What are X ray binaries</head> <body bgcolor="blue" text="white" link="yellow" alink="ff0ff" vlink="ff0000"> <center> <h1><font size=5><b>Spectral modelling of Microquasar jets</h1></b></center> <p><font size=3> A tight temporal correlation between the low hard X-ray state and the radio emission has been found and there is increasing evidence that relativistic jets may be a generic feature of the low hard state of microquasars. The observable spectral extent of microquasars can be very broad, for e.g, the classical black hole candidate, Cyg X1, has been detected from ≤1 GHz in the radio to ≥1 MeV in γ rays, covering a range of 10<sup>12</sup> in photon energy. Understanding the mechanism for production of such a huge range of energy and interpretation of the observed radio phenomenon calls for careful and detailed modelling of the expanding sources entrained in these relativistic jets.</p> <p> The seminal paper of van der Laan (1966) presents the standard model of a source expanding spherically at a constant rate with an initial number of electrons that cool adiabatically. Since then, till the present date, many authors have modified and improved upon this basic model to account for the observed radiation signatures of these sources. Some such modifications are the inclusion of: synchrotron and bremsstrahlung losses over and above the adiabatic losses (Aller and Dent, 1972), continuous electron injection into the jet (Peterson and Dent, 1976), X ray production by synchrotron-self-Compton and inverse Compton scattering (Band and Grindlay, 1986), an arbitrary time-dependent injection rate of electrons into the jet to study the electron energy evolution in a magnetized medium (Atoyan and Aharonian, 1999), external Compton scattering of photons from the companion star and/or the accetion disk by relativistic electrons in the jet, leading to significant contribution to the X-ray flux (Georganopoulos, Aharonian and Kirk, 2002). </p> <p> <h1><font size=5><b><center>Ultraluminous X-ray sources - A motivation toward Microblazar modelling </h1></b></center> <font size=3> One of the most interesting problems in extragalactic X-ray Astrophysics is the existence of Ultraluminous X-ray sources (ULXs). These sources are variable on timescales of days to months, but their luminosities are typically much higher than those observed in Galactic and Magellanic Cloud XRBs, with <i>L<sub>X</sub></i>≥10<sup>39</sup> erg s<sup>-1</sup> . These sources are displaced from the centers of their host galaxies, and if they radiate isotropically, indicate a black hole mass <i>M</i>≥ 50-100 solar masses. Severe problems are found when trying to understand the formation mechanism of such black holes, leading to the thought that perhaps ULXs can be explained as normal XRBs in which the X-ray emission is beamed towards the observer, requiring thus much lower luminosities (King et al. 2001). Such an idea of beaming led Georganopoulos (2002) to suggest microblazars as a viable model for ULXs, whereby the peak Compton luminosity appears amplified due to Doppler boosting by a factor of <i>D</i><sup>5</sup> for a continuous jet, where <i>D</i>=1/Γ(1-β cosθ), with θ being the observing angle. <p> Contradictory evidence including indications of predominantly thermal spectra of ULXs , discovery of X ray ionized nebula arguing against the hypothesis of ULXs being strongly beamed X ray emitters, and a very recent suggestion of ULXs harboring intermediate mass black holes <i>M<sub>BH</sub></i>∼ 10<sup>2-5</sup>solar masses by Miller et. al (astro-ph/0406656), call for a re-examination of the existing microblazar models, and alternative models of quasi - isotropic or at most weakly beamed emission may prove interesting in this respect. </p> <p> The huge wealth of data coming from the new generation <i>Chandra</i> and <i>XMM-Newton</i> X-ray telescopes motivates us toward a comprehensive study of the time dependent broadband (radio through X-ray or even γ-ray) radiation signatures of microblazars, including various plausible electron injection and acceleration scenarios along mildly relativistic jets in various configurations with different radiation / cooling mechanisms dominating the electron evolution along the jet. Such a study may prompt a search for serendipitous detections of microblazars in the past observations of these telescopes, and help us in investigating the connection between microblazars and ULXs. </p> </p> Back to my <a href="http://www.phy.ohiou.edu/~gupta">homepage</a>. <br> Back to <a href="http://www.phy.ohiou.edu/~astro"><i>API</i> at O.U</a>. </body></html>