-
[show abstract]
[hide abstract]
ABSTRACT: We study the multiwavelength properties of an optically selected sample of
Low Ionization Nuclear Emission-line Regions (LINERs), in an attempt to
determine the accretion mechanism powering their central engine. We show how
their X-ray spectral characteristics, and their spectral energy distribution
compare to luminous AGN, and briefly discuss their connection to their less
massive counter-parts galactic black-hole X-ray binaries.
10/2012;
-
[show abstract]
[hide abstract]
ABSTRACT: We review X-ray plasma diagnostics based on the line ratios of He-like ions.
Triplet/singlet line intensities can be used to determine electronic
temperature and density, and were first developed for the study of the solar
corona. Since the launches of the X-ray satellites Chandra and XMM-Newton,
these diagnostics have been extended and used (from CV to Si XIII) for a wide
variety of astrophysical plasmas such as stellar coronae, supernova remnants,
solar system objects, active galactic nuclei, and X-ray binaries. Moreover, the
intensities of He-like ions can be used to determine the ionization process(es)
at work, as well as the distance between the X-ray plasma and the UV emission
source for example in hot stars. In the near future thanks to the next
generation of X-ray satellites (e.g., Astro-H and IXO), higher-Z He-like lines
(e.g., iron) will be resolved, allowing plasmas with higher temperatures and
densities to be probed. Moreover, the so-called satellite lines that are formed
closed to parent He-like lines, will provide additional valuable diagnostics to
determine electronic temperature, ionic fraction, departure from ionization
equilibrium and/or from Maxwellian electron distribution.
Space Science Reviews 01/2011; 157(1). · 3.61 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We present a study of the Arches cluster based on XMM-Newton observations performed over the past 8 years. Unexpectedly, we find that the X-ray emission associated with the cluster experienced a marked brightening in March/April 2007. We investigate the origin of both the X-ray continuum emission emanating from the star cluster and the flare. To study the time variability of the total X-ray flux, we stacked the PN and MOS data of observations performed within a time interval of a few days leading to the detection of the flaring episode. We then constructed two spectral datasets, one corresponding to the flare interval (March/April 2007) and another to the normal quiescent state of the source. The X-ray light curve of the Arches cluster shows, with high significance (8.6 sigma), a 70% increase in the X-ray emission in the March/April 2007 timeframe followed by a decline over the following year to the pre-flare level; the short-term duration of the flare is constrained to be longer than four days. The temperature and the line-of-sight column density inferred from the flare spectrum do not differ from those measured in the normal activity state of the cluster, suggesting that the flux enhancement is thermal in origin. We attribute the X-ray variability to in situ stellar activity: early-type stars may be responsible for the flare via wind collisions, whereas late-type stars may contribute by means of magnetic reconnection. These two possibilities are discussed. Comment: 6 pages, 3 figures, Accepted for publication in A&AL
11/2010;
-
[show abstract]
[hide abstract]
ABSTRACT: (Abridged) We present here a long (100ks) XMM-Newton follow-up of the Seyfert 1.8 galaxy ESO113-G010 performed in November 2005, in order to study over a longer time-scale its main X-ray properties. The source was found in a higher/softer time-averaged flux state, and timing analysis of this source reveals strong, rapid variability. The Power Spectral Density (PSD) analysis indicates (at 95% c.l.) a break at 3.7 x 10^-4 Hz. This cut-off frequency is comparable to those measured in some other rapidly-variable Seyferts, such as MCG-6-30-15 and NGC4051. From the mass-luminosity-time-scale, we infer that M_BH ranges from 4 x 10^6 - 10^7 M_odot and the source is accreting at or close to the Eddington rate (or even higher). The existing data cannot distinguish between spectral pivoting of the continuum and a two-component origin for the spectral softening, primarily because the data do not span a broad enough flux range. In the case of the two-component model, the fractional offsets measured in the flux-flux plots increase significantly toward higher energies (similar to what is observed in MCG-6-30-15) as expected if there exists a constant reflection component. Contrary to May 2001, no significant highly redshifted emission line is observed (which might be related to the source flux level), while two narrow emission lines at about 6.5keV and 7keV are observed. The S/N is not high enough to establish if the lines are variable or constant. As already suggested by the 2001 observation, no significant constant narrow 6.4keV FeK line (EW~32eV) is observed, hence excluding any dominant emission from distant cold matter such as a torus in this Seyfert type 1.8 galaxy. Comment: Accepted for publication in A&A, 10 pages, 11 figures, 2 tables
06/2007;
-
[show abstract]
[hide abstract]
