55 research outputs found
Broad Band X-ray Spectra of M31 Sources with BeppoSAX
We present the first spectral study of the X-ray emitting stellar sources in
M31 in the energy band from 0.1 to 10 keV. We find that the globular cluster
sources have spectral characteristics consistent with those of the Milky Way
object, namely that the spectrum can be described by a thermal model with 6-20
keV from 2 to 10 keV. Evidence of high absorption in some of these sources is
most likely an indication that they lie in or behind the HI ring in the disk of
the galaxy.
We also find one peculiar globular cluster source, with spectral
characteristics more typically associated with either High Mass X-ray Binaries
or black hole candidates. We therefore suggest that either the source has been
wrongly identified with a globular cluster or that the system contains a Black
Hole. We confirm earlier report that the spectrum of the bulge of M31 is
consistent with the superposition of many LMXB spectra. It is likely that a
large fraction of the 15-30 keV detection obtained from the PDS instrument is
associated with the bulge, thus extending the spectral data for this complex of
sources up to 30 keV. The high energy part of the spectrum can be parameterized
with typical LMXB spectra, while at low energies an additional component is
required.Comment: Accepted for publication in A&A, main journa
The XXL Survey XI: ATCA 2.1 GHz continuum observations
We present 2.1 GHz imaging with the Australia Telescope Compact Array (ATCA)
of a 6.5 deg^2 region within the XXM-Newton XXL South field using a band of
1.1-3.1 GHz. We achieve an angular resolution of 4.7" x 4.2" in the final radio
continuum map with a median rms noise level of 50 uJy/beam. We identify 1389
radio sources in the field with peak S/N >=5 and present the catalogue of
observed parameters. We find that 305 sources are resolved, of which 77 consist
of multiple radio components. These number counts are in agreement with those
found for the COSMOS-VLA 1.4 GHz survey. We derive spectral indices by a
comparison with the Sydney University Molongolo Sky Survey (SUMSS) 843MHz data.
We find an average spectral index of -0.78 and a scatter of 0.28, in line with
expectations. This pilot survey was conducted in preparation for a larger ATCA
program to observe the full 25 deg^2 southern XXL field. When complete, the
survey will provide a unique resource of sensitive, wide-field radio continuum
imaging with complementary X-ray data in the field. This will facilitate
studies of the physical mechanisms of radio-loud and radio-quiet AGNs and
galaxy clusters, and the role they play in galaxy evolution. The source
catalogue is publicly available online via the XXL Master Catalogue browser and
the Centre de Donn\'ees astronomiques de Strasbourg (CDS).Comment: 7 pages, 6 figures. Accepted by A&A 13th October 201
The XXL Survey: : XXIX. GMRT 610 MHz continuum observations
Accepted for publication in a forthcoming issue of Astronomy & Astrophysics. Reproduced with permission from Astronomy & Astrophysics. © 2018 ESO.We present the 25 square-degree GMRT-XXL-N 610 MHz radio continuum survey, conducted at 50 cm wavelength with the Giant Metrewave Radio Telescope (GMRT) towards the XXL Northern field (XXL-N). We combined previously published observations of the XMM-Large Scale Structure (XMM-LSS) field, located in the central part of XXL-N, with newly conducted observations towards the remaining XXL-N area, and imaged the combined data-set using the Source Peeling and Atmospheric Modeling (SPAM) pipeline. The final mosaic encompasses a total area of 30:4 square degrees, with rms <150 μJy beam -1 over 60% of the area. The rms achieved in the inner 9.6 square degree area, enclosing the XMM-LSS field, is about 200 μJy beam -1, while that over the outer 12.66 square degree area (which excludes the noisy edges) is about 45 μJy beam -1. The resolution of the final mosaic is 6.5 arcsec. We present a catalogue of 5434 sources detected at ≥7 × rms. We verify, and correct the reliability of, the catalog in terms of astrometry, flux, and false detection rate. Making use of the (to date) deepest radio continuum survey over a relatively large (2 square degree) field, complete at the flux levels probed by the GMRT-XXL-N survey, we also assess the survey's incompleteness as a function of flux density. The radio continuum sensitivity reached over a large field with a wealth of multi-wavelength data available makes the GMRTXXL- N 610 MHz survey an important asset for studying the physical properties, environments and cosmic evolution of radio sources, in particular radio-selected active galactic nuclei (AGN).Peer reviewedFinal Accepted Versio
Definition of the Flexible Image Transport System (FITS) The FITS Standard Version 4.0: updated 2016 July 22 by the IAUFWG Original document publication date: 2016 July 22 Language-edited document publication date: 2018 August 13
All details on document compilation are in section 1.2 and 1.3 of the paperThe document provides the latest official version of the Standard of the FITS format, as endorsed by the International Astronomical Union, approved by the IAU FITS Working Group (IAUFWG), compiled by a dedicated task force of the IAUFWG in 2016 and language-edited by M.C.Currie and L.Chiappetti (IAUFWG Chair) in 2018
The XXL survey: XLVI. Forward cosmological analysis of the C1 cluster sample
We present the forward cosmological analysis of an selected sample of
