Measuring the Galactic Cosmic Ray flux with the LISA Pathfinder radiation monitor

Abstract

Test mass charging caused by cosmic rays will be a significant source of acceleration noise for spacebased gravitational wave detectors like LISA. Operating between December 2015 and July 2017, the technology demonstration mission LISA Pathfinder included a bespoke monitor to help characterise the relationship between test mass charging and the local radiation environment. The radiation monitor made in situ measurements of the cosmic ray flux while also providing information about its energy spectrum. We describe the monitor and present measurements which show a gradual 40% increase in count rate coinciding with the declining phase of the solar cycle. Modulations of up to 10% were also observed with periods of 13 and 26 days that are associated with co-rotating interaction regions and heliospheric current sheet crossings. These variations in the flux above the monitor detection threshold (≈ 70 MeV) are shown to be coherent with measurements made by the IREM monitor on-board the Earth orbiting INTEGRAL spacecraft. Finally we use the measured deposited energy spectra, in combination with a GEANT4 model, to estimate the galactic cosmic ray differential energy spectrum over the course of the mission.

Challenges for $Λ$CDM: An update

“…It will consist of three spacecrafts placed in an equilateral triangle with arms 2.5 million kilometers long which will be placed near the Earth in a heliocentric orbit. In order to pave the way for the LISA mission ESA launched LISA Pathfinder in 2015 and it was operational from 2016 to 2017 [1462,1463]. The results from scientific research show that LISA Pathfinder works exactly five times better than required, with a successful demonstration of the basic technologies for a large gravitational wave observatory.…”

Spacecraft and interplanetary contributions to the magnetic environment on-board LISA Pathfinder

“…Moreover, these missions contain a suite of instruments that allow a complete characterisation of the plasma, tracking parameters such as the solar wind speed or the number density of the plasma that we will refer in the following. Nonetheless, it is worth noticing that, although not designed for that, the radiation monitor on-board LISA Pathfinder (Canizares et al 2011;Armano et al 2018a) allowed for the detection of the passage of large scale interplanetary structures such as high-speed solar wind streams and interplanetary counterparts of coronal mass ejections generating recurrent and non recurrent depressions of the galactic cosmic-ray flux (Armano et al 2018c(Armano et al , 2019c.…”

“…Therefore, one of the main objectives of LISA Pathfinder is to split up the noise into different contributions and help on the design of a suitable environment for future gravitational-wave detectors. With that aim, LISA Pathfinder carried the so-called Data and Diagnostics Subsystem (DDS) which includes a temperature measurement subsystem (Sanjuán et al 2007;Armano et al 2019b), a magnetic diagnostic subsystem (Diaz-Aguiló et al 2013) and a radiation monitor (Canizares et al 2009(Canizares et al , 2011Armano et al 2018a).…”

Study of Galactic Cosmic-Ray Flux Modulation by Interplanetary Plasma Structures for the Evaluation of Space Instrument Performance and Space Weather Science Investigations

“…According to the LPF data, FDs showing in space maximum depressions <10% are suitable proxies for ICME tracking and geomagnetic storm forecasting only if the B z component of the IMF is <−20 nT and the cosmic-ray flux is not depressed by the transit of other interplanetary structures before the ICME passage. For completeness it is added that a fourth, incomplete FD was observed on board LPF on 16 July 2017 [34]. This event was characterized by a maximum percent decrease of the GCR flux of 18% in space, while polar and near-equatorial NM measurements presented percent decreases of 7% and 3%, respectively.…”