Weak Signal Detection of Virgo A
EME Conference 201218/8/2012 www.dmradas.co.uk
Astronomy• Location of Virgo A (M87)• Nature of M87• Expected signal strength & spectrum
Measurement• Choice of observing frequency• Antenna type• Receiver system• Interferometer• Transit scans• Results
Conclusions & comments
Weak Signal Detection of Virgo A
EME Conference 201218/8/2012 www.dmradas.co.uk
Nearest star is 4.3 ly away
4.5 x 109 km = 0.0005 ly
Give some idea of scale• In astronomical terms the solar system is very small
ASTRONOMY
Weak Signal Detection of Virgo A
EME Conference 201218/8/2012 www.dmradas.co.uk
SUNLocal Spur
Solar system located toward edge of Milky Way• In a local spur of a spiral arm
Plan View of Milky Way
Weak Signal Detection of Virgo A
EME Conference 201218/8/2012 www.dmradas.co.uk
Milky Way
432,
000
ly
Fornax
Milky Way is in a small group of galaxies• Approximately 400,000 ly in size
(1 parsec = 3.2 ly)
Weak Signal Detection of Virgo A
EME Conference 201218/8/2012 www.dmradas.co.uk
5m Ly
Members of the Local Group of galaxies• 10M ly diameter
To VirgoCluster
Weak Signal Detection of Virgo A
EME Conference 201218/8/2012 www.dmradas.co.uk
LocalGroup
VirgoCluster
M66 Group
Leo 1
Ursa MajorGroup
M101Group
M81 Group
Draco Group
40M ly 53M ly
35M ly
38M ly
11M ly
55M
ly
24M ly
M51 Group31M ly
The bigger picture – Virgo A (M87) is 53M ly away
Weak Signal Detection of Virgo A
EME Conference 201218/8/2012 www.dmradas.co.uk
3D map of Super Cluster
160M ly
The bigger picture in 3D
Weak Signal Detection of Virgo A
EME Conference 201218/8/2012 www.dmradas.co.uk
13hr 12:45hr 12:30hr 12:15hr 12hrRight Ascension
+200
+150
+100
+50
De
cli
na
tio
n
10
M87
Transit scan of Virgo Cluster15
0150
Inte
rfe
rom
ete
r m
ain
be
am
3dB BW ~10 x 300
Weak Signal Detection of Virgo A
EME Conference 201218/8/2012 www.dmradas.co.uk
0
1000
2000
3000
4000
5000
6000
7000
1 3 5 7 9 111315171921232527293133353739414345474951535557596163656769717375777981Assigned Galaxy No in Virgo Group
Sign
al S
tren
gth
M87
Relative Signal Strength of Members of the Virgo Group
VCC0763, (M87), Virgo A signal strength
Other galaxies in the group
M87 dominates the radio emission from the Virgo cluster of galaxies
Weak Signal Detection of Virgo A
EME Conference 201218/8/2012 www.dmradas.co.uk
110,00Ly
100,000ly
Diameter of Milky Way
100,000 ly
330,000 ly
M87 is >3x diameter of Milky Way
Giant EllipticalGalaxy
Barred Spiral Galaxy
M87 is more than 3x the size of the Milky Way
• Virgo A is one of the most remarkable objects in the sky
• It has an active galactic nucleus (AGN) and a strange jet
RA = 12 : 30.8 (h:m)DEC = +12 : 24 (deg:m)Distance ~ 53M lyVisual Brightness = 8.6 (mag)Visual extent of core = 8 arc minutes
Weak Signal Detection of Virgo A
EME Conference 201218/8/2012 www.dmradas.co.uk
5,000 ly
Neptune is 0.0005 ly away
M87
The galaxy is one of the most massive in the local Universe 200x mass of Milky Way
The jet produces the bulk of the radio emission
Consists of relativistic plasma ejected from the AGN
Jet on the other side of the galaxy is obscured
The AGN is probably a super massive black hole
Weak Signal Detection of Virgo A
EME Conference 201218/8/2012 www.dmradas.co.uk
At the core of this galaxy is a super massive Black Hole (SMBH) with an estimated mass of (6.6 ± 0.4)×109 Solar masses and a diameter larger than the orbit of Pluto
Accretion disc rotating at velocities of up to 1,000 km/s (0.2 ly radius)
Black hole in M87 may be displaced
from the galaxy centre by a distance
of about 82 ly.
