2,447 research outputs found
XMM-Newton discovery of 2.6 s pulsations in the soft gamma-ray repeater SGR 1627-41
After nearly a decade of quiescence, the soft gamma-ray repeater SGR 1627-41
reactivated on 2008 May 28 with a bursting episode followed by a slowly
decaying enhancement of its persistent emission. To search for the still
unknown spin period of this SGR taking advantage of its high flux state, we
performed on 2008 September 27-28 a 120 ks long X-ray observation with the
XMM-Newton satellite. Pulsations with P = 2.594578(6) s were detected at a
higher than 6-sigma confidence level, with a double-peaked pulse profile. The
pulsed fraction in the 2-12 keV range is 19% +/- 3% and 24% +/- 3% for the
fundamental and the second harmonic, respectively. The observed 2-10 keV flux
is 3.4E-13 erg/cm^2/s, still a factor of ~ 5 above the quiescent
pre-burst-activation level, and the spectrum is well fitted by an absorbed
power law plus blackbody model (photon index Gamma = 0.6, blackbody temperature
kT = 0.5 keV, and absorption nH = 1.2E+23 cm^-2). We also detected a shell of
diffuse soft X-ray emission which is likely associated with the young supernova
remnant G337.0-0.1.Comment: Minor changes to match the final version (to appear in The
Astrophysical Journal Letters). 5 pages in emulate-apj style, 1 table, 4
figures (1 color
A multiwavelength study on the high-energy behaviour of Fermi/LAT pulsars
Using archival as well as freshly acquired data, we assess the X-ray
behaviour of the Fermi/LAT gamma-ray pulsars listed in the First Fermi source
catalog. After revisiting the relationships between the pulsars' rotational
energy losses and their X and gamma-ray luminosities, we focus on the
distance-indipendent gamma to X-ray flux ratios. When plotting our Fgamma/Fx
values as a function of the pulsars' rotational energy losses, one immediately
sees that pulsars with similar energetics have Fgamma/Fx spanning 3 decades.
Such spread, most probably stemming from vastly different geometrical
configurations of the X and gamma-ray emitting regions, defies any
straightforward interpretation of the plot. Indeed, while energetic pulsars do
have low Fgamma/Fx values, little can be said for the bulk of the Fermi neutron
stars. Dividing our pulsar sample into radio-loud and radio-quiet subsamples,
we find that, on average, radio-quiet pulsars do have higher values of
Fgamma/Fx, implying an intrinsec faintness of their X-ray emission and/or a
different geometrical configuration. Moreover, despite the large spread
mentioned above, statistical tests show a lower scatter in the radio-quiet
dataset with respect to the radio-loud one, pointing to a somewhat more
constrained geometry for the radio-quiet objects with respect to the radio-loud
ones.Comment: 39 pages, 5 figures, 3 tables. To be published in Astrophysical
Journa
The metal contents of two groups of galaxies
The hot gas in clusters and groups of galaxies is continuously being enriched
with metals from supernovae and stars. It is well established that the
enrichment of the gas with elements from oxygen to iron is mainly caused by
supernova explosions. The origins of nitrogen and carbon are still being
debated. Possible candidates include massive, metal-rich stars, early
generations of massive stars, intermediate or low mass stars and Asymptotic
Giant Branch (AGB) stars. In this paper we accurately determine the metal
abundances of the gas in the groups of galaxies NGC 5044 and NGC 5813, and
discuss the nature of the objects that create these metals.
