M. Laurenza

On the origins of solar EIT waves

Abstract : Approximately half of the large-scale coronal waves identified in images obtained by the Extreme-Ultraviolet Imaging Telescope (EIT) on the Solar and Heliospheric Observatory from 1997 March to 1998 June were associated with small solar flares with soft X-ray intensities below C class. The probability of a given flare of this intensity having an associated EIT wave is low. For example, of ~8,000 B-class flares occurring during this 15 month period, only 1% were linked to EIT waves. These results indicate the need for a special condition that distinguishes flares with EIT waves from the vast majority of flares that lack wave association. Various lines of evidence, including the fact that EIT waves have recently been shown to be highly associated with coronal mass ejections (CMEs), suggest that this special condition is a CME. A CME is not a sufficient condition for a detectable EIT wave, however, because we calculate that 5 times as many front-side CMEs as EIT waves occurred during this period, after taking the various visibility factors for both phenomena into account. In general, EIT wave association increases with CME speed and width.

QUASI-BIENNIAL MODULATION OF SOLAR NEUTRINO FLUX AND SOLAR AND GALACTIC COSMIC RAYS BY SOLAR CYCLIC ACTIVITY

Using some solar activity indicators such as sunspot areas and green-line coronal emission during the period 1974-2001, we find that the quasi-biennial periodicity is a fundamental mode of solar variability. We provide evidence for the quasi-biennial modulation of the solar neutrino flux, thus supporting the hypothesis of a connection between solar neutrinos and solar magnetic fields, probably through direct interaction with the neutrino magnetic moment. The same periodic modulation has been detected when fluxes of solar energetic protons and galactic cosmic rays are investigated. These modulation results significantly correlate to that of the neutrino flux. Finally, the superposition of the quasi-biennial cycle to the eleven-year cycle can explain the Gnevyshev Gap phenomenon.

Search for periodicities in the IMP 8 Charged Particle Measurement Experiment proton fluxes for the energy bands 0.50–0.96 MeV and 190–440 MeV

[1] Past studies revealed that the photospheric magnetic field, as well as many solar activity phenomena, undergoes both periodic and quasiperiodic variations on different time scales. Nevertheless, only a few attempts have been made so far to detect corresponding variations in the occurrence frequency of solar energetic particle events. Here we search for periodicities in the proton fluxes, measured in the interplanetary space, on time scales ranging from a few (>6) Bartels rotations (27 days) up to the Schwabe (~11 years) period. We apply the wavelet technique to the proton fluxes recorded by the Charged Particle Measurement Experiment (CPME) instrument aboard IMP 8 spacecraft, from 1974 to 2001, in the energy bands 0.50-0.96 MeV and 190-440 MeV. The reliability of the obtained results is tested by analyzing the wavelet response to suitable artificial functions. The ~9.8, ~3.8, and -1.7-2.2 year periods are the most significant found in the interplanetary proton flux. Shorter periods (such as ~1 year) are detected in some time intervals, but they are not significant in the whole sequence of data.

The Cryogenic AntiCoincidence detector for ATHENA X-IFU: A program overview

The ATHENA observatory is the second large-class ESA mission, in the context of the Cosmic Vision 2015 - 2025, scheduled to be launched on 2028 at L2 orbit. One of the two on-board instruments is the X-IFU (X-ray Integral Field Unit): it is a TES-based kilo-pixels order array able to perform simultaneous high-grade energy spectroscopy (2.5 eV at 6 keV) and imaging over the 5 arcmin FoV. The X-IFU sensitivity is degraded by the particles background which is induced by primary protons of both solar and Cosmic Rays origin, and secondary electrons. The studies performed by Geant4 simulations depict a scenario where it is mandatory the use of reduction techniques that combine an active anticoincidence detector and a passive electron shielding to reduce the background expected in L2 orbit down to the goal level of 0.005 cts/cm2/s/keV, so enabling the characterization of faint or diffuse sources (e.g. WHIM or Galaxy cluster outskirts). From the detector point of view this is possible by adopting a Cryogenic AntiCoincidence (CryoAC) placed within a proper optimized environment surrounding the X-IFU TES array. It is a 4-pixels detector made of wide area Silicon absorbers sensed by Ir TESes, and put at a distance < 1 mm below the TES-array. On October 2015 the X-IFU Phase A program has been kicked-off, and about the CryoAC is at present foreseen on early 2017 the delivery of the DM1 (Demonstration Model 1) to the FPA development team for integration, which is made of 1 pixel “bridgessuspended” that will address the final design of the CryoAC. Both the background studies and the detector development work is on-going to provide confident results about the expected residual background at the TES-array level, and the single pixel design to produce a detector for testing activity on 2016/2017. Here we will provide an overview of the CryoAC program, discussing some details about the background assessment having impact on the CryoAC design, the last single pixel characterization, the structural issues, followed by some programmatic aspects.

