New Results in X-ray Astronomy 2016

Wednesday 28 September 2016

Chandra in flight XMM-Newton over the Earth Swift and a gamma-ray burst


Abstract submission has now closed and the programme of talks is available here. Abstracts for talks and posters at the meeting are listed below.


Jupiter's X-ray Aurora
Will Dunn (MSSL/UCL; CfA Havard & Smithsonian)
One of the only astrophysical X-ray emitters that we can visit in-situ is the planet Jupiter. Through the combination of rapid rotation, a strong magnetic field and plasma injections by its volcanic moon Io, the planet produces bright and dynamic X-ray aurorae. In the last 3 years, the arrival of NASA’s Juno spacecraft has offered the unique opportunity to connect the precise physical processes that lead the planet to produce X-ray emissions, with remote observations of those very signatures. Given that Juno does not have an X-ray instrument, to fully utilise this opportunity we acquired several Megaseconds of Jupiter X-ray observations across XMM-Newton, Chandra and NuSTAR. When combined with the simultaneous in-situ data from Juno these observations provide an irreplaceable rich and truly multi-waveband legacy dataset, which is leading to a paradigm shift in our understanding of the planet. In this presentation, I will present a few of what I think are the most exciting preliminary insights from this campaign, and show strong correlations between Jupiter’s X-ray aurora and certain types of magnetic field and particle behaviour, alongside the signatures that connect the X-ray emissions to radio and UV emissions. I will close with comparisons with Cassini data from Saturn to highlight why certain planets seem to produce X-ray aurora, while others do not.

On the satellite lines in the X-rays
Giulio Del Zanna (University of Cambridge)
I describe the new modelling I implemented in CHIANTI v.9 to calculate the intensities of the satellite lines, present some comparisons with high-resolution X-ray solar spectra and briefly discuss some of the available diagnostics. The corresponding atomic data are much improved over the previous ones. The new models will be useful for the next-generation  spectra of astrophysical objects.

CIELO-RGS: a catalog of soft X-ray ionized emission lines
Junjie Mao (Strathclyde/SRON)
High-resolution X-ray spectroscopy has advanced our understanding of the hot Universe by revealing physical properties like kinematics, temperature, and abundances of the astrophysical plasmas. Despite technical and scientific achievements, the lack of scientific products at a level higher than count spectra is hampering complete scientific exploitation of high-quality data. This talk introduces the Catalog of Ionized Emission Lines Observed by the Reflection Grating Spectrometer (CIELO-RGS) onboard the XMM-Newton space observatory. Here we focus on the methodology of the catalog generation, describing the automated line-detection algorithm. A moderate sample (~2400 observations) of high-quality RGS spectra available at XMM-Newton Science Archive is used as our starting point. A list of potential emission lines is selected based on a multi-scale peak-detection algorithm in a uniform and automated way without prior assumption on the underlying astrophysical model. The candidate line list is validated via spectral fitting with simple continuum and line profile models. We generate a catalog of emission lines ($1.2\times10^4$) detected in ~1600 observations toward stars, X-ray binaries, supernovae remnants, active galactic nuclei, and groups and clusters of galaxies. We also compare the catalog content with published literature results on a small number of exemplary sources.

X-ray view of the extreme colliding-wind binary HD 93129A during periastron
Santiago del Palacio (Instituto Argentino de Radioastronomía)
Very little information is known on the non-thermal X-ray emission from massive colliding-wind binaries, preventing us from accurately assessing their role as Galactic cosmic ray accelerators or possible gamma-ray sources. The extreme system HD 93129A is an exciting object to study, as it is made up by two of the most massive and luminous stars in the Galaxy. This system has a period close to a century and it went through periastron passage in late 2018. We participated in a multi-wavelength campaign to monitor this event from infrared to gamma rays. In particular, we observed the periastron passage with the X-ray satellites Swift, XMM-Newton, Chandra and NuSTAR. We present a preliminary analysis of the evolution of the X-ray emission of this system, highlighting a flux enhancement near periastron and the detection of emission slightly above 10 keV. We discuss the implications of such findings and the possibilities for future research on the high-energy emission of colliding-wind binaries.

