Observation of deep, distant impulsive RF transmitters by the Askaryan Radio Array John Kelley*, Ming-Yuan Lu, University of Wisconsin–Madison David Besson, University of Kansas David Seckel, Yue Pan, University of Delaware for the ARA Collaboration July 14, 2017, 35 th ICRC, Busan, Korea *speaker
Neutrino / Cosmic Ray Connections • Can neutrinos reveal origins p γ → p π 0 , n π + of ultra-high-energy cosmic π + → µ + + ν µ rays? µ + → e + + ν e + ν µ • Cosmogenic neutrino flux on CMB (E ν ~ 10 18 eV) • Neutrinos generated in accelerator region on photon background or in hadronic interactions (E ν ~ 10 15 eV) 2 July 14, 2017 J. Kelley, 35th ICRC
Radio Detection of Neutrinos • Many km 2 target needed for ultra-high-energy neutrino nucleus ν detection particle cascade • Neutrino-induced showers in dense media produce broadband radio pulses (Askaryan effect) simulated 10 18 eV neutrino event – detectable by radio antennas bipolar pulse 1000 voltage (mV) 500 • Ice is RF-transparent and plentiful 0 in Antarctica thermal -500 – O(km) attenuation lengths noise -1000 – ANITA (balloon), ARIANNA (Ross ice shelf), ARA (South Pole) 150 200 250 300 350 400 time (ns) July 14, 2017 J. Kelley, 35th ICRC 3
Askaryan Radio Array (ARA) http://arxiv.org/abs/1507.08991 http://arxiv.org/abs/1404.5285 July 14, 2017 http://arxiv.org/abs/1105.2854 4 J. Kelley, 35th ICRC
ARA Station Layout currently deployed 4 South Pole 2017–18 deployment IceCube Testbed South 3 1 Pole Station 5 2 skiway 6 2 km July 14, 2017 5 J. Kelley, 35th ICRC
Optics in South Pole Ice • Index of refraction a function of depth (firn Raytrace paths (antenna at 200m depth) layer) -500 -500 0 0 firn shadow 500 500 • Radio waves bend away Depth (meters) Depth ( Meters ) 1000 1000 from surface 1500 1500 2000 2000 • Multiple paths possible 2500 2500 0 1000 2000 3000 4000 5000 0 1000 2000 3000 4000 5000 – quasi-direct (QD) X Displacement (meters) X Displacement ( Meters ) – quasi-reflected (QR) July 14, 2017 6 J. Kelley, 35th ICRC
Deep Calibration Pulsers ARA-2 top view TH TV Vpol pulsers in BH IceCube holes BV July 14, 2017 7 J. Kelley, 35th ICRC
Raytraced Radio Paths 1.4 km ARA-2 IC-1 pulser total propagation time ~ 22 μs 3.6 km July 14, 2017 8 J. Kelley, 35th ICRC
Deep Pulser Event (IC-1 to ARA-2) mV time (ns) both pulses observed: QD (upgoing) and QR (downgoing) July 14, 2017 9 J. Kelley, 35th ICRC
Timing Analysis via Cross-correlation • Time-difference analysis via cross- top Vpol / bottom Vpol cross-correlation correlation of antenna signals cross-correlation (a.u.) – four QD/QR pairs – peaks of Hilbert envelope • Observations time difference (ns) consistent with ice model raytracing July 14, 2017 10 J. Kelley, 35th ICRC
Directional Reconstruction (QD only) • cross-correlation reconstruction of QD pulses – sum of CC pairs for all directions in sky – see also M.-Y. Lu NU080, JK poster • O(degree) directional resolution – distance reconstruction very difficult due to near-plane- wave timing July 14, 2017 11 J. Kelley, 35th ICRC
Distance Reconstruction with Both Pulses • QD+QR: stereoscopic view of event allows vertex pulser distance reconstruction reconstruction • Distance resolution of O(100) m • Next step — event-by- event reconstruction – improvement in angular resolution also expected July 14, 2017 12 J. Kelley, 35th ICRC
Hpol vs. Vpol Signals TH mV TV time (ns) fraction of Hpol arrives ~30 ns early (also on-time cross-polarization) July 14, 2017 13 J. Kelley, 35th ICRC
