Global EoR Experoments

tobascothwackUrban and Civil

Nov 15, 2013 (3 years and 10 months ago)

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Global
EoR

Experoments

Ron
Ekers
, CSIRO



CAASTRO Global
EoR

Workshop

Uluru, 17 July 2013

Summary


Strategy for technically difficult experiments


Either masochists or people who don’t know any better!


NB the Crick and Watson story on DNA structure


Global HI EoR v imaging HI EoR


Statistical v direct detection


CORE


ZEBRA


SARAS


Other global HI experiments


EDGES, BIGHORNS, COREII, DARE,


Pulse calibration


Epoch of (re)combination


July 2013

2

Global HI EoR prediction


Pritchard et al, Nature
468
, 772 (2010)

Z = 6.3

Peter
Shaver

conjecture

(200/65)
2.5
=17

The 21cm
EoR

challenge


Global

T ~30mK in few MHz


S/N easy


can reach a few
mK

in few hours



T/T < 10
-
4

to10
-
5


Calibrate the complex gain


Minimize the number of unknowns that can couple to
EoR


Remove the
forgrounds


Remove the additive constant


Correlation receiver

»
Eliminate LNA additive noise


Position switching

»

T now very small so large antenna and long integration times

»
Correlation interferometer

»
Arrays


Statistical detection


Direct detection

Zero spacing
interferometer

Zero spacing
interferometer

From
CoRE

to ZEBRA

CoRE

(Chippendale)




ZEBRA


SARAS




ZEBRA II

Calibratable

receiver

CSIRO

RRI

MRO

July 2013

5

CORE

frequency independent antenna beam


Global
EoR

system

RRI Bangalore

Ravi
Subrahmanyan

Ron
Ekers

Peter
Shaver

A.
Raghunathan

Zebra


fat dipole v1

ZEBRA Global
EoR

Experiment


ZE
ro
-
spacing
measurement of the
B
ackground
RA
dio

spectrum


Partially reflecting
resistive screen


Virtual zero spacing
interferometer


Removes all additive
errors


Modulate screen ?

Subrahmanyan,

Ekers

Patra

Partial

reflector/transmitter

X

The space beam
-
splitter:


a
resistive wire mesh


Need a space beam
-
splitter before the antenna


A lossless screen (e.g. a conducting grid)


transmitted & reflected waves are orthogonal


Resistive wire mesh


Thickness of wire < skin depth


Frequency independent


Re
-
radiated fields no longer cancel the incident field on
the far side of the wire screen


Lumped resistance on scale <<



Practical solution instead of resistance wire


Building resistive screen

The Resistive Screen

copper wire + lumped resistors


resistor value


= free space impedance/2



3x4 metres

holes to reduce wind loading

Roll up for transport


ZEBRA


interferometer

first CMB correlation 20 Jan 2011

3.4m


1.5m separation


Max sky coverage at zero spacing
26%


Contributions to correlated output


Global sky signal


Screen radiating


1.5m interferometer sky
correlation

»
One path through screen

»
Both paths miss screen


Ferrite absorber

ZEBRA at Gauribidanur

Zebra correlated output


Baseline ripple


changes with LST


Repeats

each day


Multipath

scattering of

galaxy foreground signal


Shifted location …….

SARAS receiver evolution

SARAS receiver


Patra &
Subramanyan
, EA (2013)


88
-
175MHZ


Differential correlation spectrometer


Digital correlator well separated from
receiver


Minimize number of parameters in
solution (11)


Solve for multipath propagation from
internal reflections


Eg noise from receiver input




SARAS internal reflections


Short connections to keep broad bandwidth


Long connections to decrease coupling

SARAS internal reflections


Short connections to keep broad bandwidth


Long connections to decrease coupling

SARAS waterfall plot


Pulse calibration ?

Pulse injected at
Parkes

vertex

Pulse reflected from
Parkes

focus


Inject and integrate short (

sec
) pulses


Calibrated

noise spectrum


Understand & c
alibrate reflections


Nipanjana

Patra
, Paul Roberts


Pulse calibration


Band limited pulse with
-
20db reflection


Pulse repetition rate 10
6

Hz


Accuracy 0.05%

Other Global EoR Experiments


WSRT:


Lunar occultation


EDGES: Rogers &
Bowman


Polynomial fits
Δ
z > 0.06


Absolute calibration of components for wider bandwidths


BIGHORNS:
Sokolowski
,
Tremblay
,
Wayth
,
Tingay




Low rfi site, high stability


Core II: Bannister,
Chipendale
, Dunning



Precision self calibrating receiver


DARE


Go to moon to avoid ionosphere and rfi


July 2013

23

Estimates of the sources
of error and their
magnitude expressed as
the residuals to fits with
increased numbers of
parameters along with the
bias in EOR estimation

Parameters of 10 parameter
solution:

1] EoR signature

(30 mK, 50@145MHz)

2] scale
(assumes spectral index of
-
2.5)

3] constant
(ground emission)

4] frequency

-
2
(ionosphere emission)

5] frequency

-
4.5

(ionosphere absorption)

6] Magnitude of antenna S11

7] Magnitude of LNA S11

8] S11 phase error

9] S11 delay error

10] temperature scale


Estimate of errors using simulations


for more details see EDGES memo 99

Rogers & Bowman
(EDGES memo #99)

BIGHORNS


Sokolowski
,
Tremblay
,
Wayth
,
Tingay




Low rfi site, high stability


Dynamic spectrum
normalised by the median


Dynamic range 2%


Required 10
-
4


Day

200MHz

CORE2: A global EOR experiment with a self
-
calibrating receiver
on two
antennas

CORE2: A global EOR experiment with a self
-
calibrating receiver and two antennas|
Keith Bannister | Page
26

CORE2
-
MONO

60 Degree beam

Optimised

for frequency

Independence

and low RFI and

CORE2
-
DISH

5 Degree beam

Optimised

for foreground removal

27

The Richness and Beauty of the Physics
of Cosmological Recombination


well
defined quasi
-
periodic spectral
dependence


photons are coming
from
redshifts



z

1300−1400


i.e.
before
the time of
the formation of the
CMB angular
fluctuations


Chluba

&
Sunyaev

A&A, 458, L29 (2006)

28

Observing


All sky so dish size is not relevant


Needs a wideband spectrograph in 2
-
10 GHz range


Can
measure multiple independent patches of sky


Many dishes/receivers


Need lowest possible
Tsys


Can integrate over all oscillations


Spectral dependence is accurately predicted

29

Sensitivity Required


Need
Δ
T/T = 10
-
8


Tsys

=
25K


Δν

=
10
10
Hz


2
pol



100
antennas


Time =
1month (3.10
6

sec)


Δ
T/T = 25
/(
√(
10
10
.
2.100.3.10
6
.))
= 10
-
8

!