galaxy clusters out to a redshift of unity. Following our previous 2018 study
based on the dn/dz quantity alone, we perform an upgraded cosmological analysis
of the same XXL C1 cluster catalogue (178 objects), with a detailed account of
the systematic errors. We follow the ASpiX methodology: the distribution of the
observed X-ray properties of the cluster population is analysed in a 3D
observable space (count rate, hardness ratio, redshift) and modelled as a
function of cosmology. Compared to more traditional methods, ASpiX allows the
inclusion of clusters down to a few tens of photons. We obtain an improvement
by a factor of 2 compared to the previous analysis by letting the normalisation
of the M-T relation and the evolution of the L-T relation free. Adding
constraints from the XXL cluster 2-point correlation function and the BAO from
various surveys decreases the uncertainties by 23 and 53 % respectively, and
62% when adding both. Switching to the scaling relations from the Subaru
analysis, and letting free more parameters, our final constraints are
= , = 0.296 0.034 () for the XXL sample alone. Finally, we combine XXL ASpiX,
the XXL cluster 2-point correlation function and the BAO, with 11 free
parameters, allowing for the cosmological dependence of the scaling relations
in the fit. We find = , = 0.364
0.015 (), but still compatible with Planck
CMB at 2.2. The results obtained by the ASpiX method are promising;
further improvement is expected from the final XXL cosmological analysis
involving a cluster sample twice as large. Such a study paves the way for the
analysis of the eROSITA and future Athena surveys.Comment: 20 pages, 10 figures, accepted for publication in A&A, A&A version
has the unabridged abstrac
BeppoSAX Observations of Unprecedented Synchrotron Activity in the BL Lac Object Mkn 501
The BL Lac object Mkn 501, one of the only three extragalactic sources (with
Mkn 421 and 1ES 2344+514) so far detected at TeV energies, was observed with
the BeppoSAX satellite on 7, 11, and 16 April 1997 during a phase of high
activity at TeV energies, as monitored with the Whipple, HEGRA and CAT
Cherenkov telescopes. Over the whole 0.1-200 keV range the spectrum was
exceptionally hard (alpha =< 1, with F_nu ~ nu^{-alpha}) indicating that the
X-ray power output peaked at (or above) ~100 keV. This represents a shift of at
least two orders of magnitude with respect to previous observations of Mkn 501,
a behavior never seen before in this or any other blazar. The overall X-ray
spectrum hardens with increasing intensity and, at each epoch, it is softer at
larger energies. The correlated variability from soft X-rays to the TeV band
points to models in which the same population of relativistic electrons
produces the X-ray continuum via synchrotron radiation and the TeV emission by
inverse Compton scattering of the synchrotron photons or other seed photons.
For the first time in any blazar the synchrotron power is observed to peak at
hard X-ray energies. The large shift of the synchrotron peak frequency with
respect to previous observations of Mkn 501 implies that intrinsic changes in
the relativistic electron spectrum caused the increase in emitted power. Due to
the very high electron energies, the inverse Compton process is limited by the
Klein-Nishina regime. This implies a quasi-linear (as opposed to quadratic)
relation of the variability amplitude in the TeV and hard X-ray ranges (for the
SSC model) and an increase of the inverse Compton peak frequency smaller than
that of the synchrotron peak frequency.Comment: 11 pages, Latex, 4 Postscript figures, to appear in The Astrophysical
Journal Letter
The XMM-LSS survey. Survey design and first results
We have designed a medium deep large area X-ray survey with XMM - the XMM
Large Scale Structure survey, XMM-LSS - with the scope of extending the
cosmological tests attempted using ROSAT cluster samples to two redshift bins
between 0<z<1 while maintaining the precision of earlier studies. Two main
goals have constrained the survey design: the evolutionary study of the
cluster-cluster correlation function and of the cluster number density. The
results are promising and, so far, in accordance with our predictions as to the
survey sensitivity and cluster number density. The feasibility of the programme
is demonstrated and further X-ray coverage is awaited in order to proceed with
a truly significant statistical analysis. (Abridged)Comment: Published in Journal of Cosmology and Astroparticle Physic
VizieR Online Data Catalog: 2-10keV luminosity function of AGN (Ranalli+, 2016)
The XMM-LSS, XMM-CDFS, and XMM-COSMOS are three surveys with complementary properties in terms of luminosity and redshift coverage. We used these three surveys to derive Bayesian estimates of the unabsorbed luminosity function (LF) of AGN in the 2-10keV band. The LF estimates are presented as a set of samples from the posterior probability distribution of the LF parameters. The LF is parameterised as a double power-law, with either the luminosity and density evolution (LADE) model, or the luminosity-dependent density evolution (LDDE) model. The double power-law is described by Eq.(10) in the paper. The LADE and LDDE models are described by Eqs.(11-14) and Eqs.(15-17), respectively. A Fortran 2008 implementation of these models can be found in file src2/lumf_funcs.f90 of the LFTools package, in the classes doublepowerlaw, ladevol, and lddevol (see the paper). (8 data files). <P /
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