1. 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

2. 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

3. 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

4. Paul Evenson AGU

5. 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

6. 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

7. 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

8. 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

9. 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

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

11. 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

12. >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

13. 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

14. A quick look at some sample events …

15. 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

16. 17 May 2012 Everything is Right!
Paul Evenson AGU

17. 6 Jan 2014 Definite GLE
Paul Evenson AGU

18. 29 Oct 2015 Definite GLE
Paul Evenson AGU

19. 13 March 2012 Spectral Change but no time structure
Paul Evenson AGU

20. 20 Feb 2014 Everything but a GLE
Paul Evenson AGU

21. 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