404 research outputs found
In-orbit Vignetting Calibrations of XMM-Newton Telescopes
We describe measurements of the mirror vignetting in the XMM-Newton
Observatory made in-orbit, using observations of SNR G21.5-09 and SNR
3C58 with the EPIC imaging cameras. The instrument features that complicate
these measurements are briefly described. We show the spatial and energy
dependences of measured vignetting, outlining assumptions made in deriving the
eventual agreement between simulation and measurement. Alternate methods to
confirm these are described, including an assessment of source elongation with
off-axis angle, the surface brightness distribution of the diffuse X-ray
background, and the consistency of Coma cluster emission at different position
angles. A synthesis of these measurements leads to a change in the XMM
calibration data base, for the optical axis of two of the three telescopes, by
in excess of 1 arcminute. This has a small but measureable effect on the
assumed spectral responses of the cameras for on-axis targets.Comment: Accepted by Experimental Astronomy. 26 pages, 18 figure
An XMM-Newton view of the serendipitous sources in the PKS0312-770 field
We describe an XMM-Newton observation of the PKS0312-770 field, which facilitates the spectral analysis of serendipitous sources previously detected by CHANDRA. The combination of larger effective area and longer exposure duration allows a significant increase in detected photons, and a lower limit in source detection sensitivity. In particular the hard X-ray normal galaxy unveiled by Fiore et al (2000) is most likely explained as a moderately absorbed (N_H ~ 1e22 cm^-2) AGN. We detect 52 sources (45 previously unreported) at a limiting flux of ~2e-15 cgs in the 0.5-2keV band. The LogN-LogS curve is consistent with that derived from by XMM-Newton observations of the Lockman Hole field. The flux determinations allow to check for any inconsistency between the calibrations of the two observatories, which is discussed
The history of the iron K-alpha line profile in the Piccinotti AGN ESO198-G24
This paper presents ASCA (July 1997), XMM-Newton (December 2000) and BeppoSAX
(January 2001) observations of the Piccinotti Seyfert 1 galaxy ESO198-G24. The
BeppoSAX 0.1-200 keV spectrum exhibits reprocessing features, probably produced
by an X-ray illuminated, relativistic accretion disk subtending a solid angle
\~2 pi. During the XMM-Newton observation the fluorescent iron K-alpha line
profile (centroid energy E~6.4 keV) was broad and twice as bright as in the
BeppoSAX observation. An additional emission feature (E~5.7 keV), detected at
the 96.3% confidence level, may be part of a relativistic, double-peaked
profile. By contrast, in the earlier ASCA observation the line profile is
dominated by a remarkably narrow "core" (intrinsic width <50 eV). If this
component is produced by reflection off the inner surface of a molecular torus,
its large Equivalent Width (~300 eV) most likely represents the "echo" of a
previously brighter flux state, in agreement with the dynamical range covered
by the historical X-ray light curve in ESO198-G24.Comment: 9 Latex pages, 11 figures, To appear in Astronomy & Astrophysic
New high-sensitivity, milliarcsecond resolution results from routine observations of lunar occultations at the ESO VLT
(Abridged) Lunar occultations (LO) are a very efficient and powerful
technique, that achieves the best combination of high angular resolution and
sensitivity possible today at near-infrared wavelengths. Given that the events
are fixed in time, that the sources are occulted randomly, and that the
telescope use is minimal, the technique is very well suited for service mode
observations. We have established a program of routine LO observations at the
VLT observatory, especially designed to take advantage of short breaks
available in-between other programs. We have used the ISAAC instrument in burst
mode, capable of producing continuous read-outs at millisecond rates on a
suitable subwindow. Given the random nature of the source selection, our aim
