641 research outputs found
Detection of radio emission at mas scales from HESS J0632+057 with the e-EVN
HESS J0632+057 is a variable TeV gamma-ray source. The likely low energy counterparts of the source are XMMU J063259.3+054801, the B0pe-type star MWC 148, and a point-like probable non-thermal radio source
Orbital X-Ray Variability of the Microquasar LS 5039
The properties of the orbit and the donor star in the high mass X-ray binary
microquasar LS 5039 indicate that accretion processes should mainly occur via a
radiatively driven wind. In such a scenario, significant X-ray variability
would be expected due to the eccentricity of the orbit. The source has been
observed at X-rays by several missions, although with a poor coverage that
prevents to reach any conclusion about orbital variability. Therefore, we
conducted RossiXTE observations of the microquasar system LS 5039 covering a
full orbital period of 4 days. Individual observations are well fitted with an
absorbed power-law plus a Gaussian at 6.7 keV, to account for iron line
emission that is probably a diffuse background feature. In addition, we have
taken into account that the continuum is also affected by significant diffuse
background contamination. Our results show moderate power-law flux variations
on timescales of days, as well as the presence of miniflares on shorter
timescales. The new orbital ephemeris of the system recently obtained by
Casares et al. have allowed us to show, for the first time, that an increase of
emission is seen close to the periastron passage, as expected in an accretion
scenario. Moreover, the detected orbital variability is a factor of ~4 smaller
than the one expected by using a simple wind accretion model, and we suggest
that an accretion disk around the compact object could be responsible for this
discrepancy. On the other hand, significant changes in the photon index are
also observed clearly anti-correlated with the flux variations. We interpret
the overall X-ray spectral characteristics of LS 5039 in the context of X-ray
radiation produced by inverse Compton and/or synchrotron processes in the jet
of this microquasar.Comment: published in Astrophysical Journal, submission format (real number of
pages: 7, 4 figures
The gamma-ray emitting microquasar LSI+61303
LS I +61 303 is one of the most studied X-ray binary systems because of its
two peculiarities: On the one hand being the probable counterpart of the
variable gamma ray source 2CG 135+01 (Gregory and Taylor 1978; Tavani et al.
1998) and on the other hand being a periodic radio source (Taylor and Gregory
1982). The recent discovery of a radio emitting jet extending ca. 200 AU at
both sides of a central core (Massi et al. 2004) in all evidence has shown the
occurrence of accretion/ejection processes in this system. However, the radio
outbursts do not occur at periastron passage, where the accretion is at its
maximum, but several days later. In addition, when the gamma-ray emission of
2CG 135+01 is examined along the orbital phase of LS I +61 303 one sees that
this emission seems to peak at periastron passage (Massi 2004). Here in detail
we analyse the trend of the gamma-ray data versus orbital phase and discuss the
delay between peaks at gamma-rays and in the radio band within the framework of
a two-peak accretion/ejection model proposed by Taylor et al. (1992) and
further developed by Marti' and Paredes (1995).Comment: To be published in the proceedings of the Symposium on High-Energy
Gamma-Ray Astronomy, Heidelberg, July 26-30, 2004 (AIP Proceedings Series
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