arXiv subjects

P. Ferrando

Publications and source records attributed to P. Ferrando.

33 records · Page 2Linked to original sources

arXiv2003

The X-ray flaring activity of the galactic nucleus observed with XMM-Newton

We report the results of XMM-Newton observations of Sgr A*, the radiative counterpart of the massive black hole at the nucleus of our Galaxy, performed in the frame of the guaranteed time survey program of the Galactic Center region. The discovery of bright X-ray flares from Sgr A* with Chandra in October 2000 have opened new perspectives to understand the processes at work in this object and in general in black holes accreting at low accretion rates. We report here the important results obtained with XMM-Newton on the Sgr A* high-energy flaring activity and we discuss the implications on the models and the future observational perspectives.

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arXiv2003

SIMBOL-X : a new generation hard X-ray telescope

SIMBOL-X is a hard X-ray mission, operating in the 0.5-70 keV range, which is proposed by a consortium of European laboratories for a launch around 2010. Relying on two spacecraft in a formation flying configuration, SIMBOL-X uses a 30 m focal length X-ray mirror to achieve an unprecedented angular resolution (30 arcsec HEW) and sensitivity (100 times better than INTEGRAL below 50 keV) in the hard X-ray range. SIMBOL-X will allow to elucidate fundamental questions in high energy astrophysics, such as the physics of accretion onto Black Holes, of acceleration in quasar jets and in supernovae remnants, or the nature of the hard X-ray diffuse emission. The scientific objectives and the baseline concepts of the mission and hardware design are presented.

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arXiv2003

The XMM/BeppoSAX observation of Mkn 841

Mkn 841 has been observed simultaneously by XMM and BeppoSAX in January 2001. Due to operational contingency, the 30ks XMM observation was split into two parts, separated by about 15 hours. We first report the presence of a narrow iron line which appears to be rapidly variable between the two pointings, requiring a non-standard interpretation. We then focus on the analysis of the broad band (0.3-200 keV) continuum using the XMM/EPIC, RGS and SAX/PDS data. The Mkn 841 spectrum is well fitted by a comptonization model in a geometry more photon-fed than a simple slab geometry above a passive disk. It presents a relatively large reflection (R>2) which does not agree with an apparently weak iron line. It also show the presence of a strong soft excess wellfitted by a comptonized spectrum in a cool plasma, suggesting the presence of a multi-temperature corona.

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arXiv2003

A New X-Ray Flare from the Galactic Nucleus Detected with the XMM-Newton

The compact radio source Sgr A*, believed to be the counterpart of the massive black hole at the Galactic nucleus, was observed to undergo rapid and intense flaring activity in X-rays with Chandra in October 2000. We report here the detection with XMM-Newton EPIC cameras of the early phase of a similar X-ray flare from this source, which occurred on 2001 September 4. The source 2-10 keV luminosity increased by a factor ~ 20 to reach a level of 4 10$^{34}$ erg s$^{-1}$ in a time interval of about 900 s, just before the end of the observation. The data indicate that the source spectrum was hard during the flare and can be described by simple power law of slope ~ 0.7. This XMM-Newton observation confirms the results obtained by Chandra, suggests that, in Sgr A*, rapid and intense X-ray flaring is not a rare event and therefore sets some constraints on the emission mechanism models proposed for this source.

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arXiv2002

A New X-Ray Flare from the Galactic Nucleus Detected with the XMM-Newton Photon Imaging Cameras

Sgr A*, the compact radio source, believed to be the counterpart of the massive black hole at the galactic nucleus, was observed to undergo rapid and intense flaring activity in X-rays with Chandra in October 2000. We report here the detection with XMM-Newton EPIC cameras of the early phase of a similar X-ray flare from this source, which occurred on September 4, 2001. The source 2-10 keV luminosity increased by a factor about 20 to reach a level of 4 10^{34} erg s^{-1} in a time interval of about 900 s, just before the end of the observation. The data indicate that the source spectrum was hard during the flare. This XMM-Newton observation confirms the results obtained by Chandra and suggests that, in Sgr A*, rapid and intense X-ray flaring is not a rare event. This can constrain the emission mechanism models proposed for this source, and also implies that the crucial multiwavelength observation programs planned to explore the behaviour of the radio/sub-mm and hard X-ray/gamma-ray emissions during the X-ray flares, have a good chance of success.