has been primarily the investigation of a large number of stellar sources at
the highest angular resolution in order to detect new binaries. Serendipitous
results such as resolved sources and detection of circumstellar components were
also anticipated. We have recorded the signal from background stars for a few
seconds, around the predicted time of occultation by the Moon's dark limb. At
millisecond time resolution, a characteristic diffraction pattern can be
observed. Patterns for two or more sources superimpose linearly, and this
property is used for the detection of binary stars. The detailed analysis of
the diffraction fringes can be used to measure specific properties such as the
stellar angular size and the presence of extended light sources such as a
circumstellar shell. We present a list of 191 stars for which LO data could be
recorded and analyzed. Results include the detection of 16 binary and 2 triple
stars, all but one of which were previously unknown. The projected angular
separations are as small as 4 milliarcseconds and magnitude differences as high
as ?K=5.8 mag...Comment: 10 pages, 3 figures, to be published in A&
An XMM and Chandra view of massive clusters of galaxies to z=1
The X-ray properties of a sample of high redshift (z>0.6), massive clusters
observed with XMM-Newton and Chandra are described, including two exceptional
systems. One, at z=0.89, has an X-ray temperature of T=11.5 (+1.1, -0.9) keV
(the highest temperature of any cluster known at z>0.6), an estimated mass of
(1.4+/-0.2)x10^15 solar masses and appears relaxed. The other, at z=0.83, has
at least three sub-clumps, probably in the process of merging, and may also
show signs of faint filamentary structure at large radii,observed in X-rays. In
general there is a mix of X-ray morphologies, from those clusters which appear
relaxed and containing little substructure to some highly non-virialized and
probably merging systems. The X-ray gas metallicities and gas mass fractions of
the relaxed systems are similar to those of low redshift clusters of the same
temperature, suggesting that the gas was in place, and containing its metals,
by z=0.8. The evolution of the mass-temperature relation may be consistent with
no evolution or with the ``late formation'' assumption. The effect of point
source contamination in the ROSAT survey from which these clusters were
selected is estimated, and the implications for the ROSAT X-ray luminosity
function discussed.Comment: 9 pages, in Carnegie Observatories Astrophysics Series, Vol. 3:
Clusters of Galaxies: Probes of Cosmological Structure and Galaxy Evolution,
ed. J. S. Mulchaey, A. Dressler, and A. Oemler. See
http://www.ociw.edu/ociw/symposia/series/symposium3/proceedings.html for a
full-resolution versio
Redshift determination in the X-ray band of gamma-ray bursts
If gamma-ray bursts originate in dense stellar forming regions, the
interstellar material can imprint detectable absorption features on the
observed X-ray spectrum. Such features can be detected by existing and planned
X-ray satellites, as long as the X-ray afterglow is observed after a few
minutes from the burst. If the column density of the interstellar material
exceeds ~10^{23} cm^{-2} there exists the possibility to detect the K_alpha
fluorescent iron line, which should be visible for more than one year, long
after the X-ray afterglow continuum has faded away. Detection of these X-ray
features will make possible the determination of the redshift of gamma-ray
bursts even when their optical afterglow is severely dimmed by extinction.Comment: 15 pages with 5 figures. Submitted to Ap
BeppoSAX/PDS serendipitous detections at high galactic latitudes
At a flux limit of ~10^(-11) erg/cm2/s in the 20-100 keV band, the PDS
instrument on-board BeppoSAX offers the opportunity to study the extragalactic
sky with an unprecedented sensitivity. In this work we report on the results of
a search in the BeppoSAX archive for serendipitous high energy sources at high
galactic latitudes (|b| > 13 deg). We have defined a set of twelve regions in
which the PDS/MECS cross-calibration constant is higher than the nominal value.
