377 research outputs found
Discovery of X-ray Jets in the Microquasar H 1743-322
We report on the formation and evolution of two large-scale,
synchrotron-emitting jets from the black hole candidate H 1743-322 following
its reactivation in 2003. In November 2003 after the end of its 2003 outburst,
we noticed, in observations with the Australia Telescope Compact Array, the
presence of a new and variable radio source about 4.6" to the East of H
1743-322, that was later found to move away from H 1743-322. In February 2004,
we detected a radio source to the West of H 1743-322, symmetrically placed
relative to the Eastern jet. In 2004, follow-up X-ray observations with {\em
Chandra} led to the discovery of X-ray emission associated with the two radio
sources. This likely indicates that we are witnessing the interaction of
relativistic jets from H 1743-322 with the interstellar medium causing in-situ
particle acceleration. The spectral energy distribution of the jets during the
decay phase is consistent with a classical synchrotron spectrum of a single
electron distribution from radio up to X-rays, implying the production of very
high energy ( 10 TeV) particles in those jets. We discuss the jet
kinematics, highlighting the presence of a significantly relativistic flow in H
1743-322 almost a year after the ejection event.Comment: Accepted for publication in The Astrophysical Journal. 17 pages, 9
figure
High-Resolution Images of Diffuse Neutral Clouds in the Milky Way. I. Observations, Imaging, and Basic Cloud Properties
A set of diffuse interstellar clouds in the inner Galaxy within a few hundred
pc of the Galactic plane has been observed at an angular resolution of ~1
arcmin combining data from the NRAO Green Bank Telescope and the Very Large
Array. At the distance of the clouds the linear resolution ranges from ~1.9 pc
to ~2.8 pc. These clouds have been selected to be somewhat out of the Galactic
plane and are thus not confused with unrelated emission, but in other respects
they are a Galactic population. They are located near the tangent points in the
inner Galaxy, and thus at a quantifiable distance: kpc
from the Galactic Center, and pc from the Galactic
plane. These are the first images of the diffuse neutral HI clouds that may
constitute a considerable fraction of the ISM. Peak HI column densities range
from cm. Cloud diameters vary between
about 10 and 100 pc, and their HI mass spans the range from less than a hundred
to a few thousands Msun. The clouds show no morphological consistency of any
kind except that their shapes are highly irregular. One cloud may lie within
the hot wind from the nucleus of the Galaxy, and some clouds show evidence of
two distinct thermal phases as would be expected from equilibrium models of the
interstellar medium.Comment: 81 pages, 42 figures, accepted for publication in the Astrophysical
Journal Supplement Serie
Simultaneous Chandra and RXTE Spectroscopy of the Microquasar H~1743-322: Clues to Disk Wind and Jet Formation from a Variable Ionized Outflow
We observed the bright phase of the 2003 outburst of the Galactic black hole
candidate H 1743-322 in X-rays simultaneously with Chandra and RXTE on four
occasions. The Chandra/HETGS spectra reveal narrow, variable (He-like) Fe XXV
and (H-like) Fe XXVI resonance absorption lines. In the first observation, the
Fe XXVI line has a FWHM of 1800 +/- 400 km/s and a blue-shift of 700 +/- 200
km/s, suggesting that the highly ionized medium is an outflow. Moreover, the Fe
XXV line is observed to vary significantly on a timescale of a few hundred
seconds in the first observation, which corresponds to the Keplerian orbital
period at approximately 1 E+4 gravitational radii. Our models for the
absorption geometry suggest that a combination of geometric effects and
changing ionizing flux are required to account for the large changes in line
flux observed between observations, and that the absorption likely occurs at a
radius less than 1 E+4 radii for a 10 Msun black hole. Viable models for the
absorption geometry include cyclic absorption due to an accretion disk
structure, absorption in a clumpy outflowing disk wind, or possibly a
combination of these two. If the wind in H 1743-322 has unity filling factor,
the highest implied mass outflow rate is 20 percent of the Eddington mass
accretion rate. This wind may be a hot precursor to the Seyfert-like,
outflowing "warm absorber" geometries recently found in the Galactic black
holes GX 339-4 and XTE J1650-500. We discuss these findings in the context of
ionized Fe absorption lines found in the spectra of other Galactic sources, and
connections to warm absorbers, winds, and jets in other accreting systems.Comment: 18 pages, 7 figures, 5 in color, subm. to ApJ. Uses emulateapj.sty
and apjfonts.st
Thermal radio emission from novae & symbiotics with the Square Kilometre Array
The thermal radio emission of novae during outburst enables us to derive
fundamental quantities such as the ejected mass, kinetic energy, and density
profile of the ejecta. Recent observations with newly-upgraded facilities such
as the VLA and e-MERLIN are just beginning to reveal the incredibly complex
processes of mass ejection in novae (ejections appear to often proceed in
multiple phases and over prolonged timescales). Symbiotic stars can also
exhibit outbursts, which are sometimes accompanied by the expulsion of material
in jets. However, unlike novae, the long-term thermal radio emission of
symbiotics originates in the wind of the giant secondary star, which is
irradiated by the hot white dwarf. The effect of the white dwarf on the giant's
wind is strongly time variable, and the physical mechanism driving these
variations remains a mystery (possibilities include accretion instabilities and
time-variable nuclear burning on the white dwarf's surface).
The exquisite sensitivity of SKA1 will enable us to survey novae throughout
the Galaxy, unveiling statistically complete populations. With SKA2 it will be
possible to carry out similar studies in the Magellanic Clouds. This will
enable high-quality tests of the theory behind accretion and mass loss from
accreting white dwarfs, with significant implications for determining their
possible role as Type Ia supernova progenitors. Observations with SKA1-MID in
particular, over a broad range of frequencies, but with emphasis on the higher
frequencies, will provide an unparalleled view of the physical processes
driving mass ejection and resulting in the diversity of novae, whilst also
determining the accretion processes and rates in symbiotic stars.Comment: 13 pages, 3 figures, in proceedings of "Advancing Astrophysics with
the Square Kilometre Array", PoS(AASKA14)116, in pres
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