Publications by Katherine Blundell

Exploring the nature of weak Chandra sources near the Galactic Centre

AIP CONF PROC 797 (2005) 410-415

RM Bandyopadhyay, JCA Miller-Jones, KM Blundell, FE Bauer, P Podsiadlowski, QD Wang, S Rappaport, E Pfahl

We present results from the first near-IR imaging of the weak X-ray sources discovered in the Chandra/ACIS-I survey (Wang et al. 2002) towards the. Galactic Centre (GC). These 800 discrete sources, which contribute significantly to the GC X-ray emission, represent an important and previously unknown population within the Galaxy. From our VLT observations we will identify likely IR counterparts to a sample of the hardest sources, which am most likely X-ray binaries, With these data we can place constraints on the nature of the discrete weak X-ray source population of the GC.

A refined method for measuring jet speeds

Interacting Binaries: Accretion, Evolution, and Outcomes 797 (2005) 585-588

J Miller-Jones, K Blundell, P Duffy

Jet Velocity in SS 433: Its Anticorrelation with Precession-Cone Angle and Dependence on Orbital Phase

Astrophysical Journal Letters 622 (2005) L129-L132

KM Blundell, Michael G. Bowler

The distribution of radio plasma in time and space.

Philos Trans A Math Phys Eng Sci 363 (2005) 645-654

KM Blundell

The influence of jet-ejected plasma has been an important theme of this meeting; I draw attention to the prevalence of jet-ejected plasma, in particular that which has not been properly accounted for in the past. There are three strands to this paper: important emission which is prominent only at the lowest radio frequencies; relic radio plasma which must exist if even the most basic aspects of radio source evolutionary models are correct; and evidence that some 'radio-quiet' quasars could be FR-I radio sources.

The post-outburst radio evolution of Cygnus X-3

ASTR SOC P 340 (2005) 312-314

AJ Mioduszewski, MP Rupen, JCA Miller-Jones, KM Blundell

Cygnus X-3 is one of the most famous Galactic relativistic jet sources, often undergoing flares to 1 Jy or more. Here we present VLBA imaging at 15 and 22 GHz after the September 2001 outburst and contrast the one-sided nature of the VLBI jets with the two-sided jet seen in VLA images of this source.

The impact of active galaxies on the Universe at large - Preface


J Binney, KM Blundell, JP Ostriker, SDM White

Cosmic ray transport and acceleration

PLASMA PHYS CONTR F 47 (2005) B667-B678

P Duffy, KM Blundell

We review the theory of cosmic ray transport and acceleration with an emphasis on the underlying plasma physics and examine how that theory can be applied to sources such as supernova remnants and giant radio galaxies. Starting with Fermi's original model for scattering off moving magnetized clouds, we discuss quasilinear transport theory and its application to the acceleration of particles at shock fronts. We discuss problems of injection and the excitation of MHD turbulence by the accelerated particles. In the diffusive limit and at strong shocks this mechanism produces a differential energy spectrum of N(E) (proportional to E-2. Recent observations of supernova remnants suggest that their spectra may be steeper than this value. We discuss the transport and acceleration of energetic particles in highly correlated magnetic field structures. In this case particles have an enhanced probability of escape from the shock as they are trapped on field lines and the resulting spectrum is steepened up to a value of 2.5. Fast particle transport also seems to be required by observations of the structures of giant radio galaxy lobes as a function of frequency.

Jets and outflows in microquasars

ASTR SOC P 330 (2005) 91-102

KM Blundell

I discuss the importance of studies of jets and outflows in the Galaxy from binary star systems, popularly known as microquasars. Because of the rapid timescales on which they evolve, pertinent observations of microquasar jets can help tighten up the theoretical framework in which jet properties of quasars can be interpreted. I draw attention to a new method for constraining jet speed which renders original approaches, which do not incorporate jet evolution, obsolete. I describe new results on two particular microquasars, SS 433 and Cygnus X-3. I compare and contrast the jet characteristics of these two microquasars, noting the persistent jet activity of SS 433 with the intermittent jet activity of Cygnus X-3.

Symmetry in the Changing Jets of SS 433 and Its True Distance from Us

Astrophysical Journal Letters 616 (2004) L159-L162

KM Blundell, Michael G. Bowler

Exploring the nature of weak Chandra sources near the galactic centre

Revista Mexicana de Astronomia y Astrofisica: Serie de Conferencias 20 (2004) 261-262

RM Bandyopadhyay, KM Blundell, P Podsiadlowski, JCA Miller-Jones, QD Wang, WN Brandt, S Rappaport, E Pfahl

We present early results from the first near-IR imaging of the weak X-ray sources discovered in the recent Chandra/ACIS-I survey towards the Galactic Centre (GC) (Wang et al. 2002). These ̃800 discrete sources, which contribute significantly to the GC X-ray emission, represent an important and previously unknown population within the Galaxy. From our VLT observations we will identify likely IR counterparts to a sample of the hardest sources, which are most likely X-ray binaries. With these data we can place constraints on the nature of the discrete weak X-ray source population of the GC. Once the data analysis is complete we will discuss our results in the context of binary population synthesis models. © Copyright 2004: IA, UNAM.

The 6C** sample and the highest redshift radio galaxies

(2004) 141-142

MJ Cruz, MJ Jarvis, KM Blundell, S Rawlings

We present a new radio sample, 6C** designed to find radio galaxies at z > 4 and discuss some of its near-infrared imaging follow-up results.