High density reflection spectroscopy: disc density at different black hole mass scales
Jiachen Jiang (IoA, Cambridge)
I will present a high-density disc reflection spectral analysis of a sample of Seyfert 1 galaxies to study the inner disc densities at different black hole mass scales and accretion rates. All the available XMM-Newton observations in the archive are used. OM observations in the optical/UV band are used to estimate their accretion rates. We find that 65% of sources in our sample show a disc (number) density significantly higher than 1e15 cm-3, which was assumed in previous reflection-based spectral analyses. Only an upper limit of the disc density is found for SMBHs with a high black hole mass, such as the Seyfert 1 galaxy 1H 0419-577.

A new method to determine X-ray luminosity functions of AGN and their evolution with redshift.
Ahlam Al'Qasim (MSSL/UCL)
t is thought that most or all massive galaxies today contain supermassive black holes (SMBH) at their centers. SMBHs grew by accreting material from their surroundings, shining as quasi-stellar objects (QSOs) and emitting X-rays as they did so. QSOs belong to a larger population of Active Galactic Nuclei (AGN). In this talk I will present a new method to measure the evolution of black holes over cosmic time. Normally, luminosity functions for AGN are constructed in a fixed observed energy band, which can be problematic because it probes different rest-frame energies at different redshifts. In the new method, I will construct X-ray luminosity functions (XLF) of AGN in redshift-dependent energy bands. Varying the observed energy band with redshift allows us to fix the X-ray energy band in the rest-frame. This newly proposed method, where the observed energy band varies with redshift, eliminates the need to model the redshift-dependence of X-ray absorption from material surrounding the SMBHs when determining the evolution of the population.

Modelling Pulsating Ultra Luminous X-ray Sources
Nabil Brice (MSSL/UCL)
Pulsating Ultra Luminous X-ray sources (PULXs) are thought to be X-ray bright, accreting, magnetized neutron stars. Their apparent X-ray luminosity, in the range 0.1keV to 10keV, exceeds the Eddington luminosity limit for a neutron star by up to several orders of magnitude. Strong magnetic fields intrinsic to the neutron star give rise to a beamed emission, which manifests as the observed regular sinusiodal puslations. However, the exact mechanism which powers the observed luminosity remains debated to this day. I will focus on the particular mechanism of opacity reduction due to a strong magnetic field. While this mechanism has been successful in modelling the luminosity of PULX M81 X-6, it has been unsuccessful in modelling PULX NGC 5907 due to the assumption of a purely dipolar magnetic field structure. My work will be to construct a model of accretion onto a magnetised neutron star with a multipolar magnetic field structure. I will present my results so far in considering the accretion column geometry and show the direction of future work.

A new detection of pulsations from an old ULX
Rajath Sathyaprakash (University of Durham)
The early observations of ultra-luminous X-ray sources (ULXs) prompted suggestions that they are potential candidates of accreting intermediate mass black holes. However, after two decades of further study, there is growing evidence that these sources may be dominated by a population of neutron stars and stellar mass black holes, accreting at extreme super-Eddington rates. In this talk, I will discuss the recent discovery of sinusoidal pulsations in a historically well-studied extragalactic ULX, NGC 1313 X-2. Acceleration searches reveal pulsed signals with periods of order 1.5 seconds, in individual segments of two out of seven new XMM-Newton observations of this object. The pulsations are transient, in a similar vein to previously discovered sources, but we demonstrate via Monte Carlo simulations that they are statistically significant. Our result has interesting implications for current models of accretion onto a magnetised neutron star ULX. The kinematic properties of a large bubble nebula surrounding NGC 1313 X-2 implies that it has been active for over 1 Myr. This confirms that the source has continued to pulsate for a substantial fraction of its lifetime, such that its magnetic field has not been suppressed over time by accreted material, contradicting recent models which suggest otherwise. Clearly, the object has also not collapsed into a black hole, arguing that most accreted material has been expelled over the active lifetime of the ULX, supporting physical models that include strong winds and/or jets for neutron star ULXs. We also present separate evidence from simultaneous X-ray/optical observations of NGC 1313 X-2 that can be interpreted as precession of its central regions.

