NuMoon: Status of Ultra-High-Energy Cosmic-Ray detection with LOFAR and improved limits with the WSRT

Transcription

1 NuMoon: Status of Ultra-High-Energy Cosmic-Ray detection with LOFAR and improved limits with the WSRT Sander ter Veen for the LOFAR Cosmic Ray Key Science Project Supervisor: Prof. Heino Falcke Radboud University Nijmegen The Netherlands

2 The moon as cosmic-ray detector? Large surface area: km2 >3000 x PAO CR Flux < 1 particle /km2/century if E > 1020 ev Sensitive up to very high energies Credit: Luc Viatour

3 The Askaryan Effect Very energetic particle impacts dense material Creates secondary particles: shower Excess of electrons: Kicked out by shower photons, electrons Net charge moving faster than local lightspeed Coherent Radiation UHECR + Moon => Radio Waves Shower width ~10 cm (coherent <3 Ghz, beamed) Length ~ 2 m (coherent < 150 Mhz, larger spread) G.A. Askaryan. Sov. Phys. JETP, 1962; O. Scholten, Astropart. Phys. 2006

4 Will it work for Cosmic Rays? Neutrino: Cosmic Ray d >> L, R >> d d~l Double far-field approximation Formation zone needed? Far-field approximation may not apply. L~m dneutrino=0-100 m dcr=0.1-4 m R= km

5 Exact calculation method Describe the Vector Potential A as a Fourier Transform Transform each spherical wave separately Derive the transmission coefficient from that of the Electric Potential Details: S. ter Veen et al. Phys. Rev. D 82, (2010)

6 Calculation comparison Exact method depth independent if observer far away Exact method gives same electric field as original double farfield method The double far-field method also ''works'' for Cosmic Rays Normalized intensity as a function of depth using the new method. Comparison old and new method for deep shower. S. ter Veen et al. Phys. Rev. D 2010

7 WSRT: improved cosmic ray limits Observations with Westerbork Synthesis Radio Telescope. O. Scholten et al. Phys Rev Lett 2009 S. Buitink et al. Astron. & Astroph hours No pulse above 240 kjy (87.5% prob.)

8 WSRT: improved cosmic ray limits Observations with Westerbork Synthesis Radio Telescope. O. Scholten et al. Phys Rev Lett 2009 S. Buitink et al. Astron. & Astroph hours No pulse above 240 kjy (87.5% prob.) New limit above 1022 ev (90 % confidence) S. ter Veen et al. Phys. Rev. D 2010

9 LOFAR: The worlds largest telescope > 33 stations in 5 countries Center in the Netherlands Low Band Antenna (LBA) Mhz per station High Band Antenna (HBA, Prototype). ( Mhz) 48X16 per station Central LOFAR core: The Superterp 6 stations: 576 LBA and 4608 HBA dipoles

10 LOFAR works: and can make images! Courtesy: LOFAR pulsar working group and George Heald

11 LOFAR works: and can detect pulsars! Courtesy: LOFAR pulsar working group and George Heald

12 LOFAR works: and can do both at the same time! Courtesy: LOFAR pulsar working group and George Heald

13 LOFAR works: and can detect CR air showers see presentation by John Kelley #916 Ring buffers can store raw timeseries for several seconds

14 NuMoon Technique Example Giant Pulse from Crab pulsar Detection in streaming data Reanalysis buffered data More bandwidth & more stations

15 Technical challenges see also presentation O. Scholten #86 Convert beams back to time domain Correct for atmosphere Distinguish pulses from interference signals Small delay as function of frequency destroys coherency of ns pulses Narrow band filtering and multi-beam anticoincidence required Develop efficient detection algorithm (K. Singh et al. To be submitted.) Status: Ready to verify detection algorithm

16 Conclusion Lunar Askaryan Technique also works for Cosmic Rays Highest effective area around 150 MHz Best limits above 1022 ev from WSRT data LOFAR: ready to test trigger.

17 Thank you and stay tuned! On behalf of the LOFAR Cosmic Rays KSP: Senior Staff Radboud University Nijmegen Prof. H. Falcke (spokesperson) Dr. J. R. Hörandel (PI LOFAR KSP) KVI Groningen Prof. O. Scholten (PI NuMoon) Univ. of Manchester Dr. B. Stappers Support Staff Radboud University Nijmegen M. van den Akker L. Bähren (now at UvA Amsterdam) ASTRON Dr. W. Frieswijk Dr. R. McFadden Post Docs Radboud University Nijmegen Dr. S. Buitink (now at VUB Brussels) Dr. C. W. James (now at U. Erlangen) Dr. A. Horneffer (now at MPIfR Bonn) Dr. J.L. Kelley KVI Groningen Dr. M. Mevius Dr. K. Singh (now at Edmonton) Ph. D. Students Radboud University Nijmegen A. Corstanje P. Schellart S. Thoudam S. ter Veen

18 SKA SKA: Square Kilometre Array Not yet funded Much larger than LOFAR Energy threshold 1020 ev

19 Backup: radiation principle Askaryan Radiation not pure Cherenkov Major contribution from end-points Radiation for tracks right above equals right below Radiation theory: C. W. James (under review Phys. Rev.E)