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List of accepted talks
Carlos Frenk, Durham University
X-ray coronae around spiral galaxies?
Basic galaxy formation theory predicts that spiral galaxies should have extended halos of X-ray emitting hot gas. Only recently have such halos been detected around a handful of examples and, in all cases, they are much fainter than the theory predicts. I will discuss the solution to this apparent conflict between theory and observations and its implications for the interpretation of X-ray data.
Ryan Hickox, Durham University
The edge of detection: The unresolved cosmic X-ray background in the Chandra Deep Fields
Although its origin was long mysterious, the cosmic X-ray background (CXB) is now known to be primarily the sum of emission from large number of active galactic nuclei (AGNs). The Chandra Deep Fields (CDFs) have allowed us to peer deeper than ever before into the populations that make up the CXB, and have resolved $>$80\% of the background in soft and medium X-rays (0.3--8 keV). I will give a brief overview of the composition of the CXB, and will then present results from the first absolute measurement of the unresolved CXB in the CDFs. I will then discuss the contribution of optically-detected HST galaxies to this unresolved flux, and show that at low fluxes, the CXB becomes dominated by large populations of faint star-forming galaxies rather than AGN. I will describe new measurements of the spectrum of the unresolved CXB as a function of survey flux limit, and finally will look forward to further studies of the CXB with deeper Chandra surveys and new missions such as NuSTAR.
Agnese Del Moro, Durham University
Revealing the most obscured distant AGNs: new insights from X-ray and infrared spectroscopy
One of the major outstanding issues in tracing the evolution of AGN across cosmic time is the identification of the most heavily obscured AGN (i.e. Compton-thick AGN) at high redshift, which may account for a large fraction of the X-ray background (XRB) at high energies (E>8 keV). The combination of X-ray and IR data has recently yielded promising results in the quest for candidate Compton-thick AGN, however these results rely on X-ray-IR luminosity relations defined in the local Universe, which may not hold at high redshift. We present here a detailed analysis of the X-ray-IR relation using Chandra X-ray data and Spitzer IRS spectroscopy in the GOODS-N and GOODS-S fields. We use our results to constrain the number of high-z Compton-thick AGN and reassess their contribution to the accretion history of the Universe.
Paul Giles, University of Bristol
X-ray Properties of Galaxy Clusters and comparisons to Weak-Lensing Measurements
We present work detailing the analysis of a complete, volume-limited sub-sample of 35 X-ray luminous galaxy clusters at 0.15 < z < 0.3 from observations taken with the Chandra X-ray telescope. We compare the mass estimates based upon a full hydrostatic equilibrium analysis requiring temperature profiles (where possible) to the mass estimates of weak-lensing observations based upon fitting NFW profiles to the observed shear profile of each cluster. We also compare the scaling relations of relatively simple X-ray observables (Tx, Lx, Yx) to the weak-lensing masses. The case of Abell 689 shall also be mentioned, a cluster which should be contained within this sample based upon its ROSAT luminosity but found to have strong point source contamination. The results of the analysis of the point source will be discussed.
Kathy Romer, University of Sussex
XMM Cluster Survey: the first cluster data release (500 temperatures and 1000 redshifts)
I will present the first major public data release from XCS. This includes more than 500 X-ray temperatures and 1000 redshifts for clusters detected out to z=1.4 (median redshift of z=0.4). I will discuss the future science applications of this unprecedented sample.
Beatriz Mingo Fernandez, University of Hertfordshire
Upset AGNs: bubbles & shocks in Markarian 6 and beyond
AGN-driven gas outflows observed by Chandra in massive elliptical galaxies such as M87, Hydra A or Hercules A, are known to play a fundamental role in galaxy formation and evolution. The last few years have also seen growing evidence of how these processes scale in the case of low radio power, smaller galaxies, such as Centaurus A, NGC3801 and NGC6764. The outflows in these systems have scales of a few kpc and are overpressured with respect to their surroundings, and may be thus driving shocks into the host galaxy's ISM. Understanding the energetics of these systems is a challenging but fundamental task towards improving our knowledge of how AGNs work, and constrain their timescales, feedback and impact on galaxy evolution. We present a new analysis of the extended X-ray emission associated with the radio bubbles of the galaxy Markarian 6, as seen in a recent Chandra observation. We also present the analysis of the nuclear spectrum of this galaxy using the Chandra data together with three earlier XMM-Newton observations, showing strong absorption variability, probably originated in the innermost regions of the accreting disk.