An unusual transient following GRB 071227
Rob Eyles (University of Leicester)
We present X-ray and optical observations of the short gamma-ray burst (SGRB) GRB 071227. SGRBs are generally expected to be followed by two types of transient; broadband synchrotron powered afterglows with power law spectra, and UV to IR observable kilonovae. Kilonovae are rarely observed, radioactively powered thermal transients responsible for producing the bulk of heavy elements like gold and platinum in the universe. At a relatively close redshift of z=0.381, kilonova signatures following GRB 071227 are potentially observable. We identify an optical transient at 0.2-0.3 days post burst with flux and spectral slope significantly in excess of that extrapolated from fitting the coincident X-ray spectrum. We investigate possible causes for the excess including the possibility of a kilonova component and find that the transient is broadly consistent with afterglow and additional dust extinction of E(B−V)∼0.4 mag, but a kilonova contribution may still be plausible.

The origin of ultra long gamma-ray bursts: GRB 121027A
Rhaana Starling (University of Leicester)
We present a multiwavelength analysis of GRB 121027A, which presents a highly unusual, energetic and long-lived X-ray rebrightening, placing this source in the newly emerging `ultralong' class of gamma-ray bursts. We demonstrate that the X-ray rebrightening is a manifestation of prompt emission, indicating the start of a second group of prompt pulses peaking some thousand seconds after the initial trigger, seemingly requiring an unrealistic energy budget if interpreted within the standard model. The afterglow is also atypical, in its late onset and low energy, and lies above flux predictions from the X-ray afterglow for synchrotron emission. We speculate on the origin of this GRB, including a single star two-stage collapse model with significant fallback, or a binary system as progenitor.

X-ray reverberation in Active Galactic Nuclei: Modelling the extended corona
Stephen Hancock (University of Bristol)
X-ray emission from accreting black hole systems show strong variability and reflection between the soft (0.3-1.0 keV) and hard (1-4 keV) energy bands. This reflection originates near the innermost stable circular orbit (ISCO) around the black hole where narrow spectral features are blurred out by relativistic effects. The prominent Fe k line seen at 6.4 keV is broadened and can extend down to around 3 keV as the photons are shifted to lower energies. These reverberation lags reveal the light travel time between the X-ray source and the reflecting region, providing us with an opportunity to probe the geometry of the disc and coronal region.  This research explores the dynamic features of over 20 active galactic nuclei (AGN) via relativistic reflection spectral modelling using XMM-Newton archive data. We employ the results of reverberation and spectral analysis to parameterize a new model of the extended corona using ray tracing techniques. Currently in development, this complex and computationally intensive model has been tested to estimate the location of emitting regions by recreating the time lags observed in 'X-ray snapshots' of all AGN. We employ two X-ray sources to pinpoint the location of the primary emitting X-ray continuum and upward-propagating extended coronal regions, which may also be interpreted as a relativistic jet or out-flowing material beaming vertically away from the black hole central axis.

X-ray reverberation mass measurement of accreting black holes
Adam Ingram (University of Oxford)
X-ray reverberation mapping exploits the path-length difference - and therefore light-crossing delay - between rays that have reached us directly from the hot corona located close to the black hole and those that have first irradiated and been reprocessed by the accretion disc before reaching us. Since the direct photons form a power-law continuum spectrum, and the reprocessed photons instead have a characteristic `reflection' spectrum that contains features such as a relativistically broadened ~6.4 keV iron fluorescence line, it is possible to disentangle the two spectral components with careful modelling and thus measure path length differences in the inner accretion flow of active galactic nuclei (AGN) and X-ray binary systems. I will present the publicly available XSPEC model RELTRANS, which calculates the time-averaged spectrum and Fourier cross-spectrum taking all general relativistic effects into account. Fitting this model jointly to the  time-averaged spectrum and the cross-spectrum for multiple Fourier frequencies not only enables better geometric constraints than only modelling the time-averaged spectrum, but also provides constraints on the mass of the central black hole. I will discuss our work to apply this model to the AGN Mrk 335 and the X-ray binary Cygnus X-1, which yields the first X-ray reverberation mass measurement of a stellar-mass black hole.

