“... but it’s fun”

Radio astronomy atGreen Bank, the GBT,and other cool stuff

Paul Ruffle, NRAO, May 2007

Start of Radio Astronomy

• 1933 Karl Jansky discovered Milky Wayemitted radio waves

• Grote Reber built first radio antenna dish30 feet in diameter

• 1938 mapped the distribution of radioradiation from the Milky Way

• 1942 J. S. Hey discovered low-frequencyradio bursts from the Sun and radar echosfrom meteors high in the Earth'satmosphere

Radio Astronomy

• Expanded rapidly after World War II• Early surveys found radio stars• Positions so that they might be identified• Achieved with interferometers

– Taurus A source – the Crab Nebula– Cassiopeia A source – supernova remnant– Cygnus A source – distant peculiar galaxy

• 1951 Harold Ewen and Edward Purcelldiscovered 21 cm neutral hydrogen line(predicted by H. C. van de Hulst in 1944)

Green Bank

• 250-foot Jodrell Bank completed in 1957• 1954 NSF, Cal Tech and Dept of

Terrestrial Mag. meet in Washington DC• 1955 NSF provided $85,000 grant for

detailed planning study• 1956 Plan for Observatory completed• Location: free of RFI and within 300 miles

of Washington DC• 1957 first scientists arrived at Green Bank

Jansky Laboratory

Visitor Center

Jansky Antenna

Reber Dish

Ewen-Purcell Horn

The GBT’s PredecessorThe 300 Foot Telescope1960 - Study of various design concepts

1960 - Oct: 300-ft transit concept chosen

1960 - Nov: Bob Hall designs the telescope

1960 - Dec to 1961 - March: Design refined

1961 - March: Construction Bids Requested

1961 - April: Construction Contract signed

1961 - May: Groundbreaking

1961 - Dec: Steel Work Completed

1962 - Spring: Surface attached Electronics installed

1962 - Sept: 300-ft Telescope Completed

Total time: 23 months

Total cost: $1.2M

National facility for 26 years

The 300 Foot Telescope

15 November 1988

The 300 Foot Telescope

16 November 1988

What makes theGBT Unique?

Largest MovingObject on Land

• 100 meter diameter

• High sensitivity (to low surface brightness)

• Fully steerable, tracking all declinations ≥ -46°

• Coverage of 85% of the entire celestial sphere

• Unblocked optics – high dynamic range

• Useable 75 MHz to ~100 GHz

• National Radio Quiet Zone (unique in the US)

Green Bank Telescope

• 100 x 110 m section of a parent parabola 208 m in diameter• Cantilevered feed arm is at focus of the parent parabola

Unblocked Aperture

Active OpticsQuadrant Detector LaserStructure Temperature

Air TemperatureIR Camera

Structure Temperatures (4)Air Temperature

Structure Temperatures (2)

Structure Temperatures (2)Structure Temperatures (2)

Air Temperature

Structure Temperatures (2)Air Temperature

Quadrant Detector2-Axis Inclinometers (2)

3-Axis Accelerometers (2)Elevation Encoder

Air Temperature

3-Axis AccelerometerStructure Temperatures (4)

Structure Temperatures (3)

Structure Temperatures (2)

Structure Temperature

Azimuth Encoder

Frequency Coverage

National Radio Quiet Zone

• Established by an actof congress in 1958

• Approx. 13,000 sq.mile area

• Requires coordinationfor all permanent,fixed, licensedtransmitters

• Administered throughNRAO Green Bank forthe mutual benefit ofNRAO and SugarGrove Naval Facility

GBT Structure

GBT Surface

GBT ReceiversName Freq (GHz) Polarisation Beams Trec Tsys

PF1 0.290-0.395 Lin/Circ 1 12 46

PF1 0.385-0.520 Lin/Circ 1 22 43

PF1 0.510-0.690 Lin/Circ 1 12 22

PF1 0.680-0.920 Lin/Circ 1 21 29

PF2 0.910-1.230 Lin/Circ 1 10 17

L-band 1.15-1.73 Lin/Circ 1 6 20

S-band 1.73-2.60 Lin/Circ 1 8-12 22

C-band 3.95-5.85 Lin/Circ 1 5 18

X-band 8.00-10.1 Circ 1 13 27

Ku-band 12.0-15.4 Circ 2 14 30

K-band 18.0-26.5 Circ 2 21 30-40

Ka-band 26.0-40.0 Circ 2 35 50

Q-band 39.2-49.8 Circ 2 40-70 67-134

Prime Focus Receivers

Gregorian Focus Receivers

GBT Gregorian Receivers

GBT BackendsDigital Continuum Receiver (DCR)• General purpose pointing, focus and beam-map calibrations, and point-

source on/offs, extended source mapping, etcCaltech Continuum Backend (CCB)• Sensitive, wideband exclusively with Ka-band (26-40 GHz) receiver.

