998 research outputs found
Gamma-ray binaries
Recent observations have shown that some compact stellar binaries radiate the
highest energy light in the universe. The challenge has been to determine the
nature of the compact object and whether the very high energy gamma-rays are
ultimately powered by pulsar winds or relativistic jets. Multiwavelength
observations have shown that one of the three gamma-ray binaries known so far,
PSR B1259-63, is a neutron star binary and that the very energetic gamma-rays
from this source and from another gamma-ray binary, LS I +61 303, may be
produced by the interaction of pulsar winds with the wind from the companion
star. At this time it is an open question whether the third gamma-ray binary,
LS 5039, is also powered by a pulsar wind or a microquasar jet, where
relativistic particles in collimated jets would boost the energy of the wind
from the stellar companion to TeV energies.Comment: 4 pages, 3 figures. Invited talk to appear in Proceedings of the
conference "The Multi-Messenger Approach to High-Energy Gamma-ray Sources",
Barcelona, 4-7 July 200
Precessing microblazars and unidentified gamma-ray sources
The recent discovery by Paredes et al. (2000) of a persistent microquasar
that is positionally coincident with an unidentified gamma-ray source has open
the possibility that other sources in the Third EGRET Catalog could be
interpreted as microquasars as well. In this letter we show that some variable
unidentified EGRET sources in the galactic plane could be produced by faint,
otherwise undetected microquasars with precessing jets. When the jet points
towards the observer, gamma-ray emission resulting from upscattered stellar
photons could be detectable yielding a variable source with weak or
undetectable counterpart at longer wavelengths. Strategies for detecting
these``microblazars'' with forthcoming satellites are briefly discussed.Comment: 4 pages, 3 figures, Astronomy & Astrophysics Letters in press, typing
errors correctio
Recurrent microblazar activity in Cygnus X-1?
Recurrent flaring events at X- and soft gamma-ray energies have been recently
reported for the galactic black hole candidate Cygnus X-1. The observed fluxes
during these transient outbursts are far higher than what is observed in
``normal'' episodes. Here we suggest that the origin of this radiation is
non-thermal and produced by inverse Compton interactions between relativistic
electrons in the jet and external photon fields, with a dominant contribution
from the companion star field. The recurrent and relatively rapid variability
could be explained by the precession of the jet, which results in a variable
Doppler amplification.Comment: 4 pages, 5 figures, Accepted for publication in Astronomy &
Astrophysics Letter
Kinematics of Black Hole X-ray Binary GRS 1915+105
The space velocity of a stellar black hole encodes the history of its
formation and evolution. Here we measure the 3-dimensional motion of the
microquasar GRS 1915+105, using a decade of astrometry with the NRAO Very Long
Baseline Array, together with the published radial velocity. The velocity in
the Galactic Plane deviates from circular rotation by 53-80 +_ 8 km/s, where
the range covers any specific distance from 6-12 kpc. Perpendicular to the
plane, the velocity is only 10 +_ 4 km/s. The peculiar velocity is minimized at
a distance 9-10 kpc, and is then nearly in the radial direction towards the
Galactic Center. We discuss mechanisms for the origin of the peculiar velocity,
and conclude that it is most likely a consequence of Galactic velocity
diffusion on this old binary, rather than the result of a supernova kick during
the formation of the 14 Mo black hole. Finally, a brief comparison is made with
4 other BH binaries whose kinematics are well determined.Comment: 16 pages, 4 figures. ApJ accepte
An attempt to identify the extended synchrotron structure associated with the micro-quasar GRS 1915+105
The energy ejected from the galaxy micro-quasar GRS1915+105 in the form of
jets is expected to lead to formation of an extended double lobe/hot-spot
structure with the energy content comparable to an average supernova remnant.
We used the Effelsberg 100m telescope at 10.45 GHz in attempt to identify such
structures. For this distant galactic plane source any definite identification
was not possible due to high confusion by numerous background sources, however,
a few suspect structures were pointed out.Comment: LaTeX uses a new 2001 A&A macro, 4 pages, 2 figures, A&A accepte
Funding Universal Service Obligations with an Essential Facility: Charges vs. Taxes and Subsidies
This paper compares three schemes for funding Universal Service Obligations in network industries with an essential facility: an uplift to the network access charge, the establishment of a Universal Service (US) fund financed through a lump-sum tax and a US fund financed through a unit tax. The comparison is made under a duopoly structure with a potential entrant and an incumbent, which owns the essential facility and is responsible for universal service. The incumbent is also constrained to offer the same price on all markets. Using a social welfare criteria, we show that the US fund financed with a lump sum tax dominates the other two schemes, while the US fund with unit tax is equivalent to the access charge uplift.UNIVERSAL SERVICE OBLIGATIONS; ACCESS CHARGES; REGULATION
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