Astron.Astrophys.390:27-38,2002 We report on a 20 ksec XMM observation of the distant cluster RXJ1120.1+4318,
discovered at z=0.6 in the SHARC survey. The cluster has a regular spherical
morphology, ...suggesting it is in a relaxed state. The combined fit of the
EPIC/MOS&pn camera gives a cluster mean temperature of kT=5.3\pm0.5 keV with an
iron abundance of 0.47\pm0.19. The temperature profile, measured for the first
time at such a redshift, is consistent with an isothermal atmosphere up to half
the virial radius. The surface brightness profile, measured nearly up to the
virial radius, is well fitted by a beta-model, with beta =0.78+0.06,-0.04 and
a core radius of thetac = 0.44+0.06,-0.04 arcmin. We compared the properties
of RXJ1120.1+4318 with the properties of nearby clusters for two cosmological
models: an Einstein - de Sitter Universe and a flat low density Universe with
Omega0=0.3. For both models, the scaled emission measure profile beyond the
core, the gas mass fraction and luminosity are consistent with the expectations
of the self-similar model of cluster formation, although a slightly better
agreement is obtained for a low density Universe. There is no evidence of a
central cooling flow, in spite of the apparent relaxed state of the cluster.
This is consistent with its estimated cooling time, larger than the age of the
Universe at the cluster redshift. The entropy profile shows a flat core with a
central entropy of ~ 140 keV cm^2, remarkably similar to the entropy floor
observed in nearby clusters, and a rising profile beyond typically 0.1 virial
radius. Implications of our results, in terms of non-gravitational physics in
cluster formation, are discussed.
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.
The spectrum of the 0.1-7.0 keV cosmic X-ray background (CXB) at galactic latitudes >|25| degrees has been measured using the BeppoSAX Low-Energy Spectrometer Concentrator (LECS). Above 1 keV the ...spectrum is consistent with a power-law of photon index 1.47 +/- 0.10 and normalization 11.0 +/- 0.8 photon cm^-2 s^-1 keV^-1 sr^-1 at 1keV. The overall spectrum can be modeled by a power-law with 2 thermal components, or by a broken power-law and a single thermal component. In both cases the softer thermal emission dominates at less than 0.3 keV and is seen through a column of a few 10^19 atom cm^-2. The other components have columns consistent with the mean line of sight value. The metal abundances for the thermal components are poorly constrained, but consistent with cosmic values. The power-law together with 2 thermal components model has been used to fit recent combined ASCA and ROSAT CXB measurements. Here, the soft thermal component is interpreted as emission from the local hot bubble and the hard thermal component as emission from a more distant absorbed region. While such a 2 component thermal model is consistent with the LECS spectrum, it is not required, and the hard thermal component may result from inadequate modeling of the extragalactic contribution. The observed low-energy spectral complexity may therefore originate primarily in the local hot bubble. There is no evidence for the presence of a very soft CXB component with a temperature <0.1 keV. The emission measure seen by ROSAT is rejected at 90% confidence.
Astrophys.J.541:49-53,2000 We present first results from an X-ray study of the Hubble Deep Field North
(HDF-N) and its environs obtained using 166 ks of data collected by the
Advanced CCD Imaging ...Spectrometer (ACIS) on board the Chandra X-ray
Observatory. This is the deepest X-ray observation ever reported, and in the
HDF-N itself we detect six X-ray sources down to a 0.5--8 keV flux limit of
4E-16 erg cm^-2 s^-1. Comparing these sources with objects seen in
multiwavelength HDF-N studies shows positional coincidences with the extremely
red object NICMOS J123651.74 +621221.4, an active galactic nucleus (AGN), three
elliptical galaxies, and one nearby spiral galaxy. The X-ray emission from the
ellipticals is consistent with that expected from a hot interstellar medium,
and the spiral galaxy emission may arise from a `super-Eddington' X-ray binary
or ultraluminous supernova remnant. Four of the X-ray sources have been
detected at radio wavelengths. We also place X-ray upper limits on AGN
candidates found in the HDF-N, and we present the tightest constraints yet on
X-ray emission from the SCUBA submillimeter source population. None of the 10
high-significance submillimeter sources reported in the HDF-N and its vicinity
is detected with Chandra ACIS. These sources appear to be dominated by star
formation or have AGN with Compton-thick tori and little circumnuclear X-ray
scattering.
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.
Astrophys.J.554:742-777,2001 We present results from a 221.9 ks Chandra exposure of the HDF-N and its
vicinity, concentrating on the 8.6' X 8.7' area covered by the Caltech Faint
Field Galaxy ...Redshift Survey (the `Caltech area'). The minimum detectable
fluxes in the 0.5-2 keV and 2-8 keV bands are 1.3e-16 cgs and 6.5e-16 cgs,
respectively and a total of 82 sources are detected. More than 80% of the
extragalactic X-ray background in the 2-8 keV band is resolved. Redshifts are
available for 96% of the sources with R<23; the redshift range is 0.1-3.5 with
most sources having z < 1.5. Eight of the X-ray sources are located in the
HDF-N itself, including two not previously reported. A population of X-ray
faint, optically bright, nearby galaxies emerges at soft-band fluxes of ~<
3e-16 cgs.
We set the tightest constraints to date on the X-ray emission properties of
microJy radio sources, mid-infrared sources detected by ISO, and very red
(R-K_s > 5.0) objects. Where both the infrared and the X-ray coverage are
deepest, 75% of the X-ray sources are detected by ISO; the high X-ray to
infrared matching rate bodes well for future sensitive infrared observations of
faint X-ray sources. Four of the 33 very red objects that have been identified
in the Caltech area by Hogg et al. (2000) are detected in X-rays; these four
are among our hardest Chandra sources, and we argue that they contain
moderately luminous obscured AGN. Overall, however, the small Chandra detection
fraction suggests a relatively small AGN content in the optically selected very
red object population. (Abridged)
We present the XMM-Newton first light image, taken in January 2000 with the
EPIC pn camera during the instrument's commissioning phase, when XMM-Newton was
pointing towards the Large Magellanic Cloud ...(LMC). The field is rich in
different kinds of X-ray sources: point sources, supernova remnants (SNRs) and
diffuse X-ray emission from LMC interstellar gas. The observations are of
unprecedented sensitivity, reaching a few 10^32 erg/s for point sources in the
LMC. We describe how these data sets were analysed and discuss some of the
spectroscopic results. For the SNR N157B the power law spectrum is clearly
steeper than previously determined from ROSAT and ASCA data. The existence of a
significant thermal component is evident and suggests that N157B is not a
Crab-like but a composite SNR. Most puzzling is the spectrum of the LMC hot
interstellar medium, which indicates a significant overabundance of Ne and Mg
of a few times solar.
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