Concepts in Thermal Physics 2nd Edition

, 2012

Authors:

Stephen J Blundell, Katherine M Blundell

Steve Rawlings 1961-2012

ASTRONOMY & GEOPHYSICS 53:4 (2012) 45-45

The Dynamics and Stability of Circumbinary Orbits

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 418:4 (2011) 2656-2668

Authors:

Samuel Doolin, Katherine M Blundell

Abstract:

We numerically investigate the dynamics of orbits in 3D circumbinary phase-space as a function of binary eccentricity and mass fraction. We find that inclined circumbinary orbits in the elliptically-restricted three-body problem display a nodal libration mechanism in the longitude of the ascending node and in the inclination to the plane of the binary. We (i) analyse and quantify the behaviour of these orbits with reference to analytical work performed by Farago & Laskar (2010) and (ii) investigate the stability of these orbits over time. This work is the first dynamically aware analysis of the stability of circumbinary orbits across both binary mass fraction and binary eccentricity. This work also has implications for exoplanetary astronomy in the existence and determination of stable orbits around binary systems.

The non-thermal emission of extended radio galaxy lobes with curved electron spectra

ArXiv 1111.4878 (2011)

Authors:

Peter Duffy, Katherine M Blundell

Abstract:

The existing theoretical framework for the energies stored in the synchrotron-emitting lobes of radio galaxies and quasars doesn't properly account for the curved spectral shape that many of them exhibit. We characterise these spectra using parameters that are straightforwardly observable in the era of high-resolution, low-frequency radio astronomy: the spectral curvature and the turnover in the frequency spectrum. This characterisation gives the Lorentz factor at the turnover in the energy distribution (we point out that this is distinctly different from the Lorentz factor corresponding to the turnover frequency in a way that depends on the amount of curvature in the spectrum) and readily gives the equipartition magnetic field strength and the total energy of the radiating plasma obviating the need for any assumed values of the cutoff frequencies to calculate these important physical quantities. This framework readily yields the form of the X-ray emission due to inverse-Compton (IC) scattering of Cosmic Microwave Background (CMB) photons by the electrons in the plasma having Lorentz factors of $\sim$1000. We also present the contribution to CMB anisotropies due to relativistic plasmas such as giant radio galaxy lobes, expressed in terms of the extent to which the lobes have their magnetic field and particle energies are in equipartition with one another.

The inverse-Compton ghost HDF130 and the giant radio galaxy 6C0905+3955: Matching an analytic model for double-lobed radio source evolution

Monthly Notices of the Royal Astronomical Society 417:2 (2011) 1576-1583

Authors:

P Mocz, AC Fabian, KM Blundell, PT Goodall, SC Chapman, DJ Saikia

Abstract:

We present new Giant Metre-wave Radio Telescope (GMRT) observations of Hubble Deep Field (HDF)130, an inverse-Compton (IC) ghost of a giant radio source that is no longer being powered by jets. We compare the properties of HDF130 with the new and important constraint of the upper limit of the radio flux density at 240 MHz to an analytic model. We learn what values of physical parameters in the model for the dynamics and evolution of the radio luminosity and X-ray luminosity [due to IC scattering of the cosmic microwave background (CMB)] of a Fanaroff-Riley type II (FR II) source are able to describe a source with features (lobe length, axial ratio, X-ray luminosity, photon index and upper limit of radio luminosity) similar to those of the observations. HDF130 is found to agree with the interpretation that it is an IC ghost of a powerful double-lobed radio source, and we are observing it at least a few Myr after jet activity (which lasted 5-100 Myr) has ceased. The minimum Lorentz factor of injected particles into the lobes from the hotspot is preferred to be γ~ 103 for the model to describe the observed quantities well, assuming that the magnetic energy density, electron energy density and lobe pressure at time of injection into the lobe are linked by constant factors according to a minimum energy argument, so that the minimum Lorentz factor is constrained by the lobe pressure. We also apply the model to match the features of 6C0905+3955, a classical double FR II galaxy thought to have a low-energy cut-off of γ~ 104 in the hotspot due to a lack of hotspot IC X-ray emission. The models suggest that the low-energy cut-off in the hotspots of 6C0905+3955 is γ≳ 103, just slightly above the particles required for X-ray emission. © 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS.