Publications by Katherine Blundell


Inflow and outflow from the accretion disc of the microquasar SS433: UKIRT spectroscopy

ArXiv (0)

S Perez, KM Blundell

A succession of near-IR spectroscopic observations, taken nightly throughout an entire cycle of SS433's orbit, reveal (i) the persistent signature of SS433's accretion disc, having a rotation speed of ~500 km/s, (ii) the presence of the circumbinary disc recently discovered at optical wavelengths by Blundell, Bowler and Schmidtobreick (2008) and (iii) a much faster outflow than has previously been measured for the disc wind. From these, we find a much faster accretion disc wind than has noted before, with a terminal velocity of ~1500 km/s. The increased wind terminal velocity results in a mass-loss rate of ~10e-4 M_sun/yr. These, together with the newly (upwardly) determined masses for the components of the SS433 system, result in an accurate diagnosis of the extent to which SS433 has super-Eddington flows. Our observations imply that the size of the companion star is comparable with the semi-minor axis of the orbit which is given by (1-e^2)^(1/2) 40 R_sun, where e is the eccentricity. Our relatively high spectral resolution at these near-IR wavelengths has enabled us to deconstruct the different components that comprise the Brackett-gamma line in this binary system, and their physical origins. With this line dominated throughout our series of observations by the disc wind, and the accretion disc itself being only a minority (~15 per cent) contribution, we caution against use of the unresolved Brackett-gamma line intensity as an "accretion signature" in X-ray binaries or microquasars in any quantitative way.


Multiwavelength study of Cygnus A II. X-ray inverse-Compton emission from a relic counterjet and implications for jet duty-cycles

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KC Steenbrugge, KM Blundell, P Duffy

The duty-cycle of powerful radio galaxies and quasars such as the prototype Cygnus A is poorly understood. X-ray observations of inverse-Compton scattered Cosmic Microwave Background (ICCMB) photons probe lower Lorentz-factor particles than radio observations of synchrotron emission. Comparative studies of the nearer and further lobes, separated by many 10s of kpc and thus 10s of thousands of years in light-travel time, yield additional temporal resolution in studies of the lifecycles. We have co-added all archival Chandra ACIS-I data and present a deep 200 ks image of Cygnus A. This deep image reveals the presence of X-ray emission from a counterjet i.e. a jet receding from Earth and related to a previous episode of jet activity. The non-thermal X-ray emission, we interpret as ICCMB radiation. There is an absence of any discernible X-ray emission associated with a jet flowing towards Earth. We conclude that: (1) The emission from a relic jet, indicates a previous episode of jet activity, that took place earlier than the current jet activity appearing as synchrotron radio emission. (2) The presence of X-ray emission from a relic counterjet of Cygnus A and the absence of X-ray emission associated with any relic approaching jet constrains the timescale between successive episodes of jet activity to ~10^6 years. (3) Transverse expansion of the jet causes expansion losses which shifts the energy distribution to lower energies. (4) Assuming the electrons cooled due to adiabatic expansion, the required magnetic field strength is substantially smaller than the equipartition magnetic field strength. (5) A high minimum Lorentz factor for the distribution of relativistic particles in the current jet, of a few 10^3, is ejected from the central nucleus of this active galaxy. Abridged.


The prevalence of FRI radio quasars

ArXiv (0)

I Heywood, KM Blundell, S Rawlings

We present deep, multi-VLA-configuration radio images for a set of 18 quasars, having redshifts between 0.36 and 2.5, from the 7C quasar survey. Approximately one quarter of these quasars have FRI-type twin-jet structures and the remainder are a broad range of wide angle tail, fat double, classical double, core-jet and hybrid sources. These images demonstrate that FRI quasars are prevalent in the universe, rather than non-existent as had been suggested in the literature prior to the serendipitous discovery of the first FRI quasar a few years ago, the optically powerful "radio quiet" quasar E1821+643. Some of the FRI quasars have radio luminosities exceeding the traditional FRI / FRII break luminosity, however we find no evidence for FRII quasars with luminosities significantly below the break. We consider whether the existence of such high luminosity FRI structures is due to the increasingly inhomogeneous environments in the higher redshift universe.


Lowering Inferred Cluster Magnetic Field Strengths - the radio galaxy contributions

ArXiv (0)

L Rudnick, K Blundell

We present a detailed examination of the relationship between the magnetic field structures and the variations in Faraday Rotation across PKS1246-410, a radio source in the Centaurus cluster of galaxies, using data from Taylor, Fabian and Allen. 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 from either 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 variations on scales of 2 - 10 arcsec are less than 25 rad/m^2; the standard, although model dependent, derivation of cluster fields would then lead to an upper limit of approximately 0.4 microGauss on these scales. Inspection of the distributions of Rotation Measure, polarisation angle and total intensity in 3C75, 3C465 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 shown here to derive {\it cluster-wide} magnetic fields, as is commonly done, one must first remove the local contributions; this is not possible at present.


The central engines of radio-quiet quasars

ArXiv (0)

KM Blundell, AJ Beasley

Two rival hypotheses have been proposed for the origin of the compact radio flux observed in radio-quiet quasars (RQQs). It has been suggested that the radio emission in these objects, typically some two or three orders of magnitude less powerful than in radio-loud quasars (RLQs), represents either emission from a circumnuclear starburst or is produced by radio jets with bulk kinetic powers 10^3 times lower than those of RLQs with similar luminosity ratios in other wavebands. We describe the results of high resolution (parsec-scale) radio-imaging observations of a sample of 12 RQQs using the Very Long Baseline Array (VLBA). We find strong evidence for jet-producing central engines in 8 members of our sample.


A complete sample of quasars from the 7C redshift survey

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CJ Willott, S Rawlings, KM Blundell, M Lacy

We present details of a new sample of radio-loud quasars drawn from 0.013 sr of the 7C Redshift Survey. This sample is small (21 quasars) but complete in that every object with an unresolved nucleus and/or broad emission lines with S(151MHz) > 0.5 Jy has been discovered. The dependence of the quasar fraction with redshift and radio luminosity is investigated, providing new evidence supporting the unification of radio-loud quasars and powerful radio galaxies. This 7C sample is compared with optically-selected quasars, in order to determine whether there are systematic biases in the different selection techniques. There are no lightly reddened (Av approx. 1) quasars in our sample amongst the 14 with z < 2. The discovery of a reddened quasar at z = 2.034 and its implications are discussed. A tight correlation between radio luminosity and optical/near infrared continuum luminosity for a subset of the sample is also found.


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MNRS (0)

KM Blundell, F barrio

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