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

Exploring the powering source of the TeV X-ray binary LS 5039

LS 5039 is one of the four TeV emitting X-ray binaries detected up to now. The powering source of its multi-wavelength emission can be accretion in a microquasar scenario or wind interaction in a young non-accreting pulsar scenario. These two scenarios predict different morphologic and peak position changes along the orbital cycle of 3.9 days, which can be tested at milliarcsecond scales using VLBI techniques. Here we present a campaign of 5 GHz VLBA observations conducted in June 2000 (2 runs five days apart). The results show a core component with a constant flux density, and a fast change in the morphology and the position angle of the elongated extended emission, but maintaining a stable flux density. These results are difficult to fit comfortably within a microquasar scenario, whereas they appear to be compatible with the predicted behavior for a non-accreting pulsar.Comment: 6 pages, 1 figure. Needs PoS.cls. Contributed talk at The 9th European VLBI Network Symposium on The role of VLBI in the Golden Age for Radio Astronomy and EVN Users Meeting, September 23-26, 2008, Bologna, Ital

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

A possible black hole in the gamma-ray microquasar LS 5039

The population of high energy and very high energy gamma-ray sources, detected with EGRET and the new generation of ground-based Cherenkov telescopes, conforms a reduced but physically important sample. Most of these sources are extragalactic (e.g., blazars), while among the galactic ones there are pulsars and SN remnants. The microquasar LS 5039, previously proposed to be associated with an EGRET source by Paredes et al. (2000), has recently been detected at TeV energies, confirming that microquasars should be regarded as a class of high energy gamma-ray sources. To model and understand how the energetic photons are produced and escape from LS 5039 it is crucial to unveil the nature of the compact object, which remains unknown. Here we present new intermediate-dispersion spectroscopy of this source which, combined with values reported in the literature, provides an orbital period of 3.90603+/-0.00017 d, a mass function f(M)=0.0053+/-0.0009 M_sun, and an eccentricity e=0.35+/-0.04. Atmosphere model fitting to the spectrum of the optical companion, together with our new distance estimate of d=2.5+/-0.1 kpc, yields R_opt=9.3+0.7-0.6 R_sun, log (L_opt/L_sun)=5.26+/-0.06, and M_opt=22.9+3.4-2.9 M_sun. These, combined with our dynamical solution and the assumption of pseudo-synchronization, yield an inclination i=24.9+/-2.8 degree and a compact object mass M_X=3.7+1.3-1.0 M_sun. This is above neutron star masses for most of the standard equations of state and, therefore, we propose that the compact object in LS 5039 is a black hole. We finally discuss about the implications of our orbital solution and new parameters of the binary system on the CNO products, the accretion/ejection energetic balance, the SN explosion scenario, and the behaviour of the TeV emission with the new orbital period.Comment: 10 pages, 8 figures. Accepted for publication in MNRAS. Minor changes according to referee repor

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