46,883 research outputs found
Quantitative analysis of flare accelerated electrons through their hard X-ray and microwave radiation
Hard X-ray and microwave modelling that takes into account the temporal evolution of the electron spectrum as well as the inhomogeneity of the magnetic field and the ambient medium in the radio source is presented. This method is illustrated for the June 29 1980 10:41 UT event. The implication on the process of acceleration/injection is discussed
A study of starting time in great hard X-ray flares
An analysis of the starting time in ten great hard X-ray bursts observed with the X-Ray Burst Spectrometer (HXRBS) is presented. It is shown that the impulsive phase of nine of them is composed of a preflash phase, during which the burst is observed up to an energy limit ranging from some tens of keV to 200 keV, followed ten to some tens of seconds afterwards by a flash phase, where the count rate rises simultaneously in all detector channels. For two events strong gamma-ray line emission is observed and is shown to start close to the onset of the flash phase
Solar Energetic Particle Events in the 23rd Solar Cycle: Interplanetary Magnetic Field Configuration and Statistical Relationship with Flares and CMEs
We study the influence of the large-scale interplanetary magnetic field
configuration on the solar energetic particles (SEPs) as detected at different
satellites near Earth and on the correlation of their peak intensities with the
parent solar activity. We selected SEP events associated with X and M-class
flares at western longitudes, in order to ensure good magnetic connection to
Earth. These events were classified into two categories according to the global
interplanetary magnetic field (IMF) configuration present during the SEP
propagation to 1AU: standard solar wind or interplanetary coronal mass
ejections (ICMEs). Our analysis shows that around 20% of all particle events
are detected when the spacecraft is immersed in an ICME. The correlation of the
peak particle intensity with the projected speed of the SEP-associated coronal
mass ejection is similar in the two IMF categories of proton and electron
events, . The SEP events within ICMEs show stronger correlation
between the peak proton intensity and the soft X-ray flux of the associated
solar flare, with correlation coefficient 0.670.13, compared to the
SEP events propagating in the standard solar wind, 0.360.13. The
difference is more pronounced for near-relativistic electrons. The main reason
for the different correlation behavior seems to be the larger spread of the
flare longitude in the SEP sample detected in the solar wind as compared to SEP
events within ICMEs. We discuss to which extent observational bias, different
physical processes (particle injection, transport, etc.), and the IMF
configuration can influence the relationship between SEPs and coronal activity.Comment: http://adsabs.harvard.edu.ezproxy.obspm.fr/abs/2013SoPh..282..579
Improved Templates for Photometric Redshifts of Submm Sources
There is growing evidence that some star-forming galaxies at z>1 are
characterized by high efficiencies and specific star formation rates. In the
local universe, these traits are shared by ``active'' Blue Compact Dwarf
galaxies (BCDs) with compact and dense star-forming regions. The Spectral
Energy Distributions (SEDs) of these BCDs are dominated by young massive star
clusters, embedded in a cocoon of dust. In this Letter, we incorporate these
BCD SEDs as templates for two samples of high-redshift galaxy populations
selected at submm wavelengths. Because of the severe absorption of the optical
light, the featureless mid-infrared spectrum, and the relatively flat radio
continuum, the dusty star-cluster SEDs are good approximations to most of the
submm sources in our samples. In most cases, the active BCD SEDs fit the
observed photometric points better than the ``standard'' templates, M 82 and
Arp 220, and predict photometric redshifts significantly closer to the
spectroscopic ones. Our results strongly suggest that the embedded dusty star
clusters in BCD galaxies are superior to other local templates such as M 82 and
Arp 220 in fitting distant submm starburst galaxies.Comment: Accepted by ApJL: 4 pages, 2 figures, 2 table
Multi-Frequency Study of the B3-VLA Sample II. The Database
We present total flux densities of 1049 radio sources in the frequency range
from 151 MHz to 10.6 GHz. These sources belong to the B3-VLA sample, which is
complete down to 100 mJy at 408 MHz. The data constitute a homogeneous spectral
database for a large sample of radio sources, 50 times fainter than the 3C
catalogue, and will be used to perform a spectral ageing analysis, which is one
of the critical points in understanding the physics and evolution of
extragalactic radio sources.Comment: 14 pages, 3 figures, accepted for publication in Astronomy &
Astrophysics Supplement Series, gzipped postscript file also available at
http://multivac.jb.man.ac.uk:8000/ceres/papers/papers.html or
http://gladia.astro.rug.nl:8000/ceres/papers/papers.htm
Electron acceleration sites in a large-scale coronal structure
Radio observations and interplanetary particle measurements have
shown that even in the absence of conspicuous violent processes in the low
atmosphere (such as Hα flares) electrons are accelerated in the corona, most
likely at higher altitudes than during flares (≥0.5 R above the
photosphere). The paper presents direct evidence on the acceleration sites from
a case study of radio, visible light and soft X-ray observations: electrons are
repeatedly accelerated in a large-scale coronal structure which is identified
with a streamer in coronographic observations. Energy is simultaneously
released in an active region near the base of the structure and at a height of
∼1 R , over several hours before the large-scale structure erupts. Energy
input is observed in at least two emerging active regions underneath the
streamer. The coronal configuration is three-dimensional, overlying a whole
quadrant of the Sun. It is argued that the observations trace multiple sites of
energy release presumably in current sheets embedded within the streamer, in
agreement with scenarios developed for the acceleration of electrons seen in
the corona and at 1 AU, and for the evolution of large-scale coronal structures
towards eruption
Evaluation of expected solar flare neutrino events in the IceCube observatory
Since the end of the eighties and in response to a reported increase in the
total neutrino flux in the Homestake experiment in coincidence with a solar
flare, solar neutrino detectors have searched for solar flare signals.
Neutrinos from the decay of mesons, which are themselves produced in collisions
of accelerated protons with the solar atmosphere, would provide a novel window
on the underlying physics of the acceleration process. For our studies we focus
on the IceCube Neutrino Observatory, a cubic kilometer neutrino detector
located at the geographical South Pole. Due to its Supernova data acquisition
system and its DeepCore component, dedicated to low energy neutrinos, IceCube
may be sensitive to solar flare neutrinos and thus permit either a measurement
of the signal or the establishment of more stringent upper limits on the solar
flare neutrino flux. We present an approach for a time profile analysis based
on a stacking method and an evaluation of a possible solar flare signal in
IceCube using the Geant4 toolkit.Comment: Paper submitted to the 34th International Cosmic Ray Conference, The
Hague 201
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