199 research outputs found
Status of a DEPFET pixel system for the ILC vertex detector
We have developed a prototype system for the ILC vertex detector based on
DEPFET pixels. The system operates a 128x64 matrix (with ~35x25 square micron
large pixels) and uses two dedicated microchips, the SWITCHER II chip for
matrix steering and the CURO II chip for readout. The system development has
been driven by the final ILC requirements which above all demand a detector
thinned to 50 micron and a row wise read out with line rates of 20MHz and more.
The targeted noise performance for the DEPFET technology is in the range of
ENC=100 e-. The functionality of the system has been demonstrated using
different radioactive sources in an energy range from 6 to 40keV. In recent
test beam experiments using 6GeV electrons, a signal-to-noise ratio of S/N~120
has been achieved with present sensors being 450 micron thick. For improved
DEPFET systems using 50 micron thin sensors in future, a signal-to-noise of 40
is expected.Comment: Invited poster at the International Symposium on the Development of
Detectors for Particle, AstroParticle and Synchrotron Radiation Experiments,
Stanford CA (SNIC06) 6 pages, 12 eps figure
Spatially resolved XMM-Newton analysis and a model of the nonthermal emission of MSH 15-52
We present an X-ray analysis and a model of the nonthermal emission of the
pulsar wind nebula (PWN) MSH15-52. We analyzed XMM-Newton data to obtain the
spatially resolved spectral parameters around the pulsar PSRB1509-58. A
steepening of the fitted power-law spectra and decrease in the surface
brightness is observed with increasing distance from the pulsar. In the second
part of this paper, we introduce a model for the nonthermal emission, based on
assuming the ideal magnetohydrodynamic limit. This model is used to constrain
the parameters of the termination shock and the bulk velocity of the leptons in
the PWN. Our model is able to reproduce the spatial variation of the X-ray
spectra. The parameter ranges that we found agree well with the parameter
estimates found by other authors with different approaches. In the last part of
this paper, we calculate the inverse Compton emission from our model and
compare it to the emission detected with the H.E.S.S. telescope system. Our
model is able to reproduce the flux level observed with H.E.S.S., but not the
spectral shape of the observed TeV {\gamma}-ray emission.Comment: Accepted for publication in A&A, 9 pages, 15 figure
Variable iron-line emission near the black hole of Markarian 766
We investigate the link between ionised Fe X-ray line emission and continuum
emission in the bright nearby AGN, Mrk 766. A new long (433 ks) XMM-Newton
observation is analysed, together with archival data from 2000 and 2001. The
contribution from ionised line emission is measured and its time variations on
short (5-20 ks) timescales are correlated with the continuum emission. The
ionised line flux is found to be highly variable and to be strongly correlated
with the continuum flux, demonstrating an origin for the ionised line emission
that is co-located with the continuum emission. Most likely the emission is
ionised reflection from the accretion disc within a few A.U. of the central
black hole, and its detection marks the first time that such an origin has been
identified other than by fitting to spectral line profiles. Future observations
may be able to measure a time lag and hence achieve reverberation mapping of
AGN at X-ray energies.Comment: Accepted for publication, Astronomy and Astrophysics letter
X-Ray Spectral Study of AGN Sources Content in Some Deep Extragalactic XMM-Newton Fields
We undertake a spectral study of a sample of bright X-ray sources taken from
six XMM-Newton fields at high galactic latitudes, where AGN are the most
populous class. These six fields were chosen such that the observation had an
exposure time more than 60 ksec, had data from the EPIC-pn detector in the
full-Frame mode and lying at high galactic latitude . The analysis
started by fitting the spectra of all sources with an absorbed power-law model,
and then we fitted all the spectra with an absorbed power-law with a low energy
black-body component model.The sources for which we added a black body gave an
F-test probability of 0.01 or less (i.e. at 99% confidence level), were
recognized as sources that display soft excess. We perform a comparative
analysis of soft excess spectral parameters with respect to the underlying
power-law one for sources that satisfy this criterion. Those sources, that do
not show evidence for a soft excess, based on the F-test probability at a 99%
