1. Impulsive Increase of Galactic Cosmic Ray Flux Observed by IceTop
The IceCube Collaboration†, Pierre-Simon Mangeard‡,
Pradiphat (ฝุ่น) Muangha♯, Roger Pyle♮,
David Ruffolo♯ and Alejandro Sáiz♯
Corresponding Author: Paul Evenson‡ †
‡ University of Delaware, Newark, DE 19716, USA
♯ Mahidol University, Bangkok 10400, Thailand
♮ Pyle Consulting Group, St. Charles, IL 60174, USA

2. Paul Evenson ICRC

3. 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

4. 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 4

5. 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 ICRC

6. 2017January 18 Pulse Event
IceTop and some nearby neutron monitors saw a pulse-like increase in cosmic ray fluxes.
Better statistical precision and spectral response of IceTop show that it is not a solar energetic particle event.
Paul Evenson ICRC

7. Similar Event on 2015 June 22
The IceTop event is similar to the event seen by GRAPES-3 on 2015 June 22 (Mohanty et al. PRL 117, , 2016)
Paul Evenson ICRC

8. No Pulse at IceTop on 2015 June 22
The lack of a pulse at IceTop is consistent with the interpretation of the GRAPES-3 event as a brief decrease in geomagnetic cutoff, but …
Paul Evenson ICRC

9. 2017January 18 Pulse Event
… this event could not be a lowering of cutoff – it is already zero here! It must be the result of a transient anisotropy.
Paul Evenson ICRC

10. Reconsider 2015 June 22
Examine whether this event is more probably a cutoff variation or a transient anisotropy as well.
Paul Evenson ICRC

11. Neutron monitors show a definite pattern
2015 June 22
Neutron monitors show a definite pattern
Paul Evenson ICRC

12. Pulse appearance is ordered by geographic location
2015 June 22
Pulse appearance is ordered by geographic location
Paul Evenson AGU

13. Tsyganenko Model Cutoff Decrease Calculations
Even with an extrapolation to Kp=8 it is unlikely that changes in cutoff can be local effects. They must almost certainly be global.
Paul Evenson ICRC

14. Conclusions
Both the 2017 January 18 and 2015 June 22 events are most likely due to transient anisotropy.
Detailed analysis of possible 2015 June 22 asymptotic direction variations is difficult because of the highly disturbed magnetosphere.
Paul Evenson AGU