so close
to the shock radius that it can only be explained by efficient CR acceleration which in turn makes the medium more compressible.
Together with the recently determined new value E
sn=1.2×1051 erg of the SN explosion energy this also confirms our previous conclusion that a TeV γ-ray flux of (2–5)×10−13 erg/(cm2 s) is to be expected from Tycho’s SNR. Chandra measurements and the HEGRA upper limit of the TeV γ-ray flux together limit the source distance d to 3.3≤d≤4 kpc. 相似文献
5.
We present a comparative analysis of 5 GHz VLA and 200 ks Chandra ACIS-I image. In the 5 GHz image the familiar jet and much weaker counterjet are seen, which bend as the jet propagates towards
the hotspots. Furthermore, where the lobe detected in 5 GHz emission starts to interact with the jet, we see that the jet
“threads”. In the 0.2–10 keV X-ray image we do not detect the jet, but do detect a relic of the counterjet. 相似文献
6.
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
7.
Alaa I. Ibrahim Hisham Anwer Mohamed H. Soliman Nicholas Mackie-Jones Kalvir S. Dhuga William C. Parke Jean H. Swank Tilan Ukwatta M. T. Hussein T. El-Sherbini 《Astrophysics and Space Science》2007,308(1-4):535-539
A 6.4 keV emission line was discovered in an unusual burst from the soft gamma repeater SGR 1900+14 with the Rossi X-ray Timing
Explorer (RXTE). The line was detected in part of a complex multipeak precursor that preceded the unusual burst of 1998 August
29, i.e. two days after the giant flare of August 27 from the source. The origin of the line was not firmly identified and
two possible interpretations were equally plausible including (a) Kα fluorescence from a small iron rich material that was ejected to the magnetosphere during the August 27 flare, and (b) proton
or α-particle cyclotron resonance. If the iron scenario was correct, we expect to find evidence for the line during the intervening
interval between the flare and the August 29 burst, i.e. on August 28. Here we present the results of the August 28 burst
observation, taken with RXTE. We detect a total of seven bursts whose individual and joint spectra do not show evidence for
spectral lines. We also investigated a sample of nine bursts before and after the August 29 burst (from 1998 June to December)
that do not reveal evidence for a spectral line near 6.4 keV or elsewhere. These results disfavor the iron scenario and make
the proton/α-particle cyclotron resonance interpretation more plausible. The appearance of the emission line in part of a complex burst
and its absence from the studied sample indicate that the line is likely due to a transient phenomenon that may depend on
the burst morphology, energetics and the properties of the emission region.
相似文献
8.
Randall K. Smith 《Astrophysics and Space Science》2006,305(3):321-324
The Chandra X-ray observatory, one of NASA’s “Great Observatories,” provides high angular and spectral resolution X-ray data which is freely available to all. In this review I describe the instruments on Chandra along with their current calibration, as well as the Chandra proposal system, the freely-available Chandra analysis software package CIAO, and the Chandra archive. As Chandra is in its 6th year of operation, the archive already contains calibrated observations of a large range of X-ray sources. The Chandra X-ray Center is committed to assisting astronomers from any country who wish to use data from the archive or propose for observations. 相似文献
9.
G. Chartas M. Eracleous X. Dai E. Agol S. C. Gallagher 《Astronomische Nachrichten》2006,327(10):1063-1066
Our spatial and spectral analysis of a recent deep Chandra observation of H1413+117 confirms a microlensing event in a previous Chandra observation of this object performed about 5 years earlier. We present constraints on the structure of H1413+117 based on the time‐scale of this microlensing event. The analysis of the combined spectrum of the images indicates the presence of two emission line peaks at rest‐frame energies of 5.35 keV and 6.32 keV and detected at the ≳97% and ≳99% confidence levels, respectively. The double peaked Fe emission is fit well with an accretion disk‐line model, however, the best‐fit accretion disk model parameters are neither well constrained nor unique. Another possible interpretation of the Fe emission is fluorescent Fe emission from the back‐side of the wind. Additional observations are required to constrain better the model parameters. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
10.
We present a comparative analysis of 5 GHz VLA and 200 ks Chandra ACIS-I image. In the 5 GHz image the familiar jet and much weaker counterjet are seen, which bend as the jet propagates towards
the hotspots. Furthermore, where the lobe detected in 5 GHz emission starts to interact with the jet, we see that the jet
“threads”. In the 0.2–10 keV X-ray image we do not detect the jet, but do detect a relic of the counterjet.