We mainly focus on carbon and nitrogen. We use spatially-resolved
high-resolution X-ray spectroscopy from XMM-Newton. For the spectral fitting,
multi-temperature hot gas models are used. The abundance ratios of carbon over
oxygen and nitrogen over oxygen that we find are high compared to the ratios in
the stars in the disk of our Galaxy. The oxygen and nitrogen abundances we
derive are similar to what was found in earlier work on other giant ellipticals
in comparable environments. We show that the iron abundances in both our
sources have a gradient along the cross-dispersion direction of the Reflection
Grating Spectrometer (RGS). We conclude that it is unlikely that the creation
of nitrogen and carbon takes place in massive stars, which end their lives as
core-collapse supernovae, enriching the medium with oxygen because oxygen
should then also be enhanced. Therefore we favour low-and intermediate mass
stars as sources of these elements. The abundances in the hot gas can best be
explained by a 30-40% contribution of type Ia supernovae based on the measured
oxygen and iron abundances and under the assumption of a Salpeter Initial Mass
Function (IMF).Comment: Accepted for publication in A&A, 12 pages, 10 figures. Data points on
which figs 4,5,8 and 9 are based are present as comment in the source fil
X-ray Spectroscopy of the Virgo Cluster out to the Virial Radius
We present results from the analysis of a mosaic of thirteen XMM-Newton
pointings covering the Virgo Cluster from its center northwards out to a radius
r~1.2 Mpc (~4.5 degrees), reaching the virial radius and beyond. This is the
first time that the properties of a modestly sized (M_vir~1.4e14 M_sun, kT~2.3
keV), dynamically young cluster have been studied out to the virial radius. The
density profile of the cluster can be described by a surprisingly shallow
power-law with index 1.21+/-0.12. In the radial range of 0.3r_vir<r<r_vir, the
best fit temperature drops by roughly 60 per cent. Within a radius r<450 kpc,
the entropy profile has an approximate power-law form with index 1.1, as
expected for gravitationally collapsed gas in hydrostatic equilibrium. Beyond
r~450 kpc, however, the temperature and metallicity drop abruptly, and the
entropy profile becomes flatter, staying consistently below the expected value
by a factor of 2-2.5. The most likely explanation for the unusually shallow
density profile and the flattening of entropy at large radius is clumping in
the ICM. Our data provide direct observational evidence that the ICM is
enriched by metals all the way to r_200 to at least Z=0.1 Solar.Comment: Accepted for publication in MNRA
Spectral monitoring of RX J1856.5-3754 with XMM-Newton. Analysis of EPIC-pn data
Using a large set of XMM-Newton observations we searched for long term
spectral and flux variability of the isolated neutron star RX J1856.5-3754 in
the time interval from April 2002 to October 2011. This is the brightest and
most extensively observed source of a small group of nearby, thermally emitting
isolated neutron stars, of which at least one member (RX J0720.4-3125, Hohle et
al., 2010) has shown long term variability. A detailed analysis of the data
obtained with the EPIC-pn camera in the 0.15-1.2 keV energy range reveals small
variations in the temperature derived with a single blackbody fit (of the order
of 1% around kT^inf \sim 61 eV). Such variations are correlated with the
position of the source on the detector and can be ascribed to an instrumental
effect, most likely a spatial dependence of the channel to energy relation. For
the sampled instrumental coordinates, we quantify this effect as variations of
\sim 4% and \sim 15 eV in the gain slope and offset, respectively. Selecting
only a homogeneous subset of observations, with the source imaged at the same
detector position, we find no evidence for spectral or flux variations of RX
J1856.5-3754 from March 2005 to present-day, with limits of Delta kT^inf < 0.5%
and Delta f_X < 3% (0.15-1.2 keV), with 3sigma confidence. A slightly higher
temperature (kT^inf \sim 61.5 eV, compared to kT^\inf \sim 61 eV) was instead
measured in April 2002. If this difference is not of instrumental origin, it
implies a rate of variation \sim -0.15 eV yr^-1 between April 2002 and March
2005. The high-statistics spectrum from the selected observations is best
fitted with the sum of two blackbody models, with temperatures kT_h^inf =
62.4_{-0.4}^{+0.6} eV and kT_s^\inf = 38.9_{-2.9}^{+4.9} eV, which account for
the flux seen in the optical band. No significant spectral features are
detected, with upper limits of 6 eV on their equivalent width.Comment: 11 pages, 6 figures. Accepted for publication in Astronomy and
Astrophysic
The Identification of the X-ray Counterpart to PSR J2021+4026
We report the probable identification of the X-ray counterpart to the
gamma-ray pulsar PSR J2021+4026 using imaging with the Chandra X-ray
Observatory ACIS and timing analysis with the Fermi satellite. Given the
statistical and systematic errors, the positions determined by both satellites
are coincident. The X-ray source position is R.A. 20h21m30.733s, Decl. +40 deg
26 min 46.04sec (J2000) with an estimated uncertainty of 1.3 arsec combined
statistical and systematic error. Moreover, both the X-ray to gamma-ray and the
X-ray to optical flux ratios are sensible assuming a neutron star origin for
the X-ray flux. The X-ray source has no cataloged infrared-to-visible
counterpart and, through new observations, we set upper limits to its optical
emission of i' >23.0 mag and r' > 25.2mag. The source exhibits an X-ray
spectrum with most likely both a powerlaw and a thermal component. We also