The deep X-ray view of a highly variable AGN
William Alston (IoA, Cambridge)
The fast timing properties of AGN X-ray curves allow us to probe the direct vicinity of black holes, the region most affected by strong gravity.  We present an extensive X-ray variability analysis from a 2 mega-second XMM-Newton observation of the highly variable Seyfert 1 galaxy, IRAS 13224-3809.  This is the longest observation taken to date on a nearby variable AGN. This long observation has revealed complex underlying variability processes, displaying the first non-linear rms-flux relation in any accreting source.  We will show modelling of the coronal and reverberation delays using GR ray tracing models. This allows us to build up the most detailed picture to date of the inner X-ray emitting region of AGN.

Resolving X-ray Obscuration Biases with Isotropic AGN Selection -- First Results from the NuLANDS Legacy Survey
Peter Boorman (University of Southampton)
An accurate assessment of the fraction of heavily obscured, "Compton-thick" AGN in the local Universe provides important insights into the composition and structure of AGN X-ray obscuration, as well as its connection with the evolution of supermassive black holes and their surrounding host galaxies.  However, current estimates of the Compton-thick fraction vary dramatically between ~20-70%, and it remains unclear whether this large range is driven by selection effects, inadequate sample sizes, luminosity/Eddington rate dependencies or something else entirely. The main handicap of previous works has been the inability to effectively select objects that are *representative* in terms of sampling N(H) parameter space, i.e. are unbiased even by Compton-thick obscuration. To investigate such issues, we present NuLANDS - a large far-infrared legacy survey with the X-ray satellites NuSTAR, XMM-Newton and Swift (more than 4 Ms in total) aimed at constructing an unbiased census of AGN obscuration in the local Universe. The infrared selection using AGN-like colours guarantees that we are not affected by line-of-sight X-ray obscuration biases, even into the log N(H)/cm-2 > 25 regime. In this talk, I will report on multiple new Compton-thick AGN discovered and classified with NuLANDS, complemented with multi-wavelength diagnostics.  First results further indicate a Compton-thick fraction > 30% and that hard X-ray selection alone remains biased against the most heavily obscured AGN.  NuLANDS marks a major step in completing the local census of accretion activity, and will provide vital boundary conditions for determining the composition of the Cosmic X-ray Background, as well as insights into the densest regions of the AGN torus.

Multi-epoch X-ray spectral analysis of Sy1 1H 0419-577
Jiachen Jiang (IoA, Cambridge)
We present a detailed analysis of the spectral properties of the Seyfert 1 galaxy 1H0419-577, based on the archival XMM-Newton, NuSTAR and simultaneous Swift observations taken between 2002-2015. All the observations show a broad emission line feature at the iron band. We demonstrate that the broad band spectral variability at different levels can be explained by the combination of light-bending effects in the vicinity of the central black hole plus a thin warm absorber. We obtain a black hole spin of a > 0.98 by fitting the multi-epoch spectra with the relativistic disc reflection model. 1H0419-577 is accreting at 40% of its Eddington limit and its X-ray band shows the hardest powerlaw continuum in the highest flux state, which was previously more commonly seen in AGNs with a low accretion rate (e.g. LX/LEdd<10−2). The NuSTAR observation shows a cool coronal temperature of kT=30 keV in the high flux state.

Multiwavelength Campaign on NGC 7469: Photoionisation modelling of the Emission Line Regions
Sam Grafton-Waters (MSSL/UCL)
The Seyfert 1 galaxy NGC 7469 was the target of an extensive observing campaign with XMM-Newton in 2015. Analysis of the 640 ks RGS spectrum with the spectral fitting code SPEX, and the physically self-consistent photoionisation model PION, shows that the emission line region (ELR) is multi-phased, while also accounting for three warm absorber (WA) components. For the first time we characterise the emission features in the RGS spectrum in detail and derive estimates for the distances of the ELR from the central engine. These are ~ 2.5 pc for the two narrow line components if we adopt an extended emission region and assume a volume filling factor of 0.1, making the ELR to be further out from the nuclear black hole than the WA. We discuss how adjusting the volume filling factor could resolve the differences with distance estimates obtained from variability arguments. Comparisons with other AGN, such as NGC 5548 and NGC 3783, for which we have also computed distances, will be presented.

