56 research outputs found
Observations of Electrons from the Decay of Solar Flare Neutrons
We have found evidence for fluxes of energetic electrons in interplanetary
space on board the ISEE-3 spacecraft which we interpret as the decay products
of neutrons generated in a solar flare on 1980 June 21. The decay electrons
arrived at the s/c shortly before the electrons from the flare and can be
distinguished from the latter by their distinctive energy spectrum. The time
profile of the decay electrons is in good agreement with the results from a
simulation based on a scattering mean free path derived from a fit to the flare
electron data. The comparison with simultaneously observed decay protons and a
published direct measurement of high-energy neutrons places important
constraints on the parent neutron spectrum.Comment: 4 pages (postscript), accepted by Astrophysical Journal Letter
On the Estimation of Solar Energetic Particle Injection Timing from Onset Times near Earth
We examine the accuracy of a common technique for estimating the start time
of solar energetic particle injection based on a linear fit to the observed
onset time versus 1/(particle velocity). This is based on a concept that the
first arriving particles move directly along the magnetic field with no
scattering. We check this by performing numerical simulations of the transport
of solar protons between 2 and 2000 MeV from the Sun to the Earth, for several
assumptions regarding interplanetary scattering and the duration of particle
injection, and analyzing the results using the inverse velocity fit. We find
that in most cases, the onset times align close to a straight line as a
function of inverse velocity. Despite this, the estimated injection time can be
in error by several minutes. Also, the estimated path length can deviate
greatly from the actual path length along the interplanetary magnetic field.
The major difference between the estimated and actual path lengths implies that
the first arriving particles cannot be viewed as moving directly along the
interplanetary magnetic field.Comment: 19 pages, 3 Postscript figures. Astrophys. J., in pres
Estimations of changes of the Sun's mass and the gravitation constant from the modern observations of planets and spacecraft
More than 635 000 positional observations (mostly radiotechnical) of planets
and spacecraft (1961-2010), have been used for estimating possible changes of
the gravitation constant, the solar mass, and semi-major axes of planets, as
well as the value of the astronomical unit, related to them. The analysis of
the observations has been performed on the basis of the EPM2010 ephemerides of
IAA RAS in post-newtonian approximation. The obtained results indicate on
decrease in the heliocentric gravitation constant per year at the level The positive secular
changes of semi-major axes have been obtained simultaneously
for the planets Mercury, Venus, Mars, Jupiter, Saturn, as expected if the
geliocentric gravitation constant is decreasing in century wise. The change of
the mass of the Sun due to the solar radiation and the solar wind and
the matter dropping on the Sun (comets, meteors, asteroids and dust) was
estimated. Taking into account the maximal limits of the possible
change, the value falls within the interval in year with the 95% probability. The
astronomical unit (au) is only connected with the geliocentric gravitation
constant by its definition. In the future, the connection between
and au should be fixed at the certain time moment, as it is inconvenient highly
to have the changing value of the astronomical unit.Comment: 20 pages, 4 tables, accepted for publication in Solar System
Research, 2011 (Astronomicheskii vestnik
An Extreme Solar Event of 20 January 2005: Properties of the Flare and the Origin of Energetic Particles
The extreme solar and SEP event of 20 January 2005 is analyzed from two
perspectives. Firstly, we study features of the main phase of the flare, when
the strongest emissions from microwaves up to 200 MeV gamma-rays were observed.
Secondly, we relate our results to a long-standing controversy on the origin of
SEPs arriving at Earth, i.e., acceleration in flares, or shocks ahead of CMEs.
All emissions from microwaves up to 2.22 MeV line gamma-rays during the main
flare phase originated within a compact structure located just above sunspot
umbrae. A huge radio burst with a frequency maximum at 30 GHz was observed,
indicating the presence of a large number of energetic electrons in strong
magnetic fields. Thus, protons and electrons responsible for flare emissions
during its main phase were accelerated within the magnetic field of the active
region. The leading, impulsive parts of the GLE, and highest-energy gamma-rays
identified with pi^0-decay emission, are similar and correspond in time. The
origin of the pi^0-decay gamma-rays is argued to be the same as that of lower
energy emissions. We estimate the sky-plane speed of the CME to be 2000-2600
km/s, i.e., high, but of the same order as preceding non-GLE-related CMEs from
the same active region. Hence, the flare itself rather than the CME appears to
determine the extreme nature of this event. We conclude that the acceleration,
at least, to sub-relativistic energies, of electrons and protons, responsible
for both the flare emissions and the leading spike of SEP/GLE by 07 UT, are
likely to have occurred simultaneously within the flare region. We do not rule
out a probable contribution from particles accelerated in the CME-driven shock
for the leading GLE spike, which seemed to dominate later on.Comment: 34 pages, 14 Postscript figures. Solar Physics, accepted. A typo
corrected. The original publication is available at
http://www.springerlink.co
Temporal evolution of solar energetic particle spectra
During solar flares and coronal mass ejections, solar energetic par- ticles (SEPs) may be released into the interplanetary medium and near-Earth locations. The energy spectra of SEP events at 1 AU are typically averaged over the entire event or studied in a few snapshots. In this paper we analyze the time evolution of the energy spectra of four large selected SEP events using a large number of snapshots. We use a multi-spacecraft and multi-instrument approach for the observations, obtained over a wide SEP energy range. We find large differences in the spectra at the beginning of the events as measured by different instruments. We show that over time, a wave-like structure is observed traveling through the spectra from the highest energies to the lowest energies, creating an “arch” shape which then straightens into a power law later in the event, after times of the order of 10 hours. We discuss the processes that determine SEP intensities and their role in shaping the spectral time evolution
Sources of SEP Acceleration during a Flare-CME Event
A high-speed halo-type coronal mass ejection (CME), associated with a GOES
M4.6 soft X-ray flare in NOAA AR 0180 at S12W29 and an EIT wave and dimming,
occurred on 9 November 2002. A complex radio event was observed during the same
period. It included narrow-band fluctuations and frequency-drifting features in
the metric wavelength range, type III burst groups at metric--hectometric
wavelengths, and an interplanetary type II radio burst, which was visible in
the dynamic radio spectrum below 14 MHz. To study the association of the
recorded solar energetic particle (SEP) populations with the propagating CME
and flaring, we perform a multi-wavelength analysis using radio spectral and
imaging observations combined with white-light, EUV, hard X-ray, and
magnetogram data. Velocity dispersion analysis of the particle distributions
(SOHO and Wind in situ observations) provides estimates for the release times
of electrons and protons. Our analysis indicates that proton acceleration was
delayed compared to the electrons. The dynamics of the interplanetary type II
burst identify the burst source as a bow shock created by the fast CME. The
type III burst groups, with start times close to the estimated electron release
times, trace electron beams travelling along open field lines into the
interplanetary space. The type III bursts seem to encounter a steep density
gradient as they overtake the type II shock front, resulting in an abrupt
change in the frequency drift rate of the type III burst emission. Our study
presents evidence in support of a scenario in which electrons are accelerated
low in the corona behind the CME shock front, while protons are accelerated
later, possibly at the CME bow shock high in the corona.Comment: Solar Physics, November 2007, in pres
The timing of ions in solar energetic particle event onsets
International audienc
- …