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LOFAR
LOw Frequency Array
=> most distant, high redshift Universe !?

Consortium of international partners...
Dutch ASTRON USA Haystack Observatory (MIT) USA Naval Research Lab ... `best site' = WA ... ... ...

Novel `technology telescope' - array design => no moving parts
huge, fast data network huge collecting area

(cheap)

multi-beaming


Dutch View

~ 400 km


a Lofar `station'


LOFAR
10 MHz

ATCA GMRT VLA ALMA

350µ

ground based radio techniques


LOFAR
350µ 10 MHz

ground based radio techniques


...this workshop... mm astronomy...
Simularities:

ALMA
atmosphere atmosphere tiny (/D of dish) mosaic

LOFAR
Gal. Synchrotron ionosphere nearly all sky all-sky calibration

sky noise rapid phase variation

Differences: solid angle of receiving element survey ....


Top 4 LOFAR astronomical science drivers ·
-

21cm emission/absorption from Epoch of Reionisation
mapping the neutral clouds in IGM as first sources of ionising radiation appear at redshifts between 7 and 20(?)


Top LOFAR astronomical science drivers ·
-

21cm 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(?)

UV<
Z = 20 ................ 15 .......... 10

1 ... (Gunn-Peterson Effect) 8 7 6

cold HI

HII
70 MHz 90 MHz 130 160 190 MHz


WMAP result => Z ~ 15 to 20 2 EoRs ??? ... or...
Z = 20 15

prolonged, patchy EoR ???
10 8 7 6

cold HI

HII

warm HI

HII

Pop III stars: @ 500 Solar mass


LOFAR and SKA

...

distributed star formation 10 arcmin

Quasar


Top 4 LOFAR astronomical science drivers
·
-

21cm emission/absorption from Epoch of Reionisation
mapping of neutral clouds in IGM as first sources of ionising radiation appear at redshifts between 7 and 20(?)

·
-

Highest redshift radio sources
Steep spectrum selection ( < -2) => 1 source per sample of ~30,000 => catalog of background radio sources for intervening HI absorption


Spectral Index

Redshift


Spectral Index

Redshift


Mapping intervening protogalaxies in 21cm absorption

SKAMP-III compatible !


Top 4 LOFAR astronomical science drivers
·
-

21cm emission/absorption from Epoch of Reionisation
mapping of neutral clouds in IGM as first sources of ionising radiation appear at redshifts between 7 and 20(?)

·
-

Highest redshift radio sources
Steep spectrum selection ( < -2) => 1 source per sample of ~30,000 => catalog of background radio sources for intervening HI absorption

·
-

3-D mapping of the Galactic non-thermal emission
uses free-free absorption by known extended thermal sources will determine the origin of the Galactic cosmic ray flux


Radio sky in 408 MHz continuum

(Haslam et al)

(Dominated by synchrotron emission from relativistic electrons)


holes in the Galactic radio sky...

Optically thick thermal plasma ... HII regions


mapping the synchrotron emission in front of ... and behind the opaque thermal sources ....


Top 4 LOFAR astronomical science drivers
·
-

21cm emission/absorption from Epoch of Reionisation
Mapping of neutral clouds in IGM as first sources of ionising radiation appear at redshifts between 7 and 20(?)

·
-

Highest redshift radio sources
Steep spectrum selection ( < -2) => 1 source per sample of ~30,000 => catalog of background radio sources for intervening HI absorption

·
-

3-D mapping of the Galactic non-thermal emission
uses free-free absorption by known extended thermal sources will determine the origin of the Galactic cosmic ray flux

·
-

Transient and bursting sources
no moving parts => nearly instantaneous response to trigger events central core is an all-sky (hemisphere) monitor sensitive to non-thermal, coherent emission events, should they exist(?)


