123 research outputs found
Solar Wind Speed Estimate with Machine Learning Ensemble Models for LISA
In this work we study the potentialities of machine learning models in
reconstructing the solar wind speed observations gathered in the first
Lagrangian point by the ACE satellite in 2016--2017 using as input data
galactic cosmic-ray flux variations measured with particle detectors hosted
onboard the LISA Pathfinder mission also orbiting around L1 during the same
years. We show that ensemble models composed of heterogeneous weak regressors
are able to outperform weak regressors in terms of predictive accuracy. Machine
learning and other powerful predictive algorithms open a window on the
possibility of substituting dedicated instrumentation with software models
acting as surrogates for diagnostics of space missions such as LISA and space
weather science.Comment: Submitted to Environmental Modelling & Softwar
Cosmic-ray positron measurements: on the origin of the e + excess and limits on magnetar birthrate
Fifty years after the discovery of antimatter in cosmic rays at the top of the atmosphere, the trend of the most accurate measurements of positrons indicate an excess of these particles above 7 GeV with respect to the secondary component produced by primary cosmic rays propagating in the interstellar medium. This excess is studied here within the scenario of the last 25-year magnetic spectrometer observations. The characteristics of sources contributing to the overall e + flux observed near Earth as a function of particle energy are discussed. Pulsars and magnetars are considered plausible sources of cosmic-ray leptons. The consistency of this possibility is evaluated on the basis of inferred e + source characteristics and parameters set in several other astrophysics fields for these neutron stars. In case all pulsars and magnetars in the vicinity of Earth contribute to e + -e fluxes as expected, a larger positron excess would have been observed. Disks around pulsars and magnetars may play a role in quenching pair production in the magnetosphere of these neutron stars. The magnetar birthrate may also be overestimated
Low-energy electromagnetic processes affecting free-falling test-mass charging for LISA and future space interferometers
Galactic cosmic rays and solar energetic particles charge gold-platinum,
free-falling test masses (TMs) on board interferometers for the detection of
gravitational waves in space. The charging process induces spurious forces on
the test masses that affect the sensitivity of these instruments mainly below
Hz. Geant4 and FLUKA Monte Carlo simulations were carried out to
study the TM charging process on board the LISA Pathfinder mission that
remained into orbit around the Sun-Earth Lagrange point L1 between 2016 and
2017. While a good agreement was observed between simulations and measurements
of the TMs net charging, the shot noise associated with charging fluctuations
of both positive and negative particles resulted 3-4 times higher that
predicted. The origin of this mismatch was attributed to the propagation of
electrons and photons only above 100 eV in the simulations. In this paper,
low-energy electromagnetic processes to be included in the future Monte Carlo
simulations for LISA and LISA-like space interferometers TM charging are
considered. {It is found that electrons and photons below 100 eV give a
contribution to the effective charging comparable to that of the whole sample
of particles above this energy. In particular, for incident protons ionization
contributes twice with respect to low energy kinetic emission and electron
backscattering. The other processes are found to play a negligible role. For
heavy nuclei only sputtering must be considered.Comment: Accepted for publication in Classical and Quantum Gravit
Bridging the gap between Monte Carlo simulations and measurements of the LISA Pathfinder test-mass charging for LISA
Cubic gold-platinum free-falling test masses (TMs) constitute the mirrors of
future LISA and LISA-like interferometers for low-frequency gravitational wave
detection in space. High-energy particles of Galactic and solar origin charge
the TMs and thus induce spurious electrostatic and magnetic forces that limit
the sensitivity of these interferometers. Prelaunch Monte Carlo simulations of
the TM charging were carried out for the LISA Pathfinder (LPF) mission, that
was planned to test the LISA instrumentation. Measurements and simulations were
compared during the mission operations. The measured net TM charging agreed
with simulation estimates, while the charging noise was three to four times
higher. We aim to bridge the gap between LPF TM charging noise simulations and
observations. New Monte Carlo simulations of the LPF TM charging due to both
Galactic and solar particles were carried out with the FLUKA/LEI toolkit. This
allowed propagating low-energy electrons down to a few electronvolt. These
improved FLUKA/LEI simulations agree with observations gathered during the
mission operations within statistical and Monte Carlo errors. The charging
noise induced by Galactic cosmic rays is about one thousand charges per second.
