arXiv subjects

G. Branduardi-Raymont

Publications and source records attributed to G. Branduardi-Raymont.

At least 73 records · Page 4Linked to original sources

arXiv2006

Multi-band Astronomy with LISA

We discuss astrophysical scenarios relevant to the generation of gravitational waves (GW) and effects expected to arise from the interaction of GW and electromagnetic (EM) radiation. A strong programme of coordinated GW and EM astrophysical studies must be established in order to ensure the exploitation of the full scientific potential of the LISA mission. We describe on-going astrophysical work, and suggest alternative approaches to current studies, which are relevant to these considerations.

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arXiv2005

XMM-Newton observations of X-ray emission from Jupiter

We present the results of two XMM-Newton observations of Jupiter carried out in 2003 for 100 and 250 ks (or 3 and 7 planet rotations) respectively. X-ray images from the EPIC CCD cameras show prominent emission from the auroral regions in the 0.2 - 2.0 keV band: the spectra are well modelled by a combination of emission lines, including most prominently those of highly ionised oxygen (OVII and OVIII). In addition, and for the first time, XMM-Newton reveals the presence in both aurorae of a higher energy component (3 - 7 keV) which is well described by an electron bremsstrahlung spectrum. This component is found to be variable in flux and spectral shape during the Nov. 2003 observation, which corresponded to an extended period of intense solar activity. Emission from the equatorial regions of Jupiter's disk is also observed, with a spectrum consistent with that of solar X-rays scattered in the planet's upper atmosphere. Jupiter's X-rays are spectrally resolved with the RGS which clearly separates the prominent OVII contribution of the aurorae from the OVIII, FeXVII and MgXI lines, originating in the low-latitude disk regions of the planet.

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arXiv2005

XMM-Newton observations of the Seyfert 1 AGN H0557-385

We present XMM-Newton observations of the Seyfert 1 AGN H0557-385. We have conducted a study into the warm absorber present in this source, and using high-resolution RGS data we find that the absorption can be characterised by two phases: a phase with log ionisation parameter xi of 0.50 (where xi is in units of ergs cm/s) and a column of 0.2e21 cm^-2, and a phase with log xi of 1.62 and a column of 1.3e22 cm^-2. An iron K alpha line is detected. Neutral absorption is also present in the source, and we discuss possible origins for this. On the assumption that the ionised absorbers originate as an outflow from the inner edge of the torus, we use a new method for finding the volume filling factor. Both phases of H0557-385 have small volume filling factors (< 1%). We also derive the volume filling factors for a sample of 23 AGN using this assumption and for the absorbers with log xi > 0.7 we find reasonable agreement with the filling factors obtained through the alternative method of equating the momentum flow of the absorbers to the momentum loss of the radiation field. By comparing the filling factors obtained by the two methods, we infer that some absorbers with log xi < 0.7 occur at significantly larger distances from the nucleus than the inner edge of the torus.

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arXiv2005

Principal component analysis of the X-ray variability in NGC 7469

We apply Principal Component Analysis (PCA) to study the variability of the X-ray continuum in the Seyfert 1 galaxy NGC 7469. The PCA technique is used to separate out linear components contributing to variability between multiple datasets; the technique is often used in analysis of optical spectra, but has rarely been applied to AGN X-ray spectroscopy. Running a PCA algorithm on 0.3-10 keV EPIC data from a 150 ks XMM-Newton observation of NGC 7469, we describe the spectral components extracted and evaluate the usefulness of the PCA technique for understanding the X-ray continuum in AGN.

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arXiv2004

The nature and origin of Seyfert warm absorbers

We collate the results of recent high resolution X-ray spectroscopic observations of 23 AGN, and use the resulting information to try to provide answers to some of the main open questions about warm absorbers: where do they originate, what effect do they have on their host galaxies, and what is their importance within the energetics and dynamics of the AGN system as a whole? We find that the warm absorbers of nearby Seyferts and certain QSOs are most likely to originate in outflows from the dusty torus, and that the kinetic luminosity of these outflows accounts for well under 1% of the bolometric luminosities of the AGN. Our analysis supports, however, the view that the relativistic outflows recently observed in two PG quasars have their origin in accretion disc winds, although the energetic importance of these outflows is similar to that of the Seyfert warm absorbers. We find that the observed soft X-ray absorbing ionisation phases fill less than 10% of the available volume. Finally, we show that the amount of matter processed through an AGN outflow system, over the lifetime of the AGN, is probably large enough to have a significant influence on the evolution of the host galaxy and of the AGN itself.

