198 research outputs found
EUV and HXR Signatures of Electron Acceleration During the Failed Eruption of a Filament
We search for EUV brightenings in TRACE 171 {\AA} images and HXR bursts
observed during failed eruptions. We expect that if an eruption is confined due
to interaction with overlying magnetic structures then we should observe
effects connected with reconnection between magnetic structures and
acceleration of particles. We utilized TRACE observations of three well
observed failed eruptions. EUV images were compared to HXR spatial distribution
reconstructed from Yohkoh/HXT and RHESSI data. The EUV light curves of a
selected area were compared to height profiles of eruption, HXR emission and
HXR photon spectral index of power-law fit to HXR data. We have found that EUV
brightenings are closely related to the eruption velocity decrease, to HXR
bursts and to episodes of hardening of HXR spectra. The EUV brightened areas
are observed far from the flaring structure, in footpoints of large systems of
loops observed 30-60 minutes after the maximum of a flare. These are not
`post-flare' loops that are also observed but at significantly lower heights.
The high lying systems of loops are observed at heights equal to height, at
which eruption was observed to stop. We observed HXR source spatially
correlated with EUV brightening only once. For other EUV brightened areas we
estimated the expected brightness of HXR sources. We find that EUV brightenings
are produced due to interaction between the erupting structure with overlying
loops. The interaction is strong enough to heat the system of high loops. These
loops cool down and are visible in EUV range about 30-60 minutes later. The
estimated brightness of HXR sources associated with EUV brightenings shows that
they are too weak to be detected with present instruments. However, next
generation instruments will have enough dynamic range and sensitivity to enable
such observations.Comment: A&A accepte
Sphinx measurements of the 2009 solar minimum x-ray emission
The SphinX X-ray spectrophotometer on the CORONAS-PHOTON spacecraft measured
soft X-ray emission in the 1-15 keV energy range during the deep solar minimum
of 2009 with a sensitivity much greater than GOES. Several intervals are
identified when the X-ray flux was exceptionally low, and the flux and solar
X-ray luminosity are estimated. Spectral fits to the emission at these times
give temperatures of 1.7-1.9 MK and emission measures between 4 x 10^47 cm^-3
and 1.1 x 10^48 cm^-3. Comparing SphinX emission with that from the Hinode
X-ray Telescope, we deduce that most of the emission is from general coronal
structures rather than confined features like bright points. For one of 27
intervals of exceptionally low activity identified in the SphinX data, the
Sun's X-ray luminosity in an energy range roughly extrapolated to that of ROSAT
(0.1-2.4 keV) was less than most nearby K and M dwarfs.Comment: Astrophysical Journal, in press. 14 pp, 3 figure
X-raying hot plasma in solar active regions with the SphinX spectrometer
The detection of very hot plasma in the quiescent corona is important for
diagnosing heating mechanisms. The presence and the amount of such hot plasma
is currently debated. The SphinX instrument on-board CORONAS-PHOTON mission is
sensitive to X-ray emission well above 1 keV and provides the opportunity to
detect the hot plasma component. We analyzed the X-ray spectra of the solar
corona collected by the SphinX spectrometer in May 2009 (when two active
regions were present). We modelled the spectrum extracted from the whole Sun
over a time window of 17 days in the 1.34-7 keV energy band by adopting the
latest release of the APED database. The SphinX broadband spectrum cannot be
modelled by a single isothermal component of optically thin plasma and two
components are necessary. In particular, the high statistics and the accurate
calibration of the spectrometer allowed us to detect a very hot component at ~7
million K with an emission measure of ~2.7 x 10^44 cm^-3. The X-ray emission
from the hot plasma dominates the solar X-ray spectrum above 4 keV. We checked
that this hot component is invariably present both at high and low emission
regimes, i.e. even excluding resolvable microflares. We also present and
discuss a possible non-thermal origin (compatible with a weak contribution from
thick-target bremsstrahlung) for this hard emission component. Our results
support the nanoflare scenario and might confirm that a minor flaring activity
is ever-present in the quiescent corona, as also inferred for the coronae of
other stars.Comment: 6 pages, 5 figures. Accepted for publication in A&
Exploring impulsive solar magnetic energy release and particle acceleration with focused hard X-ray imaging spectroscopy
How impulsive magnetic energy release leads to solar eruptions and how those eruptions are energized and evolve are vital unsolved problems in Heliophysics. The standard model for solar eruptions summarizes our current understanding of these events. Magnetic energy in the corona is released through drastic restructuring of the magnetic field via reconnection. Electrons and ions are then accelerated by poorly understood processes. Theories include contracting loops, merging magnetic islands, stochastic acceleration, and turbulence at shocks, among others. Although this basic model is well established, the fundamental physics is poorly understood. HXR observations using grazing-incidence focusing optics can now probe all of the key regions of the standard model. These include two above-the-looptop (ALT) sources which bookend the reconnection region and are likely the sites of particle acceleration and direct heating. The science achievable by a direct HXR imaging instrument can be summarized by the following science questions and objectives which are some of the most outstanding issues in solar physics (1) How are particles accelerated at the Sun? (1a) Where are electrons accelerated and on what time scales? (1b) What fraction of electrons is accelerated out of the ambient medium? (2) How does magnetic energy release on the Sun lead to flares and eruptions? A Focusing Optics X-ray Solar Imager (FOXSI) instrument, which can be built now using proven technology and at modest cost, would enable revolutionary advancements in our understanding of impulsive magnetic energy release and particle acceleration, a process which is known to occur at the Sun but also throughout the Universe
