Paul Evenson University of Delaware GeV Cosmic and Solar Energetic Particle Observation from Ground Based Detectors Paul Evenson University of Delaware

Observation Of Cosmic Rays With Ground-based Detectors Ground-based detectors measure byproducts of the interaction of primary cosmic rays (predominantly protons and helium nuclei) with Earth’s atmosphere Two common types: Neutron Monitor Typical energy of primary: ~1 GeV for solar cosmic rays, ~10 GeV for Galactic cosmic rays Muon Detector / Hodoscope Typical energy of primary: ~50 GeV for Galactic cosmic rays (surface muon detector) NIPR: November 2016

New Type: Cherenkov “Tanks” Such as Auger, HAWC and IceTop IceTop: Blocks of clear ice produced in tanks at the Pole Cherenkov radiation measured by standard IceCube photon detectors Two tanks separated by 10 meters form a station 2 m 0.9 m Diffusely reflecting liner NIPR: November 2016

Why IceTop Works as a GeV Particle Spectrometer Neutron monitors are comparatively insensitive to the particle spectrum IceTop detectors are thick (90 g/cm2) so the Cherenkov light output is a function of both the species and energy of incoming particles Individual waveform recording, and extensive onboard processing, allow the return of pulse height spectra with ten second time resolution even at the kilohertz counting rate inherent to the detector NIPR: November 2016

Secondary Particle Spectra At the South Pole, spectra of secondary particles “remember” a lot of information about the primary spectrum. NIPR: November 2016

Response Functions Analog information from IceTop yields multiple response functions simultaneously NIPR: November 2016 11

Solar Particle Spectrum Published in Ap J Letters Excess count rate as a function of pre-event counting rate. Each point represents one discriminator in one DOM. By using the response function for each DOM we fit a power law (in momentum) to the data assuming that the composition is the same as galactic cosmic rays The lines show one sigma (systematic) errors NIPR: November 2016

IceTop and PAMELA Credit: M. Casolino NIPR: November 2016

Neutron Monitors and IceTop Good agreement (with understanding of viewing direction) IceTop determines a precise spectrum Anisotropy comes entirely from the monitor network Here we see the failure of the “separability” assumption in one particular analysis of neutron monitor data alone NIPR: November 2016

Neutron Monitors and IceTop Cherenkov and neutron monitor response functions are similar but have significant differences NIPR: November 2016

ENERGY SPECTRUM: POLAR BARE METHOD South Pole station has a 3-NM64 and detectors with no lead shielding. These “Polar Bares” responds to lower particle energy on average. NIPR: November 2016

ENERGY SPECTRUM: POLAR BARE METHOD “Polar Bares” responds to lower energy particles. Bare to NM64 ratio provides information on the particle spectrum. This event shows a dispersive onset as the faster particles arrive first. Spectrum softens to ~P – 5 (where P is rigidity), which is fairly typical for GLE. Dip around 06:55 UT may be related to the change in propagation conditions indicated by our transport model Element composition is a source of systematic error in the spectral index NIPR: November 2016

Element Composition and Spectrum from IceTop and the Neutron Monitor Simulated loci of count rate ratios, varying spectral index (horizontal) and helium fraction (vertical). Statistical errors (+/- one sigma) are shown by line thickness. 20 January 2005 spectrum “Galactic” composition IceTop (black, blue) lines converge in the “interesting” region Bare/NM64 (red) line crosses at the proper (i.e. simulation input) values NIPR: November 2016

Spacecraft now approach the energy range of ground based observations (deNolfo 2015) NIPR: November 2016

Role of IceTop AMS-02 has approximately the same collecting power as the South Pole neutron monitor. It has massively better energy and composition sensitivity, but only “looks” is one, constantly changing, direction at a time. The duration of one orbit is much longer than the timescale of the evolution of anisotropy in a typical solar event. The neutron monitor network will remain a vital partner for the life of AMS-02 (if we ever see another large GLE). IceTop can work with the neutron monitor at the South Pole to understand event systematics. Is the lack of GLE in the present solar cycle due to the overall size of the event, or is it a spectral effect? The present study is intended to characterize the present solar cycle in terms of “detections”, with possible spectral analysis as a future topic. NIPR: November 2016

Objective Determine the extent to which multi – GeV particles are present in solar particle events. Specifically, can IceTop detect any events that are not seen as “classic” GLE (Ground Level Enhancements) Traditionally, the Pole Neutron Monitor qualifies as “ground level”. NIPR: November 2016

A Really Clear Case 17 May 2012 Pink and Blue shading show “off source” and “on source” intervals selected for the event survey Threshold (Low to High) MPE Low/High Ratio Neutron Monitor Bare to NM64 ratio GOES 10, 50, 100 MeV NIPR: November 2016

Methodology Construct a list of SEP (Solar Energetic Particles) seen by GOES (Geostationary Operational Environmental Satellite) in the 100 MeV channel. Develop a template based on known GLE Apply the template to the list to get detections or limits NIPR: November 2016

Status Construct a list of SEP (Solar Energetic Particles) seen by GOES (Geostationary Operational Environmental Satellite) in the 100 MeV channel. Done Develop a template based on known GLE The three known GLE are clearly visible Apply the template to the list to get detections or limits Preliminary results are available NIPR: November 2016

GOES Event List – 10 and 100 MeV NIPR: November 2016

Another Case 6 Jan 2014 Pink and Blue shading show “off source” and “on source” intervals selected for the event survey Threshold (Low to High) MPE Low/High Ratio Neutron Monitor Bare to NM64 ratio GOES 10, 50, 100 MeV NIPR: November 2016

2014 Jan 6 Change vs Base The SPE thresholds in IceTop are set to a range of thresholds. The lower rate DOMs have higher thresholds A “soft” solar particle spectrum produces larger increases at lower threshold NIPR: November 2016

Preliminary Results Red points are negative values – indicative of fluctuations. All of the GLE are seen More blue than red, but other detections are “iffy” NIPR: November 2016

Spectral Variations are Large Test study using GOES 700 MeV – note how little the 700 MeV predicts the IceTop result. The “known GLE” are also high at 700MeV, but other events are just as high at 700 MeV and not seen at all by IceTop This is possibly different from our findings in the last solar cycle NIPR: November 2016