1,171 research outputs found
Near-infrared synchrotron emission from the compact jet of GX339-4
We have compiled contemporaneous broadband observations of the black hole
candidate X-ray binary GX 339-4 when in the low/hard X-ray state in 1981 and
1997. The data clearly reveal the presence of two spectral components, with
thermal and non-thermal spectra, overlapping in the optical -- near-infrared
bands. The non-thermal component lies on an extrapolation of the radio spectrum
of the source, and we interpret it as optically thin synchrotron emission from
the powerful, compact jet in the system. Detection of this break from
self-absorbed to optically thin synchrotron emission from the jet allows us to
place a firm lower limit on the ratio of jet (synchrotron) to X-ray
luminosities of %. We further note that extrapolation of the optically
thin synchrotron component from the near-infrared to higher frequencies
coincides with the observed X-ray spectrum, supporting models in which the
X-rays could originate via optically thin synchrotron emission from the jet
(possibly instead of Comptonisation).Comment: Accepted for publication in ApJ Lette
Slow Positron Surface Studies
Positron-electron annihilation in condensed matter provides a way to investigate the electronic structure. the annihilation characteristics depending on the electronic structure of the environment sampled by positrons. The relatively recent production of intense low energy positron beams has made the study of surfaces with positrons possible. The near surface region can be studied by implantation of slow monoenergetic positrons via positron electron annihilation and, in addition. via positron diffusion length measurements. This is a powerful method to study vacancy type defects in the near surface region because positively charged positrons are normally very efficiently trapped by vacancy defects. The experiments reviewed in this tutorial paper show that, by using slow positron beams, one can study (i) vacancy profile defects in the near surface region, vacancy defects at interfaces, (ii) electron momentum density, electron density of states and magnetism at surface, and (iii) surface structure
On the Origin of Radio Emission in the X-ray States of XTE J1650-500 during the 2001-2002 Outburst
We report on simultaneous radio and X-ray observations of the black hole
candidate XTE J1650-500 during the course of its 2001-2002 outburst. The
scheduling of the observations allowed us to sample the properties of XTE
J1650-50 in different X-ray spectral states, namely the hard state, the steep
power-law state and the thermal dominant state, according to the recent
spectral classification of McClintock & Remillard. The hard state is consistent
with a compact jet dominating the spectral energy distribution at radio
frequencies; however, the current data suggest that its contribution as direct
synchrotron emission at higher energies may not be significant. In that case,
XTE J1650-50 may be dominated by Compton processes (either inverse
Comptonization of thermal disk photons and/or SSC from the base of the compact
jet) in the X-ray regime. We, surprisingly, detect a faint level of radio
emission in the thermal dominant state that may be consistent with the emission
of previously ejected material interacting with the interstellar medium,
similar (but on a smaller angular scale) to what was observed in XTE J1550-564
by Corbel and co-workers. Based on the properties of radio emission in the
steep power-law state of XTE J1650-50, and taking into account the behavior of
other black hole candidates (namely GX 339-4, XTE J1550-564, and XTE J1859+226)
while in the intermediate and steep power-law states, we are able to present a
general pattern of behavior for the origin of radio emission in these two
states that could be important for understanding the accretion-ejection
coupling very close to the black hole event horizon.Comment: Accepted for publication in The Astrophysical Journal. 33 pages, 10
figure
Is the `IR Coincidence' Just That?
(Abridged) Motch (1985) suggested that in the hard state of GX 339-4 the soft
X-ray power-law extrapolated backward in energy agrees with the IR flux. Corbel
& Fender (2002) showed that the hard state radio power-law extrapolated forward
in energy meets the extrapolated X-ray power-law at an IR break, which was
explicitly observed twice in GX 339-4. This `IR coincidence' has been cited as
further evidence that a jet might make a significant contribution to the X-rays
in hard state systems. We explore this hypothesis with a series of simultaneous
radio/X-ray observations of GX 339-4, taken during its 1997, 1999, and 2002
hard states. We fit these spectra, in detector space, with a simple, but
remarkably successful, doubly broken power-law that requires an IR spectral
break. For these observations, the break position and the integrated radio/IR
flux have stronger dependences upon the X-rays than the simplest jet
predictions. If one allows for a softening of the X-ray power law with
increasing flux, then the jet model agrees with the correlation. We also find
evidence that the radio/X-ray fcorrelation previously observed in GX 339-4
shows a `parallel track' for the 2002 hard state. The slope of the 2002
correlation is consistent with prior observations; however, the radio amplitude
is reduced. We then examine the correlation in Cyg X-1 through the use of radio
data, obtained with the Ryle radio telescope, and RXTE data, from the ASM and
pointed observations. We again find evidence of `parallel tracks', and here
they are associated with `failed transitions' to the soft state. We also find
that for Cyg X-1 the radio flux is more fundamentally correlated with the hard
X-ray flux.Comment: To Appear in the July 2005 Astrophysical Journal; 9 Pages, uses
emulateapj.st
Neutrino flux predictions for known Galactic microquasars
It has been proposed recently that Galactic microquasars may be prodigious
emitters of TeV neutrinos that can be detected by upcoming km^2 neutrino
telescopes. In this paper we consider a sample of identified microquasars and
microquasar candiates, for which available data enables rough determination of
the jet parameters. By employing the parameters inferred from radio
observations of various jet ejection events, we determine the neutrino fluxes
that should have been produced during these events by photopion production in
the jet. Despite the large uncertainties in our analysis, we demonstrate that
in several of the sources considered, the neutrino flux at Earth, produced in
events similar to those observed, would exceed the detection threshold of a
km^2 neutrino detector. The class of microquasars may contain also sources with
bulk Lorentz factors larger than those characteristic of the sample considered
here, directed along our line of sight. Such sources, which may be very
difficult to resolve at radio wavelengths and hence may be difficult to
identify as microqusar candidates, may emit neutrinos with fluxes significantly
larger than typically obtained in the present analysis. These sources may
eventually be identified through their neutrino and gamma-ray emission.Comment: 17 pages. Submitted to Ap
Opening angles, Lorentz factors and confinement of X-ray binary jets
We present a collation of the available data on the opening angles of jets in
X-ray binaries, which in most cases are small (less than 10 degrees). Under the
assumption of no confinement, we calculate the Lorentz factors required to
produce such small opening angles via the transverse relativistic Doppler
effect. The derived Lorentz factors, which are in most cases lower limits, are
found to be large, with a mean greater than 10, comparable to those estimated
for AGN and much higher than the commonly-assumed values for X-ray binaries of
2 to 5. Jet power constraints do not in most cases rule out such high Lorentz
factors. The upper limits on the opening angles show no evidence for smaller
Lorentz factors in the steady jets of Cygnus X-1 and GRS 1915+105. In those
sources in which deceleration has been observed (notably XTE J1550-564 and
Cygnus X-3), some confinement of the jets must be occurring, and we briefly
discuss possible confinement mechanisms. It is however possible that all the
jets could be confined, in which case the requirement for high bulk Lorentz
factors can be relaxed.Comment: 11 pages, 4 figures (2 colour), accepted for publication in MNRA
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