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arXiv2002

A rapidly variable narrow X-ray iron line in Mkn 841

We report on the detection of a rapidly variable narrow Fe K$α$ line in Mkn 841. The source has been observed two times by XMM-Newton and simultaneously with BeppoSAX. The two observations, of about 10ks long each, were separated by $\sim$ 15 hours. The line flux reaches a maximum during the first observation and is significantly reduced in the second one. The continuum shape and flux, instead, keep roughly constant between the two pointings. Such rapid variability of a narrow (unresolved by the XMM-pn instrument) line has never been reported in the past. These results are not easily explained in the standard cold reflection model where the narrow line component is supposed to be produced far from the primary X-ray source (e.g. from the torus) and is thus not expected to vary rapidly. Different interpretations are discussed.

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arXiv2002

Status of the EPIC/MOS calibration

The XMM-Newton observatory has the largest collecting area flown so far for an X-ray imaging system, resulting in a very high sensitivity over a broad spectral range. In order to exploit fully these performances, a very accurate calibration of the XMM-Newton instruments is required, and has led to an extensive ground and flight calibration program. We report here on the current status of the EPIC/MOS cameras calibrations, highlighting areas for which a reasonably good accuracy has been achieved, and noting points where further work is needed.

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arXiv2002

XMM-Newton observation of the bursting pulsar GRO J1744-28 in quiescence

The XMM-Newton X-ray observatory performed a pointed observation of the bursting pulsar GRO J1744-28 in April 2001 for about 10 ks during a program devoted to the scan of the Galactic center region. After the discovery of this source by BATSE in December 1995 during a very active bursting phase, it has been in quiescence since April 1997. We present here the first detection of GRO J1744-28 in its quiescent state at a position which is consistent with previous high-energy positions (but not consistent with a proposed IR counterpart). The observed luminosity of the source in quiescence is about 6 orders of magnitude weaker than the luminosity in outburst.

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arXiv2001

XMM-Newton Spectroscopy of the Galactic Microquasar GRS 1758-258 in the Peculiar Off/Soft State

We report on an XMM-Newton Reflection Grating Spectrometer observation of the black hole candidate and Galactic microquasar GRS 1758-258. The source entered a peculiar "off/soft" state in late February, 2001, in which the spectrum softened while the X-ray flux -- and the inferred mass accretion rate -- steadily decreased. We find no clear evidence for emission or absorption lines in the dispersed spectra, indicating that most of the observed soft flux is likely from an accretion disk and not from a cool plasma. The accretion disk strongly dominates the spectrum in this lower-luminosity state, and is only mildly recessed from the marginally stable orbit. These findings may be difficult to explain in terms of advection-dominated accretion flow, or "ADAF" models. We discuss these results within the context of ADAF models, simultaneous two-flow models, and observed correlations between hard X-ray flux and jet production.

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arXiv2001

XMM-Newton Observation of the Black Hole Microquasar GRS 1758-258

The XMM-Newton X-ray observatory pointed the galactic black hole candidate and microquasar GRS 1758-258 in September 2000 for about 10 ks during a program devoted to the scan of the Galactic Center regions. Preliminary results from EPIC MOS camera data are presented here. The data indicate that the source underwent a state transition from its standard low-hard state to an intermediate state. For the first time in this source the ultra-soft component of the accretion disk, which black hole binaries display in intermediate or high-soft states, was clearly detected and measured thanks to the high spectral capabilities of XMM-Newton.

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arXiv2000

XMM-Newton observation of the Lockman Hole; I. The X-ray Data

We report on the first deep X-ray survey with the XMM-Newton observatory during the performance verification phase. The field of the Lockman Hole, one of the best studied sky areas over a very wide range of wavelengths, has been observed. A total of ~100 ksec good exposure time has been accumulated. Combining the images of the European Photon Imaging Camera (EPIC) detectors we reach a flux limit of 0.31, 1.4 and 2.4 X 10^{-15} erg cm^{-2} s^{-1}, respectively in the 0.5-2, 2-10, and 5-10 keV band. Within an off-axis angle of 10 arcmin we detect 148, 112 and 61 sources, respectively. The log(N)-log(S) relation in the three bands is compared with previous results. In particular in the 5-10 keV band these observations present the deepest X-ray survey ever, about a factor 20 more sensitive than the previous BeppoSAX observations. Using X-ray spectral diagnostics and the set of previously known, spectroscopically identified ROSAT sources in the field, the new sources can be classified. XMM-Newton detects a significant number (~40%) of X-ray sources with hard, probably intrinsically absorbed X-ray spectra, confirming a prediction of the population synthesis models for the X-ray background.

