1. Probing the field of Radio Astronomy with the SKA and the Hartebeesthoek Radio Observatory: An Engineer’s perspective Sunelle Otto Hartebeesthoek Radio Astronomy Observatory (HartRAO) July 2011

2. Outline Introduction The Square Kilometre Array - Background, Pathfinders, Key Science Projects, System design Hartebeesthoek Radio Astronomy Observatory - Background, Research work Conclusion

3. Introduction MSc (Electronic Engineering) at Stellenbosch University - thesis work on SKA Intern at HartRAO (Hartebeesthoek Radio Astronomy Observatory) - research work Stellenbosch University

4. Background Square Kilometre Array (SKA) largest, most sensitive radio telescope thousands of small dishes and aperture arrays total collecting area of 1 km² South Africa vs. Australia International project smaller projects to assist in research SKA pathfinders to demonstrate the technologies The Square Kilometre Array SKA configuration design

5. Pathfinders MeerKAT (South Africa) Started with the XDM (eXperimental Development Model) 15m diameter parabolic reflector dish 7 horn cluster feed Located at HartRAO The Square Kilometre Array XDM antenna 7 horn feed

6. Pathfinders KAT-7 (Karoo Array Telescope) Array of 7 parabolic reflector antennas each 12m in diameter Wide-band single pixel feeds (WBSPFs) Demonstrates working of an interferometer The Square Kilometre Array KAT-7

7. Pathfinders MeerKAT: final phase of KAT 64 offset Gregorian antennas 13.5m diameter unblocked aperture multiple receiver systems The Square Kilometre Array MeerKAT antenna design (credit: SKA fact sheet 1: MeerKAT, June 2011, www.ska.ac.za)www.ska.ac.za

8. Pathfinders ASKAP (Australian Square Kilometre Array Pathfinder) Goal: 36 parabolic reflectors each 12m diameter Phased array feeds (PAFs) Multiple beam formation capability The Square Kilometre Array ASKAP Phased Array Feed

9. Pathfinders EMBRACE (Electronic Multi Beam Radio Astronomy Concept) THEA (Thousand Element Array) Dense Aperture Arrays Vivaldi antennas LOFAR (Low Frequency Array) Sparse Aperture Arrays Dipole antennas The Square Kilometre Array Dense Aperture Array Sparse Aperture Array

10. Key Science Projects Science observations requested by the radio astronomers, SKA drivers The Cradle of Life - terrestrial planet formation, molecular chemistry and the search for intelligent life Strong-Field Tests of Gravity using Pulsars and Black Holes - Pulsar search and timing, test relativistic gravity and detect gravitational waves The Origin and Evolution of Cosmic Magnetism - map the origin and evolution of magnetic fields Galaxy Evolution, Cosmology and Dark Matter - study the cosmic evolution of HI (neutral hydrogen), dark energy and dark matter Probing the Dark Ages - study the epoch of reionisation (EoR) The Square Kilometre Array

11. System design The Square Kilometre Array

12. Hartebeesthoek Radio Astronomy Observatory (HartRAO) Background HartRAO is the only major radio astronomy observatory in Africa; KAT-7 is still in testing, MeerKAT in design phase 26m radio telescope Single dish observations VLBI (very large baseline interferometry) 26 m Telescope at HartRAO

13. Pointing model Telescope needs to find and track sources accurately Need good pointing model Pointing scans for various sources Data used to improve the pointing model HartRAO – research work Hour Angle pointing error vs HADeclination pointing error vs HA

14. Rubidium and Hydrogen Maser clocks Hydrogen Maser - frequency standard, accurate timing Rubidium clock, GPS10RB - Less accurate, corrects time by periodically comparing it with GPS (global positioning system) satellites Measure difference between :  Maser and Rubidium clock times  Maser and GPS clock times performance of Rubidium HartRAO – research work

15. Rubidium and Hydrogen Maser clocks slope in the graph : frequency drift of the Maser clock Phase noise: due to GPS signal path variations through the atmosphere HartRAO – research work Rubidium vs Hydrogen maserGPS vs Hydrogen maser

16. Rubidium and Hydrogen Maser clocks 5min averages made, see how Rubidium follows the GPS Look at frequency stability: Rubidium has short term stability, while GPS has long term stability HartRAO – research work 5min averages (Rubidium, GPS)Frequency stability (Rubidium, GPS)

17. Building a 1.4GHz receiver Receiver for a satellite TV antenna 3m diameter Testbed for demonstrating practical radio astronomy at school and University level Cylindrical waveguide horn feed with choke ring HartRAO – research work 3 m dish with 1.4 GHz receiver

18. H₂0 Maser in Orion KL Observations of H₂0 Masers in the Orion KL source region 22GHz March 2011 to present Why? Flares occurred in 1984, 1998 Flux density reached millions of Janskys HartRAO – research work Orion KL

19. H₂0 Maser in Orion KL Average spectrum Flux Density: 80,000 Jy compare with data from 2007 when maser was not flaring (light blue) HartRAO – research work Average spectrum (lcp and rcp added)

20. H₂0 Maser in Orion KL Time series plot at main peak velocities HartRAO – research work Time series plots (lcp)

21. Conclusion The Square Kilometre Array - Pathfinders - Key Science Projects - System design Hartebeesthoek Radio Astronomy Observatory - Pointing model - Rubidium and Hydrogen Maser clocks - 1.4GHz receiver - H₂0 Maser in Orion KL

22. Thank you!