Radio Detection of Cosmic Rays with LOFAR. Heino Falcke

Transcription

1 Radio Detection of Cosmic Rays with LOFAR Heino Falcke Radboud University Nijmegen ASTRON, Dwingeloo & NIKHEF & LOFAR Cosmic Ray KSP Advanced Grant S. Buitkink, A. Corstanje, J.R. Hörandel, A.Nelles, L. Rossetto, S. Thoudam, J.P. Rachen, O.Scholten (RUG), S. ter Veen, T. Huege (KIT)

2 LOFAR Memo 1970ies P.L. Biermann Falcke & Gorham (2001, memo) F&G (2003, Astropart. Phys.)

3 Cosmic ray all-particle spectrum knee 2nd knee Galactic ankle transition? cut-off extra galactic

4 Cosmic Ray Spectrum ( E 3 ) Supernovae? knee 2 nd knee ankle Jets, GRBs,??? Hörandel (2008)

5 Air showers: simulations proton photon iron nucleus

6 p Extensive Air Shower e + e - γ γ e + e - π 0 π - n p π + γ µ γ - e + e - e - e + γ e - e + e - γ µ - π - p electromagnetic hadronic muonic shower components p n p π - π - n n π + µ + Proton ev: On ground: 10 6 particles 80% photons 18% el./positron 1.7% Muons 0.3% Hadrons J. Hörandel

7 Radio Radiation Geomagnetic aka. geosynchrotron charge excess & separation From Glaser et al. (2017)

8 Monte Carlo Simulation of Radiation Processes: The Endpoint Formalism ^ r β 1 β 2 delay: R/c discrete formulation for arbitrarily complex motion radiation only from endpoints Couple to CR Monte Carlo: CORSIKA CoREAS (Huege et al.) endpoints: decelerate from β 1 to 0 accelerate from 0 to β 2 antenna James, Falcke, Huege, Ludwig (2011), Phys. Rev. E see also Alvarez-Muniz, Vàsquez, Zas 2000, Phys. Rev. D.

9 Coherent Geosynchrotron Radio Pulses in Earth Atmosphere Earth B-Field ~0.3 G UHECRs produce particle showers in atmosphere Shower front is ~2-3 m thick ~ wavelength at 100 MHz e ± emit synchrotron in geomagnetic field Emission from all e ± (N e ) add up coherently Radio power grows quadratically with N e coherent E-Field E total =N e *E e Power E e 2 N e 2 GJy flares on 20 ns scales Falcke & Gorham (2003), Huege & Falcke (2004,2005), Scholten et al. ( )

10 Effelsberg: First Tests Slide from (2003)

11 Dwingeloo: Test- Setup Detection of the sun in cosmic ray mode Series of artificially triggered data sets Frequency solar burst Time all-sky map (16 events of 1ms each)

12 Building LOPES Area 0.3 km2 Antennas 30 Type inverted V crossed dipole CODALEMA

13 Radio detection of CRs: Complementarity approach modern pioneering experiments CODALEMA LOPES Simulations (CoREAS, ZHAires, EVA, Selfas) Complementarity AERA Prototyping sparse array cross-calibration energy LOFAR Operational telescope dense yet patchy array physics of radio emission

14 AUGER TUNKA-REX Radio-add ons Area 17 km 2 Antennas 150 Type LPDA/ Butterfly Advanced Grant Area 1 km 2 Antennas 20 Type SALLA

15 The LOFAR Superterp 6 innermost LOFAR stations Central LOFAR area: 6/48 stations of LOFAR 1 station = 48 crossed dipoles Superterp ( 400 m): 6 stations = 300 dipoles Core area ( 2 km): 28 stations = 1300 dipoles terp (NL) = little hill! Radio triggered by LORA (LOFAR-Radboud Airshower array) 20 scintillator detectors (from KASCADE) (Hörandel, Thoudam et al)

16 Footprint of an Air Shower S. ter Veen

17 Imaging through direct beamforming direction from LORA Cosmic ray radio signal imaged with data! from single LOFAR station

18 Wavefront Radio Shower Shape Precise shower front allows directional accuracy of 0.1 Emission for finite relativistic track: arrival time [ns] nanosecond precision! intermediate cone+sphere close: cone (supersonic boom) radial distance to core [m] Corstanje et al. (2014, Astropart. Phys.) distant: sphere (point source)