Provides optimized RF (not IF) detector circuits and rapid beamswitching tosuppress instrumental gain fluctuations

Spectrometer• Various spectral line observing modes: auto and cross correlations; dual

polarization IFs in a range, different feeds, or combinations.Wide BW 800 and 200 MHz or narrow BW 50 and 12.5 MHz

Spectral Processor• Fast Fourier Transform (FFT) for high time-resolution pulsar observations.

Also total power or frequency switched spectral line observations wherestrong interference is a problem

Spigot Card• Supports pulsar observations by taking output from the Spectrometer's A/D

samplers and dumping the data to disk.VLB• Observations are supported with a Mark5 VLBA recorder. Can also be used

in a "single-dish" mode to make high time-resolution observations

Collecting Area Gain

Incredible gain (point source response)

Gain = 1.5 K/Jy

The GBT is an extremelyfast telescope

2' FOV3.9900.5"-36"0.393516-25ATCA 6x23m

2' FOV1.5340.1"-3"1.950-8018-26.5(E)VLA 27x25m

Interferometers

28643120"0.074516-25Mopra 23m

3580072"0.1512020-25Haystack 37m

only 45m usable3682378"0.1714021-24Parkes 64m

7-beam multibeam, scheduledcompletion date: Dec. 20085.412478"0.6548118-26.5Sardinia 64m

only 3x600 MHz blocks available,limited astronomy time available3.58048"0.7540-8019.9-

24.21Tidbinbilla 70m

3.88840"0.8468-8017.9-26.24Effelsberg 100m

1.02333"1.530-4018-26.5GBT 100m

Single Dish

NotesRelativeT/G

T(sys)/Gain(Jy)

BeamSize

Gain(K/Jy)

T(sys)(K)

Freq.(GHz)Telescope

GBT speed vs comparable telescopes

The integration time required to reach a fixed S/N is proportional to (T/G)2

Telescope diameter Resolution

100 m diameterResolution 8″ at 3mm

At 3mm, comparable to low-resolutioninterferometer observations,but with a filled aperture

Incredible surface brightness sensitivityunique property of the GBT

High Dynamic Range

Balser et al 1995, ApJS, 100, 371.

Effelsberg 100 m GBT 100 m

GBT 2006 Highlights

• Aperture efficiencies of70% at ≤ 1.4 GHz at all elevations45% at 43 GHz at elevations above 20 degrees

• 10 commissioned receivers at 290 MHz - 50 GHz;

• RMS surface accuracy of 350 microns underbenign observing conditions

• More time available for scientific observing(>70% of all hours are scheduled for astronomy)

• First light observations at 3mm, demonstrating thecapability of the telescope at these wavelengths

Backend ImprovementsBaseline performance in all receivers

• Q-band receiver upgraded:expanded frequency range (39.2-49.8GHz) and improved baselines.

• C-band receiver upgraded:Tsys reduced from 22K to 15K.

• The Caltech Continuum Backend:digital backend used with Ka-Bandreceiver taking full advantage of thewideband fast-switching pseudo-correlation receiver, with 14 GHzinstantaneous bandwidth

Improved C-band receiver

GBT Research Areas

• Solar System Studies• Pulsars and Compact Objects• Astrochemistry• Star Formation and Evolution• The Content of Nearby Galaxies• Galactic Evolution• The Universe at High Redshift• Cosmology

Recent GBT Discoveries• 4 new pre-biotic interstellar molecules, shedding light on

the origin of the chemistry of life

• First negatively charged molecule (C6H-) seen in space

• Water megamasers in 21 galaxies – of 100 knownmegamasers, 40 have been discovered with the GBT

• As part of the High Sensitivity Array, the GBT contributedthe critical sensitivity in the first VLBI image of a sub-parsec maser disk at a distance of over 100 Mpc

