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1.
We present the VLBI map of a superluminal radio source AO 0235+164 at 5 GHz. This shows that the object's radio structure is dominated by a strong, nearly unresolved core with two extended asymmetric weak jet components. Based on the variation of its flux density with time at 5 GHz, we suggest that the flux density of AO 0235+164 exhibits two periodic variations: a shorter-period variation of 1.81±0.06 yr and a longer-period one of 3.64±0.08 yr. These two periodic variations could be the result of the joint action of jet outbursts and jet rotation. 相似文献
2.
Frank M. Rieger 《Astrophysics and Space Science》2007,309(1-4):271-275
Supermassive binary black holes (SBBHs) are a natural outcome of galaxy mergers. Here we show that low-frequency (f≤10−6 Hz) quasi-periodic variability observed from cosmic blazar sources can provide substantial inductive support for the presence
of close (d≲0.1 pc) SBBHs at their centers. It is argued on physical grounds that such close binary systems are likely to give rise to
different (although not independent) periodicities in the radio, optical and X-ray/TeV regime, and, hence that detection of
appropriate period ratios significantly corroborates the SBBH interpretation. This is illustrated for a binary model where
optical longterm periodicity is related to accretion disk interactions, radio periodicity to Newtonian jet precession, and
periodicities in the high energy bands to the orbital motion of the jet. We use the observed periodicities to constrain the
properties for a sample of SBBH candidates including OJ 287 and AO 0235+16, and discuss the results within the context of
jet activity and binary evolution. 相似文献
3.
V. S. Bychkova A. E. Volvach L. N. Volvach N. S. Kardashev M. G. Larionov V. V. Vlasyuk O. I. Spiridonova A. Lähteenmäki M. Tornikoski J. Tammi E. Järvelä R. J. C. Vera W. Chamani S. Enestam 《Astrophysical Bulletin》2018,73(3):293-297
The active core of the galaxy AO0235+164 is monitored in the optical and radio bands at millimeter wavelengths. Using the multifrequency data obtained in gamma, optical and radio bands, the characteristics of its radiation in the active phase of 2015–2016 are studied. The cross-correlation method was used to determine the delays of the 2015 flare that took place in AO0235+164 in different bands. The analysis made it possible to establish that, in comparison with the previous flare phenomena, changes in the orientation of the emissions (jets) have occurred. The angle θ between the jets and the direction towards the observer has decreased by a factor of \(\sqrt 2 \), resulting in a twofold increase in the γ-factor. The obtained value γ ≈ 40 is the most extreme value ever observed in AO0235+164 over the entire span of observations. 相似文献
4.
The astrophysical jet experiment at Caltech generates a T=2–5 eV, n=1021–1022 m−3 plasma jet using coplanar disk electrodes linked by a poloidal magnetic field. A 100 kA current generates a toroidal magnetic
field; the toroidal field pressure inflates the poloidal flux surface, magnetically driving the jet. The jet travels at up
to 50 km/s for ∼20–25 cm before colliding with a cloud of initially neutral gas. We study the interaction of the jet and the
cloud in analogy to an astrophysical jet impacting a molecular cloud. Diagnostics include magnetic probe arrays, a 12-channel
spectroscopic system and a fast camera with optical filters. When a hydrogen plasma jet collides with an argon target cloud,
magnetic measurements show the magnetic flux compressing as the plasma jet deforms. As the plasma jet front slows and the
plasma piles up, the density of the frozen-in magnetic flux increases. 相似文献
5.
收集了AO0235+164天体射电4.8GHz和14.5GHz波段的光变测量数据,并获得了长期的光变曲线,从光变曲线可以看出其活动是非常剧烈的。利用Jurkevieh方法和自相关函数方法分别对AO0235+164射电波段宽带谱指数进行周期性分析,并对流量和谱指数进行相关性分析,研究结果表明:(1)AO0235+164天体射电波段4.8GHz-14.5GHz对应的宽带谱指数,可能存在5.30年的光变周期,与Liu等人用功率谱法在射电波段发现其流量密度可能存在5.59±0.47年的光变周期基本吻合;(2)宽带谱指数与流量密度之间存在相关性。 相似文献
6.