Galaxy cluster science with XCS and DES
Paul Giles (University of Sussex)
The XMM Cluster Survey (XCS) has analysed the entire XMM public archive with the primary aim of producing a large catalogue of X-ray selected clusters. To date, over 5,000 extended sources have been identified as clusters of galaxies. In this presentation we will preview the second XCS data release and utilise recent DES data to describe a series of recent science results that include: the evolution and interpretation of various scaling relations (optical richness to T_x; L_x - T_x; M_x - T_x; velocity dispersion - T_x; M_lens - T_x; Y_sz - T_x); the evolution of the red sequence; constraints on modified gravity models. The presentation will feature several joint XCS-DES (Dark Energy Survey) results.

FCtrlA: Automated hydrostatic masses of XCS galaxy clusters
David Turner (University of Sussex)
The XMM Cluster Survey Sample contains tens of thousands of extended objects, hundreds of these are Galaxy Clusters that should be suitable for hydrostatic mass measurements. The scale of this task requires that the process be completely automated, and the XCS X-ray source sample can be uniquely leveraged for this. This talk will also cover XCSim, a new suite of code to produce realistic XMM-Newton data products from hydrodynamical  simulations of clusters, including BAHAMAS, ILLUSTRIS-TNG, and the 300 project.

X-ray Selected AGN in Dwarf Galaxies
Keir Birchall (University of Leicester)
Black holes are near ubiquitous higher up the galactic mass scale so AGN activity is inevitable at some point in the host's lifetime, but how prevalent are AGN in the regime of dwarf galaxies? In this work we present one of the first robust and large-scale quantifications of X-ray selected AGN in local (z<0.25) dwarf galaxies (Mstellar<3e9Msun). We define a parent sample of 4,331 dwarf galaxies found within the footprint of the MPA-JHU catalogue (based on SDSS DR8) and 3XMM DR7, performed a careful review to remove misidentifications and produced a sample of 61 dwarf galaxies that exhibit nuclear X-ray activity indicative of an AGN. To better understand these AGN we performed several measurements. First, we compared X-ray selection to BPT diagnostics and found this method misses 85% of our AGN population. We then calculated the growth rates of the black holes powering our AGN in terms of their accretion rates (proportional to Lx/M∗) and found a wide range of specific accretion rates. After correcting the observed sample for the varying sensitivity of 3XMM, we found further evidence for a wide range of X-ray luminosities and specific accretion rates, described by a power law. With this corrected AGN sample we found the AGN fraction increases with host galaxy mass (up to about 6%) for galaxies with X-ray luminosities between 10e39.17 erg/s and 10e41.79 erg/s, and by extending the power law to higher luminosities, we found evidence that luminous AGN (Lx>10e42.4 erg/s) fraction is constant to z = 0.7.

The shocking behaviour of 3C 15
Beatriz Mingo (Open University)
3C 15 is a radio-loud AGN that straddles the divide between high- and low-luminosity sources both in the radio (FRI/II, L_1.4GHz ~ 5e25 W/Hz) and the X-rays (LINER/Seyfert, L_2-10keV ~10e42 erg/s). It has radio lobes spanning ~50 kpc, also an intermediate case between those found on galaxy-scales (e.g. Circinus, Mrk 6, NGC 3801) and the large radio galaxies depositing large amounts of energy on cluster scales. Our Chandra observations show that 3C 15 might be driving a strong shock into a low-density environment, showing behaviour that is also intermediate between the thermally-dominated, low radio power sources, and the high-power FRIIs where inverse-Compton emission dominates in the X-rays, and where strong shocks are rare (e.g. 3C 444). The "middle ground" behaviour of 3C 15 could prove key to understanding the physical conditions of the under-studied population of intermediate-power radio-loud AGN, their lifetimes, and their impact on their surroundings.