19 Absolute Calibration Auger collaboration (Aab et al. 2016, Glaser et al. 2017)

20 Absolute Calibration Auger collaboration (Aab et al. 2016) Using LOFAR parameterization from Nelles et al.

21 Absolute Calibration Glaser et al. (2017)

22 Radio Emission Pattern inherently 2D v x v x B v x v x B v x B v x B CoREAS simulation E-field vectors geomagnetic E-field vectors charge excess vector sum of geomagnetic and charge excess component relativistic beaming Cherenkov-like propagation effects (n 1) All radiation effects covered in simulations automatically by endpoint-method!

23 Emission Pattern at Low Frequencies: Theory & Observation Background color: simulation Colored circles: LOFAR data CoREAS simulation LBA MHz Zenith angle: antennas χ2 / ndf = 1.02

24 Polarization Charge Excess Radiation >99% polarized! Fractional contribution of charge excess radiation as function of distance v v B direction [m] observed geomagnetic azimuth Charge excess Charge excess makes up 5%-20% of total emission. v B direction [m] LOFAR: ~ 3% - 20% pioneered at AERA (Auger): ~ 14% Schellart et al. (2014, JCAP)

25 Schellart et al., in prep. Polarization Thunderstorms and Geoelectric Fields During thunderstorm conditions the electric field dominates the magnetic field and changes the emission pattern significantly!

26 Radio Lateral Distribution Function (LDF) Cherenkov ring asymmetry

27 Analyzing the first LOFAR Events LOFAR data vs. CoREAS sim. Buitink et al. (2014, in prep.) First sample: ~100 brightest events, no thunderstorms antennas per event. All events reproduced with reduced χ2 from ! Radiation mechanism finally completely understood!

28 Linear & Circular Polarization Scholten et al. (2017)

29 ID Emission Pattern at High HBA MHz Frequencies: Cherenkov-Like Ring Background color: simulation Colored circles: LOFAR data HBA MHz Zenith angle: antennas χ2 / ndf = 1.9 Nelles et al. (2014), Astropart. Phys., subm.

30 Reconstructing X max for each shower: Simulate 25 proton and 15 iron showers for same energy and direction Find best-fitting simulation for radio & particle detectors Iterate core & energy red. χ 2 Fe p X max [g/cm 2 ] Atmospheric variations sim-vs-best-fit sim for error Check for systematics: different hadronic models (QGSJETII, EPOS, SIBYLL) Different radio codes (CoREAS, ZHAireS, EVA, Selfas) Resolution < 20 g/cm 2! Buitink et al. (2014, PRD)

31 Radio comparison with other methods Auger optical fluorescence Tunka-Rex optical Cherenkov Gaté et al. (2016) Bezyazeekov et al. (2017)

32 QGSJETII.04 μ = -1.5 g/cm 2 EPOS-LHC 10 showers 10 showers μ = g/cm 2 Shower simulated with QGSJETII EPOS & SIBYLL Reconstructed using QGSJETII 10 showers; 25 p + 15 Fe each Systematic effect on Xmax reconstruction is small geometrical measurements SIBYLL 10 showers μ = g/cm 2

33 Unbinned Composition Analysis Calculate energy-independent mass parameter a for each event. a = X proton X proton X shower X iron Simulated distribution of iron and proton showers for LOFAR resolution proton (a=0) iron (a=1) X max Energy Buitink et al. (2014, PRD) deep shallow High X max resolution allows distinction between pure iron, pure proton, or mixed composition!

34 LOFAR Xmax

35 Cumulative distribution function for 50 events We can already separate 2 mass components with only 50 showers! p Energy ~ ev Fe He Buitink et al. (2014, in prep.)

36 Cumulative mass distribution Best fit: 80% light particles (p+he) at ev [ within 38% - 98% at 99% C.L. ] p+fe p p+he+cno+fe Fe deep showers Relative shower depth (a) shallow showers Buitink et al. (2016, Nature)

37 Energy Spectrum Thoudam et al. (2016) Supernovae Galactic Pevatron e.g., SNe in WR-stars Extragalactic e.g. AGN

38 Mean atomic mass Thoudam et al. (2016)

39 All Particle Cosmic Ray Spectrum LOFAR Cosmic Rays IceTop Supernova Remnants Auger Second Galactic component!? Galactic Pevatron GRBs? AGN?