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arXiv2004

The Seyfert-LINER Galaxy NGC 7213: An XMM-Newton Observation

We examine the XMM X-ray spectrum of the LINER-AGN NGC 7213, which is best fit with a power law, K-alpha emission lines from Fe I, Fe XXV and Fe XXVI and a soft X-ray collisionally ionised thermal plasma with kT=0.18 +0.03/-0.01 keV. We find a luminosity of 7x10^(-4) L_Edd, and a lack of soft X-ray excess emission, suggesting a truncated accretion disc. NGC 7213 has intermediate X-ray spectral properties, between those of the weak AGN found in the LINER M81 and higher luminosity Seyfert galaxies. This supports the notion of a continuous sequence of X-ray properties from the Galactic Centre through LINER galaxies to Seyferts, likely determined by the amount of material available for accretion in the central regions.

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arXiv2004

XMM-Newton observations of the heavily absorbed Seyfert 1 galaxy IC 4329A

We detect seven distinct absorbing systems in the high-resolution X-ray spectrum of the Seyfert 1 galaxy IC 4329A, taken with XMM-Newton. Firstly we detect absorption due to cold gas in our own Galaxy and warm gas in the Galactic halo or the Local Group. This local warm gas is only detected through O VII absorption, from which we deduce a temperature between 0.03 and 0.2 keV. In IC 4329A we detect absorption from the host galaxy as well as from a warm absorber, close to the nucleus, which has 4 components. The absorption from the host galaxy is well modeled by neutral material. The warm absorber detected in IC 4329A is photoionized and has an ionization range between log $ξ$ = -1.37 and log $ξ$ = 2.7. A broad excess is measured at the O VIII Ly$α$ and N VII Ly$α$ emission lines, which can be modeled by either disklines or multiple Gaussians. From the lightcurve we find that the source changed luminosity by about 20 % over the 140 ks observation, while the spectral shape, i.e. the softness ratio did not vary. In the EPIC spectra a narrow Fe K$α$ and Fe XXVI Ly$α$ emission line are detected. The narrowness of the Fe K$α$ line and the fact that there is no evidence for flux variability between different observations leads us to conclude that the Fe K$α$ line is formed at a large distance from the central black hole.

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arXiv2004

Relationship between X-ray and ultraviolet emission of flares from dMe stars observed by XMM-Newton

We present simultaneous ultraviolet and X-ray observations of the dMe-type flaring stars AT Mic, AU Mic, EV Lac, UV Cet and YZ CMi obtained with the XMM-Newton observatory. During 40 hours of simultaneous observation we identify 13 flares which occurred in both wave bands. For the first time, a correlation between X-ray and ultraviolet flux for stellar flares has been observed. We find power-law relationships between these two wavelength bands for the flare luminosity increase, as well as for flare energies, with power-law exponents between 1 and 2. We also observe a correlation between the ultraviolet flare energy and the X-ray luminosity increase, which is in agreement with the Neupert effect and demonstrates that chromospheric evaporation is taking place.

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arXiv2004

The X-ray spectrum of NGC 7213 and the Seyfert--LINER connection

We present an XMM-Newton observation of the Seyfert-LINER galaxy NGC 7213. The RGS soft X-ray spectrum is well fitted with a power law plus soft X-ray collisionally ionised thermal plasma (kT = 0.18 +0.03/-0.01 keV). We confirm the presence of Fe I, XXV and XXVI K-alpha emission in the EPIC spectrum and set tighter constraints on their equivalent widths of 82 +10/-13, 24 +9/-11 and 24 +10/-13 eV respectively. We compare the observed properties together with the inferred mass accretion rate of NGC 7213, to those of other Seyfert and LINER galaxies. We find that NGC 7213 has intermediate X-ray spectral properties lying between those of the weak AGN found in the LINER M81 and higher luminosity Seyfert galaxies. There appears to be a continuous sequence of X-ray properties from the Galactic Centre through LINER galaxies to Seyferts, likely determined by the amount of material available for accretion in the central regions.

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arXiv2004

XMM-Newton observations of warm absorbers in PG quasars

We present XMM-Newton EPIC observations of warm absorbers in the quasars PG 1114+445 and PG 1309+355, both of which exhibit evidence for absorption by warm material in the line-of-sight. We find the absorption in PG 1114+445 to be in two phases, a `hot' phase with a log ionisation parameter xi of 2.57, and a `cooler' phase with log xi of 0.83; an unresolved transition array (UTA) of M-shell iron is observed in the cooler phase. The absorption in this quasar is similar to that observed in the Seyfert 1 NGC 3783. The absorption in PG 1309+355 consists of a single phase, with log xi of 1.87. The absorbing gas lies at distances of 10^{18} - 10^{22} cm from the continuum radiation sources in these AGN, which suggests that it could originate in a wind emanating from a molecular torus. We derive distances assuming that these X-ray warm absorbers have the same velocity as the UV warm absorbers observed in these quasars. The distances to the warm absorbers from the central continuum source scale approximately with the square root of the AGN ionising luminosity, a result consistent with the warm absorber originating as a torus wind. The kinetic luminosities of these outflowing absorbers represent insignificant fractions (< 10^{-3}) of the energy budgets of the AGN.