Thermonuclear Burning on the Neutron Star Surface: Studying the Transition Between Unstable and Stable Burning Regimes
Giulio Mancuso (Instituto Argentino de Radioastronomía)
A low-mass X-ray binary is a system where one of the components is a compact object that is accreting H/He from a companion star, usually of spectral type A or later. In particular, if the compact object is a neutron star, depending on the accretion rate, theory predicts that the H/He is "burnt" in different regimes. Particularly, at a specific accretion rate, an oscillatory mode of burning is predicted. In this presentation I will describe the different burning regimes and explain why these particular type of oscillations can help us answer fundamental questions related to neutron stars and accretion flows.


A NICER spectral and timing analysis of the Rapid Burster

Angel Castro (University of Southampton)

We report a spectral-timing analysis of observations of the low mass X-ray binary MXB 1730-335, also known as Rapid Burster, obtained in July 2018 with the Neutron star Interior Composition Explorer (NICER). The Rapid Burster is the only object known to show both quickly repetitive type-II X-ray bursts, believed to be caused by instabilities in the accretion process, and type-I bursts, associated with thermonuclear burning. Its NICER 0.2-10 keV light curve shows the presence of several typical type-II bursts with different duration and one candidate thermonuclear type-I burst. The timing resolution and low-energy coverage of NICER allow us to perform time-resolved spectroscopy for some of the bursts. A preliminary analysis indicates the presence of a varying soft component, which implies that the type-II burst spectra change as the bursts evolve. This is the first time such a soft component is detected in type II bursts, suggesting that these bursts could be the result of limit cycles similar to those identified in the black hole systems GRS 1915+105 and IGR J17091-3624.

IC vs. ICM: distinguishing between X-ray emission from radio galaxy lobes and their host galaxy groups

Judith Ineson (University of Southampton)

Upcoming X-ray spectroscopy missions will provide the accuracy to make detailed investigations of the intra-cluster medium, and targets will be provided by catalogues of galaxy clusters and groups. At present, the long exposure times required severely limit surveys of non-local galaxy groups. This will improve with the new generation of X-ray telescopes - Athena WFI surveys should detect groups out to z∼2. Radio-loud AGN are hosted by galaxy groups; they also produce X-ray inverse Compton (IC) emission from their lobes that can be confused with the thermal emission from the groups. This will need to be resolved when calculating group properties. We can predict radio galaxy populations using recent LOFAR surveys. We can also predict their IC emission and the properties of their host groups. We use these to look at the numbers and properties of groups where IC emission will be problematic, and where high-resolution spectroscopy may be needed to distinguish between the X-ray sources.

Isolated Neutron Stars: Seven New Discoveries using RASS+SDSS

Lauren Conway (University of Sussex)

We present new isolated neutron star (INS) candidates discovered in the ROSAT All Sky Survey (RASS) public source catalogue. They were discovered using a cross match with the Sloan Digital Sky Survey Data Release 12 (SDSS DR12). For the initial selection we used the characteristic of a high X-ray to optical flux ratio: SDSS magnitudes fainter than g=23.348 and a minimum PSPC count rate of 0.327 counts per second. Visual inspection of the resulting 307 candidates was used to eliminate any RASS sources that were obviously not INS (e.g. in regions where the SDSS was masked). The remaining ten sources include the 3 previously known isolated neutron stars in the SDSS DR12 footprint. The next stage would be to carry out a snapshot Chandra observing campaign of the seven new candidates. We would welcome collaborators would would be willing to write the Chandra proposal.

Swift UVOT and XRT observations of the 2015 outburst of V404 Cygni

Sam Oates (University of Warwick)

In this poster we present Neil Gehrels Swift observatory observations of the black-hole binary, V404 Cygni, that went into outburst in June 2015, after 26 years of X-ray quiescence. We will compare the optical/UV observations taken with the Ultra-violet Optical Telescope with the X-ray observations obtained by the X-ray Telescope. We will provide evidence for a small inhomogeneous high density absorber containing a negligible amount of dust, close to the black hole. We will also discuss the variability in the light curves and suggest it may be produced by a complex combination of processes, resulting from the presence of the local, inhomogeneous and dust-free absorber and/or driven by the accretion flow: the X-rays are produced in the inner accretion disc, some of which are reprocessed to the optical/UV; and/or the X-ray and optical/UV emission is produced within the jet.

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