Physics of jet formation is
not fully understood
Rotation of black hole magnetic
field produces particle accelerating
E fields Radio emission is by Synchrotron
process
Weak Signal Detection of Virgo A
EME Conference 201218/8/2012 www.dmradas.co.uk
Synchrotron emission• Relativistic particles confined by magnetic field lines• High intensity highly beamed polarized emission
magnetic field
charged particle
vr
circularpolarization linear
polarization
Radio beam
Signal strength falls with frequency – 100MHz – 1GHz best
But antenna gains low at low frequencies (small antennas)
Best frequency for detection is complex issue
Synchrotron Spectrum of Virgo A
10
100
1000
10000
0 1000 2000 3000 4000 5000 6000
Frequency MHz
Sig
nal
Str
eng
th J
y
Spectral index x 0.79
S = k f -x
Virgo A Spectrum (Log-Log)
10
100
1000
10000
1 1.5 2 2.5 3 3.5 4
Log Frequency
Sig
nal
Str
eng
th J
y (L
og
)
Spectral Index = 0.79
EMMISION MECHANISM
Weak Signal Detection of Virgo A
EME Conference 201218/8/2012 www.dmradas.co.uk
Signal strength plotted against wavelength shows increase with longer wavelength
Virgo A is a weak source compared with Cassiopeia and Cygnus A
Expected signal strength
at 408MHz is 560Jy
1Jy = 10-26W/m2/Hz
Hercules
Virgo
Cygnus
Cassiopeia
1cm 10cm 1m 10m
Wavelength
10
10
2
103
1
04
Po
we
r fl
ux
de
ns
ity
(1
0-2
6 W
m-2 H
z-1)
P x (=wavelength, x=spectral index)
Weak Signal Detection of Virgo A
EME Conference 201218/8/2012 www.dmradas.co.uk
• Virgo A is one of the weakest sources
• It is 53M ly away
• It emits ~ 1033 Watts (<1GHz)
• Note – big gap to pulsars
1
1
0
1
02
1
03
1
04
1
05
1
06
1
07
1
08
1
09
Po
wer
Den
sity
J
y (
10-2
6 W
m-2
Hz-1
)
Solar storms& plages
Quiet sun
Solar bursts
Su
n
Tau
rus
A
Vir
go
A
Pu
lsar
s
Jup
iter
Cas
sio
pei
a A
Cyg
nu
s A
Radio Source
Ori
on
Neb
ula
Sig
nal
str
eng
th (
log
scal
e)
• Signal strengths of astronomical radio sources
Weak Signal Detection of Virgo A
EME Conference 201218/8/2012 www.dmradas.co.uk
Choice of frequency & antenna type• On balance observation at <1GHz is best for (x)=0.79
• For interferometer we need two antennas
• Could use two dishes at around 1420 MHz but
away from H line
• Did not have two suitable (3m) dishes
• Opted for easy to build low cost Yagis at 408MHz• Chose SARA 408MHz Quagi design (Hal Braschwitz and Jim Carroll )
Predicted beam pattern
Z =45.51 +j 3.36 ohms.