Near-infrared imaging and the K-z relation for radio galaxies in the 7C Redshift Survey 

Monthly Notices of the Royal Astronomical Society 339 (2003) 173-188

SG Rawlings, Blundell, K, Jarvis, M, Willott, C

A Relativistic Jet in the Radio-quiet Quasar PG 1407+263

Astrophysical Journal Letters 591 (2003) L103-L106

KM Blundell, Anthony J. Beasley, Geoffrey V. Bicknell

The mass of radio galaxies from low to high redshift

ESO ASTROPHY SYMP (2003) 148-153

MJ Jarvis, S Rawlings, S Eales, KM Blundell, CJ Willott

Using a new radio sample, 6C* designed to find radio galaxies at z > 4 along with the complete 3CRR and 6CE sample we extend the radio galaxy K - z relation to z similar to 4.5. The 6C* K - z data significantly improve delineation of the K - z relation for radio galaxies at high redshift (z > 2). In a spatially flat universe with a cosmological constant (Omega(M) = 0.3 and Omega(A) = 0.7), the most luminous radio sources appear to be associated with galaxies with a luminosity distribution with a high mean (approximate to 5L*), and a low dispersion (sigma similar to 0.5 mag) which formed their stars at epochs corresponding to z greater than or similar to 2.5).

The ruff of equatorial emission around the SS433 jets: its spectral index and origin

Proceedings of the 4th Microquasar Workshop (2003)

KM Blundell, MP Rupen, AJ Mioduszewski, TWB Muxlow, P Podsiadlowski

We present unique radio observations of SS433, using MERLIN, the VLBA, and the VLA, which allow us to, for the first time, properly image and derive a meaningful spectral index for the `ruff' of equatorial emission which surrounds SS433's jet. We interpret this smooth ruff as a wind-like outflow from the binary.

Lowering inferred cluster magnetic field strengths: The radio galaxy contributions

Astrophysical Journal 588 (2003) 143-154

L Rudnick, KM Blundell

We present a detailed examination of the relationship between the magnetic field structures and the variations in Faraday rotation across PK.S 1246-410, a radio source in the Centaurus cluster of galaxies, using data from Taylor, Fabian, & Alien. We find a significant relationship between the intrinsic position angle of the polarization and the local amount of Faraday rotation. The most plausible explanation is that most or all of the rotation is local to the source. We suggest that the rotations local to cluster radio galaxies may result either from thermal material mixed with the radio plasma, or from thin skins of warm, ionized gas in pressure balance with the observed galaxy or hot cluster atmospheres. We find that the contribution of any unrelated cluster rotation measure (RM) variations on scales of 2″-10″ are less than 25 rad m-2 the standard, although model-dependent, derivation of cluster fields would then lead to an upper limit of ≈0.4μG on these scales. Inspection of the distributions of rotation measure, polarization angle, and total intensity in 3C 75, 3C 465, and Cygnus A also shows source-related Faraday effects in some locations. Many effects can mask the signatures of locally dominated RMs, so the detection of even isolated correlations can be important, although difficult to quantify statistically. In order to use radio sources such as those shown here to derive cluster-wide magnetic fields, as is commonly done, one must first remove the local contributions. This is not possible at present.

Evidence for interaction with a surrounding medium in several BL lacertae objects.

ASTR SOC P 250 (2002) 200-203

AB Pushkarev, DC Gabuzda

In February 1997, we obtained multi-frequency polarization VLBA observations of 23 sources from a complete sample of northern BL Lac objects. Total intensity and linear polarization images of two sources (0745+241 and 0820+225) showing evidence for the presence of sheaths of longitudinal magnetic field surrounding their jets are presented. These results suggest that appreciable amounts of thermal plasma are often present on parsec scales, and that the jet magnetic field can be influenced by interaction with this surrounding medium.

What triggers radio galaxies?

ESO ASTROPHY SYMP (2002) 125-127

MJ Cruz, KM Blundell

We are investigating possible triggering scenarios which may give rise to powerful jetted active galaxies such as classical double radio galaxies. Important clues come from studying those objects which have most recently been triggered. The newly discovered 'Youth-Redshift Degeneracy' for classical double radio galaxies means that the highest redshift objects in a flux-limited survey will be observed to be significantly younger (more recently triggered) than the more nearby objects. We are pursuing this investigation with a new sample specially filtered to favour the detection of high-redshift radio galaxies. We will present some preliminary results of a near-IR imaging campaign using the UIFTI on the UKIRT.

Double-double radio galaxies: probing duty cycles in AGN and the cocoons of powerful radio sources

ASTR SOC P 250 (2002) 408-411

A Schoenmakers

Recently, we have identified a small number of extended radio sources that consist of two double-lobed radio sources, which axe well aligned and centered on a common nucleus. We have called these 'Double-double radio galaxies' (DDRGs). The observed structures strongly suggest interrupted central activity as the origin of these sources. We have developed a model based on this assumption with which we are able to explain several observed properties. Since the inner structures of the DDRGs advance inside the cocoon originally formed by the outer lobes, these allow us to probe the cocoon medium. Our results indicate that the cocoon density must be higher than has been assumed in earlier models.

Beam powers, active lifetimes, and total energies of FRIIb radio galaxies

ASTR SOC P 250 (2002) 417-421

EJ Guerra, RA Daly

Multi-frequency radio observations of a powerful classical double radio galaxies can be used to determine the beam power of the jets emanating from the AGN, the total time the source will actively produce jets, and the total energy available to power the jets during their lifetime. Empirical determinations of these quantities are presented for 20 classical double radio galaxies. The model assumptions, trends with redshift, and implications for energy extracted from central engines are discussed.