收集了AO 0235+164天体射电4.8 GHz和14.5 GHz波段的光变测量数据,并获得了长期的光变曲线,从光变曲线可以看出其活动是非常剧烈的。利用Jurkevich方法和自相关函数方法分别对AO 0235+164射电波段宽带谱指数进行周期性分析,并对流量和谱指数进行相关性分析,研究结果表明:(1)AO 0235+164天体射电波段4.8 GHz~14.5 GHz对应的宽带谱指数,可能存在5.30年的光变周期,与Liu等人用功率谱法在射电波段发现其流量密度可能存在5.59±0.47年的光变周期基本吻合;(2)宽带谱指数与流量密度之间存在相关性。 相似文献
7.
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
8.
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
9.
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
10.
In January 2005 spectral observations of the radio source Z0254+43 were made on the BTA at the Special Astrophysical Observatory
(SAO) of the Russian Academy of Sciences (RAN) and its red shift was found to be z=4.057. The BVRI magnitudes were found to
be 22.68, 21.19, 19.94, and 19.23, respectively. Photometric observations in December 2005 on the Zeiss-1000 at the SAO revealed
no significant variation in the optical emission from this object over that year. We can discuss its variability on an hourly
time scale with some caution. The variability of the flux from Z0254+43 was observed from 1990–2005 on the RATAN-600 over
a wide range of frequencies. It turns out that the amplitude of the variability is minimal at a frequency of ∼8 GHz. A model
for the variability has been constructed which yields an estimate of ∼28° for the orientation of the jet of Z0254+43 to the
line of sight. The luminosity of Z0254+43 in the optical range is ∼2·1026 W/Hz and in the radio frequency range, ∼2·1027 W/Hz.
__________
Translated from Astrofizika, Vol. 49, No. 2, pp. 209–220 (May 2006). 相似文献
11.
The structure of the AGN object 1803+784 has been investigated at a wavelength of 7 mm with a limiting angular resolution
reaching 20 μas. The ejector nozzle surrounded by a ring structure, an accretion disk, has been identified. The nozzle size
is ∼0.1 pc, the diameter of the ring structure is ∼1.4 pc, and its width is ∼0.25 pc. The reaction of the plasma flow produces
a multimode precession responsible for the conical helical structure of the jet with a variable step and a curved axis. The
viewing angle of the flow ejection is ∼40°. The central part of the ejected flow moving along the axis accelerates to a relativistic
velocity. The apparent velocity reaches 12 s at a distance of ∼1 mas or ∼6 pc from the ejector. The outer part of the flow
moves along a helix around a high-velocity component whose step is a factor of 4 smaller, because the longitudinal velocity
is relatively low. The plasma is ejected almost toward the observer, as confirmed by its high brightness temperature T
b ≈ 8 × 1013 K and highly beamed emission. The polarized emission from the nozzle is axisymmetric. The orientation of the polarization
of the flow along the whole length is aligned with the direction of its motion, suggesting the excitation of a ring magnetic
field around it and self-focusing. 相似文献
12.
Hongtao Wang 《Astrophysics and Space Science》2014,351(1):281-287
BL Lac object AO 0235+164 is a well-known object. We collect a large number of effective observation in B, V, R and I band from historical literatures. The possible periods are analyzed by means of discrete correlation function (DCF) method, structure function (SF) method and Jurkevich (J-K) method. The results show that there are possible periodic variations of 2.63–2.66 years in B band, 2.79–2.84 years in V band, 2.57–2.87 years in R band, 2.62–2.88 years in I band, respectively. 相似文献
13.
Evidence is presented indicating that the bursting component of the X-ray radiation detected in the nuclear region of the
active radio galaxy 3C 111 comes from the blobs ejected in the pc-scale jet and not from the accretion disc. After each new
outburst the radio flux density associated with it increases to a peak in ∼1 year and then subsides over a period of 1–2 years
with the flux falling off exponentially as the blob moves outward and dissipates. Similar peaks (bursts) are seen in the X-ray
light curve and a cross-correlation between the two shows a very high correlation with the X-ray peaks leading the radio peaks
by ∼100 days. A second cross-correlation, this time between the radio event start times and the X-ray light curve, also shows
a significant correlation. When this is taken together with the long (∼1 yr) delay between the start of each ejection event
and its associated X-ray peak it indicates that this bursting component of the X-ray flux must be associated with the ejected
blobs in the pc-scale jet and not with the accretion disc. Because X-ray telescopes do not have the resolution required to
resolve the accretion disc area from the pc-scale jet, this paper is the first to present observational evidence that can
pinpoint the point of origin of at least those long-timescale X-ray bursts with durations of 1–3 yrs. 相似文献
14.
