Poster Talk abstract details
Magnetic reconnection in accretion disk systems: from Black Holes to Neutron Stars and YSOs
Abstract
We here investigate the role of violent accretion and magnetic reconnection in different jet/disk accretion astrophysical systems, namely young stellar objects (YSO's), microquasars, neutron stars, and active galactic nuclei (AGN's).
In the case of microquasars and AGN's, we find that violent reconnection episodes between the magnetic field lines of the inner disk region (which are established by a turbulent dynamo) and those that are anchored into the black hole are able to heat the coronal/disk gas and accelerate particles to relativistic velocities through a diffusive first-order Fermi-like process within the reconnection site that will produce relativistic blobs or plasmons. The heating of the coronal/disk gas is able to produce an X-ray spectrum with a luminosity that is consistent with the observations and we argue that the soft component is being produced mainly at the foot of the reconnection zone and the hard component by inverse Compton in the corona, while a Fermi-like acceleration process within the reconnection site results a power-law electron distribution $N(E) \propto E^{-\alpha_E}$, with $\alpha_E = 2.5$, and a corresponding synchrotron radio power-law spectrum with a spectral index that is compatible with that observed during the radio flares in microquasars ($ S_{\nu} \propto \nu^{-0.75}$). The scaling laws that we derive for AGN's indicate that the same mechanism is likely to be also operating in these sources.
In the case of the YSO's, a similar magnetic configuration can be reached. The amount of magnetic energy that can be extracted from the inner disk region can heat the coronal gas to temperatures of the order of $10^8$ K and could explain the observed X-ray flaring emission in some sources.
Preliminary results of MHD numerical simulations of these reconnection sites and the resulting particle heating and acceleration will be also presented.
Finally, young neutron stars, right after the supernovae explosion that originated them, can also retain a fallback accretion disk. We argue that supergiant flares in SGRs can be associated to the core combustion of a neutron star having a magnetic field $\sim 10^{12}$ G and a fallback disk around it. We show that, in a timescale of $\sim 10^5$ yrs, accretion from the fallback disk can increase the mass of the central object up to the critical mass for the conversion of the core of the star into quark matter. A small fraction of the neutrino-antineutrino emission from the hot just-converted quark-matter core annihilates into electron-positron pairs above the neutron star surface originating a supergiant gamma flare emission (with a light curve similar to that observed, in the SGR 1806-20). We also argue that the same mechanism could explain the short Gamma-Ray-Bursts produced in nearby galaxies.
In the case of microquasars and AGN's, we find that violent reconnection episodes between the magnetic field lines of the inner disk region (which are established by a turbulent dynamo) and those that are anchored into the black hole are able to heat the coronal/disk gas and accelerate particles to relativistic velocities through a diffusive first-order Fermi-like process within the reconnection site that will produce relativistic blobs or plasmons. The heating of the coronal/disk gas is able to produce an X-ray spectrum with a luminosity that is consistent with the observations and we argue that the soft component is being produced mainly at the foot of the reconnection zone and the hard component by inverse Compton in the corona, while a Fermi-like acceleration process within the reconnection site results a power-law electron distribution $N(E) \propto E^{-\alpha_E}$, with $\alpha_E = 2.5$, and a corresponding synchrotron radio power-law spectrum with a spectral index that is compatible with that observed during the radio flares in microquasars ($ S_{\nu} \propto \nu^{-0.75}$). The scaling laws that we derive for AGN's indicate that the same mechanism is likely to be also operating in these sources.
In the case of the YSO's, a similar magnetic configuration can be reached. The amount of magnetic energy that can be extracted from the inner disk region can heat the coronal gas to temperatures of the order of $10^8$ K and could explain the observed X-ray flaring emission in some sources.
Preliminary results of MHD numerical simulations of these reconnection sites and the resulting particle heating and acceleration will be also presented.
Finally, young neutron stars, right after the supernovae explosion that originated them, can also retain a fallback accretion disk. We argue that supergiant flares in SGRs can be associated to the core combustion of a neutron star having a magnetic field $\sim 10^{12}$ G and a fallback disk around it. We show that, in a timescale of $\sim 10^5$ yrs, accretion from the fallback disk can increase the mass of the central object up to the critical mass for the conversion of the core of the star into quark matter. A small fraction of the neutrino-antineutrino emission from the hot just-converted quark-matter core annihilates into electron-positron pairs above the neutron star surface originating a supergiant gamma flare emission (with a light curve similar to that observed, in the SGR 1806-20). We also argue that the same mechanism could explain the short Gamma-Ray-Bursts produced in nearby galaxies.