J/A+A/670/A51 MESSENGER/EPS electron meas. 2010-2015 (Rodriguez-Garcia+, 2023)
Solar energetic electron events measured by MESSENGER and Solar Orbiter.
Peak intensity and energy spectrum radial dependences: Statistical analysis.
Rodriguez-Garcia L., Gomez-Herrero R., Dresing N., Lario D., Zouganelis I.,
Balmaceda L.A., Kouloumvakos A., Fedeli A., Espinosa Lara F., Cernuda I.,
Ho G.C., Wimmer-Schweingruber R.F., Rodriguez-Pacheco J..
<Astron. Astrophys. 670, A51 (2023)>
=2023A&A...670A..51R 2023A&A...670A..51R (SIMBAD/NED BibCode)
ADC_Keywords: Sun
Keywords: Sun: particle emission - Sun: coronal mass ejections (CMEs) -
Sun: flares - Sun: corona - Sun: heliosphere
Abstract:
We present a list of 61 solar energetic electron (SEE) events measured
by the MESSENGER mission and the radial dependences of some parameters
associated with these SEE events. The analysis covers the period from
2010 to 2015, when the heliocentric distance of MESSENGER varied
between 0.31 and 0.47au. We also show the radial dependences for a
shorter list of 12 SEE events measured in February and March 2022 by
spacecraft near 1 au and by Solar Orbiter at about its first close
perihelion at 0.32au. Aims. We study the radial dependences of the
electron peak intensity and the energy spectrum of the electron
intensity at the time of the SEE event peak intensity, taking
advantage of multi-spacecraft measurements.
We compiled the list of SEE events measured by MESSENGER and Solar
Orbiter using hourly averages to find the prompt component of the
near-relativistic (∼70-110keV) electron peak intensities and to
calculate the peak-intensity energy spectra. We also obtained the peak
intensities and energy spectra for the same events as measured by the
STEREO-A, -B, ACE, or Wind spacecraft when one of these spacecraft was
in close nominal magnetic connection with MESSENGER or Solar Orbiter
to derive the radial dependences of these SEE parameters.
(1) Because the background intensity level of the particle instrument
on board MESSENGER is high, the SEE events measured by this mission
are necessarily large and intense; most of them are accompanied by a
shock driven by a coronal mass ejection and are widely spread in
heliolongitude. The SEE events display relativistic (∼1MeV) electron
intensity enhancements. For this SEE sample, we found that (2) the SEE
peak intensity shows a radial dependence that can be expressed as R,
where the median value of the index is αMed=-3.3±1.4 for a
subsample of 28 events for which the nominal magnetic footpoints of
the near 0.3au and 1 au spacecraft were close in heliographic
longitude. (3) The mean spectral index of a subset of 42 events for
which the energy spectrum could be analysed is <≥-1.9 0.3, which is
harder than the value found in previous studies using data from
spacecraft near 1au. SEE events observed by Solar Orbiter also
display harder energy spectra than previous studies using data
obtained near 1au.
There is a wide variability in the radial dependence of the electron
peak intensities, but on average and within uncertainties, the
∝R-3 dependence found in previous observational and
modelling studies is confirmed. The electron spectral index found in
the energy range around 200keV (δ200) of the backward-scattered
population near 0.3au measured by MESSENGER is harder by a median
factor of 20% and 10% when comparing to the near 1au anti-sunward
propagating beam and the backward-scattered population, respectively.
Description:
We analysed the MESSENGER/EPS data from 2010 February 7 to 2015 April
30. MESSENGER was initially en route to Mercury on 2004 August 3 and
finally inserted into an orbit about the innermost planet on 2011
March 18 until the end of the mission on 2015 April 30. During the
time of analysis, which coincided with most of the rising, maximum,
and early decay phase of solar cycle 24, the MESSENGER radial distance
therefore varied from 0.31 to 0.47au.
The EPS instrument measured electrons from 25keV to 1MeV.
These data are the hourly averages electron measurements from the
sector S02 of the EPS instrument on board MESSENGER.
These are the data used to generate figure 1 of the study referenced
above.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table.dat 271 45768 MESSENGER data
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Byte-by-byte Description of file:table.dat
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Bytes Format Units Label Explanations
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1- 4 I4 yr Obs.Y Observation date, year (UT)
6- 8 I3 yr Obs.D Observation date, day of year (UT)
10- 11 I2 h Obs.h Observation date, hour (UT)
13- 14 I2 min Obs.m Observation date, minute (UT)
16- 18 F3.1 s Obs.s Observation date, second (UT)
20- 30 F11.7 1/cm2.sr.s.keV e20-28 ? Electrons in the energy bin
from 20.0 to 28.0keV
32- 41 F10.7 1/cm2.sr.s.keV e_e20-28 ? Uncertainty of the electrons in the
energy bin from 20.0 to 28.0keV
43- 55 F13.7 1/cm2.sr.s.keV e28-35 ? Electrons in the energy bin
from 28.0 to 35.0keV
57- 67 F11.7 1/cm2.sr.s.keV e_e28-35 ? Uncertainty of the electrons in the
energy bin from 28.0 to 35.0keV
69- 80 F12.6 1/cm2.sr.s.keV e35-56 ? Electrons in the energy bin
from 35.0 to 56.0keV
82- 92 F11.7 1/cm2.sr.s.keV e_e35-56 ? Uncertainty of the electrons in the
energy bin from 35.0 to 56.0keV
94-106 F13.7 1/cm2.sr.s.keV e56-71 ? Electrons in the energy bin
from 56.0 to 71.0keV
108-118 F11.7 1/cm2.sr.s.keV e_e56-71 ? Uncertainty of the electrons in the
energy bin from 56.0 to 71.0keV
120-132 F13.7 1/cm2.sr.s.keV e71-112 ? Electrons in the energy bin
from 71.0 to 112.0keV
134-144 F11.7 1/cm2.sr.s.keV e_e71-112 ? Uncertainty of the electrons in the
energy bin from 71.0 to 112.0keV
146-158 F13.7 1/cm2.sr.s.keV e112-141 ? Electrons in the energy bin
from 112.0 to 141.0keV
160-170 F11.7 1/cm2.sr.s.keV e_e112-141 ? Uncertainty of the electrons in the
energy bin from 112.0 to 141.0keV
172-184 F13.7 1/cm2.sr.s.keV e141-224 ? Electrons in the energy bin
from 141.0 to 224.0keV
186-195 F10.7 1/cm2.sr.s.keV e_e141-224 ? Uncertainty of the electrons in the
energy bin from 141.0 to 224.0keV
197-209 F13.7 1/cm2.sr.s.keV e224-447 ? Electrons in the energy bin
from 224.0 to 447.0keV
211-220 F10.7 1/cm2.sr.s.keV e_e224-447 ? Uncertainty of the electrons in the
energy bin from 224.0 to 447.0keV
222-234 F13.8 1/cm2.sr.s.keV e447-708 ? Electrons in the energy bin
from 447.0 to 708.0keV
236-246 F11.8 1/cm2.sr.s.keV e_e447-708 ? Uncertainty of the electrons in the
energy bin from 447.0 to 708.0keV
248-260 F13.8 1/cm2.sr.s.keV e708-1000 ? Electrons in the energy bin
from 708.0keV to 1.0 MeV
262-271 F10.8 1/cm2.sr.s.keV e_e708-1000 ? Uncertainty of the electrons in the
energy bin from 708.0keV to 1.0MeV
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Acknowledgements:
Laura Rodriguez-Garcia, l.rodriguezgarcia(at)edu.uah.es
(End) Patricia Vannier [CDS] 05-Dec-2022