Updates on the background estimates for the X-IFU instrument onboard of the ATHENA mission

ATHENA is the second large mission in ESA Cosmic Vision 2015-2025, with a launch foreseen in 2028 towards the L2 orbit. The mission addresses the science theme “The Hot and Energetic Universe”, by coupling a high-performance X-ray Telescope with two complementary focal-plane instruments. One of these, the X-ray Integral Field Unit (X-IFU) is a TES based kilo-pixel array, providing spatially resolved high-resolution spectroscopy (2.5 eV at 6 keV) over a 5 arcmin FoV. The background for this kind of detectors accounts for several components: the diffuse Cosmic Xray Background, the low energy particles (< ~100 keV) focalized by the mirrors and reaching the detector from inside the field of view, and the high energy particles (> ~100 MeV) crossing the spacecraft and reaching the focal plane from every direction. In particular, these high energy particles lose energy in the materials they cross, creating secondaries along their path that can induce an additional background component. Each one of these components is under study of a team dedicated to the background issues regarding the X-IFU, with the aim to reduce their impact on the instrumental performances. This task is particularly challenging, given the lack of data on the background of X-ray detectors in L2, the uncertainties on the particle environment to be expected in such orbit, and the reliability of the models used in the Monte Carlo background computations. As a consequence, the activities addressed by the group range from the reanalysis of the data of previous missions like XMMNewton, to the characterization of the L2 environment by data analysis of the particle monitors onboard of satellites present in the Earth magnetotail, to the characterization of solar events and their occurrence, and to the validation of the physical models involved in the Monte Carlo simulations. All these activities will allow to develop a set of reliable simulations to predict, analyze and find effective solutions to reduce the particle background experienced by the X-IFU, ultimately satisfying the scientific requirement that enables the science of ATHENA. While the activities are still ongoing, we present here some preliminary results already obtained by the group. The L2 environment characterization activities, and the analysis and validation of the physical processes involved in the Monte Carlo simulations are the core of an ESA activity named AREMBES (Athena Radiation Environment Models and Effects), for which the work presented here represents a starting point.

DRIFT EFFECTS ON THE GALACTIC COSMIC RAY MODULATION

Cosmic ray (CR) modulation is driven by both solar activity and drift effects in the heliosphere, although their role is only qualitatively understood as it is difficult to connect the CR variations to their sources. In order to address this problem, the Empirical Mode Decomposition technique has been applied to the CR intensity, recorded by three neutron monitors at different rigidities (Climax, Rome, and Huancayo-Haleakala (HH)), the sunspot area, as a proxy for solar activity, the heliospheric magnetic field magnitude, directly related to CR propagation, and the tilt angle (TA) of the heliospheric current sheet (HCS), which characterizes drift effects on CRs. A prominent periodicity at ~six years is detected in all the analyzed CR data sets and it is found to be highly correlated with changes in the HCS inclination at the same timescale. In addition, this variation is found to be responsible for the main features of the CR modulation during periods of low solar activity, such as the flat (peaked) maximum in even (odd) solar cycles. The contribution of the drift effects to the global Galactic CR modulation has been estimated to be between 30% and 35%, depending on the CR particle energy. Nevertheless, the importance of the drift contribution is generally reduced in periods nearing the sunspot maximum. Finally, threshold values of ~40°, ~45°, and >55° have been derived for the TA, critical for the CR modulation at the Climax, Rome, and HH rigidity thresholds, respectively.

THE EMPIRICAL MODE DECOMPOSITION TO STUDY THE QUASI-BIENNIAL MODULATION OF SOLAR MAGNETIC ACTIVITY AND SOLAR NEUTRINO FLUX

The time variability of solar activity indices such as sunspot areas (SAs) and green-line coronal emission, fluxes of solar energetic protons and galactic cosmic rays (CRs) in the period 1974–2001 has been investigated through the empirical mode decomposition (EMD). We found that the quasi-biennial periodicity is a prominent time scale of solar variability, having the energetic particle indices an amplitude comparable with the 11 years one. Moreover, we provide evidence for the quasi-biennial modulation of the solar neutrino flux, which results to be also significantly correlated with the fluxes of solar energetic protons and galactic CRs. The significance of all the correlation has been tested by applying both bootstrap and Monte Carlo methods.

The Weibull functional form for SEP event spectra

The evolution of the kinetic energy spectra of two Solar Energetic Particle (SEP) events has been investigated through the Shannons differential entropy during the different phases of the selected events, as proposed by [1]. Data from LET and HET instruments onboard the STEREO spacecraft were used to cover a wide energy range from ~ 4 MeV to 100 MeV, as well as EPAM and ERNE data, on board the ACE and SOHO spacecraft, respectively, in the range 1.6 – 112 MeV. The spectral features were found to be consistent with the Weibull like shape, both during the main phase of the SEP events and over their whole duration. Comparison of results obtained for energetic particles accelerated at corotating interaction regions (CIRs) and transient-related interplanetary shocks are presented in the framework of shock acceleration.

Derivation of relativistic SEP properties through neutron monitor data modeling

The Ground Level Enhancement (GLE) data recorded by the worldwide Neutron Monitor (NM) network are useful resources for space weather modeling during solar extreme events. The derivation of Solar Energetic Particles (SEPs) properties through NM-data modeling is essential for the study of solar-terrestrial physics, providing information that cannot be obtained through the exclusive use of space techniques; an example is the derivation of the higher-energy part of the SEP spectrum. We briefly review how the application of the Neutron Monitor Based Anisotropic GLE Pure Power Law (NMBANGLE PPOLA) model (Plainaki et al. 2010), can provide the characteristics of the relativistic SEP flux, at a selected altitude in the Earths atmosphere, during a GLE. Technically, the model treats the NM network as an integrated omnidirectional spectrometer and solves the inverse problem of the SEP-GLE coupling. As test cases, we present the results obtained for two different GLEs, namely GLE 60 and GLE 71, occurring at a temporal distance of ~ 11 years.

Cosmic ray intensity for about five solar cycles

Continuous records of the cosmic ray nucleonic component have been achieved at Rome (SVIRCO Group) by using data from different types and locations of neutron monitors (first at La Sapienza University: 41.90°N, 12.52°E, altitude about 60 m a.s.l., and then at Roma Tre University: 41.86°N, 12.47°E, about sea level). The normalized data, covering the whole period from July 1957 to June 2014, are available to the scientific community by simple request. Here we illustrate some useful results derived from them.