1. L O F A R The Low-Frequency Array ASTRON / MIT / NRL / UvA / UL / RUG / KUN IBM / BSIK partners / Many others...

2. A brief history of LOFAR… Late 1990s: George Miley comes up with the concept 1999-2003: Internal consortium of ASTRON – MIT – NRL signs a Memorandum of Understanding (M.O.U.) Nov 2003: BSIK proposal (including UvA/UL/RUG/KUN and industrial partners) approved: 52MEuro for LOFAR in NL Dec 31, 2003: International M.O.U. terminates Feb 2004: US and Australia indicate that they do not wish to participate in a Dutch LOFAR. IBM agrees to provide BlueGene/L supercomputer for the project. 2004+ : Increasing interest from European partners (notably Germany and Sweden, also France, UK, and entire EVN consortium). LOFAR test stations in operation…

3. ground based radio techniques 10 MHz 350  VLAALMA ATCA GMRT LOFAR

4. Radio sky in 408 MHz continuum (Haslam et al)

5. LOFAR in The Netherlands Hang on, what are these things?

6. They are the Low-band antennae (LBAs) Optimised for 30-80 MHz range (10-90 MHz full) Sky response The high-band antennae (HBAs) will be optimised for the 110-240 MHz band, and are in the design phase

7. LOFAR will consist of a central virtual core of diameter ~2km containing 3200 LBA, 3200 HBA (~10-20% of total) There will be ~100 stations further afield, each with ~100 LBA / HBA ‘compound elements’ Maximum baselines of 100- 150km with design allowing extensions towards Bremen (E-W) and Limburg (N-S) Has LOFAR been de-scoped ? Only significantly in terms of longest baselines (virtual core exactly as spec’d)

8. Freq (MHz) 1  1s array (mJy) 1  1s VC (mJy) Beam array Beam VC f.o.v. array f.o.v. VC 3011829025”21’650’90 O 1204.2106.0”5.2’160’23 0 Real specifications for the LOFAR we expect to build… An example mode for transients: the VC scans a huge area, delivers the position of a transient with arcmin- accuracy, the full array ‘zooms in’ and delivers arcsec position… within seconds.

9. Key Science Areas The epoch of reionization (RUG, de Bruyn) The high redshift Universe (UL, Rottgering) The bursting and transient Universe (UvA, Fender  Wijers) Cosmic ray showers (KUN, Kuijpers) (Space Weather) (Ionosphere) NOVA-II proposal

10. Z = 20 ……………. 15 ………. 10 8 7 6 cold H I H II 21cm (1.4 GHz) emission/absorption from Epoch of Reionisation -mapping of neutral residue of IGM as first sources of ionising radiation appear at redshifts between 7 and 20(?) -WMAP results suggest EoR at 15<z<20… there could be multiple phases 70 MHz 90 MHz 130 160 190 MHz

11. 10 arcmin Quasar distributed star formation (Groningen)

12. Mapping all radio loud AGN Physics of radio sources Radio galaxies as probes of blackhole, galaxy and cluster formation

13. Basis –Redshift ~ spectral index –Most distant radio sources luminous at low frequencies Science –Formation and evolution of massive blackholes, galaxies and clusters –As probes of epoch before reionisation to study HI absorption Radio galaxy surveys (Leiden)

14. Starbursts: SFR > 10 M/yr Many starclusters with OB stars –That are initally dust- enshrouded –SN explosion  radio emission The Hunt: – (sub-)millimeters survey – UV dropout techniques, –Lya/Ha emission lines –mJy radio sources Importance –Study star fomation in galaxies –Significant fraction of the starformation rate –Mark transition of spirals to ellipticals

15. Distant starburst galaxies –dominant population at low flux densities –in few years observing: 10 8 galaxies Star formation rate of 10 M/yr up to z=3 –important complement SIRTF, Omegacam, NGST, VISTA, ALMA –star formation history, nature of starbursts, clustering

16. Galaxy surveys with LOFAR will be an overwhelmingly statistical exercise (Leiden, 5 years from now…)

17. Observing Frequency (MHz) Angular Resolution (arcsec) limit 1 (10 σ) (mJy) Surface density of sources (No. per arcmin) Area covered after 1 year (sq. deg) Total number of sources after 1 year 1015300.530005.4 million 305.22430004.3 million 752.10.325605.3 million 1201.30.1666215 million 2000.8101257.53.3 million

