10292020 1 LowFrequency Array LOFAR More than an

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Low-Frequency Array LOFAR More than an Eo. R Telescope. . . 10/29/2020 2

General: • simple antennas, but many: 25000 in the full LOFAR design. • spread over an area of ultimately 350 km in diameter. • phase 1: 15000 antennas funded, max. baselines 100 km • data rate many Tbits/sec, processing power T-FLOPS. 10/29/2020 3

LOFAR Phase 1: • compact core • 45 remote stations • equipped with 100 high-band antennas, 100 low-band antennas and • 13 three-axis vibration sensors (geophones), • 3 micro-barometers (for infrasound detection) • several auxiliary systems (weather monitoring, and GPS time/position measurements) 10/29/2020 4

Low-band antenna elements • optimised for 30 - 80 MHz range (sharp cut-off at 80 MHz) • suppression below 30 MHz is matched to the environment • can be used down to 30 degrees elevation. High-band antenna elements • can be used between 120 - 240 MHz (FM band suppressed) • composite system consisting of 4 x 4 dualpolarization dipoles and a dual-polarization RF beamformer. 10/29/2020 5

Beam shape of single antennas 10/29/2020 6

uv-coverage and synthesized beam 10/29/2020 7

Antenna signals • handled by a broad-band integrated receiver and digital processing system • direct conversion of a 100 MHz band • each receiver connected to a low- and a high-band antenna • 100 MHz signal will be buffered for ~1 sec (CR) detection and transient processing) • first digital processing step: 256 k. Hz subbands formed • only a subset of these bands is further processed • max. total bandwidth for further processing 32 MHz • each remote station delivers - single dual-polarization beam at 32 MHz, - or 8 dual polarization beams at 4 MHz, - or any combination in between. 10/29/2020 8

Software • extensive “System Health Management function” (self-diagnosing and possibly self-healing) • very large data streams: e. g. 6 TB of raw visibility data for an 8 -beam, 4 hour synthesis observation, after integration for 1 sec and over 10 k. Hz • 1 month of observing in this mode: 1 Peta. Byte of data • systematic long-term storage extremely expensive! • … resulting output data rate is 2 Gb/s; secondary filtering stage (to 1 -k. Hz channels) is done in the Central Processing system 2 16 bits 2 32 MHz poln. Amp. + phase bandwidth 10/29/2020 9

Central processing sytem • input section of Central Processor dimensioned such that 32 core and 50 remote stations can be accommodated simultaneously at their full bandwidth • core of CEP: IBM “Blue. Gene/L” (Groningen), 27. 4 Teraflops • BG/L surrounded by PC clusters with infiniband backbones 10/29/2020 10

Astronomy application modes: • synthesis imaging • transient detection (probably using correlation of large numbers of lowbandwidth beams) • tied array beam-forming • antenna-based buffering of 1 sec at full-digitised bandwidth and limited detection/triggering (in particular for UHECR events) at station level 10/29/2020 11

Ionosphere …! 2 sources observed with GMRT at 150 MHz 8 hours of data, one frame = 1 minute (de Bruyn et al. ) 10/29/2020 12

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LOFAR in brief: • 15000 (25000) dipoles clustered in 100 stations simple frontend hardware, but complex digital correlation. . . • 400 km across • frequency coverage 10 MHz - 200 MHz • collecting area 1 km 2 • b = 2 - 40 • correlation via optical fibres • fully digital! • low costs ( 60 MЄ) 10/29/2020 15

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LOFAR in Germany: • GLOW = German LOng Wavelength consortium • 6 (7) stations at Bonn (MPIf. R), Bremen (IUB), Garching, Hamburg, Jülich, Potsdam, (Göttingen) : 2006 - 2009 • plus another 6 : 2009 – 2012 • White Paper, to be presented to the Ministry of Science White Paper presented to • RDS during fall meeting of the AG • to ASTRON October 4, 2005 10/29/2020 19

Science: - re-ionization 5 < z < 20 ‘step’ at 70 ··· 240 MHz expected - high-z universe - relic synchrotron sources (census of past AGN activity) - bursting and transient universe, GRBs - 327 MHz deuterium line - solar-terrestrial relationships - CRs 10/29/2020 20

re-ionization: onset of star and galaxy formation: end of "Dark Ages” between z ~ 6 and 20 first indications now: “Gunn-Peterson trough” 10/29/2020 21

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Cosmic rays: LOPES @ Forschungszentrum Karlsruhe (H. Falcke) 10/29/2020 23

Interdisciplinarity: - astronomy - precision agriculture - geophysics - meteorology (weather prediciton) - wind energy (wind-flow models) - water management (Rhine-delta complex) - electricity transport - traffic flow - passive radar (get airplanes down more quckly) 10/29/2020 24