Weak Signal Detection of Virgo A EME Conference 2012 18/8/2012 Astronomy Location of Virgo A (M87)...

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



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



SUNLocal Spur

Solar system located toward edge of Milky Way• In a local spur of a spiral arm

Plan View of Milky Way



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)



5m Ly

Members of the Local Group of galaxies• 10M ly diameter

To VirgoCluster



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



3D map of Super Cluster

160M ly

The bigger picture in 3D



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



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



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



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



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



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



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)



• 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



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



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



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



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


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



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



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


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



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


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



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


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



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



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


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


EME Conference 2012

M87 Virgo ARA = 12 : 30.8 (h:m)DEC = +12 : 24 (deg:m)Distance ~ 53M ly

Weak Signal Detection of Virgo A EME Conference 2012 18/8/2012 Astronomy Location of Virgo A (M87)...

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Transcript of Weak Signal Detection of Virgo A EME Conference 2012 18/8/2012 Astronomy Location of Virgo A (M87)...