25 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
High-energy gamma-ray emission from the inner jet of LS I+61 303: the hadronic contribution revisited
LS I+61 303 has been detected by the Cherenkov telescope MAGIC at very high
energies, presenting a variable flux along the orbital motion with a maximum
clearly separated from the periastron passage. In the light of the new
observational constraints, we revisit the discussion of the production of
high-energy gamma rays from particle interactions in the inner jet of this
system. The hadronic contribution could represent a major fraction of the TeV
emission detected from this source. The spectral energy distribution resulting
from p-p interactions is recalculated. Opacity effects introduced by the photon
fields of the primary star and the stellar decretion disk are shown to be
essential in shaping the high-energy gamma-ray light curve at energies close to
200 GeV. We also present results of Monte Carlo simulations of the
electromagnetic cascades developed very close to the periastron passage. We
conclude that a hadronic microquasar model for the gamma-ray emission in LS I
+61 303 can reproduce the main features of its observed high-energy gamma-ray
flux.Comment: 6 pages. Sligth improvements made. Accepted version by Astrophysics
and Space Scienc
Results from MAGIC's first observation cycle on galactic sources
During its Cycle I, the MAGIC telescope targeted about 250 hours several
galactic sources sought to be, or detected previously by other experiments in
the same energy domain, gamma-ray emitters. This paper reviews some results of
such MAGIC observations covering, among others, supernova remnants, the
Galactic Center and microquasars. We will concentrate on the recent discovery
at very high energy gamma-rays of the microquasar LS I +61 303.Comment: 6 pages, 8 figures. Prepared for "The Multi-messenger Approach to
High-energy Gamma-ray Sources", Barcelona (Spain) 4-7 July 200
A supernova constraint on bulk majorons
In models with large extra dimensions all gauge singlet fields can in
principle propagate in the extra dimensional space. We have investigated
possible constraints on majoron models of neutrino masses in which the majorons
propagate in extra dimensions. It is found that astrophysical constraints from
supernovae are many orders of magnitude stronger than previous accelerator
bounds. Our findings suggest that unnatural types of the "see-saw" mechanism
for neutrino masses are unlikely to occur in nature, even in the presence of
extra dimensions.Comment: Minor changes, matches the version to appear in PR
Theoretical overview on high-energy emission in microquasars
Microquasar (MQ) jets are sites of particle acceleration and synchrotron
emission. Such synchrotron radiation has been detected coming from jet regions
of different spatial scales, which for the instruments at work nowadays appear
as compact radio cores, slightly resolved radio jets, or (very) extended
structures. Because of the presence of relativistic particles and dense photon,
magnetic and matter fields, these outflows are also the best candidates to
generate the very high-energy (VHE) gamma-rays detected coming from two of
these objects, LS 5039 and LS I +61 303, and may be contributing significantly
to the X-rays emitted from the MQ core. In addition, beside electromagnetic
radiation, jets at different scales are producing some amount of leptonic and
hadronic cosmic rays (CR), and evidences of neutrino production in these
objects may be eventually found. In this work, we review on the different
physical processes that may be at work in or related to MQ jets. The jet
regions capable to produce significant amounts of emission at different
wavelengths have been reduced to the jet base, the jet at scales of the order
of the size of the system orbital semi-major axis, the jet middle scales (the
resolved radio jets), and the jet termination point. The surroundings of the
jet could be sites of multiwavelegnth emission as well, deserving also an
insight. We focus on those scenarios, either hadronic or leptonic, in which it
seems more plausible to generate both photons from radio to VHE and high-energy
neutrinos. We briefly comment as well on the relevance of MQ as possible
contributors to the galactic CR in the GeV-PeV range.Comment: Astrophysics & Space Science, in press (invited talk in the
conference: The multimessenger approach to the high-energy gamma-ray
sources", Barcelona/Catalonia, in July 4-7); 10 pages, 6 figures, 2 tables
(one reference corrected
Unidentified gamma-ray sources off the Galactic plane as low-mass microquasars?
A subset of the unidentified EGRET gamma-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 deg) and small (~1 deg) 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.Comment: 11 pages, 5 figures. Contributed paper to the "Multiwavelength
Approach to Unidentified Gamma-Ray Sources", Eds. K.S. Cheng & G.E. Romero,
to appear in Astrophysics and Space Science journa
Gamma-Ray Pulsars
Gamma-ray photons from young pulsars allow the deepest insight into the
properties and interactions of high-energy particles with magnetic and photon
fields in a pulsar magnetosphere. Measurements with the Compton Gamma-Ray
Observatory have led to the detection of nearly ten gamma-ray pulsars. Although
quite a variety of individual signatures is found for these pulsars, some
general characteristics can be summarized: (1) the gamma-ray lightcurves of
most high-energy pulsars show two major peaks with the pulsed emission covering
more than 50% of the rotation, i.e. a wide beam of emission; (2) the gamma-ray
spectra of pulsars are hard (power law index less than 2), often with a
luminosity maximum around 1 GeV. A spectral cutoff above several GeV is found;
(3) the spectra vary with rotational phase indicating different sites of
emission; and (4) the gamma-luminosity scales with the particle flux from the
open regions of the magnetosphere (Goldreich-Julian current).Comment: 9 pages, 9 figures, 2 tables. To appear in the Proceedings of the
270. WE-Heraeus Seminar on Neutron Stars, Pulsars and Supernova Remnants,
Jan. 21-25, 2002, Physikzentrum Bad Honnef, eds W. Becker, H. Lesch & J.
Truemper. Proceedings are available as MPE-Report 27