confidence level, were also fitted with the absorbed power-law with a low
energy black-body component model with the black-body temperature fixed at 0.1
and 0.2 keV. We establish upper limits on the soft excess flux for those
sources at these two temperatures. Finally we have made use of Aladdin
interactive sky atlas and matching with NASA/IPAC Extragalactic Database (NED)
to identify the X-ray sources in our sample. For those sources which are
identified in the NED catalogue, we make a comparative study of the soft excess
phenomenon for different types of systems
High redshift X-ray galaxy clusters. I. The impact of point sources on the cluster properties
The current generation of X-ray observatories like Chandra allows studies
with very fine spatial details. It is now possible to resolve X-ray point
sources projected into the cluster diffuse emission and exclude them from the
analysis to estimate the ``correct'' X-ray observables. In order to verify the
incidence of point sources on the cluster thermal emission and to evaluate the
impact of their non-thermal emission on the determination of cluster
properties, we used a sample of 18 high-z (0.25 < z < 1.01) clusters from the
Chandra archive. We performed a detailed analysis of the cluster properties and
compared the changes observed in the X-ray observables, like temperature and
luminosity or their inter-relation, when one keeps the point sources in the
analysis. The point sources projected into the cluster extended emission affect
the estimates of cluster temperature or luminosity considerably (up to 13% and
17% respectively). These percentages become even larger for clusters with z >
0.7 where temperature and luminosity increase up to 24% and 22%, respectively.
Thus the point sources should be removed to correctly estimate the cluster
properties. However the inclusion of the point sources does not impact
significantly the slope and normalization of the L-T relationship since for
each cluster the correction to be applied to T and L produces a moderate shift
in the L-T plane almost parallel to the best-fit of the ``correct'' L-T
relation.Comment: 16 pages, 18 postscript figures. Accepted for publication in
Astronomy & Astrophysic
Properties of the background of EPIC-pn onboard XMM-Newton
We have investigated the background properties of EPIC-pn onboard XMM-Newton
to establish the background subtraction method. Count rates of the background
vary violently by two orders of magnitude at the maximum, while during the most
quiet period, these are stable within 8 % at a 1 level. The overall
spectrum is dominated by particle events above 5 keV, and its spatial variation
is also found. The long-term variation of the background is also investigated
with CAL CLOSED data, where the filter wheel was in closed position with the
internal calibration source illuminating the sensitive area. The average
background count rate decreased by 20 % from March 2000 to January 2001, but it
regained in February 2001. For the modeling of the background spectrum, we
investigate relations between the 2.0--7.0 keV count rate and some
characteristic parameters. The 2.0--7.0 keV background count rate shows a good
correlation with the count rate of events outside the field of view. This
correlation is usable for the modeling of the background.Comment: 9 pages, submitted to A&
XMM-Newton spectral and timing analysis of the faint millisecond pulsars PSR J0751+1807 and PSR J1012+5307
We present XMM-Newton MOS imaging and PN timing data of the faint millisecond
pulsars PSR J0751+1807 and PSR J1012+5307. We find 46 sources in the MOS field
of view of PSR J0751+1807 searching down to an unabsorbed flux limit of 3 x
10^-15 ergs cm^-2 s^-1 (0.2-10.0 keV). We present, for the first time, the
X-ray spectra of these two faint millisecond pulsars. We find that a power law
model best fits the spectrum of PSR J0751+1807, Gamma=1.59+/-0.20, with an
unabsorbed flux of 4.4 x 10^-14 ergs cm^-2 s^-1 (0.2-10.0 keV). A power law is
also a good description of the spectrum of PSR J1012+5307, Gamma=1.78+/-0.36,
with an unabsorbed flux of 1.2 x 10^-13 ergs cm^-2 s^-1 (0.2-10.0 keV).
However, a blackbody model can not be excluded as the best fit to this data. We
present some evidence to suggest that both of these millisecond pulsars show
pulsations in this X-ray band. We find some evidence for a single broad X-ray
pulse for PSR J0751+1807 and we discuss the possibility that there are two
pulses per spin period for PSR J1012+5307.Comment: 8 pages, 9 figures, accepted for publication in Astronomy &
Astrophysic
X-ray Bright Optically Inactive Galaxies (XBONG) in XMM-Newton/SDSS fields: more diluted than absorbed?