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
15.
We study the kinematical characteristics and 3D geometry of a large-scale coronal wave that occurred in association with the
26 April 2008 flare-CME event. The wave was observed with the EUVI instruments aboard both STEREO spacecraft (STEREO-A and
STEREO-B) with a mean speed of ∼ 240 km s−1. The wave is more pronounced in the eastern propagation direction, and is thus, better observable in STEREO-B images. From
STEREO-B observations we derive two separate initiation centers for the wave, and their locations fit with the coronal dimming
regions. Assuming a simple geometry of the wave we reconstruct its 3D nature from combined STEREO-A and STEREO-B observations.
We find that the wave structure is asymmetric with an inclination toward East. The associated CME has a deprojected speed
of ∼ 750±50 km s−1, and it shows a non-radial outward motion toward the East with respect to the underlying source region location. Applying
the forward fitting model developed by Thernisien, Howard, and Vourlidas (Astrophys. J. 652, 763, 2006), we derive the CME flux rope position on the solar surface to be close to the dimming regions. We conclude that the expanding
flanks of the CME most likely drive and shape the coronal wave. 相似文献
16.
We report the discovery of a decay in the superorbital period of the binary X-ray pulsar LMC X-4. Combining archival data
and published long term X-ray light curves, we have found a decay in the third period in this system (P ∼ 30.3 day, P ∼ −2 × 10−5 s s−1). Along with this result, a comparison of the superorbital intensity variations in LMC X-4, Her X-1 and SMC X-1 is also presented. 相似文献
17.
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
18.
The morphological and velocity structures in the gaseous (HI and CO) and stellar components of two interacting systems are
examined. Both Arp 140 and Arp 104 reveal extended tidal tails in the HI. The Hα and FIR fluxes of Arp 140 yield similar SFR
of ∼ 0.8 M⊙ yr-1. In contrast the Hα flux of Arp 104 yields a SFR of ∼ 0.05 M⊙ yr-1, ∼ 20 times smaller than that obtained from the FIR flux. Spectra were used to examine the changing velocity of atomic and
molecular gas in NGC 5218 (Arp 104). The atomic and molecular gas were found to be dynamically similar with comparable velocities
and velocity widths across the galaxy; consistent with the two phases responding similarly to the interaction, or enhanced
HI to CO conversion in the centre of the galaxy.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
19.
Mark Cropper Silvia Zane Roberto Turolla Luca Zampieri Matteo Chieregato Jeremy Drake Aldo Treves 《Astrophysics and Space Science》2007,308(1-4):161-166
We report XMM-Newton observations of the isolated neutron star RBS1774 and confirm its membership as an XDINS. The X-ray spectrum is best fit
with an absorbed blackbody with temperature kT=101 eV and absorption edge at 0.7 keV. No power law component is required. An absorption feature in the RGS data at 0.4 keV
is not evident in the EPIC data, but it is not possible to resolve this inconsistency. The star is not seen in the UV OM data
to m
AB
∼21. There is a sinusoidal variation in the X-ray flux at a period of 9.437 s with an amplitude of 4%. The age as determined
from cooling and magnetic field decay arguments is 105–106 yr for a neutron star mass of 1.35–1.5 M⊙.
相似文献
20.
I. A. Grenier M. M. Kaufman Bernadó G. E. Romero 《Astrophysics and Space Science》2005,297(1-4):109-118
A subset of the unidentified EGRET γ-ray sources with no active galactic nucleus or other conspicuous counterpart appears
to be concentrated at medium latitudes. Their long-term variability and their spatial distribution indicate that they are
distinct from the more persistent sources associated with the nearby Gould Belt. They exhibit a large scale height of 1.3
± 0.6 kpc above the Galactic plane. Potential counterparts for these sources include microquasars accreting from a low-mass
star and spewing a continuous jet. Detailed calculations have been performed of the jet inverse Compton emission in the radiation
fields from the star, the accretion disc, and a hot corona. Different jet Lorentz factors, powers, and aspect angles have
been explored. The up-scattered emission from the corona predominates below 100 MeV whereas the disc and stellar contributions
are preponderant at higher energies for moderate (∼15∘) and small (∼1∘) aspect angles, respectively. Yet, unlike in the high-mass, brighter versions of these systems, the external Compton emission
largely fails to produce the luminosities required for 5 to 10 kpc distant EGRET sources. Synchrotron-self-Compton emission
appears as a promising alternative. 相似文献