421 research outputs found
A rotating hollow cone anisotropy of TeV emission from binary systems
We show that TeV gamma-ray emission produced via interactions of high-energy
particles with anisotropic radiation field of a massive star in binary systems
should have a characteristic rotating hollow cone anisotropy pattern. The
hollow cone, whose axis is directed away from the massive star, rotates with
the period equal to the orbital period of the system. We note that the two
maxima pattern of the TeV energy band lightcurve of the gamma-ray loud binary
LS 5039 can be interpreted in terms of this rotating hollow cone model.
Adopting such an interpretation, we are able to constrain the geometry of the
system - either the inclination angle of the binary orbit, or the elevation of
the gamma-ray emission region above the orbital plane.Comment: Ap.J.Lett., accepte
The Black Hole Candidate LSI+61303
In recent years, fundamental relationships for the black hole X-ray binaries
have been established between their X-ray luminosity and the photon index
of their X-ray spectrum. For the moderate-luminosity regime, an
anti-correlation between and has been observed. In this article,
aimed to verify if the moderate luminous X-ray binary system LSI +61303 is a
black hole, we analyse observations of LSI +61303. We compare the
derived vs distribution, first with the statistical trend for
black hole X-ray binaries, then with the trend of the pulsar PSR B1259-63, and
finally with the individual trends of the black hole X-ray binaries Swift
J1357.2-0933 and V404 Cygni. We find that the system PSR B1259-63 shows a
positive correlation between and , whereas in contrast LSI +61303
shows the same anti-correlation as for black hole X-ray binaries. Moreover, the
trend of LSI +61303 in the / plane overlaps with
that of the two black holes Swift J1357.2-0933 and V404 Cygni. All three
systems, Swift J1357.2-0933, V404 Cygni and LSI +61303 well trace the last part
of the evolution of accreting black holes at moderate-luminosity until their
drop to quiescence.Comment: 5 pages, 4 figures, MNRAS accepte
Discovery and study of the accreting pulsar 2RXP J130159.6-635806
We report on analysis of the poorly studied source 2RXP J130159.6-635806 at
different epochs with ASCA, Beppo-SAX, XMM-Newton, and INTEGRAL. The source
shows coherent X-ray pulsations at a period ~700s with an average spin up rate
of about dnu/dt ~ 2x10^{-13} Hz/s. A broad band (1-60 keV) spectral analysis of
2RXP J130159.6-635806 based on almost simultaneous XMM-Newton and INTEGRAL data
demonstrates that the source has a spectrum typical of an accretion powered
X-ray pulsar, i.e. an absorbed power law with a high energy cut-off with a
photon index Gamma ~ 0.5-1.0 and a cut-off energy of ~25 keV. The long term
behaviour of the source, its spectral and timing properties, tend to indicate a
high mass X-ray binary with Be companion. We also report on the identification
of the likely infrared counterpart to 2RXP J130159.6-635806. The interstellar
reddening does not allow us to strongly constrain the spectral type of the
counterpart. The latter is, however, consistent with a Be star, the kind of
which is often observed in accretion powered X-ray pulsars.Comment: 8 pages, 9 figures, accepted for publication in MNRAS; caption for
Figure 1 is correcte
Leptonic origin of the 100 MeV gamma-ray emission from the Galactic Centre
The Galactic centre is a bright gamma-ray source with the GeV-TeV band
spectrum composed of two distinct components in the 1-10 GeV and 1-10 TeV
energy ranges. The nature of these two components is not clearly understood. We
investigate the gamma-ray properties of the Galactic centre to clarify the
origin of the observed emission. We report imaging, spectral, and timing
analysis of data from 74 months of observations of the Galactic centre by
FERMI/LAT gamma-ray telescope complemented by sub-MeV data from approximately
ten years of INTEGRAL/PICsIT observations. We find that the Galactic centre is
spatially consistent with the point source in the GeV band. The tightest 3
sigma upper limit on its radius is 0.13 degree in the 10-300 GeV energy band.
The spectrum of the source in the 100 MeV energy range does not have a
characteristic turnover that would point to the pion decay origin of the
signal. Instead, the source spectrum is consistent with a model of inverse
Compton scattering by high-energy electrons. In this a model, the GeV bump in
the spectrum originates from an episode of injection of high-energy particles,
which happened ~300 years ago. This injection episode coincides with the known
activity episode of the Galactic centre region, previously identified using
X-ray observations. The hadronic model of source activity could be still
compatible with the data if bremsstrahlung emission from high-energy electrons
was present in addition to pion decay emission.Comment: To match the accepted versio
Hadronic model for radio-to-TeV gamma-ray emission from PSR B1259-63
We discuss the implications of the recent X-ray and TeV gamma-ray
observations of the PSR B1259-63 system (a young rotation powered pulsar
orbiting a Be star) for the theoretical models of interaction of pulsar and
stellar winds. We show that previously considered models in which the pulsar
wind is purely electron loaded have problems to account for the observed
behaviour of the system in the TeV and X-ray bands. We develop a model in which
the broad band (radio, X-ray and high energy gamma-ray) emission from the
binary system is produced in result of collisions of GeV-TeV energy protons
accelerated by the pulsar wind and interacting with the stellar disk. In this
model the high energy gamma-rays are produced in the decays of secondary
neutral pions, while radio and X-ray emission are synchrotron and inverse
Compton emission produced by low-energy (< 100 MeV) electrons from the decays
of secondary charged pi mesons. This model can explain not only the observed
energy spectra, but also the correlations between TeV, X-ray and radio emission
components.Comment: Proceeding of "The multi messenger approach to high energy gamma ray
sources", Barcelona, June 200
XMM-Newton observations of PSr B1259-63 near the 2004 periastron passage
PSR B1259-63 is in a highly eccentric 3.4 year orbit with a Be star and
crosses the Be star disc twice per orbit, just prior to and just after
periastron. Unpulsed radio, X-ray and gamma-ray emission observed from the
binary system is thought to be due to the collision of pulsar wind with the
wind of Be star. We present here the results of new XMM-Newton observations of
the PSR B1259-63 system during the beginning of 2004 as the pulsar approached
the disc of Be star.We combine these results with earlier unpublished X-ray
data from BeppoSAX and XMM-Newton as well as with ASCA data. The detailed X-ray
lightcurve of the system shows that the pulsar passes (twice per orbit) through
a well-defined gaussian-profile disk with the half-opening angle (projected on
the pulsar orbit plane) ~18.5 deg. The intersection of the disk middle plane
with the pulsar orbital plane is inclined at ~70 deg to the major axis of the
pulsar orbit. Comparing the X-ray lightcurve to the TeV lightcurve of the
system we find that the increase of the TeV flux some 10--100 days after the
periastron passage is unambiguously related to the disk passage. At the moment
of entrance to the disk the X-ray photon index hardens from 1.8 up to 1.2
before returning to the steeper value 1.5. Such behaviour is not easily
accounted for by the model in which the X-ray emission is synchrotron emission
from the shocked pulsar wind. We argue that the observed hardening of the X-ray
spectrum is due to the inverse Compton or bremsstrahlung emission from 10-100
MeV electrons responsible for the radio synchrotron emission.Comment: 9 pages, accepted to MNRA
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