* This paper has previously been published in Astrophysics and Space Science, vol. 310:3–4. 相似文献
11.
Markus Böttcher 《Astrophysics and Space Science》2007,309(1-4):95-104
Blazars are the most violent steady/recurrent sources of high-energy gamma-ray emission in the known Universe. They are prominent
emitters of electromagnetic radiation throughout the entire electromagnetic spectrum. The observable radiation most likely
originates in a relativistic jet oriented at a small angle with respect to the line of sight. This review starts out with
a general overview of the phenomenology of blazars, including results from a recent multiwavelength observing campaign on
3C279. Subsequently, issues of modeling broadband spectra will be discussed. Spectral information alone is not sufficient
to distinguish between competing models and to constrain essential parameters, in particular related to the primary particle
acceleration and radiation mechanisms in the jet. Short-term spectral variability information may help to break such model
degeneracies, which will require snap-shot spectral information on intraday time scales, which may soon be achievable for
many blazars even in the gamma-ray regime with the upcoming GLAST mission and current advances in Atmospheric Cherenkov Telescope
technology. In addition to pure leptonic and hadronic models of gamma-ray emission from blazars, leptonic/hadronic hybrid
models are reviewed, and the recently developed hadronic synchrotron mirror model for TeV γ-ray flares which are not accompanied by simultaneous X-ray flares (“orphan TeV flares”) is revisited.
The U.S. Government’s right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged. 相似文献
12.
Jet models for the high-energy emission of Galactic X-ray binary sources have regained significant interest with detailed
spectral and timing studies of the X-ray emission from microquasars, the recent detection by the HESS collaboration of very-high-energy
γ-rays from the microquasar LS 5039, and the earlier suggestion of jet models for ultraluminous X-ray sources observed in many
nearby galaxies. Here we study the synchrotron and Compton signatures of time-dependent electron injection and acceleration,
and adiabatic and radiative cooling in the jets of Galactic microquasars. 相似文献
13.
Markus Ackermann 《Astrophysics and Space Science》2007,309(1-4):421-427
The AMANDA-II telescope, operated by the IceCube collaboration, is currently the world’s most sensitive telescope to fluxes
of neutrinos from individual sources. A data sample of 4282 neutrino induced events collected in 1001 days of detector livetime
during the years 2000–2004 have now been analyzed looking for a neutrino signal from point-like sources. A sensitivity to
fluxes of
of d
Φ/dE=1.0×10−10(E/TeV)−2 TeV−1 cm−2s−1 was reached in the energy range between 1.7 TeV and 2.4 PeV. So far no statistically significant localized excess of events
over the background of atmospheric neutrinos has been found, which would be ascribed to a neutrino source. However, the flux
upper limits derived from the non-observation of a signal are comparable to observed fluxes of high energy gamma rays from
blazars and within the range of current models for neutrino emission from selected sources. Possible constraints on these
models are discussed.
相似文献
14.
Large-scale, decelerating, relativistic X-ray jets from microquasar XTE J1550−564 has been recently discovered with Chandra by Corbel et al. (2002). We find that the dynamical evolution of the approaching jet at the late time is consistent with
the well-known Sedov evolutionary phase R∝ t
2/5. A trans-relativistic external shock dynamic model by analogy with the evolution of gamma-ray burst remnants, is shown to
be able to fit the proper-motion data of the approaching jet reasonably well. The inferred interstellar medium density around
the source is well below the canonical value n
ISM∼1 cm−3. The rapidly fading X-ray emission can be interpreted as synchrotron radiation from the non-thermal electrons in the adiabatically
expanding ejecta. These electrons were accelerated by the reverse shock (moving back into the ejecta) which becomes important
when the inertia of the swept external matter leads to an appreciable slowing down of the original ejecta. 相似文献
15.
Stephen Skinner Manuel Güdel Werner Schmutz Svetozar Zhekov 《Astrophysics and Space Science》2006,304(1-4):97-99
We present an overview of recent X-ray observations of Wolf-Rayet (WR) stars with XMM-Newton and Chandra. These observations are aimed at determining the differences in X-ray properties between massive WR + OB binary systems and putatively single WR stars. A new XMM spectrum of the nearby WN8 + OB binary WR 147 shows hard absorbed X-ray emission (including the Fe Kα line complex), characteristic of colliding wind shock sources. In contrast, sensitive observations of four of the closest known single WC (carbon-rich) WR stars have yielded only non-detections. These results tentatively suggest that single WC stars are X-ray quiet. The presence of a companion may thus be an essential factor in elevating the X-ray emission of WC + OB stars to detectable levels. 相似文献
16.