Adam Patrick, Keele University
Iron Line Profiles in Suzaku Spectra of Bare Seyfert Galaxies
We methodically model the broad-band Suzaku spectra of a small sample of six 'bare' Seyfert galaxies: Ark 120, Fairall 9, MCG-02-14-009, MRK 335, NGC 7469 and SWIFT J2127.4+5654. The analysis of bare Seyferts allows a consistent and physical modelling of AGN due to the lack of any significant intrinsic warm absorption, providing a simpler spectrum to model. Through effective modelling of the broad-band spectrum and investigating the presence of narrow neutral or ionized emission lines and reflection from distant material, we obtain an accurate and detailed description of the Fe K line region using models such as Laor, kerrdisk and kerrconv. Results suggest that ionized emission lines at 6.7 keV and 6.97 keV are more common than previously thought and the inclusion of these lines can greatly affect the parameters obtained with relativistic models i.e. spin, emissivity, inner radius of emission. Moderately broad components are found in all objects, but typically the emission originates from tens of Rg, rather than within <6Rg of the black hole. Results obtained with kerrdisk line profiles suggest an average emissivity of q~2.3 at intermediate spin values with all objects ruling out a maximally spinning black hole at the 90% confidence level.
Dan Wilkins, University of Cambridge
Determination of the Emissivity Profiles of AGN Accretion Discs and their Physical Implications
When modelling the X-ray reflection spectrum from the accretion disc around the central black hole of an AGN, a power law emissivity profile is typically assumed and parameters fit to the observed spectra. Here, rather than fitting a profile, we directly obtain the emissivity profile of the disc from the observed spectrum by considering the spectrum as the sum of contributions from successive radii and fitting to find the weightings of these components. This method has successfully recovered known emissivity profiles from synthetic spectra and is applied to XMM Newton spectra of the Narrow Line Seyfert 1 galaxy 1H0707-495 to obtain its emissivity profile. Results are compared to a range of theoretical emissivity profiles calculated in ray-tracing simulations and possible constraints on the location and geometry of the hard X-ray source from observed emissivity profiles are explored.
Simon Vaughan, University of Leicester
What can we learn from multiple XMM-Newton observations of NGC 4051?
We will discuss the results of a recent ~600 ks XMM-Newton observation of the prototypical low-mass Seyfert 1 galaxy NGC 4051. The XMM-Newton observation comprise 15 observations spread over 45 days and were enhanced with overlapping Swift XRT/UVOT and on-going RXTE monitoring. These data comprise one of the most photon-rich AGN X-ray observations to date, covers a wide range in timescales (minutes-weeks), and reveal details of the X-ray spectrum as the source flux varies by more than an order of magnitude. In the time available we will attempt to discuss some of the main results to come out of this campaign.
Missagh Mehdipour, MSSL-UCL
The optical-UV-X-ray variability connection in Mrk 509
We present our analysis of XMM-Newton observations of the Seyfert-1/QSO Mrk 509, part of an unprecedented multi-instrument campaign, investigating the nuclear environment of this AGN. The data are from a series of 10 observations of ~ 60 ks each, spaced from each other by about 4 days, taken in Oct-Nov 2009 with XMM-Newton. After photometric and spectroscopic corrections due to the host galaxy and a three-ionisation-phase warm absorber, we have investigated the intrinsic variability of this AGN using simultaneous optical/UV data (taken with the OM filters and the optical grism) and X-ray data (taken with the EPIC-pn camera). We discuss the flux and spectral correlation between the optical-UV black body emission from the accretion disk and X-ray emission which comprises both a soft and a hard power-law components. We attempt to explain the variability in terms of physical changes in the central region of this AGN over the duration of our monitoring campaign.
