LOFAR

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LOFAR
LOw Frequency Array gt 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
gt no moving parts (cheap) - huge, fast
data network - huge collecting area -
multi-beaming
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Dutch View
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a Lofar station
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ATCA
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this workshop mml astronomy
ALMA
LOFAR Simularities sky noise
atmosphere Gal. Synchrotron rapid phase
variation atmosphere
ionosphere Differences solid angle of
tiny (l/D of dish) nearly all sky
receiving element survey .
mosaic all-sky calibration
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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(?)

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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(?)

Z 20 . 15 . 10 8 7 6
cold HI
HII
70 MHz 90 MHz 130 160
190 MHz
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WMAP result gt Z 15 to 20
2 EoRs ??? or prolonged, patchy
EoR ???
Z 20 15 10 8
7 6
cold HI
warm HI
HII
HII
Pop III stars _at_ 500 Solar mass
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LOFAR and SKA
distributed star formation
Quasar
10 arcmin
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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 (a lt -2) gt 1 source per
  sample of 30,000
• gt catalog of background radio sources for
  intervening HI absorption

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Spectral Index
Redshift
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Spectral Index
Redshift
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Mapping intervening protogalaxies in
21cm absorption
SKAMP-III compatible !
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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 (a lt -2) gt 1 source per
  sample of 30,000
• gt 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

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Radio sky in 408 MHz continuum (Haslam et al)
(Dominated by synchrotron emission from
relativistic electrons)
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holes in the Galactic radio sky
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mapping the synchrotron emission in front of
and behind the opaque thermal sources .
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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 (a lt -2) gt 1 source per
  sample of 30,000
• gt 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 gt nearly instantaneous response
  to trigger events
• central core is an all-sky (hemisphere) monitor
• sensitive to non-thermal, coherent emission
  events, should they exist(?)

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The SUN
Coronal Mass Ejections, CMEs
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LOFAR astronomical science drivers
Franks 3 favorites

• Highest redshift radio sources
• Steep spectrum selection (a lt -2) gt 1 source per
  sample of 10,000
• gt 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 radiation appear at redshifts
  between 7 and 20(?)
• 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 gt nearly instantaneous response
  to trigger events
• central core is an all-sky (hemisphere) monitor
• sensitive to non-thermal, coherent emission
  events, should they exist(?)

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Dipole ground plane
conducting ground plane
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Dipole ground plane
equivalent to dipole plus mirror image
i2pft
-I e
o
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Dipole element response
equivalent to dipole plus mirror image
i2pft
-I e
o
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Dipole
q
zenith angle
equivalent to dipole plus mirror image
i2pft
-I e
o
(maximize response at q0 if hl/4 )
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Dipole
q
f
azimuth
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2
2
P(q) sin 2ph cos(q)/l 1 - sin q sin f
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The Sky above dipole
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sin projection
line of constant zenith angle
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sin projection
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sin projection
gives little weight to sky close to horizon !
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X
Y
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Dipole
over ground plane
Tuned for 150 MHz
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Dipole
Tuned for 150 MHz

• 150
• 180 210 MHz 240
  MHz

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What are these things?
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Crossed Dipoles for dual polarization
conducting plane
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LOFAR-Low Band dipole element
Droopy Dipoles for broad-band, dual
polarization
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4x4 array of dipoles on ground plane
- the LOFAR-High band element
h
s
s
(many analogies to gratings for optical
wavelengths)
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4x4
Tuned for 150 MHz sin projection
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ZA 0 deg 15
30 45
60 75
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4x4 Patterns

• ZA 30 deg
• tuned for 150 MHz

• 120 150
• 180 210 240

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Lofar stations ???
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a station 101 4x4 tiles
Size in l
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a station as 101 omni-directional elements
Size in l
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Station Beam no 4x4 envelope
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Station Beam using 4x4 envelope
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Station Beam 4x4 envelope and taper
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Station Beam
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Offset Station Beam
Centered station beam
inside the 4x4 beam
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Latitude 53.5 deg Decl 4x4 45 Offset
5 _at_ p.a. 45
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Slices through 4x4 Beam And Station beams
taper
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a station 101 4x4 tiles
Size in l
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Zenith no offset
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Zenith 5 offset
o
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Radio sky in 408 MHz continuum (Haslam et al)
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-30 deg
north
east
west
south
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North
Latitude -30
East
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North
Latitude 53.5
East
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north
53.5 deg
east
west
south
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-30 deg
north
east
west
south
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Top 4 LOFAR astronomical science drivers

• 21cm emission/absorption from Epoch of
  Reionisation

• Highest redshift radio sources
• gt catalog of background radio sources for
  intervening HI absorption
• 3-D mapping of the Galactic non-thermal emission
• Transient and bursting sources

65
Top 4 LOFAR astronomical science drivers

• 21cm emission/absorption from Epoch of
  Reionisation

• Highest redshift radio sources
• gt catalog of background radio sources for
  intervening HI absorption
• 3-D mapping of the Galactic non-thermal emission
• Transient and bursting sources

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Effect of moving station beam w.r.t. 4x4
beam
ZA 30 deg for 4x4 5 deg Offset for
station beam
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GAIN dB
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2.5 deg offset
GAIN dB
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7.5 deg offset
GAIN dB
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GAIN dB
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4x4 ZA 30 deg
GAIN dB
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