The SUN
Coronal Mass Ejections, CMEs



Frank's 3 favorites LOFAR astronomical science drivers
·
-

Highest redshift radio sources
Steep spectrum selection ( < -2) => 1 source per sample of 10,000 => catalog of background radio sources for intervening HI absorption

·
-

21cm emission/absorption from Epoch of Reionisation
Tomography of neutral residue of IGM as first sources of ionising very tough to rachieve fts between 7 and 20(risk / high gain radiation appea at redshi sensitivity: high ?)

#3 #1

·
-

3-D mapping of the Galactic non-thermal emission
uses free-free absorption by known extended thermal sources will determine the origin of the Galactic cosmic ray flux

·
-

Transient and bursting sources

no moving parts => nearly instantaneous response to trigger events central core is an all-sky (hemisphere) monitor sensitive to non-thermal, coherent emission events, should they exist(?)

#2



Dipole + ground plane

conducting ground plane


Dipole + ground plane
Ioe i2ft

equivalent to dipole plus mirror image

-Ioe

i2ft


Dipole element response h
equivalent to dipole plus mirror image

Ioe i2ft

h -Ioe
i2ft


Dipole

=

zenith angle Ioe i2ft

h
equivalent to dipole plus mirror image 2

h -Ioe
i2ft

P() ~ sin [2h cos()/]
(maximize response at

=0

if h=/4 )


Dipole


Ioe i2ft

azimuth



h

P() ~ sin [2h cos()/] {1 - sin sin }

2

2

2









The `sin projection' of hemisphere onto a plane:

The Sky above dipole


`sin projection'

line of constant zenith angle


`sin projection'


`sin projection'

gives little weight to sky close to horizon !


X Y


Y X


Dipole
over ground plane Tuned for 150 MHz

Y X


Dipole
Tuned for 150 MHz

120 180

150 210 MHz

240 MHz


What are these things?


Crossed Dipoles for dual polarization

conducting plane


Droopy Dipoles for broad-band, dual polarization

LOFAR-Low Band dipole element


4x4 array of dipoles on ground plane
- the `LOFAR-High band' element

h

s

s

(many analogies to gratings for optical wavelengths)


4x4
Tuned for 150 MHz sin projection


ZA = 0 deg 45

15 60

30 75


4x4 Patterns
· · ZA = 30 deg tuned for 150 MHz

120 150 180 210 240


Lofar stations ???


a `station' = 101 `4x4 tiles'

Size in




a `station' as 101 omni-directional elements

Size in




Station Beam: no 4x4 envelope


Station Beam: using 4x4 envelope


Station Beam: 4x4 envelope and taper


Station Beam


Offset Station Beam

Centered station beam

inside the 4x4 beam


Latitude: +53.5 deg Decl 4x4: 45 Offset: 5 @ p.a. 45


Slices through 4x4 Beam And Station beams

taper


a `station' = 101 `4x4 tiles'

Size in




Zenith

no offset


Zenith + o 5 offset


Radio sky in 408 MHz continuum

(Haslam et al)


-

30 deg

north

east

west

south


North
Latitude -30

East


North
Latitude +53.5

East


+53.5 deg

north

east

west

south


-

30 deg

north

east

west

south


Top 4 LOFAR astronomical science drivers
· · 21cm emission/absorption from Epoch of Reionisation Highest redshift radio sources
[ => catalog of background radio sources for intervening HI absorption ]

· ·

3-D mapping of the Galactic non-thermal emission Transient and bursting sources


Top 4 LOFAR astronomical science drivers
· · 21cm emission/absorption from Epoch of Reionisation Highest redshift radio sources
[ => catalog of background radio sources for intervening HI absorption ]

· ·

3-D mapping of the Galactic non-thermal emission Transient and bursting sources


Effect of moving station beam w.r.t. 4x4 beam ZA = 30 deg for 4x4 5 deg Offset for station beam


GAIN dB


2.5 deg offset

GAIN dB


7.5 deg offset

GAIN dB


GAIN dB


4x4 ZA = 30
GAIN dB

deg