726 research outputs found
Radio emission of the Galactic X-rays binaries with relativistic jets
Variable non-thermal radio emission from Galactic X-ray binaries is a trace
of relativistic jets, created near accretion disks. The spectral
characteristics of a lot of radio flares in the X-ray binaries with jets (RJXB)
is discussed in this report. We carried out several long daily monitoring
programs with the RATAN-600 radio telescope of the sources: SS433, Cyg X-3,
LSI+61o303, GRS 1915+10 and some others. We also reviewed some data from the
GBI monitoring program at two frequencies and hard X-ray BATSE (20-100 keV) and
soft X-ray RTXE (2-12 keV) ASM data. We confirmed that flaring radio emission
of Cyg X-3 correlated with hard and anti-correlated with soft X-ray emission
during the strong flare (>\tau$ depends upon frequency as tau \propto \nu^{-0.4} in the first
flare and does not depend upon frequency in the second flare, and is equal to
\tau=6+-1 days at frequencies from 0.96 to 21.7 GHz in the last flare in May
1999. Many flaring RJXB show two, exponential and power, laws of flare decay.
Moreover, these different laws could be present in one or several flares and
commonly flare decays are faster at a higher frequency. The decay law seems to
change because of geometric form of the conical hollow jets. The synchrotron
and inverse Compton losses could explain general frequency dependences in flare
evolution. In conclusion we summarized the general radio properties of RJXB.Comment: 10 pages, LaTeX, 14 Postscript figures, talk given at the Gamov
Memorial International Conference (GMIC'99) "Early Universe: Cosmological
Problems and Instrumental Technologies" in St.Petersburg, 23-27 August, 1999,
to appear in Astron. Astrophys. Trans., 200
Dynamics of Relativistic Flows
Dynamics of relativistic outflows along the rotation axis of a Kerr black
hole is investigated using a simple model that takes into account the
relativistic tidal force of the central source as well as the Lorentz force due
to the large-scale electromagnetic field which is assumed to be present in the
ambient medium. The evolution of the speed of the flow relative to the ambient
medium is studied. In the force-free case, the resulting equation of motion
predicts rapid deceleration of the initial flow and an asymptotic relative
speed with a Lorentz factor of 2^1/2. In the presence of the Lorentz force, the
long-term relative speed of the clump tends to the ambient electrical drift
speed.Comment: 17 pages, 5 figures, expanded version to appear in Int. J. Mod. Phys.
X-Ray Emission from the Jets of XTE J1550-564
We report on X-ray observations of the the large-scale jets recently
discovered in the radio and detected in X-rays from the black hole candidate
X-ray transient and microquasar XTE J1550-564. On 11 March 2002, X-ray emission
was detected 23 arcsec to the West of the black hole candidate and was extended
along the jet axis with a full width at half maximum of 1.2 arcsec and a full
width at 10% of maximum intensity of 5 arcsec. The morphology of the X-ray
emission matched well to that of the radio emission at the same epoch. The jet
moved by 0.52 +/- 0.13 arcsec between 11 March and 19 June 2002. The apparent
speed during that interval was 5.2 +/- 1.3 mas/day. This is significantly less
than the average apparent speed of 18.1 +/- 0.4 mas/day from 1998 to 2002,
assuming that the jet was ejected in September 1998, and indicates that the jet
has decelerated. The X-ray spectrum is adequately described by a powerlaw with
a photon index near 1.8 subject to interstellar absorption. The unabsorbed
X-ray flux was 3.4 x 10^-13 erg cm^-2 s^-1 in the 0.3-8 keV band in March 2002,
and decreased to 2.9 x 10^-13 erg cm^-2 s^-1 in June. We also detect X-rays
from the eastern jet in March 2002 and show that it has decelerated and dimmed
since the previous detections in 2000.Comment: accepted for publication in ApJ, 11 pages, several figures in colo
Discovery of extended radio emission in the young cluster Wd1
We present 10 micron, ISO-SWS and Australia Telescope Compact Array
observations of the region in the cluster Wd1 in Ara centred on the B[e] star
Ara C. An ISO-SWS spectrum reveals emission from highly ionised species in the
vicinity of the star, suggesting a secondary source of excitation in the
region. We find strong radio emission at both 3.5cm and 6.3cm, with a total
spatial extent of over 20 arcsec. The emission is found to be concentrated in
two discrete structures, separated by 14''. The westerly source is resolved,
with a spectral index indicative of thermal emission. The easterly source is
clearly extended and nonthermal (synchrotron) in nature. Positionally, the B[e]
star is found to coincide with the more compact radio source, while the
southerly lobe of the extended source is coincident with Ara A, an M2 I star.