report on the X-ray and visible light properties of the 43 other sources
detected in our Chandra observation.Comment: Accepted for publication in the Astrophysical Journa
X-ray observations of the galaxy cluster Abell 2029 to the virial radius
We present Suzaku observations of the galaxy cluster Abell 2029, which
exploit Suzaku's low particle background to probe the ICM to radii beyond those
possible with previous observations (reaching out to the virial radius), and
with better azimuthal coverage. We find significant anisotropies in the
temperature and entropy profiles, with a region of lower temperature and
entropy occurring to the south east, possibly the result of accretion activity
in this direction. Away from this cold feature, the thermodynamic properties
are consistent with an entropy profile which rises, but less steeply than the
predictions of purely gravitational hierarchical structure formation. Excess
emission in the northern direction can be explained due to the overlap of the
emission from the outskirts of Abell 2029 and nearby Abell 2033 (which is at
slightly higher redshift). These observations suggest that the assumptions of
spherical symmetry and hydrostatic equilibrium break down in the outskirts of
galaxy clusters, which poses challenges for modelling cluster masses at large
radii and presents opportunities for studying the formation and accretion
history of clusters.Comment: 15 pages, 14 figures. Accepted for publication in the Monthly Notices
of the Royal Astronomical Societ
Cool core remnants in galaxy clusters
X ray clusters are conventionally divided into two classes: "cool core" (CC)
and "non cool core" (NCC) objects, on the basis of the observational properties
of their central regions. Recent results have shown that the cluster population
is bimodal (Cavagnolo et al. 2009). We want to understand whether the observed
distribution of clusters is due to a primordial division into two distinct
classes rather than to differences in how these systems evolve across cosmic
time. We systematically search the ICM of NCC clusters in a subsample of the
B55 flux limited sample of clusters for regions which have some characteristics
typical of cool cores, namely low entropy gas and high metal abundance We find
that most NCC clusters in our sample host regions reminiscent of CC, i. e.
characterized by relative low entropy gas (albeit not as low as in CC systems)
and a metal abundance excess. We have dubbed these structures "cool core
remnants", since we interpret them as what remains of a cool core after a
heating event (AGN giant outbursts in a few cases and more commonly mergers).
We infer that most NCC clusters have undergone a cool core phase during their
life. The fact that most cool core remnants are found in dynamically active
objects provides strong support to scenarios where cluster core properties are
not fixed "ab initio" but evolve across cosmic time.Comment: Accepted for publication in Astronomy & Astrophysics. Version with
full resolution figures available at:
http://www.iasf-milano.inaf.it/~rossetti/public/CCR/rossetti.pd
OPERAS SIG on Tools for Open Scholarly Communication : White Paper 2021
This white paper is the output of the OPERAS Special Interest Group (SIG) Tools and R&D for scholarly communication; it is an updated version of a previous 2018 white paper1. With a focus on scholarly publishing tools, the objectives of the SIG Tools are to: provide a landscape analysis, identify emerging trends, and list the areas of potential improvements, developments, and collaborations. Since 2018, various studies and initiatives confirmed the necessity to both coordinate the developments of tools and provide guidance to the users. Similarly, OPERAS emphasizes the importance of building the open science scholarly communication infrastructure in Social Sciences and Humanities on community driven tools. The white paper brings information on the existing tools for scholarly publishing, as well as recommendations that will support the building of such an open scholarly communication infrastructure.
The paper first examines tools types, definitions, and criteria that are able to facilitate their description and selection. The tools are then analyzed according to publishing main functions. For authoring, the development of online and collaborative tools represents an interesting perspective, especially when relying on structured formats, but also increases the risk of lock-in within multi-functional proprietary services. In peer reviewing, alongside widely used commercial tools, open peer review represents an innovative area, both in terms of usage and tools. Open source tools for publishing already offer a high level of service, but face interoperability challenges with the integration of an increasing variety of third-party services. A specific section is dedicated to communicating tools allowing for comments and annotations, as such function is transversal to the others.
To complement this description, the SIG tools also identified major trends that should impact the future of scholarly communication, namely: preprint servers, artificial intelligence, data papers, and user-centric developments. In conclusion, the white paper provides a list of recommendations able to address the challenges identified and to provide building blocks for the envisioned open scholarly infrastructure. The recommendations suggest: to establish user-centric criteria for tools, a toolsâ observatory, a set of training materials, guidelines about publishing workflows, and collaborations with other community initiatives
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