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arXiv2004

First observation of Jupiter by XMM-Newton

We present the first X-ray observation of Jupiter by XMM-Newton. Images taken with the EPIC cameras show prominent emission, essentially all confined to the 0.2-2.0 keV band, from the planet's auroral spots; their spectra can be modelled with a combination of unresolved emission lines of highly ionised oxygen (OVII and OVIII), and a pseudo-continuum which may also be due to the superposition of many weak lines. A 2.8 sigma enhancement in the RGS spectrum at 21-22 A (~0.57 keV) is consistent with an OVII identification. Our spectral analysis supports the hypothesis that Jupiter's auroral emissions originate from the capture and acceleration of solar wind ions in the planet's magnetosphere, followed by X-ray production by charge exchange. The X-ray flux of the North spot is modulated at Jupiter's rotation period. We do not detect evidence for the ~45 min X-ray oscillations observed by Chandra more than two years earlier. Emission from the equatorial regions of the planet's disk is also observed. Its spectrum is consistent with that of scattered solar X-rays.

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arXiv2003

Intrinsic absorbers in BL Lac objects: the XMM-Newton view

We present XMM-Newton observations of four BL Lac objects (1H1219+301, H1426+428, Markarian 501 and PKS 0548-322), which have been found with past X-ray missions to contain evidence of broad soft X-ray absorption features. Observations with the high resolution Reflection Grating Spectrometers on XMM-Newton provide the best chance yet of investigating these features. No broad absorption features are observed in any of the objects. Neither do we find convincing evidence for narrow emission and absorption lines in the RGS spectra. We discuss the history of observations of broad absorption features in these four objects, finding that if the features exist then they must be transient, and that - given the frequency of reported observations of them - we can rule out the existence of transient broad absorption features in these objects at 93% confidence.

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arXiv2003

Spatially resolved X-ray spectroscopy of cooling clusters of galaxies

We present spatially resolved X-ray spectra taken with the EPIC cameras of XMM-Newton of a sample of 17 cooling clusters and three non-cooling clusters for comparison. The deprojected spectra are analyzed with a multi-temperature model, independent of any a priori assumptions about the physics behind the cooling and heating mechanisms. All cooling clusters show a central decrement of the average temperature, most of them of a factor of ~2. At each radius within the cooling region the gas is non-isothermal. The differential emission measure distribution peaks near the maximum (ambient) temperature, and steeply declines towards lower temperatures, proportional to T^3, or alternatively a cut-off at about a quarter to half of the maximum temperature. In general, we find a poor correlation between radio flux of the central galaxy and the temperature decrement of the cooling flow. This is interpreted as evidence that except for a few cases heating by a central AGN is not the most common cause of weak cooling flows. We investigate the role of heat conduction by electrons and find that the theoretically predicted conductivity rates are not high enough to balance radiation losses. The differential emission measure distribution has remarkable similarities with the predictions from coronal magnetic loop models. Also the physical processes involved (radiative cooling, thermal conduction along the loops, gravity) are similar for clusters loops and coronal loops. If coronal loop models apply to clusters, we find that a few hundred loops per scale height should be present. The typical loop sizes deduced from the observed emission measure distribution are consistent with the characteristic magnetic field sizes deduced from Faraday rotation measurements.

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arXiv2003

Can a Dusty Warm Absorber Model Reproduce the Soft X-ray Spectra of MCG-6-30-15 and Mrk 766?

XMM-Newton RGS spectra of MCG-6-30-15 and Mrk 766 exhibit complex discrete structure, which was interpreted in a paper by Branduardi-Raymont et al. (2001) as evidence for the existence of relativistically broadened Lyman alpha emission from carbon, nitrogen, and oxygen, produced in the inner-most regions of an accretion disk around a Kerr black hole. This suggestion was subsequently criticized in a paper by Lee et al. (2001), who argued that for MCG-6-30-15, the Chandra HETG spectrum, which is partially overlapping the RGS in spectral coverage, is adequately fit by a dusty warm absorber model, with no relativistic line emission. We present a reanalysis of the original RGS data sets in terms of the Lee et al. (2001) model, and demonstrate that spectral models consisting of a smooth continuum with ionized and dust absorption alone cannot reproduce the RGS spectra of both objects. The original relativistic line model with warm absorption proposed by Branduardi-Raymont et al. (2001) provides a superior fit to the RGS data, both in the overall shape of the spectrum and in the discrete absorption lines. Limits on the amount of X-ray absorption by dust particles are discussed. We also discuss a possible theoretical interpretation for the putative relativistic Lyman alpha line emission in terms of the photoionized surface layers of the inner regions of an accretion disk.

