272 research outputs found
A highly-ionized absorber as a new explanation for the spectral changes during dips from X-ray binaries
Until now, the spectral changes observed from persistent to dipping intervals
in dipping low-mass X-ray binaries were explained by invoking progressive and
partial covering of an extended emission region. Here, we propose a novel and
simpler way to explain these spectral changes, which does not require any
partial covering and hence any extended corona, and further has the advantage
of explaining self-consistently the spectral changes both in the continuum and
the narrow absorption lines that are now revealed by XMM-Newton. In 4U 1323-62,
we detect Fe XXV and Fe XXVI absorption lines and model them for the first time
by including a complete photo-ionized absorber model rather than individual
Gaussian profiles. We demonstrate that the spectral changes both in the
continuum and the lines can be simply modeled by variations in the properties
of the ionized absorber. From persistent to dipping the photo-ionization
parameter decreases while the equivalent hydrogen column density of the ionized
absorber increases. In a recent work (see Diaz Trigo et al. in these
proceedings), we show that our new approach can be successfully applied to all
the other dipping sources that have been observed by XMM-Newton.Comment: 5 pages, 5 figures, to appear in the proceedings of "The X-ray
Universe 2005", San Lorenzo de El Escorial (Spain), 26-30 September 200
BeppoSAX observations of low-energy spectral features in AGN
The combination of the broad band coverage and moderate spectral resolution
of the LECS and MECS instruments on-board BeppoSAX allow the spectra of AGN to
be studied in unprecedented detail down to 0.1 keV. We describe the calibration
and the performance of the LECS and report on observations of low-energy
absorption features in the spectra of both a low (MCG-6-30-15) and a high
luminosity (3C 273) AGN. These features provide important diagnostics on the
location and nature of the material surrounding the AGN. A comparison of LECS
and ASCA/SIS low energy performance is also presented in the case of 3C 273.Comment: 5 pages. To appear in symposium proceedings: The Active X-Ray Sky,
Rome, October 199
The broad band spectral properties of galactic X-ray binary pulsars
BeppoSAX observed several galactic binary X-ray pulsars during the Science
Verification Phase and in the first year of the regular program. The complex
emission spectra of these sources are an ideal target for the BeppoSAX
instrumentation, that can measure the emission spectra in an unprecedented
broad energy band. Using this capability of BeppoSAX a detailed observational
work can be done on the galactic X-ray pulsars. In particular the 0.1-200 keV
energy band allows the shape of the continuum emission to be tightly
constrained. A better determination of the underlying continuum allows an
easier detection of features superimposed onto it, both at low energy (Fe K and
L, Ne lines) and at high energies (cyclotron features). We report on the
spectral properties of a sample of X-ray pulsars observed with BeppoSAX
comparing the obtained results. Some ideas of common properties are also
discussed and compared with our present understanding of the emission
mechanisms and processes.Comment: 6 pages, 2 figures. Uses espcrc2.sty (included).To appear in
Proceedings of "The Active X-ray Sky: Results from BeppoSAX and Rossi-XTE
BeppoSAX observations of the X-ray binary pulsar 4U1626-67
We report on observations of the low-mass X-ray binary 4U1626-67 performed
during the BeppoSAX Science Verification Phase. We present the broad-band
0.1-100 keV pulse averaged spectrum, that is well fit by a two-component
function: a 0.27 +/- 0.02 keV blackbody and an absorbed power law with a photon
index of 0.89 +/- 0.02. A very deep and narrow absorption feature at 38 keV,
attributable to electron cyclotron resonance, is clearly visible in the
broad-band spectrum. It corresponds to a neutron star magnetic field strength
of 3.3 x 10^{12} G. The 4U1626-67 pulse profiles show a dramatic dependance on
energy: the transition between the low energy (E<10 keV) "bi-horned" shape to
the high-energy (E>10 keV) sinusoidal profile is clearly visible in our data.