ABSTRACT: Investigating the spectral and temporal characteristics of the X-rays coming from Sagittarius A* (Sgr A*) is essential to our development of a more complete understanding of the emission mechanisms in this supermassive black hole located at the center of our Galaxy. Several X-ray flares with varying durations and spectral features have already been observed from this object. Here we present the results of two long XMM-Newton observations of the Galactic nucleus carried out in 2004, for a total exposure time of nearly 500 ks. During these observations we detected two flares from Sgr A* with peak 2-10 keV luminosities about 40 times (L ~ 9x10^34 erg s−1) above the quiescent luminosity: one on 2004 March 31 and another on 2004 August 31. The first flare lasted about 2.5 ks and the second about 5 ks. The combined fit on the Epic spectra yield photon indeces of about 1.5 and 1.9 for the first and second flare respectively. This hard photon index strongly suggests the presence of an important population of non-thermal electrons during the event and supports the view that the majority of flaring events tend to be hard and not very luminous. Comment: 8 pages, 7 figures, Accepted for publication in the Astrophysical Journal
The Astrophysical Journal 08/2005; · 6.02 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We have calculated the equivalent widths of the absorption lines produced by Fe xxv and Fe xxvi in a Compton-thin, low-velocity photoionized material illuminated by the nuclear continuum in active galactic nuclei. The results, plotted against the ionization parameter and the column density of the gas, are a complement to those presented by Bianchi & Matt for the emission lines from the same ionic species. As an extension to the work by Bianchi & Matt, we also present a qualitative discussion on the different contributions to the He-like iron emission line complex in the regimes where recombination or resonant scattering dominates, providing a useful diagnostic tool to measure the column density of the gas. Future high-resolution missions (e.g. Astro-E2) will allow us to fully take advantage of these plasma diagnostics. In the meantime, we compare our results with an up-to-date list of Compton-thick and unobscured (at least at the iron line energy) Seyfert galaxies with emission and/or absorption lines from H- and He-like iron observed with Chandra and XMM–Newton.
Monthly Notices of the Royal Astronomical Society 01/2005; 357(2):599 - 607. · 4.90 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Absorption spectra of iron L-lines are observed in AGN by Chandra and
XMM-Newton. FeXXIV to Fe XVII lines corespond to transitions between
ground and excited levels whereas Fe XVI to Fe VII lines involve
autoionizing levels as upper levels. Theoretical atomic data for n=2-3
and n=2-4 radiative transitions will be presented : wavelengths
radiative and autoionization probability rates. We shall also discuss
their applications to the photoionized plasmas in Seyfert galaxies.
Highlights of Astronomy. 12/2004; 13:627.
-
[show abstract]
[hide abstract]
ABSTRACT: We present an XMM-Newton observation of the radio-quiet quasar Q0056-363 (z=0.162). This is the first time that this quasar is observed in the hard X-ray range (above 2 keV). We find that Q0056-363 is a powerful X-ray quasar, with a 0.3-12 keV unabsorbed luminosity of about 1.2 x 10^45 erg s-1 with the largest part (~67%) emitted below 2 keV. The spectrum reveals a large featureless soft X-ray excess below 2 keV and a strong broad FeKalpha line at 6.4 keV (in the quasar frame). The FeK alpha line is due to low to moderate ionization states of iron (i.e., < Fe XVII), with an equivalent width of about 250 eV and a velocity width of about 25,000 km s-1. Q0056-363 is presently the most luminous AGN known to exhibit such a broad and intense FeKalpha line profile from near neutral iron. The line can be fitted with a relativistic profile from an accretion disc around either a Schwarzschild (non-rotating) or a Kerr (rotating) black hole. A combination of two thermal Comptonization components and a disc reflection model is favored to explain both the continuum over the energy range 0.3-12 keV and the FeK alpha line. A patchy corona covering a large part of the inner disc surface is needed in order to be compatible with the accretion rate inferred from the spectral energy distribution of Q0056-363, unless the mass of the black hole is much higher than about 5 x 10^8 M_odot. Comment: Accepted for publication in Astronomy and Astrophysics; 8 pages, 5 figures
06/2003;
-
[show abstract]
[hide abstract]
ABSTRACT: The 1s2-1s2l lines are the most intense He-like ions lines. They are used as spectroscopic diagnostics for solar active regions as well as for different laboratory plasmas. Nowadays, it exits very high spectral resolution instruments and, for intense X-ray sources, one can do spectroscopic diagnostics from line ratios. With XMM (RGS) and Chandra (LETGS, HETGS) spectral resolutions and for several atomic elements, it is particularly possible to separate a 3 blended line set, the so-called He-like triplet: Resonance (r), Intercombination (i) and Forbidden (f), which are dominated respectively by lines issued from the following levels : 1s2p 1P1, 1s2p 3P1,2 and 1s2s 3S1. We shall show that the measurement of two different ratios between these 3 lines (R = f/i and G = (f + i)/r) give quantitative informations on the nature of the emitting plasma (photo-ionized or collisional) and on its electronic density and temperature. A more refined analysis must also include satellite line contributions.
