L O F A RThe Low-Frequency Array

ASTRON / MIT / NRL / UvA / UL / RUG / KUNIBM / BSIK partners /Many others...

LOFAR_E211003.exe

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…

ground basedradio techniques

10 MHz

350VLAALMAATCAGMRT

LOFARLOFAR

Radio sky in 408 MHz continuum (Haslam et al)

LOFAR in The Netherlands

Hang on, what are these things?

They are theLow-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

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)

Freq (MHz)

11s array (mJy)

11s VC (mJy)

Beam array

Beam VC

f.o.v. array

f.o.v. VC

30 118 290 25” 21’ 650’ 90O

120 4.2 10 6.0” 5.2’ 160’ 230

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.

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

Z = 20 ……………. 15 ………. 10 8 7 6

coldHI

HII

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

10 arcmin

QuasarQuasardistributeddistributedstar formationstar formation

(Groningen)

Mapping all radio loud AGN

Physics of radio sourcesRadio galaxies as probes of blackhole, galaxy and cluster formation

• 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)

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

Distant starburst galaxies– dominant population at low flux densities– in few years observing: 108 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

Galaxy surveys with LOFAR will be an overwhelmingly statistical exercise

(Leiden, 5 years from now…)

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

10 15 30 0.5 3000 5.4 million

30 5.2 2 4 3000 4.3 million

75 2.1 0.3 25 60 5.3 million

120 1.3 0.1 66 62 15 million

200 0.8 10 125 7.5 3.3 million

• 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’

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

Object Variability Timescale

No. of Events per year

How far?

Radio Supernovae days-months 3 2 - 3 further than Virgo Cluster

GRB Afterglows days-months 100 Observable Universe

GalacticBlackHoles and Neutron Stars

days - months 10 Local Group

Pulsars milli-second few thousand Whole Galaxy and M31

Intermediate mass BH

days? 1 - 5 Virgo Cluster

Exoplanets minutes-hours 10 ? 20 pc

Flare Stars millisec - hours 100 <1kpc

LIGO events millisec few ? Observable Universe

Transients we expect to see… (don’t forget serendipity…)

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)

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)

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)

LOFAR and radio pulsarsBecause 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)

LOFAR Prototype StationsTHETA ~ 10 elements

Location: Dwingeloo

LOPES 10 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

LOPES10 at KASCADE

Andreas Horneffer, Heino Falcke

Radio emission from air showers:Coherent ‘Geo-synchrotron emission’

Falcke & Gorham (2003)Huege & Falcke (2003)

Hardware of LOPES10

LOPES-Antenna

Promising EventLayout (8 antennas)

E/-Detector RFI

Promising EventE-Field

Promising EventE-Field after Beamforming

Promising EventBeamformed Power

LOFAR Test Station

ITS 24h-movie of the sky at ~ 30

MHz 200 frames, one per ~ 7

minT=0.2s ,

B=10 kHz, N=25

antennas

Full cross correlation

matrix obtained

Beam forming for the whole

sky

Noise ~ 2000 Jy

Resolution ~70

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 minT=0.2s , B=10 kHz, N=25 antennas

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

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

The End.