Birefringence • consistent time delay across events, antenna pairs • evidence of birefringence – previously observed with near- vertical pulses in deep ice § – order-of-magnitude of effect reasonable (~10 -3 ) • next steps: fully understand and model this effect § Kravchenko et al., Astropart. Phys. 34, 10 (2011) July 14, 2017 14 J. Kelley, 35th ICRC
SPICE Hole Logging (2018) • two calibration pulsers lowered into ice core hole to 1700m in January 2018 • observation by 6 ARA stations + ARIANNA-like surface station • test n(z), birefringence, firn shadow model • layering / horizontal propagation? July 14, 2017 15 J. Kelley, 35th ICRC
Conclusions • Observation of deep calibration pulser events in ARA – validates ice model, geometric optics paradigm • Reflected pulses allow distance reconstruction of distant event – close events via direct ray timing (wavefront curvature) • Evidence of birefringence from Hpol signals – potentially another handle on vertex distance • SPICE hole logging planned for this pole season – refine model of index of refraction vs. depth – birefringence vs. depth, ice flow July 14, 2017 16 J. Kelley, 35th ICRC
Backup July 14, 2017 17 J. Kelley, 35th ICRC
Previous Measurements July 14, 2017 18 J. Kelley, 35th ICRC
Hpol/Vpol Cross-Correlations Peak V - H correlation ● vs expected | Peak V - H correlation ● vs expected | Peak V - H correlation ● vs expected | Peak V - H correlation ● vs expected | 20000 7000 20000 s1:tv, s1:th, rays: { QD, QD } s2:tv, s2:th, rays: { QD, QD } s3:tv, s3:th, rays: { QD, QD } s4:tv, s4:th, rays: { QD, QD } 14000 6000 12000 15000 15000 5000 10000 4000 a.u. a.u. a.u. a.u. 8000 10000 10000 3000 6000 2000 4000 5000 5000 1000 2000 0 0 0 0 - 50 0 50 100 - 50 0 50 100 - 50 0 50 100 - 50 0 50 100 δ t ( ns ) δ t ( ns ) δ t ( ns ) δ t ( ns ) Peak V - H correlation ● vs expected | Peak V - H correlation ● vs expected | Peak V - H correlation ● vs expected | Peak V - H correlation ● vs expected | s1:bv, s1:bh, rays: { QD, QD } s2:bv, s2:bh, rays: { QD, QD } s3:bv, s3:bh, rays: { QD, QD } s4:bv, s4:bh, rays: { QD, QD } 10000 15000 20000 25000 8000 20000 15000 10000 6000 a.u. a.u. a.u. a.u. 15000 10000 4000 10000 5000 5000 2000 5000 0 0 0 0 - 50 0 50 100 - 50 0 50 100 - 50 0 50 100 - 100 - 50 0 50 δ t ( ns ) δ t ( ns ) δ t ( ns ) δ t ( ns ) Peak V - H correlation ● vs expected | Peak V - H correlation ● vs expected | Peak V - H correlation ● vs expected | Peak V - H correlation ● vs expected | 25000 1.0 8000 s2:tv, s2:th, rays: { QR, QR } s4:tv, s4:th, rays: { QR, QR } s1:tv, s1:th, rays: { QR, QR } 15000 s3:tv, s3:th, rays: { QR, QR } 20000 0.5 6000 10000 15000 a.u. a.u. a.u. a.u. 0.0 4000 10000 5000 - 0.5 2000 5000 0 0 - 1.0 0 - 50 0 50 100 - 50 0 50 100 - 500 - 450 - 400 - 350 - 50 0 50 100 150 δ t ( ns ) δ t ( ns ) δ t ( ns ) δ t ( ns ) Peak V - H correlation ● vs expected | Peak V - H correlation ● vs expected | Peak V - H correlation ● vs expected | Peak V - H correlation ● vs expected | 1.0 14000 1.0 10000 s4:bv, s4:bh, rays: { QR, QR } s2:bv, s2:bh, rays: { QR, QR } s1:bv, s1:bh, rays: { QR, QR } s3:bv, s3:bh, rays: { QR, QR } 12000 8000 0.5 0.5 10000 6000 8000 a.u. a.u. a.u. a.u. 0.0 0.0 6000 4000 4000 - 0.5 - 0.5 2000 2000 - 1.0 0 - 1.0 0 - 550 - 500 - 450 - 400 - 100 - 50 0 50 - 250 - 200 - 150 - 100 - 50 0 50 100 δ t ( ns ) δ t ( ns ) δ t ( ns ) δ t ( ns ) July 14, 2017 19 J. Kelley, 35th ICRC
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