This value increases to tens of thousands charges per second during solar
energetic particle events. Similar results are expected for the LISA TM
charging.Comment: 11 pages, 9 figure
Recurrent galactic cosmic-ray flux modulation in L1 and geomagnetic activity during the declining phase of the solar cycle 24
Galactic cosmic-ray (GCR) flux short-term variations (1 month) in the
inner heliosphere are mainly associated with the passage of high-speed solar
wind streams (HSS) and interplanetary (IP) counterparts of coronal mass
ejections (ICMEs). Data gathered with a particle detector flown on board the
ESA LISA Pathfinder (LPF) spacecraft, during the declining part of the solar
cycle 24 (February 2016 - July 2017) around the Lagrange point L1, have allowed
to study the characteristics of recurrent cosmic-ray flux modulations above 70
MeV n. %These modulations are observed when the solar wind speed is
400 km s and/or the IP magnetic field intensity 10 nT. It is shown
that the amplitude and evolution of individual modulations depend in a unique
way on both IP plasma parameters and particle flux intensity before HSS and
ICMEs transit. By comparing the LPF data with those gathered contemporaneously
with the magnetic spectrometer experiment AMS-02 on board the International
Space Station and with those of Earth polar neutron monitors, the GCR flux
modulation was studied at different energies during recurrent short-term
variations. It is also aimed to set the near real-time particle observation
requirements to disentangle the role of long and short-term variations of the
GCR flux to evaluate the performance of high-sensitivity instruments in space
such as the future interferometers for gravitational wave detection. Finally,
the association between recurrent GCR flux variation observations in L1 and
weak to moderate geomagnetic activity in 2016-2017 is discussed. Short-term
recurrent GCR flux variations are good proxies of recurrent geomagnetic
activity when the B component of the IP magnetic field is directed
northern
Study of Galactic Cosmic-Ray Flux Modulation by Interplanetary Plasma Structures for the Evaluation of Space Instrument Performance and Space Weather Science Investigations
The role of high-energy particles in limiting the performance of on-board instruments was studied for the European Space Agency (ESA) Laser Interferometer Space Antenna (LISA) Pathfinder (LPF) and ESA/National Astronautics and Space Administration Solar Orbiter missions. Particle detectors (PD) placed on board the LPF spacecraft allowed for testing the reliability of pre-launch predictions of galactic cosmic-ray (GCR) energy spectra and for studying the modulation of proton and helium overall flux above 70 MeV n − 1 on a day-by-day basis. GCR flux variations up to approximately 15% in less than a month were observed with LPF orbiting around the Lagrange point L1 between 2016 and 2017. These variations appeared barely detected or undetected in neutron monitors. In this work the LPF data and contemporaneous observations carried out with the magnetic spectrometer AMS-02 experiment are considered to show the effects of GCR flux short-term variations with respect to monthly averaged measurements. Moreover, it is shown that subsequent large-scale interplanetary structures cause a continuous modulation of GCR fluxes. As a result, small Forbush decreases cannot be considered good proxies for the transit of interplanetary coronal mass ejections and for geomagnetic storm forecasting
A novel approach in magnetic cloud-driven Forbush decrease modeling
Interplanetary coronal mass ejections (ICMEs) are large-scale solar wind disturbances propagating from the
Sun and causing a depression of the galactic-cosmic ray (GCR) intensity known as Forbush decrease (FD). IC-
MEs generally contain coherent plasma structures called magnetic clouds (MCs). A unique and powerful data
analysis tool allowing for the study of the quasi-3-D configuration of a MC is the Grad-Shafranov (GS) recons -
truction. The aim of this work is to investigate the role played by the MC configuration in the formation of a FD.