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arXiv2003

Chandra LETGS and XMM-Newton observations of NGC 4593

In this paper, we analyze spectra of the Seyfert 1 galaxy NGC 4593 obtained with the Chandra Low Energy Transmission Grating Spectrometer (LETGS), the Reflection Grating Spectrometer (RGS) and the European Photon Imaging Camera's (EPIC) onboard of XMM-Newton. The two observations were separated by ~7 months. In the LETGS spectrum we detect a highly ionized warm absorber corresponding to an ionization state of 400x10^{-9} W m, visible as a depression at 10-18 Å. This depression is formed by multiple weak Fe and Ne lines. A much smaller column density was found for the lowly ionized warm absorber, corresponding to xi = 3x10^{-9} W m. However, an intermediate ionization warm absorber is not detected. For the RGS data the ionization state is hard to constrain. The EPIC results show a narrow Fe Kalpha line.

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arXiv2003

Multiwavelength studies of the Seyfert 1 galaxy NGC7469. II - X-ray and UV observations with XMM-Newton

We present an XMM-Newton observation of NGC 7469, including studies of the X-ray and UV variability, 0.2-10 keV spectral continuum, Fe K-alpha emission line and the first-ever high-resolution X-ray spectrum of the soft X-ray warm absorber. We compare the properties of this X-ray warm absorber with the UV warm absorber as seen in a FUSE observation one year previously. The 0.2-10 keV spectral continuum is best fitted by a power-law plus two blackbody model. An Fe K-alpha emission line is visible which consists of a single narrow component and is well-modelled by a simple gaussian. Narrow absorption and emission lines in the soft X-ray RGS spectrum demonstrate the existence of a multi-phase warm absorber with a range in log xi of ~ 2 to ~ -2 where xi is in erg cm s^-1. The warm absorber is blueshifted by several hundred km s^-1. The highest-ionisation phase of the absorber is the best constrained and has an overall equivalent Hydrogen column of order 10^20 cm^-2; we find that its ionisation parameter is consistent with that of the warm emitter which generates the narrow emission lines. We identify this high ionisation absorber with the low-velocity phase of the UV absorber observed by FUSE.

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arXiv2003

Multiwavelength studies of the Seyfert 1 galaxy NGC7469. I - Far UV observations with FUSE

We obtained far-ultraviolet spectra of the Seyfert 1 galaxy NGC 7469 using the FUSE on 1999 December 6. Our spectra cover the wavelength range 990-1187 A with a resolution of 0.05 A. We see broad emission lines of CIII, NIII, OVI, and HeII as well as intrinsic absorption lines in the OVI 1032,1038 resonance doublet. The absorption arises in two distinct kinematic components at systemic velocities of -569 km/s and -1898 km/s. Both components are very highly ionized- no significant Ly beta absorption is present. The higher blueshift component is not quite saturated, and it has a total OVI column density of 8e14/cm2. It covers more than 90% of the continuum and broad-line emission. The lower blue shift component is heavily saturated and covers only 50% of the continuum and broad-line emission. It too has a column density of 8e14/cm2, but this is less certain due to the high saturation. We set an upper limit of <1.5e18/cm2 on the OVI column density of this component. Its line depth is consistent with coverage of only the continuum, and thus this component may lie interior to the broad emission-line gas. The component at -569 km/s has a velocity comparable to the high-ionization X-ray absorption lines seen in the XMM-Newton grating spectrum of NGC 7469, and photoionization models show that the observed column densities of OVI and HI are compatible with their formation in the same gas as that causing the X-ray absorption. The gas at -1898 km/s has lower ionization and column density, and no significant X-ray absorption is associated with it.

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arXiv2003

X-ray emission line gas in the LINER galaxy M81

We present the soft X-ray spectrum of the LINER galaxy M81 derived from a long observation with the XMM RGS. The spectrum is dominated by continuum emission from the active nucleus, but also contains emission lines from Fe L, and H-like and He-like N, O, and Ne. The emission lines are significantly broader than the RGS point-source spectral resolution; in the cross dispersion direction the emission lines are detected adjacent to, as well as coincident with, the active nucleus. This implies that they originate in a region of a few arc-minutes spatial extent (1 arc-minute ~ 1 kpc in M81). The flux ratios of the OVII triplet suggest that collisional processes are responsible for the line emission. A good fit to the whole RGS spectrum is obtained using a model consisting of an absorbed power law from the active nucleus and a 3 temperature optically thin thermal plasma. Two of the thermal plasma components have temperatures of 0.18+-0.04 keV and 0.64+-0.04 keV, characteristic of the hot interstellar medium produced by supernovae; the combined luminosity of the plasma at these two temperatures accounts for all the unresolved bulge X-ray emission seen in the Chandra observation by Tennant et al. (2001). The third component has a higher temperature (~1.7 keV), and we argue that this, along with some of the 0.64 keV emission, comes from X-ray binaries in the bulge of M81.

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