Pradiphat (ฝุ่น) Muangha2 David J Ruffolo2 GeV Solar Energetic Particle Observation and Search by IceTop from 2011 to 2016 Paul Arthur Evenson1 Pradiphat (ฝุ่น) Muangha2 David J Ruffolo2 (1)University of Delaware, Newark, DE, United States (2)Mahidol University, Bangkok, Thailand For The IceCube Collaboration

Why Should We Understand GLE? (Ground Level Enhancements / Events) Only Solar Energetic Particle (SEP) events of relevance to radiation hazards at aircraft altitude Provide the first indication of SEP event onset for fast arrival events Time profiles correlate well with profiles of relativistic electron acceleration With precision transport modeling: Infer the time profile of acceleration to GeV energies Investigate mean free paths and unusual transport conditions (such as magnetic bottlenecks and loops) in the interplanetary medium Is the lack of GLE in the present solar cycle due to the overall size of the event, or is it a spectral effect? Paul Evenson AGU

Spacecraft Now Approach The Energy Range Of Ground Based Observations 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” in 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. Credit: deNolfo 2015 Paul Evenson AGU

Paul Evenson AGU

IceCube and IceTop IceCube uses a large volume (one cubic kilometer) of ice at the South Pole to detect rare neutrino interactions. The Delaware contribution to IceCube is IceTop, the air shower array on the surface. Paul Evenson AGU

Why IceTop Works as a GeV Particle Spectrometer Diffusely reflecting liner IceTop “tanks” are thick (90 g/cm2) blocks of clear ice. Cherenkov light output is a function of both species and energy of incoming particles 6

Secondary Particle Spectra At the South Pole high altitude and low geomagnetic cutoff yield spectra of secondary particles that “remember” the primary spectrum. The left panel shows secondary spectra for typical galactic cosmic ray primaries. The right panel shows secondary spectra for a primary solar (P-4) spectrum that doubles the count rate of a neutron monitor. This is called a “100% GLE” Paul Evenson AGU

Particle Response Functions (Arbitrary Normalization) IceTop particle response functions change with counting discriminator threshold. Simple count rates from IceTop, above different discriminator thresholds, yield multiple response functions simultaneously. A neutron monitor has only a single response function. Paul Evenson AGU

Solar Particle Spectrum of the Last Big GLE (2006 Dec 13 as Published in Ap J Letters) Excess count rate (averaged over approximately one hour near the peak of the event) as a function of pre-event counting rate. Each point represents one discriminator in one ice “tank”. By using the response function for each tank we fit a power law (in momentum) to the data. Paul Evenson AGU

IceTop Agreement With Neutron Monitors and PAMELA Paul Evenson AGU Credit: M. Casolino

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

>100 MeV >10 MeV > 0.14 /cm2 sr s > 1.0 /cm2 sr s Methodology Start with a list of 34 SEP (Solar Energetic Particle) events seen by GOES (Geostationary Operational Environmental Satellite) in the 100 MeV channel. Develop a template based on known GLE Apply the template to events in the list to get detections or limits Paul Evenson AGU

The Good News and the Bad News Are the Same News Statistical precision of IceTop (650 kHz) greatly exceeds that of the neutron monitor (300 Hz) IceTop has spectral resolution Bad News Increased statistical precision reveals significant temporal and spectral time structure This will affect the detection limit for both IceTop and spacecraft Silver Lining Jokipii and Owens style analysis can be extended to a new regime with the addition of energy resolution. Paul Evenson AGU

A quick look at some sample events …

Event Display Format Pink and Blue shading show “off source” and “on source” intervals selected for the event survey Threshold (Low to High) Low/High Ratio Neutron Monitor Bare to NM64 ratio GOES 10, 50, 100 MeV Paul Evenson AGU

17 May 2012 Everything is Right! Paul Evenson AGU

6 Jan 2014 Definite GLE Paul Evenson AGU

29 Oct 2015 Definite GLE Paul Evenson AGU

13 March 2012 Spectral Change but no time structure Paul Evenson AGU

20 Feb 2014 Everything but a GLE Paul Evenson AGU

Conclusions Background due to natural fluctuations has been more severe than anticipated. We do not claim any detections other than the three known GLE … but curiously there are more positive than negative fluctuations. We are working to establish more precise statements as to limits of detection. Paul Evenson AGU