Seminars and Discussions on the Radio Astronomy in Asia Pacific

Region.

RAFCAP Meeting

Kuala Lumpur

May 19 –20, 2004

Radio Astronomy in India

N. Udaya Shankar RRI

T.L. Venkatasubramani NCRA

Introduction

• Radio Astronomy in India began with the installation of 32 dishes of 1.8 m dia.

• 1965 Kalyan near Bombay (Present Mumbai)…..G.Swarup

• The latest installation: GMRT Pune near Bombay 30 Antennas of 45m dia Spread over 25Km Freqs: 150, 325, 610/235, 1000-1420 MHz

RADIO ASTRONOMY INSTALLATIONS IN INDIA

Name and Operating Agency

Location Spectrum Needs

Giant Meterwave Radio Telescope,

TIFRhttp://www.gmrt.ncra.

tifr.res.in

Khodad, Maharashtra

19°6’ N; 74 °3’ E

37.5-38.25; 151-154; 230-234; 322-328.6; 406.1-410; 608-614; 1400-1427; 1610.6-1613.8 and 1660-1670 MHz

(Licensed bands of operation)

Ooty Radio Telescope, TIFRhttp://www.ncra.tifr.res.in

Ooty, TamilNadu

11°23’ N; 76 °40’ E

322-328.6 MHz

(Licensed band of operation)

mm-wave Telescope,

RRIhttp://www.rri.res.in

Bangalore, Karnataka

12°58’ N; 77 °38’ E

6-7; 11.5-12.5; 22-24; 42-49

and 80-115 GHz

TIFR: Tata Institute of Fundamental Research RRI: Raman Research Institute

Radio Astronomy Radio Astronomy Installations in India Installations in India

Radio Astronomy Installations in India

Name and Operating Agency

Location Spectrum Needs

Decameter T-array,

IIA,RRIhttp://www.iiap.res.in

Gauribidbur, Karnataka

13°36’ N; 77 °27’ E

33.5-34.5 MHz

Solar Radio Heliograph,

IIA

Gauribidbur, Karnataka

13°36’ N; 77 °27’ E

37.5-38.25; 53-55; 73-77; 150-153 and 322-328.6 MHz

IPS Array,

PRLhttp://www.prl.ernet.in

Rajkot, Gujarat

22°18’ N; 70°56’ E

103 MHz

Cluster Antenna Array

(PROPOSED) RRI, TIFR

Khodad, Maharashtra

19°6’ N; 74 °3’ E

2 to 10 GHz, supplementing current GMRT coverage up to

2 GHz.

IIA: Indian Institute of Astrophysics PRL: Physical Research Laboratory

Introduction

• Ooty Radio Telescope 327 MHz• 10.4 m mm wave Telescope mm wave• Gauribidanur Radio telescope 34.5 MHz• Mauritius Radio Telescope 150 MHz• GMRT 150-1400 MHz• Future Installations GMRT upgrades Comapct Cluster / 500-8000 MHzParticipation in SKA

Main Focus Of Indian RA• Low Frequency Meter and Decameter wavelengths (Exception of 10.4m telescope)• India Offers Unique advantages 1. Lesser RFI than west 2. Labour Intensive nature 3. Coverage of both N and S Hemispheres 4. Bootstrapping---- One Experience leading to another

• Is it Scientifically rewarding to have such a focus ?

• Primordial Hydrogen

• Oldest and diffuse electrons….Source Evolution

• Pulsars

• Sub-luminous matter in the early universe

• Deuterium Abundance

• Recombination lines of carbon

Study of atoms which are almost of a

micron size……n=574.

Ooty Radio Telescope

ORT specification

ORT

• Parabolic Cylinder 530m 30m

• 1100 SS wires 0.38mm dia

• Built on a hill with a slope of 11º– Equal to the latitude of the observatory– ORT equatorially mounted telescope

• Effective collecting area 8000 m2

– Eq of a 138m Dish

Cosmological Evolution

• Ooty Days in 1970• Steady State Vs Evolving Universe• Ooty Observations Angular Size -Flux density

Observations Using Lunar Occultations• 1 to 10 Arcsec ..unachieved in those days for a

large sample of weak sources• Number density of Radio Sources higher at earlier

epochs but had smaller linear sizes

• A very strong support for evolution

Interplanetary Scintillations

• Twinkling of stars

• Extragalactic sources…..IPM

• Solar wind studies Sweeping past the earth 400 Km / Sec

• Source Structures

• Space Weather Studies

10.4m telescope

RRI 10.4m Telescope

• The first mm wave telescope of India• Late 1970’s …75 micron surface accuracy

was an achievement

Sio Masers 86.2 GHz…..CO emission 115.3

A study of Molecular clouds …After effects of star formation ….Condensates forming cometary globules…..Gum Nebula.

• 6.7 GHz Methanol Maser Survey…Galactic Plane

Gauribidanur T Array

GBD_image

MRT Aerial View

Images

• Sky Coverage (1 )Right Ascension: 18 to 24 hrsDeclination : -700 to -100

•Frequency : 151.6 MHz•Resolution : 4'x4'•Integration time : 4 s•Bandwidth : 1 MHz•Noise(achieved) : 100-350 mJy/beam (expected) : 50-120 mJy/beam•Almost complete uv coverage

Deconvolution of MRT Images

Raw Image Deconvolved Image

• A deconvolved image of a small region of the sky seems satisfactory.