Observation of the region at 10micron reveals strong emission with an almost
identical spatial distribution to the radio emission. Ara C is found to have an
extreme radio luminosity in comparison to prior radio observations of hot stars
such as O and B supergiants and Wolf-Rayet stars, given the estimated distance
to the cluster. An origin in a detatched shell of material around the central
star is therefore suggested; however given the spatial extent of the emission,
such a shell must be relatively young (10^3 yrs). The extended non thermal
emission associated with the M star Ara A is unexpected; to the best of our
knowledge this is a unique phenomenon. SAX (2-10keV) observations show no
evidence of X-ray emission, which might be expected if a compact companion were
present.Comment: 5 pages including encapsulated figures, figure 3 separate. Accepted
for MNRAS pink page
Radio emission and jets from microquasars
To some extent, all Galactic binary systems hosting a compact object are
potential `microquasars', so much as all galactic nuclei may have been quasars,
once upon a time. The necessary ingredients for a compact object of stellar
mass to qualify as a microquasar seem to be: accretion, rotation and magnetic
field. The presence of a black hole may help, but is not strictly required,
since neutron star X-ray binaries and dwarf novae can be powerful jet sources
as well. The above issues are broadly discussed throughout this Chapter, with a
a rather trivial question in mind: why do we care? In other words: are jets a
negligible phenomenon in terms of accretion power, or do they contribute
significantly to dissipating gravitational potential energy? How do they
influence their surroundings? The latter point is especially relevant in a
broader context, as there is mounting evidence that outflows powered by
super-massive black holes in external galaxies may play a crucial role in
regulating the evolution of cosmic structures. Microquasars can also be thought
of as a form of quasars for the impatient: what makes them appealing, despite
their low number statistics with respect to quasars, are the fast variability
time-scales. In the first approximation, the physics of the jet-accretion
coupling in the innermost regions should be set by the mass/size of the
accretor: stellar mass objects vary on 10^5-10^8 times shorter time-scales,
making it possible to study variable accretion modes and related ejection
phenomena over average Ph.D. time-scales. [Abridged]Comment: 28 pages, 13 figures, To appear in Belloni, T. (ed.): The Jet
Paradigm - From Microquasars to Quasars, Lect. Notes Phys. 794 (2009
Orbital dynamics of Cygnus X-3
Orbital-phased-resolved infrared spectra of Cygnus X-3 in outburst and
quiescence, including tomographic analysis, are presented. We confirm the
phasing of broad HeII and NV lines in quiescence, such that maximum blue shift
corresponds to the X-ray minimum at phase = 0.00 +/- 0.04. In outburst,
double-peaked HeI structures show a similar phasing with two significant
differences: (a) although varying in relative strength, there is continuous
line emission in blue and red peaks around the orbit, and (b) an absorption
component, ~1/4 of an orbit out of phase with the emission features, is
discerned. Doppler tomograms of the double-peaked profiles are consistent with
a disk-wind geometry, rotating at velocities of 1000 km/s. Regrettably, the
tomography algorithm will produce a similar ring structure from alternative
line sources if contaminated by overlying P Cygni profiles. This is certainly
the case in the strong 2.0587 micron HeI line, leading to an ambiguous solution
for the nature of double-peaked emission. The absorption feature, detected 1/4
of an orbit out of phase with the emission features, is consistent with an
origin in the He star wind and yields for the first time a plausible radial
velocity curve for the system. We directly derive the mass function of the
system, 0.027 M_sun. If we assume a neutron star accretor and adopt a high
orbital inclination, i > 60 degrees, we obtain a mass range for the He star of
5 M_sun < M_WR < 11 M_sun. Alternatively if the compact object is a black hole,
we estimate M_BH < 10 M_sun. We discuss the implications of these masses for
the nature and size of the binary system.Comment: Accepted for publication in ApJ main journa
Cygnus X-3 with ISO: investigating the wind