A suited full-orbit test-particle simulation has been developed in order to evaluate FD amplitude and time pro-
file produced by the MC obtained with the GS reconstruction. Particle trajectories are computed starting from
an isotropic flux outside the MC region. In addition, particle diffusion has been modeled by superimposing a
small-angle scattering over the unperturbed charged particle motion at each time step. The model allows us to
investigate the MC effect on GCR propagation and to study the energy dependence of the physical processes in -
volved, as it provides an estimate of ground-based GCR counts observations at different latitudes. A comparison
between model results and both space-based cosmic-ray measurements in L1 and ground-based observations
suggests a major role of drifts in producing the FD and a reduced contribution of GCR particle diffusion
The role of low-energy electrons in the charging process of LISA test masses
The estimate of the total electron yield is fundamental for our understanding of the test-mass charging associated with cosmic rays in the Laser Interferometer Space Antenna (LISA) Pathfinder mission and in the forthcoming gravitational wave observatory LISA. To unveil the role of low energy electrons in this process owing to galactic and solar energetic particle events, in this work we study the interaction of keV and sub-keV electrons with a gold slab using a mixed Monte Carlo (MC) and ab-initio framework. We determine the energy spectrum of the electrons emerging from such a gold slab hit by a primary electron beam by considering the relevant energy loss mechanisms as well as the elastic scattering events. We also show that our results are consistent with experimental data and MC simulations carried out with the GEANT4-DNA toolkit
A New Method to Model Magnetic Cloud-driven Forbush Decreases: The 2016 August 2 Event
Interplanetary coronal mass ejections (ICMEs), generally containing magnetic clouds (MCs), are associated with galactic-cosmic ray (GCR) intensity depressions known as Forbush decreases (FDs). An ICME was observed at L1 between 2016 August 2 at 14:00 UT and August 3 at 03:00 UT. The MC region was identified and its magnetic configuration was retrieved by using the Grad-Shafranov (GS) reconstruction. A weak FD in the GCR count-rate was observed on 2016 August 2 by a particle detector on board the European Space Agency LISA Pathfinder mission. The spacecraft orbited around L1 and the particle detector allowed us to monitor the GCR intensity at energies above 70 MeVn(-1). A 9% decrease in the cosmic-ray intensity was observed during the ICME passage. The first structure of the ICME caused a 6.4% sharp decrease, while the MC produced a 2.6% decrease. A suited full-orbit test-particle simulation was performed on the MC configuration obtained through the GS reconstruction. The FD amplitude and time profile obtained through the simulation show an excellent agreement with observations. The test-particle simulation allows us to derive the energy dependence of the MC-driven FD providing an estimate of the amplitude at different rigidities, here compared with several neutron monitor observations. This work points out the importance of the large-scale MC configuration in the interaction between GCRs and ICMEs and suggests that particle drifts have a primary role in modulating the GCR intensity within the MC under study and possibly in at least all slowly expanding ICMEs lacking a shock/sheath region
Astrodynamical Space Test of Relativity using Optical Devices I (ASTROD I) - A class-M fundamental physics mission proposal for Cosmic Vision 2015-2025: 2010 Update
This paper on ASTROD I is based on our 2010 proposal submitted for the ESA
call for class-M mission proposals, and is a sequel and an update to our
previous paper [Experimental Astronomy 23 (2009) 491-527; designated as Paper
I] which was based on our last proposal submitted for the 2007 ESA call. In
this paper, we present our orbit selection with one Venus swing-by together
with orbit simulation. In Paper I, our orbit choice is with two Venus
swing-bys. The present choice takes shorter time (about 250 days) to reach the
opposite side of the Sun. We also present a preliminary design of the optical
bench, and elaborate on the solar physics goals with the radiation monitor
payload. We discuss telescope size, trade-offs of drag-free sensitivities,
thermal issues and present an outlook. ASTROD I is a planned interplanetary
space mission with multiple goals. The primary aims are: to test General
Relativity with an improvement in sensitivity of over 3 orders of magnitude,
improving our understanding of gravity and aiding the development of a new
quantum gravity theory; to measure key solar system parameters with increased
accuracy, advancing solar physics and our knowledge of the solar system; and to
measure the time rate of change of the gravitational constant with an order of
magnitude improvement and the anomalous Pioneer acceleration, thereby probing
dark matter and dark energy gravitationally. It is envisaged as the first in a
series of ASTROD missions. ASTROD I will consist of one spacecraft carrying a
telescope, four lasers, two event timers and a clock. Two-way, two-wavelength
laser pulse ranging will be used between the spacecraft in a solar orbit and
deep space laser stations on Earth, to achieve the ASTROD I goals.Comment: 15 pages, 11 figures, 1 table, based on our 2010 proposal submitted
for the ESA call for class-M mission proposals, a sequel and an update to
previous paper [Experimental Astronomy 23 (2009) 491-527] which was based on
our last proposal submitted for the 2007 ESA call, submitted to Experimental
Astronom
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