Date:
Tue, 01/12/200912:30-13:30
Location:
Kaplun Bldg, seminar room, 2nd floor
A Model for Emission from Microquasar Jets: Consequences of a Single Acceleration Episode
There are strong evidence for powerful jets in the low/hard state of black-hole candidates X-ray binaries (BHXRBs). I present a model in which electrons are accelerated once at the base of the jet, and are cooled by synchrotron emission and possible adiabatic energy losses. The accelerated electrons assume a Maxwellian distribution at low energies and possible energetic power law tail. These characteristic energies, combined with the decay of the magnetic field along the jet,
introduce a wealth of spectra. I will identify critical values of the magnetic field, and show that: (I) the decay of the magnetic field along the jet enables, for wide jets, production of flat radio spectra
without the need for electrons re-acceleration along the jet. (II) An increase of the magnetic field above a critical value of ~10^5 G leads to a sharp decrease in the flux at the radio band, while the flux at higher frequencies saturates to a constant value. (III) For strong magnetic field, the flux decays in the optical/UV band as F_
u ~
u^{-1/2}, irrespective of the electrons initial distribution. (IV) For B_0 ~ 10^4 G, the flux at the X-ray band gradually steepens. (V) With adiabatic energy losses, flat spectrum can be obtained only at a limited frequency range, and under certain conditions (VI) For narrow jets, r(x) ~ x^{\alpha} with \alpha < 1/2, flat radio spectrum cannot be obtained.
There are strong evidence for powerful jets in the low/hard state of black-hole candidates X-ray binaries (BHXRBs). I present a model in which electrons are accelerated once at the base of the jet, and are cooled by synchrotron emission and possible adiabatic energy losses. The accelerated electrons assume a Maxwellian distribution at low energies and possible energetic power law tail. These characteristic energies, combined with the decay of the magnetic field along the jet,
introduce a wealth of spectra. I will identify critical values of the magnetic field, and show that: (I) the decay of the magnetic field along the jet enables, for wide jets, production of flat radio spectra
without the need for electrons re-acceleration along the jet. (II) An increase of the magnetic field above a critical value of ~10^5 G leads to a sharp decrease in the flux at the radio band, while the flux at higher frequencies saturates to a constant value. (III) For strong magnetic field, the flux decays in the optical/UV band as F_
u ~
u^{-1/2}, irrespective of the electrons initial distribution. (IV) For B_0 ~ 10^4 G, the flux at the X-ray band gradually steepens. (V) With adiabatic energy losses, flat spectrum can be obtained only at a limited frequency range, and under certain conditions (VI) For narrow jets, r(x) ~ x^{\alpha} with \alpha < 1/2, flat radio spectrum cannot be obtained.