EQUIPMENT
Single 3m dish
Weak Signal Detection of Virgo A
EME Conference 201218/8/2012 www.dmradas.co.uk
Single Yagi 0.1V=5dB (RHS of yagi is first)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1 20 39 58 77 96 115 134 153 172 191 210 229 248 267 286 305 324 343 362 381 400 419 438
Azimuth Angle -90 -0 - +90
Sig
nal
Lev
el 0
.1V
=5d
B
19dB
-3dB BW = 33.90
22/1/08
Single SARA Quagi Beam Pattern-3dB BW = 330 , SL @ -19dB
Twin Horizontal Yagis 1.2m Spacing 0.1V=2dB ( RHS First)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1 19 37 55 73 91 109 127 145 163 181 199 217 235 253 271 289 307 325 343 361 379 397 415
Azimuth Angle -90 - 0 - 90
Sig
nal
Lev
el 0
.1V
=2d
B
14.1dB
-3dB BW = 17.50
22/1/08
RHS LHS
Twin SARA Quagis stacked 1.2m apartCompromise on BW & SL Levels
-3dBW = 170 , SL at -14dB
Stacked Quagis at 408MHz
Weak Signal Detection of Virgo A
EME Conference 201218/8/2012 www.dmradas.co.uk
Antenna head amplifier
Antenna Preamps• RAS 408MHz (WD5AGO 0.33dB NF)
• Mini circuits ZX60-33LN (50-3000MHz,1dB NF)
44dB combined Gain
406.
2MH
z
411.
8MH
z
Weak Signal Detection of Virgo A
EME Conference 201218/8/2012 www.dmradas.co.uk
Receiving system and Temp control• Preamps and receiver were
temperature controlled
ICOM IC-R7000 Receiver
Temperature control Unit
Today, I would use an SDRlike the FunCUBE dongle
Weak Signal Detection of Virgo A
EME Conference 2012
Transit scan across Galactic Plane using ‘FunCube Dongle’ SDRS
ign
al L
evel
dB
(0.
1d
B/d
iv)
~ 2 hours
Centre of galactic plane
1.2d
B
Sig
nal
Lev
el d
B (
0.1
dB
/div
)
FCD 1420.4MHz Signal strength recording
TimeStart End
Sig
nal
Lev
el d
B (
0.1
dB
/div
)
~ 2 hours
Centre of galactic plane
1.2d
B
• An SDR Radio Telescope www. britastro/org/radio
18/8/2012
Weak Signal Detection of Virgo A
EME Conference 201218/8/2012 www.dmradas.co.uk
Simple Interferometer configuration
East AntennaWest Antenna
Receiver output
Phase difference
Radio source
signal
baseline
normal to baseline
Single antenna beam
East AntennaWest Antenna
Receiver output
Phase difference
Radio source
signal
baseline
normal to baseline
Single antenna beam
No
rth
–S
ou
th b
eam
East – West beamA
nte
nn
a g
ain
E-W beam angle
Interferometer Beam Pattern
beamwidth of a single antenna
No
rth
–S
ou
th b
eam
East – West beamA
nte
nn
a g
ain
E-W beam angle
Interferometer Beam Pattern
beamwidth of a single antenna
Interferometer can distinguish between diffuse background and ‘point sources’• Total power receiver gives ‘smeared’ response due to larger
beamwidth
INTERFEROMETER
Weak Signal Detection of Virgo A
EME Conference 201218/8/2012 www.dmradas.co.uk
The two twin Quagi antennas were mounted >2 above the ground on towers separated by 30m• Fringe period = 5.6 minutes
30mWest arm East arm
Weak Signal Detection of Virgo A
EME Conference 2012
Crab Nebula used as point source to examine beam pattern• Taurus A is ~ 3 x power of Virgo A (~1200Jy at 408MHz)
Half power beam width of Main Lobe ~ 0.60
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
406.5MHz Interferometer Beam Pattern
Line
ar
Sca
le
360 Deg / 24 hours/ Transit
11th /12 Feb 08
Measurement limits
Weak Signal Detection of Virgo A
EME Conference 201218/8/2012 www.dmradas.co.uk
13hr 12:45hr 12:30hr 12:15hr 12hrRight Ascension
+200
+150
+100
+50
De
cli
na
tio
n
10
M87
150
Inte
rfe
rom
ete
r b
ea
m
Signal Strength
Beam profile calibrated from Taurus A measurement
Weak Signal Detection of Virgo A
EME Conference 201218/8/2012
• Navigating the sky (setting up transit observations)