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arXiv2000

The Extended X-ray Halo of the Crab-like SNR G21.5-0.9

Recent XMM-Newton observations reveal an extended (150") low-surface brightness X-ray halo in the supernova remnant G21.5-0.9. The near circular symmetry, the lack of any limb brightening and the non-thermal spectral form, all favour an interpretation of this outer halo as an extension of the central synchrotron nebula rather than as a shell formed by the supernova blast wave and ejecta. The X-ray spectrum of the nebula exhibits a marked spectral softening with radius, with the power-law spectral index varying from Gamma = 1.63 +/- 0.04 in the core to Gamma = 2.45 +/- 0.06 at the edge of the halo. Similar spectral trends are seen in other Crab-like remnants and reflect the impact of the synchrotron radiation losses on very high energy electrons as they diffuse out from the inner nebula. A preliminary timing analysis provides no evidence for any pulsed X-ray emission from the core of G21.5-0.9.

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arXiv2000

The eclipsing bursting X-ray binary EXO 0748-676 revisited by XMM-Newton

The bright eclipsing and bursting low-mass X-ray binary EXO 0748-676 has been observed at several occasions by XMM-Newton during the initial calibration and performance verification (CAL/PV) phase. We present here the results obtained from observations with the EPIC cameras. Apart from several type-I X-ray bursts, the source shows a high degree of variability with the presence of soft flares. The wide energy coverage and high sensitivity of XMM-Newton allows for the first time a detailed description of the spectral variability. The source is found to be the superposition of a central (~2 10^8 cm) Comptonized emission, most probably a corona surrounding the inner edge of an accretion disk, associated with a more extended (~3 10^10 cm) thermal halo at a typical temperature of ~0.6 keV with an indication of non-solar abundances. Most of the variations of the source can be accounted for by a variable absorption affecting only the central comptonized component and reaching up to NH ~1.3 10^23 cm^{-2}. The characteristics of the surrounding halo are found compatible with an irradiated atmosphere of an accretion disc which intercepts the central emission due to the system high inclination.

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arXiv2000

XMM-Newton observations of NGC 253: Resolving the emission components in the disk and nuclear area

The high XMM-Newton throughput allows a detailed investigation of the spatial, spectral and variability properties of the extended and point source emission of the starburst galaxy NGC 253 simultaneously. We characterize the brightest sources by their hardness ratios, detect a bright X-ray transient, and show the spectrum and light curve of the brightest point source, most likely a black-hole X-ray binary. The unresolved emission of two disk regions can be modeled by two thin thermal plasma components of 0.13 and 0.4 keV plus residual harder emission, with the lower temperature component originating from above the disk, the nuclear spectrum by a three temperature plasma (~0.6, 0.9, and 6 keV) with the higher temperatures increasingly absorbed. The high temperature component most likely originates from the starburst nucleus. No non-thermal component, that would point at a significant contribution from an active nucleus (AGN), is needed. Assuming that type IIa supernova remnants (SNRs) are mostly responsible for the E>4 keV emission, the detection with EPIC of the 6.7 keV line allows us to estimate a supernova rate within the nuclear starburst of 0.2 yr^-1. RGS spectra and EPIC images reveal that the limb-brightening of the plume is mostly seen in higher ionization emission lines, while in the lower ionization lines, and below 0.5 keV, the plume is more homogeneously structured. (abridged)

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arXiv2000

XMM-Newton observation of an unusual iron line in the quasar Markarian 205

XMM-Newton observations of the low luminosity, radio-quiet quasar Markarian 205 have revealed a unique iron K emission line profile. In marked contrast to the broad and redshifted iron K line commonly seen in ASCA observations of Seyfert 1 galaxies, we find that a substantial amount of the line flux in Mrk 205 occurs above the neutral line energy of 6.4 keV. Furthermore, we find that the iron line emission has two distinct components, a narrow, unresolved neutral line at 6.4 keV and a broadened line centred at 6.7 keV. We suggest that the most likely origin of the 6.7 keV line is from X-ray reflection off the surface of a highly ionised accretion disk, whilst the 6.4 keV component may arise from neutral matter distant from the black hole, quite possibly in the putative molecular torus. Overall this observation underlines the potential of XMM-Newton for using the iron K line as a diagnostic of matter in the innermost regions of AGN.

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