• The Problems of PSF changes due to non-coplanar have already been addressed.

• Chromatic Aberration effects are being included.

= 0.05 upto 3Hogbom clean

GMRT

GMRT Y

18 Arm antennas ---25 Longest Baseline 12 CSQ ant 1.1 SqKm

Current PerformanceMeasured System Parameters

Frequency (MHz) ============== 153 235 325 610 1420Primary Beam (Degrees) 3.8 2.5 1.8 0.9 0.4

System Temperature (K) 450 180 100 90 70

Ant Temp (K/ Jy/ Antenna) 0.35 0.3 0.35 0.3 0.25

Synthesised Beam Whole Array (arcsec)* 20 12 9 5 2

Largest Detectable source (arcmin) 68 44 32 17 7

Sensitivity (rms image noise mJy/MHz/min)** 5.2 3.9 1.2 1.2 1.2

Astronomically Usable Frequency Range (MHz) 146-158

230-240

305-360

580-640

850-1450

Source: The Giant Meterwave Radio Telescope S. Ananthakrishnan and A. Pramesh Rao. Multicolour Universe Conference, 2001

*~ x20 with only the Central Square ** ~x2, with only the Central Square

Current PerformanceAstronomical Usage

• An independent GMRT Time Allocation Committee (GTAC), appointed by the NCRA Management Board issues periodic calls for proposals to observe with the GMRT, rates the proposals for scientific merit and allots time.

• 1st Cycle: Jan – May 1992; About 1600 hours of time has been allotted per cycle.

• Time Allotment for ~70 proposals for the 4th GTAC Cycle in progress

• 26 publications from GMRT (end-2002 status)

• We are able to go down to 30-40 microJansky flux density level.

• A point source map with 0.11 million dynamic range has been recently made.

Research areas covered by GMRT during the GTAC Cycle 3

Category of proposal No. of Prop. Time Allotted (in Hrs)

Key Projects (Galactic Plane, Pulsars, Nearby Galaxies, Clusters of

galaxies, DLAs)4 252

HI Emission 7 170

HI Absorption 4 130

OH/ HI Absorption 2 80

Continuum Imaging (Extragalactic) 12 364

Continuum Imaging (Galactic) 8 178

Pulsars 3 192

Micro- Quasars 2 30

Solar System (Jupiter) 1 80

Sun 2 24

3C236Red shift=.09Dist=300 MpcV=20,000Km/s

New Pulsar 0514-40A

• In Globular Cluster NGC 1851

• Most eccentric orbit known, e=0.89

• Period=4.99 (common Tens of millisecs)

• Companion Mass > 0.9 Solar Mass

• First Pulsar Discovered by GMRT

GMRT Specifications 

Parabolic Reflector Diameter 45m

Focal Length 18.54 m

Physical aperture 1590 m2

Sensitivity of single dish 0.3 K/Jy

Feed Support Quadripod

Mounting Altitude-azimuth

Elevation Limits Software Limit 17-90 degreesHardware Limit 15-110 degrees

Azimuth Limits Software Limit -265 to +265 degreesHardware Limit -270 to +270 degrees

Slew rate Azimuth 30 degree/minuteElevation 20 degree/minute

Design wind speeds Operation up to 40 km/h(3 sec peak at 10 m height) Slew up to 80 km/h

Survival 133 km/h

Size of wire mesh of 20x20 mm, outer 1/3 areareflecting surface 15x15 mm, middle 1/3 area

10x10 mm, inner 1/3 area

Maximum rms surface errors, 20 mm, outer 1/3 areaat wind speed of 40 kmph 12 mm, middle 1/3 area

08 mm, inner 1/3 area

Tracking and pointing accuracy 1' rms at wind speeds of < 20 km/h

Interference Excision at MRT

Problem areas for the future• Mobile phones (2004-05?)

-- Rich village with turn-over of ~$500,000 per year in grapes (Note: Excellent champagne! ) and onion

• 4-lane Super Highway (2007??)-- 1 vehicle/ 3 minutes in 1985 with 2 lanes-- 3 vehicles/ 1 minute in 2004 with 2.25 lanes!

• New International Airport at Chakan, about half-way between Pune and Narayangaon (2010???)

• New Railway line linking Pune and Nashik, probably crossing through the array (2015????)

• An intensive Interference Monitoring is under way Joardar etal

Why should we take up A New Cluster Antenna Array At GMRT Campus??

• Certain science drivers

• Projection of this as India’s initiative in SKA related activities

• Attempt to get into cm-wavelengths which would be of common interest to Radio Astronomers and ISRO

• Need for creating a pool of young talented engineers interested in RA

• A Platform to test ideas and instruments meant for GMRT- Upgrade

• Important drivers for initiating a collaborative project

Scientific Goals

• Compact Cluster to measure short spacings

• Profitable Usage of a Modest Collecting Area Rather than Scattering a Smaller Number Of Antennas For Higher Angular Resolution.

• Low Surface Brightness Radio Sources

Nine- 12m antennas in reuleuxaux configurationplaced within the central square

A possible remedy..

C9-C2 = C5-D0

24 antennas in a reuleuxaux triangle

24 antennas in a reuleuxaux triangle

Conclusion• Definitely a cluster added to GMRT will

improve its low spatial frequency coverage

• What is optimum ?

• Where to locate it ?

• What should be the antenna sizes ?

• Effects of shadowing ?

A lot more interesting questions…..