• Helical magnetic field wrapped around the Orion MolecularCloud, providing insight into the processes by whichmolecular clouds form stars in the Milky Way

Pulsar Science

• Neutron star discoveries include thefastest spinning pulsar, at 716 Hz, in theglobular cluster Terzan 5

• Detection of pulses at 42 GHz from theradio emitting Magnetar XTE J1810-197

• Timing of the Double Pulsar providedstrong-field tests of general relativity withuncertainties at the 0.05% level

Highly Redshifted Lines

GBT spectrum of 12CO (J = 1–0) emission fromQuasar BR 1202-0725 (Riechers et al, 2006)

Discovery of molecular lineemission from four high-redshiftgalaxies, including CO emissionfrom three z > 4 objects

HI and FeII424 MHz at z = 2.35

(Kanekar et al, 2006)

Neutral HydrogenGalactic Superbubble

• HI (neutral hydrogen) haloof the Milky Way near theScutum spiral arm

• 600 square degrees

• 7 kpc from Sun and4 kpc from Galactic center

• Total mass ~ 1M solarmasses

• Energy powering outflow~100 supernova explosions

• 10-30 million years old Yurii Pidopryhora, Jay Lockman and Joe Shields

Huge Superbubble blowingout of the Milky Way

RADAR Images of the Moon• Arecibo Observatory transmits RADAR signal• GBT used as the receiving antenna

Images courtesy of NRAO/AUI and BruceCampbell/Smithsonian Institution

20m resolution imageshows no ice in theShackleton Crater

Mercury's Core Molten• Goldstone 70m antenna transmitted radar beam• GBT and Goldstone received reflected signal• Measured variations in Mercury's spin rate

GB Developments 2007

• GBT track replacement May-August• Further improvements in receiver sensitivity• Begin work on pulsar detector upgrades• Development of Dynamic Scheduling• Improved performance at high frequencies• Zpectrometer for 26-40 GHz• Focal plane arrays?• Single Dish Summer School• Workshop on Pulsars

MUSTANG

• 64 pixel TES bolometer• First light in September

2006 on the GBT• First time a TES bolometer

used for high resolutioncontinuum imaging

NRAO

U. Penn

NIST

NASA/GSFC

U. Penn

Fundedby NRAO

InstrumentationProgramme

Multiplexed SQUID/TES Array for 90 GHz

3mm continuum image of the W3main starforming region acquired with MUSTANG.

PAPER (Precision Array to Probethe Epoch of Reionization)

• Berkeley/ NRAO/ UVA CollaborationSearching for hyperfine (spin-flip)hydrogen transition

• Signature of reionization at the endof the “Dark Ages”

• Prototype in GB NRQZ for deploymentto Western Australia

Solar Radio Burst Spectrometer• Prototype for the Frequency Agile

Solar Radiotelescope (FASR)• Collaboration with U. Maryland• Supported by an MRI grant from

NSF/ATM division• Basic research tool for solar

radiophysics• Data made available to the

community in near real time

Type III Event2007 01 23 18:44 – 18:52

One of a series of events this dayassumed to be over the east limb

NRAO Green Bank45ft radio telescope

Wider Green Bank Activities• Strong University Collaborations

– GBT Instrument Development• Caltech Continuum Backend (Caltech)• MUSTANG (U. Penn / NIST / GSFC)• Zpectrometer (U. Maryland)• New Pulsar Backend (U. Cincinnati, West Virginia University)

– Non-GBT activities (NRQZ use, PAPER…)– Student Support Program– West Virginia University Initiatives

• Education and Public Outreach (EPO) Program• National Radio Quiet Zone

– Unique location for radio work– MIT/LL collaboration (Bi-static Radar collaboration studying Earth's Ionosphere)– Frequency Agile Solar Radiotelescope (FASR) prototype– 20m telescope (test bed for RFI/BFA investigations with Brigham Young University)– PAPER – Berkeley / UVA / NRAO collaboration

• Support of other NRAO activities and other observatories– ALMA and EVLA work– Central Instrument Shop– Anechoic Chamber and Antenna Test Range

• State and local community involvement

The Future….

Imaging Arrays

Continued telescopeperformance improvements

• The GBT is a fantastic telescope,performing great science, with hugepotential for future development

• The Green Bank Observatoryprovides a wealth of resources tothe astronomical community

Summary

Next call for proposals 1 June 2007