05/2002;
-
[show abstract]
[hide abstract]
ABSTRACT: We present He-like line ratios (resonance, intercombination and forbidden lines) for totally and partially photoionized media. For solar plasmas, these line ratios are already widely used for density and temperature diagnostics of coronal (collisional) plasmas. In the case of totally and partially photoionized plasmas, He-like line ratios allow for the determination of the ionization processes involved in the plasma (photoionization with or without an additional collisional ionization process), as well as the density and the electronic temperature. With the new generation of X-ray satellites, Chandra/AXAF, XMM and Astro-E, it will be feasible to obtain both high spectral resolution and high sensitivity observations. Thus in the coming years, the ratios of these three components will be measurable for a large number of non-solar objects. In particular, these ratios could be applied to the Warm Absorber-Emitter, commonly present in Active Galactic Nuclei (AGN). A better understanding of the Warm Absorber connection to other regions (Broad Line Region, Narrow Line Region) in AGN (Seyferts type-1 and type-2, low- and high-redshift quasars...) will be an important key to obtaining strong constraints on unified schemes. We have calculated He-like line ratios, for Z=6, 7, 8, 10, 12 and 14, taking into account the upper level radiative cascades which we have computed for radiative and dielectronic recombinations and collisional excitation. The atomic data are tabulated over a wide range of temperatures in order to be used for interpreting a large variety of astrophysical plasmas. Comment: 23 pages, 11 figures, 14 tables. A&AS, in press
02/2000;
-
[show abstract]
[hide abstract]
ABSTRACT: Thanks to the new generation of X-ray satellites such as Chandra and XMM, high resolution and high sensitivity spectra are available. In particular, for the first time, the three most intense lines (resonance, intercombination and forbidden) of low charged (low Z) He-like ions are splitted for non solar plasmas. We present density, ionizing process and temperature diagnostics, for totally and partially photoionized plasmas, based on ratios of these three lines. These powerful plasma diagnostics could be used for hot astrophysical plasmas such as AGN, starburst galaxies, X-ray binaries, etc. In particular, they could be applied to Warm Absorber often seen in Active Galactic Nuclei (Porquet & Dubau 2000), which is an important key tool to understand central region of different types of AGN (Seyfert 1 and 2, high and low redshift quasars).
01/2000;
-
[show abstract]
[hide abstract]
ABSTRACT: Thanks to the new generation of X-ray satellites such as Chandra and XMM, high resolution and high sensitivity spectra are available. In particular, for the rst time, the three most intense lines (resonance, intercombination and forbidden) of low charged (low Z) He-like ions are split for non-solar plasmas. We present density, ionizing process and temperature diagnostics, for totally and partially photoionized plasmas, based on ratios of these three lines. These powerful plasma diagnostics could be used for hot astrophysical plasmas such as AGN, starburst galaxies, X-ray binaries, etc. In particular, they could be applied to the Warm Absorbers often seen in Active Galactic Nuclei (Porquet & Dubau 2000), which is an important tool for understanding the central regions of di erent types of AGN (Seyfert 1 and 2, high and low redshift quasars).
Revista Mexicana de Astronomía y Astrofísica. 01/2000;
