2 research outputs found
Accretion Discs in Blazars
The characteristic properties of blazars (rapid variability, strong
polarization, high brightness) are widely attributed to a powerful relativistic
jet oriented close to our line of sight. Despite the spectral energy
distributions (SEDs) being strongly jet-dominated, a "big blue bump" has been
recently detected in sources known as flat spectrum radio quasars (FSRQs).
These new data provide a unique opportunity to observationally test coupled
jet-disc accretion models in these extreme sources. In particular, as energy
and angular momentum can be extracted by a jet magnetically coupled to the
accretion disc, the thermal disc emission spectrum may be modified from that
predicted by the standard model for disc accretion. We compare the
theoretically predicted jet-modified accretion disc spectra against the new
observations of the "big blue bump" in FSRQs. We find mass accretion rates that
are higher, typically by a factor of two, than predicted by standard accretion
disc theory. Furthermore, our results predict that the high redshift blazars
PKS 0836+710, PKS 2149-307, B2 0743+25 and PKS 0537-286 may be predominantly
powered by a low or moderate spin (a < 0.6) black hole with high mass accretion
rates mdot_a ~ 50 - 200 msol/yr, while 3C 273 harbours a rapidly spinning black
hole (a = 0.97) with mdot_a ~ 20 msol/yr. We also find that the black hole
masses in these high redshift sources must be > 5 * 10^9 msol.Comment: Accepted for publication (17 August 2009) in MNRA
Probing the behaviour of the X-ray binary Cygnus X-3 with very-long-baseline radio interferometry
In order to test the recently proposed classification of the radio/X-ray
states of the X-ray binary Cyg X-3, we present an analysis of the radio data
available for the system at much higher spatial resolutions than used for
defining the states. The radio data set consists of archival VLBA data at 5 or
15 GHz and new e-EVN data at 5 GHz. We also present 5 GHz MERLIN observations
of an outburst of Cyg X-3. In the X-ray regime we use quasi-simultaneous with
radio, monitoring and pointed RXTE observations. We find that when the radio
emission from both jet and core is globally considered, the behaviour of Cyg
X-3 at milliarcsecond scales is consistent with that described at arcsecond
scales. However, when the radio emission is disentangled in a core component
and a jet component the situation changes. It becomes clear that in active
states the radio emission from the jet is dominating that from the core. This
shows that in these states the overall radio flux cannot be used as a direct
tracer of the accretion state.Comment: Accepted for publication in MNRA