SphinX soft X-ray spectrophotometer: Science objectives, design and performance
The goals and construction details of a new design Polish-led X-ray spectrophotometer are described. The instrument is aimed to observe emission from entire solar corona and is placed as a separate block within the Russian TESIS X- and EUV complex aboard the CORONAS-PHOTON solar orbiting observatory. SphinX uses silicon PIN diode detectors for high time resolution measurements of the solar spectra in the range 0.8–15 keV. Its spectral resolution allows for discerning more than hundred separate energy bands in this range. The instrument dynamic range extends two orders of magnitude below and above these representative for GOES. The relative and absolute accuracy of spectral measurements is expected to be better than few percent, as follows from extensive ground laboratory calibrations
The Importance of Correlations and Fluctuations on the Initial Source Eccentricity in High-Energy Nucleus-Nucleus Collisions
In this paper, we investigate various ways of defining the initial source
eccentricity using the Monte Carlo Glauber (MCG) approach. In particular, we
examine the participant eccentricity, which quantifies the eccentricity of the
initial source shape by the major axes of the ellipse formed by the interaction
points of the participating nucleons. We show that reasonable variation of the
density parameters in the Glauber calculation, as well as variations in how
matter production is modeled, do not significantly modify the already
established behavior of the participant eccentricity as a function of collision
centrality. Focusing on event-by-event fluctuations and correlations of the
distributions of participating nucleons we demonstrate that, depending on the
achieved event-plane resolution, fluctuations in the elliptic flow magnitude
lead to most measurements being sensitive to the root-mean-square, rather
than the mean of the distribution. Neglecting correlations among
participants, we derive analytical expressions for the participant eccentricity
cumulants as a function of the number of participating nucleons,
\Npart,keeping non-negligible contributions up to \ordof{1/\Npart^3}. We
find that the derived expressions yield the same results as obtained from
mixed-event MCG calculations which remove the correlations stemming from the
nuclear collision process. Most importantly, we conclude from the comparison
with MCG calculations that the fourth order participant eccentricity cumulant
does not approach the spatial anisotropy obtained assuming a smooth nuclear
matter distribution. In particular, for the Cu+Cu system, these quantities
deviate from each other by almost a factor of two over a wide range in
centrality.Comment: 18 pages, 10 figures, submitted to PR
SphinX: The Solar Photometer in X-Rays
Solar Photometer in X-rays (SphinX) was a spectrophotometer developed to observe the Sun in soft X-rays. The instrument observed in the energy range ≈ 1 - 15 keV with resolution ≈ 0.4 keV. SphinX was flown on the Russian CORONAS-PHOTON satellite placed inside the TESIS EUV and X telescope assembly. The spacecraft launch took place on 30 January 2009 at 13:30 UT at the Plesetsk Cosmodrome in Russia. The SphinX experiment mission began a couple of weeks later on 20 February 2009 when the first telemetry dumps were received. The mission ended nine months later on 29 November 2009 when data transmission was terminated. SphinX provided an excellent set of observations during very low solar activity. This was indeed the period in which solar activity dropped to the lowest level observed in X-rays ever. The SphinX instrument design, construction, and operation principle are described. Information on SphinX data repositories, dissemination methods, format, and calibration is given together with general recommendations for data users. Scientific research areas in which SphinX data find application are reviewed
System size and centrality dependence of charged hadron transverse momentum spectra in Au+Au and Cu+Cu collisions at sqrt(s) = 62.4 and 200 GeV
We present transverse momentum distributions of charged hadrons produced in
Cu+Cu collisions at sqrt(s) = 62.4 and 200 GeV. The spectra are measured for
transverse momenta of 0.25 < p_T < 5.0 GeV/c at sqrt(s) = 62.4 GeV and 0.25 <
p_T < 7.0 GeV/c at sqrt(s) = 200 GeV, in a pseudo-rapidity range of 0.2 < eta <
1.4. The nuclear modification factor R_AA is calculated relative to p+p data at
both collision energies as a function of collision centrality. At a given
collision energy and fractional cross-section, R_AA is observed to be
systematically larger in Cu+Cu collisions compared to Au+Au. However, for the
same number of participating nucleons, R_AA is essentially the same in both
systems over the measured range of p_T, in spite of the significantly different
geometries of the Cu+Cu and Au+Au systems.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let
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