Recent results of the gamma-ray Cherenkov astronomy definitely prove the existence of fast variability in the very high energy
(V.H.E.) gamma-ray flux of some active galactic nuclei. The BL Lac PKS 2155-304 for instance showed variations down to a few
minutes time scale. From standard light travel time argument, these variations put extremely strong constraints on the size
of the TeV emitting zone, which has to be of the order of a few Schwarzschild radius, even for high values of the relativistic
Doppler factor of the emitting jets. Such discovery is a challenge for particle acceleration scenarios, which have to imagine
efficient acceleration processes at work in a very compact zone. Eventually, the immediate vicinity of the central black hole
appears as the most conservative choice for the location of the TeV emission region of active galactic nuclei. In this paper,
we propose a two-step mechanism for charged particle acceleration in the magnetosphere of a massive black hole surrounded
by an accretion disk. Particles first gain energy by a stochastic process during the accretion phase. It is shown that effective
proton acceleration up to energies 1017–1019 eV is possible in a low-luminosity magnetized accretion disk with 2D turbulent motion. The distribution function of energetic
protons over energies is a power law function with typical index ≃−1. Here electrons are not very efficiently accelerated
because of their drastic losses by synchrotron radiation. In a second time, part of the fast particles escape from the disk
and are then entrained by the magnetic structure above the disk, in the rotating black hole magnetosphere. They thus gain
additional energy by direct centrifugal mechanism, up to about 1020 eV for the protons and to 10–100 TeV for the electrons when they cross the light cylinder surface. Such energetic particles
can further radiate in the TeV spectral range observed by Cherenkov experiments as HESS, MAGIC and VERITAS. Energetic protons
can produce γ-radiation in the energy band 1 GeV–100 TeV and above mainly by nuclei collisions with the disk matter, clouds, or ambient
low energy photons. Energetic electrons can also reach the required spectral range by inverse Compton emission. However their
acceleration is less efficient due to heavy radiation losses, and only gained by centrifugal process during the second phase
of the whole mechanism we describe. Our present analysis would therefore favor hadronic scenarios for TeV emission of active
galactic nuclei. It is tempting to relate long term variability over years of TeV active galactic nuclei to the first stochastic
acceleration phase, which also provides the needed power law particle distributions, while short term variability over minutes
is more likely due to perturbations of the second fast direct acceleration phase. 相似文献
17.
Some unidentified EGRET sources have been reported to have probable X-ray counterparts. Periodicities in the X-ray data of
those sources, if found, may help to strengthen the identification and to reveal their nature. We performed a detailed search
of periodicities with a photon-counting method, the H-test, in the XMM and ASCA data of RX J0007.0+7302, which is the most probable X-ray counterpart to the EGRET source 3EG J0010+7309.
Although no periods with enough significance were found, a possible one, at 0.1275433± 0.0000001 s (MJD 52327.03399), is quite
intriguing based on results of cross-checking the two data sets. We suggest future analysis with other data to search the
vicinity of this period. 相似文献
18.
Stephen Skinner Manuel Güdel Kevin Briggs Stanislav Melnikov Marc Audard 《Astrophysics and Space Science》2006,304(1-4):165-167
We present new results from recent X-ray observations of the accreting pre-main sequence stars FU Orionis and T Tauri. XMM-Newton observations of the close binary system FU Ori reveal an unusual X-ray spectrum consisting of a cool moderately-absorbed component and a hot component viewed through much higher absorption. The two components thus originate in physically distinct regions. The double absorption spectrum is qualitatively different than observed in typical coronal sources and may signal either non-coronal emission or separate unresolved X-ray contributions from more than one star in the system. High-resolution Chandra imaging of the T Tau triple system shows that its X-ray emission is dominated by the optically-revealed northern component T Tau N. X-ray spectra of T Tau obtained with XMM can be acceptably fitted with a moderately absorbed two-temperature thermal plasma model. Its spectral properties are similar to those seen in coronal X-ray sources. 相似文献
19.
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
20.
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