40 Conclusions LOFAR data & COREAS simulations agree in great detail: intensity profile, polarisation (full Stokes), spectrum Auger, Tunka: Absolute energy calibration of CRs with radio, confirmation of Xmax measurement LOFAR can measure cosmic ray mass composition X max resolution of < 20 g/cm 2 at least similar to fluorescence detection + higher duty cycle LOFAR composition results based on 100+ events: light mass component at ev (2 nd knee) Consistent with 2nd Galactic component (Wolf-Rayet SN?) Factor 3 more data to be analyzed by end of this year. Hoping for SKA CR capability in the future!

41 Mean Xmax for 50 showers LOFAR

42 Fit for each simulation Minimize χ 2 of radio and particle data simultaneously 4 fit parameters: core position radio power scale factor particle density scale factor

43 Uncertainty on Xmax Monte Carlo vs Monte Carlo method reconstruct Xmax for many simulations of the same event construct region that contains 68% of Xreco - Xtrue σmeth = 12.7 g/cm 2 σatm = 1 g/cm 2 (after correction) σ = 13 g/cm 2 first 50 showers first event sample: σ ranges from 7.5 to 37 g/cm 2 mean value 17 g/cm 2 SB et al. PRD (2014).

44 Energy resolution Ereco = fp * Esim if fp is large: run new simulation at Ereco until convergence consistency: fr/fp should be constant! energy resolution: 40% misreconstructed core position

45 Pulse power (a.u.) CoREAS Selfas 682 g/cm g/cm 2 Simulation workshop Nijmegen (february 2014) simulation by all 4 codes for 10 LOFAR events Pulse power (a.u.) ZHaireS 668 g/cm 2 EVA 690 g/cm 2 Preliminary results: Microscopic models (CoREAS & ZHaireS) very similar Macroscopic models are close; parametrizations break down near shower axis?

46 large circles: simulation background color: interpolation small circles: verification error < 2.5% of Pmax

47 no bias due to multivariate fit

48 ID Emission Pattern at High HBA MHz Frequencies: Cherenkov-Like Ring Background color: simulation Colored circles: LOFAR data HBA MHz Zenith angle: antennas χ2 / ndf = 1.9 Nelles et al. (2014), Astropart. Phys., subm.

49 Xmax ~ 600 g/cm 2 Xmax ~ 650 g/cm 2 Xmax ~ 700 g/cm 2 Pulse power (a.u.) shape depends on Xmax LOFAR: antennas/event fit full 2D pattern! distance along v x B axis (m)

50 Radio Emission from Air Showers in Geomagnetic Field Earth B-Field ~0.3 G UHECR initiates air shower Shower thickness: ~2-3 m ~ wavelength at 100 MHz e ± bent by magnetic field Waves add up coherently Radio power grows quadratically with N e coherent E-Field E total =N e *E e Power E e 2 N e 2 GJy flares on 20 ns scales Experimental verification: LOPES, Codalema, Auger, TunkaRex, LOFAR... Kahn & Lerche (1966), Falcke & Gorham (2003), Huege & Falcke (2004,2005), Scholten et al. ( )

51 Galactic - Extragalactic Transition dip model ankle model Aloisio et al. (2007)

52 All Particle Cosmic Ray Spectrum LOFAR Cosmic Rays IceTop Supernova Remnants Second Galactic component? Transition at ankle or earlier? Sources of IceCube neutrinos? Auger GRBs? AGN?

53 The International LOFAR Telescope (ILT) Europe- wide radio interferometry MHz Offers unprecedented resolution, sensitivity, and flexibility at the lowest frequencies! 44 operational stations 38 stations in NL 8 international stations (double size) 4 additional stations funded (D, 3 PL)

54 Low-Band Antennas (LBAs): MHz ~2000 crossed dipoles in NL ~850 in D, UK, F, S High-Band Antennas (HBAs): MHz ~ crossed dipoles in NL ~ in D, UK, F, S ASTRON

55 LOFAR Analysis LORA LOFAR Radboud Array scintillator detectors LORA (Scintillator) High-Band Low-Band trigger buffer low band antenna offline analysis Pim Schellart et al., A&A 560, 98 (2013)