Dom Walton, University of Cambridge
Ultraluminous X-ray Sources in Nearby Galaxies
Since their discovery, Ultraluminous X-ray sources (ULXs) have attracted attention due to their combination of extreme X-ray luminosities and extra-nuclear locations. However, they are a fairly rare phenomenon, and attempts to investigate the general properties of the ULX population have been hindered by a relative lack of known sources. In order to undertake such work, we have compiled a large catalogue of 655 X-ray observations of 475 ULX candidates, from the 2XMM Serendipitous Survey. Here, we present some analysis of this population, focusing on the spectral curvature seen, often at ~6 keV, in the highest quality ULX data.
Roberto Soria, MSSL-UCL
X-ray hot spots, optical nebula and radio lobes of a powerful microquasar in NGC 7793
We have discovered that the large (300 x 150 pc) shock-ionized nebula S26 in NGC7793 is powered by a pair of collimated jets, probably from a stellar black hole. From the Balmer line width and luminosity, and the Halpha/HeII 4686 flux ratio, we determine a mechanical power of a few 10^{40} erg/s, a bubble expansion velocity of 250 km/s, and a characteristic age of 2 x 10^5 yr. The X-ray core is in a low/hard state (LX ~ 6 x 10^{36} erg/s); the radio core is not detected; the bright optical core has Wolf-Rayet features. The X-ray hot spots are well fitted with thermal-plasma models; they are associated with prominent radio lobes. Thus, this microquasar is a scaled-down version of an FRII radio galaxy; a long-sought analog of SS433, but larger and more powerful. More generally, it is a missing link between ULXs (in which we have seen ionized bubbles but no collimated jets) and ordinary microquasars. It suggests that black holes can have collimated jets even at such high accretion rates. It gives us a clue to model how black hole jets heat the surrounding medium.
Antonia Rowlinson, University of Leicester
The unusual X-ray emission of the short Swift GRB 090515: Evidence for the formation of a magnetar?
The majority of short gamma-ray bursts (SGRBs) are thought to originate from the merger of compact binary systems collapsing directly to form a black hole. However, it has been proposed that SGRBs may, on rare occasions, form an unstable millisecond pulsar (magnetar) prior to final collapse. These objects, with a multi-stage collapse to a black hole, will be interesting targets for future gravitational wave observatories. GRB 090515, detected by the Swift satellite was extremely short, with a T90 of 0.036 +/- 0.016 s, a very low fluence and faint optical afterglow. Despite this, the 0.3 - 10 keV flux in the first 200 s was the highest observed for a SGRB by the Swift X-ray Telescope (XRT). The X-ray light curve showed an unusual plateau and steep decay, becoming undetectable after ~500 s. This behaviour is similar to that observed in some long bursts proposed to have magnetars contributing to their emission. We discuss potential causes of the unusual 0.3 - 10 keV emission and suggest it might be energy injection from an unstable millisecond pulsar. Using the duration and flux of the plateau of GRB 090515, we place constraints on the millisecond pulsar spin period and magnetic field.
Wynn Ho, University of Southampton
Lessons from the youngest neutron star in the Galaxy
We recently identified, using Chandra X-ray observations, the compact source at the centre of the Cassiopeia A supernova remnant as a ~330-year-old neutron star, thus making the neutron star the youngest-known in the Milky Way. We describe our continuing work in studying the properties of this star, including measuring for the first time in a single young neutron star, the cooling of the star. Some of these properties may be unique due to the neutron star's youth, while others give us insights into the extreme physics of neutron star interiors, including the nuclear equation of state and neutrino emission processes.