We explore the properties of X-ray Bright Optically Inactive Galaxies (XBONG)
detected in the 0.5-8 keV spectral band in 20 public XMM fields overlapping
with the SDSS. We constrain our sample to optically extended systems with log
(f_X/f_o > -2) that have spectroscopic identifications available from the SDSS
(r<19.2 mag). The resulting sample contains 12 objects with L_X (0.5-8keV)= 5 x
10^41 - 2x10^44 erg s-1 in the redshift range 0.06 < z < 0.45. The X-ray
emission in four cases is extended suggesting the presence of hot gas
associated with a cluster or group of galaxies. The X-ray spectral fits show
that two additional sources are best fit with a thermal component emission (kT
\~ 1 keV). Three sources aremost likely associated with AGN: their X-ray
spectrum is described by a steep photon index ~ 1.9 typical of unobscured AGN
while, they are very luminous in X-rays (L_X (0.5-8 keV) ~ 10^43 - 10^44 erg
s-1.) Finally, three more sources could be associated with either normal
galaxies or unobscured Low Luminosity AGN (L_X < 10^42 erg s-1). We find no
evidence for significant X-ray absorbing columns in any of our XBONGs. The
above suggest that XBONGs, selected in the total 0.5-8 keV band, comprise a
mixed bag of objects primarily including normal elliptical galaxies and type-1
AGN whose optical nuclear spectrum is probably diluted by the strong stellar
continuum. Nevertheless, as our sample is not statistically complete we cannot
exclude the possibility that a fraction of optically fainter XBONG may be
associated with heavily obscured AGN.Comment: 8 pages to appear in MNRA
An XMM-Newton study of the sub-structure in M87's halo
The high signal to noise and good point spread function of XMM have allowed
the first detailed study of the interaction between the thermal and radio
emitting plasma in the central regions of M87. We show that the X-ray emitting
structure, previously seen by ROSAT, is thermal in nature and that the east and
southwest extensions in M87's X-ray halo have a significantly lower temperature
(kT= 1.5 keV) than the surrounding ambient medium (kT= 2.3 keV). There is
little or no evidence for non-thermal emission with an upper limit on the
contribution of a power law component of spectral index flatter than 3 being
less than 1% of the flux in the region of the radio lobes.Comment: 6 pages, 8 color figures, to be published in A&A, number 36
The XMM-Newton/2dF survey VII. Is there any X-ray absorption in optically selected QSOs?
We explore the X-ray properties of optically selected QSOs spectroscopically
identified in the course of the 2dF QSO survey (2QZ). Our main goal is to
expand to higher redshifts previous findings suggesting the presence of a
fraction of X-ray obscured sources among the low redshift optically selected
broad line AGN population. The X-ray data are from the wide field (~2.5 sq.
deg), shallow $[f(0.5 - 8 keV) ~10^-14 egs s^-1 cm^-2 XMM-Newton/2dF survey. A
total of 96 2QZ QSOs overlap with the area covered by our X-ray survey. 66 of
them have X-ray counterparts while 30 remain undetected in our X-ray survey.
The 66 X-ray detected QSOs have a mean photon index of ~2 suggesting little or
no X-ray obscuration for most of these sources. Individual X-ray spectral
fittings reveal only 1 source (intrinsic Lx(0.5-8 keV) ~ 10^44 erg s^-1 at
z=0.82) that is likely to be obscured (NH~10^23 cm^-2) at the 90% confidence
level. Additionally, there are 9 2QZ sources that show evidence for moderate
absorption (mean observed NH of ~10^21 cm^-2). For the 30 QSOs that remain
undetected in our X-ray survey we use stacking analysis to estimate a mean
hardness ratio of -0.59 +/- 0.11 suggesting that the bulk of this population
has NH consistent with the Galactic value. However, we cannot exclude the
possibility that some of these sources have enhanced photoelectric absorption
that is not revealed in the mean stacked spectrum. We estimate a lower limit to
the fraction of optically selected QSO with X-ray absorption of about 10% (10
out of 96).Comment: To appear in MNRAS, 9 pages, 8 figure
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