We attribute this mismatch to the presence of a serendipitous source in the PDS
field of view.In four cases the likely high energy emitter is also present in
the MECS field of view. In these cases, we have performed a broad band spectral
analysis (1.5-100 keV) so as to understand the source spectral behaviour and
compare it with previous BeppoSAX observations when available. In eight cases
the identification of the source likely to provide the PDS spectrum is based on
indirect evidence (extrapolation to lower energies and/or comparison to
previous observations). This approach leads to the discovery of six new hard
X-ray emitting objects (PKS 2356-611, 2MASX J14585116-1652223, NGC 1566, NGC
7319, PKS 0101-649 and ESO 025-G002) and to the presentation the PDS spectrum
of NGC 3227 for the first time. In the remaining five cases we provide extra
BeppoSAX observations that can be compared with measurements which are already
published and/or in the archive.Comment: 16 pages, 9 figures, accepted for publication in A&A, main journa
Statistics of relativistically broadened Fe K-alpha lines in AGN
We present preliminary results on the properties of relativistically
broadened Fe K-alpha lines in a collection of more then 100 Active Galactic
Nuclei (AGN) observed by the XMM-Newton EPIC-pn camera. Our main conclusions
can be summarized as follows: a) we detect broad lines in about 25% of the
sample objects. This fraction increases to 42+/-13% if we consider only objects
with more than 10000 counts in the hard (2-10 keV) band, and to 50+/-32% for
the small sub-sample (6 objects) of type~1 Piccinotti AGN with optimal
XMM-Newton exposure (at least 200000 counts in the hard band); b) we find no
significant difference in the detection rate of broad lines between obscured
and unobscured AGN; c) the strongest relativistic profiles are measured in
low-luminosity (< 10^43 erg/s) AGN; d) Equivalent Widths (EWs) associated with
relativistic profiles in stacked spectra are ~150 eV for all luminosity
classes; e) models of relativistically broadened iron line profiles ("kyrline",
Dovciak et al. 2005), which include full relativistic treatment of the
accretion disk emission around a Kerr black hole in the strong gravity regime,
yield an average disk inclination angle ~30 degrees, and a radial dependence of
the disk emissivity profile ~-3. The distribution of EW is very broad, with
=2.4. We estimate that an investment of about 1 Ms of XMM-Newton time
would be required to put these results on a sound statistical basis.Comment: 4 pages, 9 figures, to appear in Astronomische Nachrichten,
Proceedings of the ESAC Workshop "Variable and broad lines around black
holes
An absorption event in the X-ray lightcurve of NGC 3227
We have monitored the Seyfert galaxy NGC 3227 with the Rossi X-ray Timing
Explorer (RXTE) since January 1999. During late 2000 and early 2001 we observed
an unusual hardening of the 2-10 keV X-ray spectrum which lasted several
months. The spectral hardening was not accompanied by any correlated variation
in flux above 8 keV. We therefore interpret the spectral change as transient
absorption by a gas cloud of column density 2.6 10^23 cm^-2 crossing the line
of sight to the X-ray source. A spectrum obtained by XMM-Newton during an early
phase of the hard-spectrum event confirms the obscuration model and shows that
the absorbing cloud is only weakly ionised. The XMM-Newton spectrum also shows
that ~10% of the X-ray flux is not obscured, but this unabsorbed component is
not significantly variable and may be scattered radiation from a large-scale
scattering medium. Applying the spectral constraints on cloud ionisation
parameter and assuming that the cloud follows a Keplerian orbit, we constrain
the location of the cloud to be R~10-100 light-days from the central X-ray
source, and its density to be n_H~10^8cm^-3, implying that we have witnessed
the eclipse of the X-ray source by a broad line region cloud.Comment: 5 pages, 6 figures, accepted for publication in MNRAS letter
A prominent relativistic iron line in the Seyfert 1 MCG-02-14-009
I report the discovery of a prominent broad and asymmetrical feature near 6.4
keV in the Seyfert 1 MCG-02-14-009 (z=0.028) with XMM-Newton/EPIC. The present
short X-ray observation (PN net exposure time ~5 ks) is the first one above 2
keV for MCG-02-14-009. The feature can be explained by either a relativistic
iron line around either a Schwarzschild (non-rotating) or a Kerr (rotating)
black hole. If the feature is a relativistic iron line around a Schwarzschild
black hole, the line energy is 6.51 (+0.21,-0.12) keV with an equivalent width
of 631 (+259,-243) eV and that the inclination angle of the accretion disc
should be less than 43 degrees. A relativistically blurred photoionized disc
model gives a very good spectral fit over the broad band 0.2-12keV energy
range. The spectrum is reflection dominated and this would indicate that the
primary source in MCG-02-14-009 is located very close to the black hole, where
gravitational light bending effect is important (about 3-4 Rg), and that the
black hole may rapidly rotate.Comment: Accepted for publication, A&A Letters, 5 pages, 3 figures, and 1
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