6,046 research outputs found
Electromagnetic radiation initiated by hadronic jets from microquasars in the ISM
Microquasars are potential candidates to produce a non-negligible fraction of
the observed galactic cosmic rays. The protons accelerated at the jet
termination shock interact with the interstellar medium and may produce
detectable fluxes of extended emission at different energy bands: high-energy
and very high-energy gamma-rays produced by neutral pion-decay, synchrotron and
bremsstrahlung emission in a wide energy range generated by the secondary
electrons produced by charged pion-decay. We discuss the association between
this scenario and some of the unidentified EGRET sources in the galactic plane.Comment: (1)Universitat de Barcelona (2)Max Planck institute fur kernphysik,
11 pages, 14 figures, accepted for publication in Astronomy & Astrophysic
Broad-band electromagnetic radiation from microquasars interacting with ISM
Microquasars (MQs) are galactic objects with relativistic jets that
constitute a source population which can be responsible for production of a
non-negligible fraction of the observed galactic cosmic rays. These
relativistic protons, associated with the termination of the jet, interact with
the interstellar medium and, at certain surrounding conditions, may lead to
production of detectable fluxes of high-energy and very high-energy gamma-rays.
This radiation is accompanied by the broad-band emission of secondary electrons
from decays of -mesons produced through synchrotron, bremstrahlung and
inverse Compton process. The features of broad-band emission initiated by
proton-proton (pp) interactions in such a scenario is discussed in the context
of the strategy of search for counterparts of high-energy and very high-energy
gamma-ray sources in the galactic plane.Comment: High Energy Gamma-Ray Astronomy: 2nd International Symposium,
Proceedings of the conference held 26-30 July 2004 in Heidelberg (Germany).
Edited by Felix A. Aharonian, Heinz J. Volk, and Dieter Horns. AIP Conference
Proceedings, Volume 745. New York: American Institute of Physics, 2005.,
p.317-32
Leptonic emission from microquasar jets: from radio to very high-energy gamma-rays
Microquasars are sources of very high-energy gamma-rays and, very probably,
high-energy gamma-ray emitters. We propose a model for a jet that can allow to
give accurate observational predictions for jet emission at different energies
and provide with physical information of the object using multiwavelength data.Comment: 2 pages, 1 figure. Proceedings of the conference: "International
Astronomical Union Symposium No. 230: Populations of High Energy Sources in
Galaxies". Edited by Evert J.A. Meurs & Giuseppina Fabbian
Observations of microquasars with the MAGIC telescope
We report on the results from the observations in very high energy band (VHE,
E_gamma > 100GeV) of the black hole X-ray binary (BHXB) Cygnus X-1. The
observations were performed with the MAGIC telescope, for a total of 40 hours
during 26 nights, spanning the period between June and November 2006. We report
on the results of the searches for steady and variable gamma-ray signals,
including the first experimental evidence for an intense flare, of duration
between 1.5 and 24 hours.Comment: Contribution to the 30th ICRC, Merida Mexico, July 2007 on behalf of
the MAGIC Collaboratio
The discovery of a highly polarized bipolar nebula
During a search for the optical counterparts of IRAS sources whose flux peaks at 25 microns, a small faint bipolar nebula was discovered in Monoceros at the position of IRAS 07131-0147. The CCD images display the object's considerable structure. The central star seems relatively free of closeby nebulosity: the two lobes have a bow-tie structure with those parts nearest to the star consisting of series of small knots. The outer parts of the lobes seem to be made up of filaments streaming away from knots. On the basis of its optical spectrum, the central star was classified as a M5-6 giant. In the IRAS color classification scheme of Van der Veen and Habing (1988), the central star is VIb which indicates that there are distinct hot and cold components of circumstellar dust and that the mass loss process may have temporarily abated. Therefore, it is proposed that the object is in the post main sequence stage of evolution and is a protoplanetary nebulae. Young protoplanetary nebulae have totally obscured central stars illuminating reflective lobes whereas older ones such as M2-9 have lobes seen in emission from gas ionized by the central hot star which is clearly visible. Since the central object of IRAS07131-0147 is a relatively unobscured late type star and the lobes are seen only by reflection, it is suggested that this nebula is a protoplanetary nebula in an evolutionary stage intermediate between that of CRL2688 and M2-9
Leptonic secondary emission in a hadronic microquasar model
Context: It has been proposed that the origin of the very high-energy photons
emitted from high-mass X-ray binaries with jet-like features, so-called
microquasars (MQs), is related to hadronic interactions between relativistic
protons in the jet and cold protons of the stellar wind. Leptonic secondary
emission should be calculated in a complete hadronic model that include the
effects of pairs from charged pion decays inside the jets and the emission from
pairs generated by gamma-ray absorption in the photosphere of the system. Aims:
We aim at predicting the broadband spectrum from a general hadronic microquasar
model, taking into account the emission from secondaries created by charged
pion decay inside the jet. Methods: The particle energy distribution for
secondary leptons injected along the jets is consistently derived taking the
energy losses into account. We also compute the spectral energy distribution
resulting from these leptons is calculated after assuming different values of
the magnetic field inside the jets. The spectrum of the gamma-rays produced by
neutral pion-decay and processed by electromagnetic cascades under the stellar
photon field. Results: We show that the secondary emission can dominate the
spectral energy distribution at low energies (~1 MeV). At high energies, the
production spectrum can be significantly distorted by the effect of
electromagnetic cascades. These effects are phase-dependent, and some
variability modulated by the orbital period is predicted.Comment: 8 pages, 5 figures. Accepted for publication in Astronomy &
Astrophysic
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