The modulation index shows a monotonic increase with energy.Comment: 4 pages, 2 figures. Uses espcrc2.sty (included). To appear in
Proceedings of "The Active X-ray Sky: Results from BeppoSAX and Rossi-XTE
The broad band spectral properties of binary X-ray pulsars
The X-ray telescopes on board BeppoSAX are an optimal set of instruments to
observe bright galactic binary pulsars. These sources emit very hard and quite
complex X-ray spectra that can be accurately measured with BeppoSAX between 0.1
and 200 keV. A prototype of this complexity, the source Her X-1, shows at least
seven different components in its spectrum. A broad band measure is therefore
of paramount importance to have a thorough insight into the physics of the
emitting region. Moreover the detection of cyclotron features, when present,
allows a direct and highly significant measure of the magnetic field intensity
in the emission region. In this paper we briefly report the results obtained
with BeppoSAX on this class of sources, with emphasis on the detection and on
the measured properties of the cyclotron lines.Comment: 10 Latex pages, 4 figures, uses psfig.sty. Accepted for publication
in Advances in Space Research, in Proceedings of 32nd Scientific Assembly of
COSPAR - Symposium E1.1: "Broad-Band X-ray Spectroscopy of Cosmic Sources
Lorentz breaking Effective Field Theory and observational tests
Analogue models of gravity have provided an experimentally realizable test
field for our ideas on quantum field theory in curved spacetimes but they have
also inspired the investigation of possible departures from exact Lorentz
invariance at microscopic scales. In this role they have joined, and sometime
anticipated, several quantum gravity models characterized by Lorentz breaking
phenomenology. A crucial difference between these speculations and other ones
associated to quantum gravity scenarios, is the possibility to carry out
observational and experimental tests which have nowadays led to a broad range
of constraints on departures from Lorentz invariance. We shall review here the
effective field theory approach to Lorentz breaking in the matter sector,
present the constraints provided by the available observations and finally
discuss the implications of the persisting uncertainty on the composition of
the ultra high energy cosmic rays for the constraints on the higher order,
analogue gravity inspired, Lorentz violations.Comment: 47 pages, 4 figures. Lecture Notes for the IX SIGRAV School on
"Analogue Gravity", Como (Italy), May 2011. V.3. Typo corrected, references
adde
Formation of dense partonic matter in relativistic nucleus-nucleus collisions at RHIC: Experimental evaluation by the PHENIX collaboration
Extensive experimental data from high-energy nucleus-nucleus collisions were
recorded using the PHENIX detector at the Relativistic Heavy Ion Collider
(RHIC). The comprehensive set of measurements from the first three years of
RHIC operation includes charged particle multiplicities, transverse energy,
yield ratios and spectra of identified hadrons in a wide range of transverse
momenta (p_T), elliptic flow, two-particle correlations, non-statistical
fluctuations, and suppression of particle production at high p_T. The results
are examined with an emphasis on implications for the formation of a new state
of dense matter. We find that the state of matter created at RHIC cannot be
described in terms of ordinary color neutral hadrons.Comment: 510 authors, 127 pages text, 56 figures, 1 tables, LaTeX. Submitted
to Nuclear Physics A as a regular article; v3 has minor changes in response
to referee comments. Plain text data tables for the points plotted in figures
for this and previous PHENIX publications are (or will be) publicly available
at http://www.phenix.bnl.gov/papers.htm
An Observational Overview of Solar Flares
We present an overview of solar flares and associated phenomena, drawing upon
a wide range of observational data primarily from the RHESSI era. Following an
introductory discussion and overview of the status of observational
capabilities, the article is split into topical sections which deal with
different areas of flare phenomena (footpoints and ribbons, coronal sources,
relationship to coronal mass ejections) and their interconnections. We also
discuss flare soft X-ray spectroscopy and the energetics of the process. The
emphasis is to describe the observations from multiple points of view, while
bearing in mind the models that link them to each other and to theory. The
present theoretical and observational understanding of solar flares is far from
complete, so we conclude with a brief discussion of models, and a list of
missing but important observations.Comment: This is an article for a monograph on the physics of solar flares,
inspired by RHESSI observations. The individual articles are to appear in
Space Science Reviews (2011
Study of doubly strange systems using stored antiprotons
Bound nuclear systems with two units of strangeness are still poorly known despite their importance for many strong interaction phenomena. Stored antiprotons beams in the GeV range represent an unparalleled factory for various hyperon-antihyperon pairs. Their outstanding large production probability in antiproton collisions will open the floodgates for a series of new studies of systems which contain two or even more units of strangeness at the P‾ANDA experiment at FAIR. For the first time, high resolution γ-spectroscopy of doubly strange ΛΛ-hypernuclei will be performed, thus complementing measurements of ground state decays of ΛΛ-hypernuclei at J-PARC or possible decays of particle unstable hypernuclei in heavy ion reactions. High resolution spectroscopy of multistrange Ξ−-atoms will be feasible and even the production of Ω−-atoms will be within reach. The latter might open the door to the |S|=3 world in strangeness nuclear physics, by the study of the hadronic Ω−-nucleus interaction. For the first time it will be possible to study the behavior of Ξ‾+ in nuclear systems under well controlled conditions
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