We observed the energetic binary Cygnus X-3 in both quiescent and flaring
states between 4 and 16 microns using the ISO satellite. We find that the
quiescent source shows the thermal free-free spectrum typical of a hot, fast
stellar wind, such as from a massive helium star. The quiescent mass-loss rate
due to a spherically symmetric, non-accelerating wind is found to be in the
range 0.4-2.9 x 10E-4 solar masses per year, consistent with other infrared and
radio observations, but considerably larger than the 10E-5 solar masses per
year deduced from both the orbital change and the X-ray column density. There
is rapid, large amplitude flaring at 4.5 and 11.5 microns at the same time as
enhanced radio and X-ray activity, with the infrared spectrum apparently
becoming flatter in the flaring state. We believe non-thermal processes are
operating, perhaps along with enhanced thermal emission.Comment: Accepted for publication in MNRAS, 11 pages, 6 figure
The Generalized Jacobi Equation
The Jacobi equation in pseudo-Riemannian geometry determines the linearized
geodesic flow. The linearization ignores the relative velocity of the
geodesics. The generalized Jacobi equation takes the relative velocity into
account; that is, when the geodesics are neighboring but their relative
velocity is arbitrary the corresponding geodesic deviation equation is the
generalized Jacobi equation. The Hamiltonian structure of this nonlinear
equation is analyzed in this paper. The tidal accelerations for test particles
in the field of a plane gravitational wave and the exterior field of a rotating
mass are investigated. In the latter case, the existence of an attractor of
uniform relative radial motion with speed is pointed
out. The astrophysical implications of this result for the terminal speed of a
relativistic jet is briefly explored.Comment: LaTeX file, 4 PS figures, 28 pages, revised version, accepted for
publication in Classical and Quantum Gravit
A 2.4 - 12 microns spectrophotometric study with ISO of Cygnus X-3 in quiescence
We present mid-infrared spectrophotometric results obtained with the ISO on
the peculiar X-ray binary Cygnus X-3 in quiescence, at orbital phases 0.83 to
1.04. The 2.4-12 microns continuum radiation observed with ISOPHOT-S can be
explained by thermal free-free emission in an expanding wind with, above 6.5
microns, a possible additional black-body component with temperature T ~ 250 K
and radius R ~ 5000 solar radii at 10 kpc, likely due to thermal emission by
circumstellar dust. The observed brightness and continuum spectrum closely
match that of the Wolf-Rayet star WR 147, a WN8+B0.5 binary system, when
rescaled at the same 10 kpc distance as Cygnus X-3. A rough mass loss estimate
assuming a WN wind gives ~ 1.2 10^{-4} M(sun)/yr. A line at ~ 4.3 microns with
a more than 4.3 sigma detection level, and with a dereddened flux of 126 mJy,
is interpreted as the expected He I 3p-3s line at 4.295 microns, a prominent
line in the WR 147 spectrum. These results are consistent with a
Wolf-Rayet-like companion to the compact object in Cygnus X-3 of WN8 type, a
later type than suggested by earlier works.Comment: 8 pages, 10 figures ; Accepted in A&
Very High Angular Resolution Science with the Square Kilometre Array
Preliminary specifications for the Square Kilometre Array (SKA) call for 25%
of the total collecting area of the dish array to be located at distances
greater than 180 km from the core, with a maximum baseline of at least 3000 km.
The array will provide angular resolution ~ 40 - 2 mas at 0.5 - 10 GHz with
image sensitivity reaching < 50 nJy/beam in an 8 hour integration with 500 MHz
bandwidth. Given these specifications, the high angular resolution component of
the SKA will be capable of detecting brightness temperatures < 200 K with
milliarcsecond-scale angular resolution. The aim of this article is to bring
together in one place a discussion of the broad range of new and important high
angular resolution science that will be enabled by the SKA, and in doing so,
address the merits of long baselines as part of the SKA. We highlight the fact
that high angular resolution requiring baselines greater than 1000 km provides
a rich science case with projects from many areas of astrophysics, including
important contributions to key SKA science.Comment: 13 pages, 6 figure
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