18. Diffuse, extended and bright at low frequencies > LOFAR 1. Relics 2. Smooth centrally located radio halos 1 yr LOFAR survey at 120 MHz should detect 800 halos, 140 with z>0.3 Cluster ‘relics’ and ‘haloes’

19. Detections with `ASM’ can be rapidly (<sec) followed up with full array

20. ObjectVariability Timescale No. of Events per year How far? Radio Supernovaedays-months32 - 3 further than Virgo Cluster GRB Afterglowsdays-months100Observable Universe GalacticBlackHoles and Neutron Stars days - months10Local Group Pulsarsmilli-secondfew thousandWhole Galaxy and M31 Intermediate mass BH days?1 - 5Virgo Cluster Exoplanetsminutes-hours10 ?20 pc Flare Starsmillisec - hours100<1kpc LIGO eventsmillisecfew ?Observable Universe Transients we expect to see… (don’t forget serendipity…)

21. Black holes, neutron stars and gamma-ray bursts: mapping out in-situ particle acceleration Comparing directly to current X- ray all-sky monitors, LOFAR will be x10 more sensitive and provide (very rapidly) ~arcsec positions. This will be the instrument providing the alerts for Target- of-Opportunity observations with ‘pointed’ instruments e.g. Chandra, XMM-Newton, H(JW)ST, VLT, VLBI etc. Decelerating relativistic jets from a black hole binary system  in-situ acceleration of particles to TeV energies via deceleration of the jets… (Amsterdam)

22. Radio emission from extrasolar ‘hot Jupiters’ Jupiter is very bright at low radio frequencies ‘Hot Jupiters’ closer to their parent stars (not uncommon judging by other planet-finding surveys…) will be detected to distances of tens of pc. (Nancay group) Gamma-ray bursts: we expect to detect O~1 afterglow/day, and be able to deliver arcsec- accuracy positions immediately. Maybe even ‘prompt emission’… ? (Amsterdam)

23. Will we see many of these variable sources ? Yes ! Sky distribution of known flare stars and X-ray binaries north of -30 (Geers & Fender 2003)

24. LOFAR and radio pulsars Because of their steep radio spectrum, LOFAR will discover many faint nearby pulsars In this large sample, LOFAR is likely to find: Geminga-like pulsars SGRs / AXPs Exotic systems (e.g. PSR-PSR, PSR-BH), probing GR… LOFAR should also discover ~10 radio pulsars in a ~10hr observation of M31!! Van Leeuwen & Stappers (2004) (ASTRON/Amsterdam)

25. LOFAR Prototype Stations THETA~ 10 elements Location: Dwingeloo LOPES10 elements Location: Karlsruhe/Kaskade Test Station (ITS & FTS) 60-100 elements Location: LOFAR Core (Borger Odoorn) Remote Station 01 100 elements Location: between Core and WSRT

26. LOPES10 at KASCADE Andreas Horneffer, Heino Falcke

27. Radio emission from air showers: Coherent ‘Geo-synchrotron emission’ Falcke & Gorham (2003) Huege & Falcke (2003)

28. Hardware of LOPES10 LOPES-Antenna

29. Promising Event Layout (8 antennas) E/  -Detector RFI

30. Promising Event E-Field

31. Promising Event E-Field after Beamforming

32. Promising Event Beamformed Power

33. LOFAR Test Station

34. ITS 24h- movie of the sky at ~ 30 MHz 200 frames, one per ~ 7 min T=0.2s, B=10 kHz, N=25 antennas Full cross correlation matrix obtained Beam forming for the whole sky Noise ~ 2000 Jy Resolution ~7 0 N W S E LOFAR as an all-sky monitor (ASM) – it works!! ITS 24h-movie of the sky at ~ 30 MHz 200 frames, one per ~ 7 min T=0.2s, B=10 kHz, N=25 antennas

35. ITS image at ~30 MHz N= 60 dipoles T=6 sec, B=40 kHz (CLEANED) Cas A (SNR) Cyg A (radio galaxy) Virgo A (radio galaxy) North Polar Spur (diffuse structure) NORTH

36. LOFAR is (a) reality: The Netherlands / Europe will be at the forefront of radio astronomy for the next ~decade What does the future hold ? 1.Astroparticle physics… Cosmic-ray astrophysics (already happening…) Coordination with neutrino detectors 2. An expanded pan-European LOFAR Long baselines Physical (and psychological) preparation for SKA

37. The End.