Mike Hill, Durham University
The X-ray AGN contribution to the FIR and sub-mm backgrounds
We first show that a model of obscured AGN which fits the hard X-ray background also gives an excellent fit to the LABOCA sub-mm source counts in the Extended Chandra Deep Field South (ECDFS). The model also explains well ECDFS correlations between sub-mm flux and X-ray flux, X-ray luminosity and hardness ratio, We also show that the model suggests that AGN are a major contributor to source counts in the Herschel 250, 350 and 500 micron bands. We therefore suggest that sub-mm/FIR sources may contain the long-sought obscured AGN population.
Adam Ingram, Durham University
Low frequency QPOs: a precession model in the context of mass accretion rate fluctuations
Although it has been known for over 20 years, there is still no consensus in the literature as to the origin of the low frequency Quasi-Periodic Oscillations (QPOs) observed in the PSD of X-ray binaries. I describe a model that associates the QPO with Lense-Thirring precession of the hot inner flow and show how this process is effected by fluctuations in mass accretion rate. I then show that this model, in addition to producing the observed correlations between characteristic frequencies, predicts many other properties of the PSD including its observed shape, harmonic structure and evolution.
Pablo Cassatella, University of Southampton
Time lags from reflection in BHXRBs
It is thought that the propagation of accretion fluctuations throughout accretion discs in black hole X-ray binaries accounts for most of the time lags that are observed between the soft and hard bands. However, from observations of some BHXRBs such as Cygnus X-1 and GX 339-4, it is possible to say that reflection from a flared accretion disc must play a role. Here we show the first reflection model that can be used within ISIS or XSPEC to fit timing products such as time lags or covariance spectra, and therefore put some constrains on the accretion geometry of these systems.
Lucy Heil, University of Leicester
The rms-flux relation in black hole binaries
In order to test the ubiquity of the linear rms-flux relation, and its dependence on timescale, energy, source state, and so on we have analysed most of the data available in the RXTE archive for 9 BH XRBs (2077 observations), the majority of which showed a clear rms-flux relation. This is an indicator that a linear rms-flux relation is indeed a common property of BH XRBs. Most of the observations have been taken when the sources are in outburst, the relation has been observed in a range of different states and variability levels. We have compared the gradient (k) and the x-intercept (C) over the course of these outbursts and observe not only clear differences in these parameters dependent on spectral hardness, but also striking similarities between different sources. By taking the average of the rms and flux in each observation it is also possible to study the long term rms-flux relation, this long term relationship shows changes and distinct patterns relating to hardness over the course of the outburst. We will also discuss the energy and frequency dependence of this relation in individual observations. Finally, we will discuss an analysis of the rms-flux properties of an Ultra-Luminous X-ray source (ULX) and the relation observed from QPOs.
Tony Wilkinson, University of Southampton
GX 339-4 in 2004 and 2009: Is the PSD break time-scale a signature of the disc truncation radius?
Studies of relativistically broadened iron-lines in black hole X-ray binaries (BHXRBs) can provide constraints on the truncation radius of the accretion disk. A common model of the hard state of BHXRBs suggests that the disc becomes more truncated as the source becomes harder. At the same time, frequencies of the Lorentzian features in the Fourier power-spectrum decrease, suggesting that these frequencies are linked to characteristic time-scales in the inner disc. To test this interpretation of hard-state behaviour and our understanding of broad iron lines, we recently obtained an XMM-Newton TOO observation of the BHXRB GX 339-4 in its hard state, at a time when the low-frequency Lorentzian timing signature was 5 times lower than observed in a hard-state observation of the source obtained in 2004. We present a comparison of these spectra here, in an effort to establish whether or not the low-frequency Lorentzian in the power-spectrum of this source is a signature of the viscous timescale at the boundary between the thin disc and inner hot flow.
Mike Watson, University of Leicester
The next 15 years: future developments in X-ray astronomy
This talk will offer an overview of the X-ray astronomy missions planned for the next 15 years, highlighting how future missions will complement and expand current capabilities. I will also include an update on the IXO concept and its current status.