1,292 research outputs found
Non-thermal radiation from Cygnus X-1 corona
Cygnus X-1 was the first X-ray source widely accepted to be a black hole
candidate and remains among the most studied astronomical objects in its class.
The detection of non-thermal radio, hard X-rays and gamma rays reveals the fact
that this kind of objects are capable of accelerating particles up to very high
energies.
In order to explain the electromagnetic emission from Cygnus X-1 in the
low-hard state we present a model of a black hole corona with both relativistic
lepton and hadron content. We characterize the corona as a two-temperature hot
plasma plus a mixed non-thermal population in which energetic particles
interact with magnetic, photon and matter fields. Our calculations include the
radiation emitted by secondary particles (pions, muons and electron/positron
pairs). Finally, we take into account the effects of photon absorption. We
compare the results obtained from our model with data of Cygnus X-1 obtained by
the COMPTEL instrument.Comment: 6 pages, 10 figures, presented as a poster in HEPRO II, Buenos Aires,
Argentina, October 26-30 2009 / accepted for publication in Int. Jour. Mod.
Phys.
The X-ray properties of Be/X-ray pulsars in quiescence
Observations of accreting neutron stars (NS) with strong magnetic fields can
be used not only for studying the accretion flow interaction with NS
magnetospheres, but also for understanding the physical processes inside NSs
and for estimating their fundamental parameters. Of particular interest are (i)
the interaction of a rotating neutron star (magnetosphere) with the in-falling
matter at different accretion rates, and (ii) the theory of deep crustal
heating and the influence of a strong magnetic field on this process. Here, we
present results of the first systematic investigation of 16 X-ray pulsars with
Be optical companions during their quiescent states, based on data from the
Chandra, XMM-Newton and Swift observatories. The whole sample of sources can be
roughly divided into two distinct groups: i) relatively bright objects with a
luminosity around ~10^34 erg/s and (hard) power-law spectra, and ii) fainter
ones showing thermal spectra. X-ray pulsations were detected from five objects
in group i) with quite a large pulse fraction of 50-70 per cent. The obtained
results are discussed within the framework of the models describing the
interaction of the in-falling matter with the neutron star magnetic field and
those describing heating and cooling in accreting NSs.Comment: 18 pages, 4 figures, 3 tables, accepted by MNRA
A Complexity-Brightness Correlation in Gamma Ray Bursts
We observe strong correlations between the temporal properties of gamma ray
bursts (GRBs) and their apparent peak brightness. The strongest effect (with a
significance level of 10^{-6}) is the difference between the brightness
distributions of simple bursts (dominated by a single smooth pulse) and complex
bursts (consisting of overlapping pulses). The latter has a break at a peak
flux of 1.5 ph/cm^2/s, while the distribution of simple bursts is smooth down
to the BATSE threshold. We also observe brightness dependent variations in the
shape of the average peak aligned time profile (ATP) of GRBs. The decaying
slope of the ATP shows time dilation when comparing bright and dim bursts while
the rising slope hardly changes. Both slopes of the ATP are deformed for weak
bursts as compared to strong bursts. The interpretation of these effects is
simple: a complex burst where a number of independent pulses overlap in time
appears intrinsically stronger than a simple burst. Then the BATSE sample of
complex bursts covers larger redshifts where some cosmological factor causes
the break in the peak brightness distribution. This break could correspond to
the peak in the star formation rate that was recently shown to occur at a
redshift of z~1.5.Comment: 13 pages; 11 figures; replaced with the published versio
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