•Use ‘Radio Eyes’ software
•All sky radio map @ 408MHz
•Find location of Virgo A and set beam position for transit
•Ensure high beam elevation (avoid ground noise)
•Measure signal level for 5 hours either side of transit
Virgo A
Main beam
Dec
linat
ion
0
Right Ascension hrs Radio Eyes 408MHZAll Sky map
500 E
leva
tion
Horizon
Virgo A
www.dmradas.co.uk
Beam moves this way
Weak Signal Detection of Virgo A
EME Conference 201218/8/2012 www.dmradas.co.uk
Measurement results• Transit scans performed on 11th/12th & 12th/13th Feb. 2008• Stable results from both days added to improve S/N • 30m baseline interferometer at 406.5MHz (0.60 HP BW)• Plot shows signal scan across source Virgo A• Diffuse galactic background emission is ‘resolved’ so shows
no fringes• Virgo a ‘point source’ (~10’ dia) - is not resolved and
produces fringes• Can separate out ‘total power’ plot and fringes
• Resultant plot is the Virgo A fringe pattern
MEASUREMENTS
Weak Signal Detection of Virgo A
EME Conference 2012
One day Transit Scan through Taurus A and Virgo A
Sig
nal A
mpl
itude
(lin
)D
eclin
atio
n
Right Ascension (hrs)
200
100
300
00
18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2
Taurus A
Outer Galactic Plane
Inner Galactic Plane
Virgo A
Continuous Signal record over 17 hours
Virgo A Taurus A
Beam track
18/8/2012
Weak Signal Detection of Virgo A
EME Conference 201218/8/2012 www.dmradas.co.uk
Raw data shows both ‘total power’ and fringes from Virgo A• Remove total power to leave fringe pattern
Virgo A, 406.5MHz FM , 50El,180Az, Twin Quagi Antenna Interferometer, end @ 09:04GMT, 13/2/08
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Time GMT (hrs)
Inte
rfer
om
eter
Sig
nal
Lev
el
09:0007:0005:0003:0001:0023:00
Icom-R7000FM,Wilk.Comb. 6db Ntype Att, HP Att=6dB,Orig SPU Gain=Max,Amp=7,Input Offset=2.4,TC=6
To the Outer GP To the Inner GP
Virgo A
Virgo A expected @ 03:12 GMT
Full data record (blue)
Average signal (yellow)
Increase in signal due to Virgo A
Virgo A,406.5MHz FM , 50El,180Az,Twin Quagi Antenna Interferometer, Records of 12th& 13th Feb 08 Summed
0
0.2
0.4
0.6
0.8
1
1.2
1.4
Time GMT (hrs)
Inte
rfe
rom
ete
r F
rin
ge
Sig
na
l
03:00 04:0002:00
Icom-R7000FM,Wilk.Comb. 6db N type Att, HP Att=6dB,Orig SPU Gain=Max,Amp=7,Input Offset=2.4,TC=6
Noise in the signal is reduced by summing the records on two days
Expected transit
Represents a signal level of ~560Jy, 5.6x10-24W/m2/Hz
Weak Signal Detection of Virgo A
EME Conference 201218/8/2012 www.dmradas.co.uk
Summary & Conclusions
• A low cost, simple interferometer can be used to detect the extragalactic radio source Virgo A (M87)
• Stacked SARA Quagi antennas have sufficient gain at 408MHz
• With modest temperature control of amplifiers & receiver, records from different days can be added to improve S/N
• Virgo A signal strength of ~560Jy is near limit for detection by simple system
• Improvements can be made by:
• Stacking more Quagis
• Using a stable SDR receiver
• Phase Switched interferometer
• I need time to do it !MAPS-010143 part
Weak Signal Detection of Virgo A
EME Conference 2012
The EME Community & Radio Astronomy• Has excellent receivers & antennas• Could work around 408MHz and 1400MHz• Probably enough sensitivity• May need gain & noise stabilization• Could easily undertake some Radio Astronomy• Think about it ? Why not try ?
DL7APV
WD5AGO
DL3OH
Weak Signal Detection of Virgo A
EME Conference 2012
M87 Virgo ARA = 12 : 30.8 (h:m)DEC = +12 : 24 (deg:m)Distance ~ 53M ly