360 research outputs found
The Swift X-ray Telescope Cluster Survey II. X-ray spectral analysis
(Abridged) We present a spectral analysis of a new, flux-limited sample of 72
X-ray selected clusters of galaxies identified with the X-ray Telescope (XRT)
on board the Swift satellite down to a flux limit of ~10-14 erg/s/cm2 (SWXCS,
Tundo et al. 2012). We carry out a detailed X-ray spectral analysis with the
twofold aim of measuring redshifts and characterizing the properties of the
Intra-Cluster Medium (ICM). Optical counterparts and spectroscopic or
photometric redshifts are obtained with a cross-correlation with NED.
Additional photometric redshifts are computed with a dedicated follow-up
program with the TNG and a cross-correlation with the SDSS. We also detect the
iron emission lines in 35% of the sample, and hence obtain a robust measure of
the X-ray redshift zX. We use zX whenever the optical redshift is not
available. Finally, for all the sources with measured redshift,
background-subtracted spectra are fitted with a mekal model. We perform
extensive spectral simulations to derive an empirical formula to account for
fitting bias. The bias-corrected values are then used to investigate the
scaling properties of the X-ray observables. Overall, we are able to
characterize the ICM of 46 sources. The sample is mostly constituted by
clusters with temperatures between 3 and 10 keV, plus 14 low-mass clusters and
groups with temperatures below 3 keV. The redshift distribution peaks around
z~0.25 and extends up to z~1, with 60% of the sample at 0.1<z<0.4. We derive
the Luminosity-Temperature relation for these 46 sources, finding good
agreement with previous studies. The quality of the SWXCS sample is comparable
to other samples available in the literature and obtained with much larger
X-ray telescopes. Our results have interesting implications for the design of
future X-ray survey telescopes, characterised by good-quality PSF over the
entire field of view and low background.Comment: 27 pages, 15 figures; minor typos corrected. To be published in A&A,
Volume 567, July 2014. Websites of the SWXCS project:
http://www.arcetri.astro.it/SWXCS/ and http://swxcs.ustc.edu.cn
V39: an unusual object in the field of IC 1613
The variable star V39 in the field of IC 1613 is discussed in the light of
the available photometric and new spectroscopic data. It has strong emission
Balmer lines, and the observed characteristics could be explained by a W Vir
pulsating star with a period of 14.341 d, located at more than 115 kpc, that is
in the very outer halo of our Galaxy. It should have an apparent companion, a
long period (1118d) red variable, belonging to IC 1613. The main uncertainty in
this interpretation is an emission feature at 668.4 nm, which we tentatively
identified as a He I line.Comment: 5 pages; accepted for publication in Astronomy & Astrophysic
Optical and infrared photometry of the blazar PKS0537-441
We present a large collection of photometric data on the Blazar PKS 0537-441
in the VRIJHK bands taken in 2004-2009. At least three flare-like episodes with
months duration, and >3 mag amplitude are apparent. The spectral energy
distribution is consistent with a power law, and no indication of a thermal
component is found. We searched for short time scale variability, and an
interesting event was identified in the J band, with a duration of ~25 minutes.Comment: 10 pages, 3 figures, in press in ApJ
Trustworthiness-related uncertainty of semantic web-style metadata : a possibilistic approach
We discuss the specific type of uncertainty deriving from the non-uniform trustworthiness of Semantic Web style metadata sources, arguing toward the feasibility of modal possibilistic reasoning based on trust assertions expressing such uncertainty
Open world reasoning in semantics-aware access control: A preliminary study
We address the relationships between theoretical foundations of Description Logics and practical applications of security-oriented Semantic Web techniques. We first describe the advantages of semantics-aware Access Control and review the state of the art; we also introduce the basics of Description Logics and the novel semantics they share. Then we translate the principle underlying the Little House Problem of DL into a real-world use case: by applying Open World Reasoning to the Knowledge Base modelling a Virtual Organization, we derive information not achievable with traditional Access Control methodologies. With this example, we also show that a general problem such as ontology mapping can take advantage of the enhanced semantics underlying OWL Lite and OWL DL to handle under-specified concepts
GRB 000911: Evidence for an Associated Supernova?
We present photometric and spectroscopic observations of the late afterglow of GRB 000911. We detect a moderately significant re-brightening in the R, I and J lightcurves, associated with a sizable reddening of the spectrum. This can be explained through the presence of an underlying supernova, outshining the afterglow ~ 30 days after the burst event
SN 2002lt and GRB 021211: a SN/GRB Connection at z = 1
We present spectroscopic and photometric observations of the afterglow of GRB
021211 and the discovery of its associated supernova, SN 2002lt. The spectrum
shows a broad feature (FWHM = 150 A), around 3770 A (in the rest-frame of the
GRB), which we interpret as Ca H+K blueshifted by 14400 km/s. Potential sources
of contamination due to the host galaxy and/or residuals of telluric absorption
have been analyzed and ruled out. Overall, the spectrum shows a suggestive
resemblance with the one of the prototypical type-Ic SN 1994I. This might
indicate that GRBs are produced also by standard type-Ic supernovae.Comment: 6 pages, 5 color figures. Proceedings of the 2003 GRB Conference
(Santa Fe, NM, 2003 Sep 8-12). Needs aipprocs LaTeX clas
The Pleiotropic Effects of GATA1 and KLF1 in Physiological Erythropoiesis and in Dyserythropoietic Disorders
In the last few years, the advent of new technological approaches has led to a better knowledge of the ontogeny of erythropoiesis during development and of the journey leading from hematopoietic stem cells (HSCs) to mature red blood cells (RBCs). Our view of a well-defined hierarchical model of hematopoiesis with a near-homogeneous HSC population residing at the apex has been progressively challenged in favor of a landscape where HSCs themselves are highly heterogeneous and lineages separate earlier than previously thought. The coordination of these events is orchestrated by transcription factors (TFs) that work in a combinatorial manner to activate and/or repress their target genes. The development of next generation sequencing (NGS) has facilitated the identification of pathological mutations involving TFs underlying hematological defects. The examples of GATA1 and KLF1 presented in this review suggest that in the next few years the number of TF mutations associated with dyserythropoietic disorders will further increase
- …