1. 1 Reflections on the discovery of pulsars (pulsating radio stars) Jocelyn Bell Burnell University of Oxford Astrophysics And Mansfield College

2. 1957 2

3. 3 Crab PSR almost discovered I Late summer 1957; an Open Night at McDonald; 82 inch (Struve) telescope trained on Minkowski’s star. Elliott Moore (newly graduated from Chicago) was assisting. Female visitor – ‘That star’s flashing’ No instruments existed to provide follow-up.

4. 1966 4

5. 5 PSR 0329+54 almost discovered January 1966 408 MHz survey (Europe) using large telescopes Last week of observing; one pen-recorder misbehaving Early hours of morning, that pen recorder started ‘misbehaving’ Observer said ‘Damn!’ and thumped pen recorder – behaviour stopped!

6. 6 PSR0329 +54 contd Observer said 'Good!', put on his coat and went home!........ He had made the first observation of PSR 0329+54. No entry in log book Following the discovery of the first pulsars (which did not include 0329+54) no search of their data for pulsars.

7. Oct/Nov 1967 7

8. Crab PSR almost discovered II Sue Simkin (NRAO) – Oct/Nov 1967 Carnegie Image Spectrograph, Kitt Peak 84-inch telescope. Lo Woltjer asked her to take a spectrum of Minkowski's star. Spectrum dull, but Sue observed flickering, or as if there were waves going out from it. LW said it couldn't be, but when PSR discovered said it must have been.

9. 1967 - 8

10. Crab Pulsar – almost - III E-mail message received by ATNF, June 2007 from Charles Schisler: “As a USAF technician during a one year period back in 1967-68 at a Ballistic Missile Early Warning Site in Alaska I discovered fourteen pulsing signals on our extremely powerful radars….”

11. Crab Pulsar – almost - II Not related to our mission my Air Force supervisors did not appreciate the possible scientific implications of my discovery. And the highly classified nature of our work made it impossible for me to publish, etc…..contd

12. 12 Crab Pulsar contd…. “At the time I carefully made notes and their approximate location by RA and Dec. Ten or eleven of them have been identified as being pulsars as I have just discovered from the ATNF catalogue of 1771 pulsars. It is possible that all of them were pulsars. The first one that I discovered back in 1967 was the Crab Nebula and may have been the first pulsar ever noted by anyone……I am now 81 years OLD but I am still curious about a very exciting thing that happened to me forty years ago!”

13. 1967 - 8 The actual discovery 13

14. 14 First build your radio telescope (through hail, rain and sunshine) 2048 81.5MHz λ/2 antennae (16 E-W rows of 64 + 64), 1000+ wooden posts, 120 miles/192 km wire and cable, area 57 tennis courts. Grant £12k. 6 people for 2 years. Typical working conditions for a PhD student?

15. The 4.5 acre * radio telescope ( * 1.8 hectares), looking W Interferometric array; phased with delay cables; operated with 4 beams. Valve phase-switching receiver!

16. 16 The programme Using interplanetary scintillation to identify quasars (and measure their angular diameter) Short time constant (short integration time) essential – IPS produces a rapidly fluctuating signal. τ = 0.1 s. 6 months’ observing, starting July 1967

17. Data analysis No computer! 3-pen chart paper 100’ (30m) / day 400’ (120m)/sky scan 3.3 miles (5.3km) total

18. Discovery of pulsars II Occasionally ¼ ” (0.5 cm) in the 400’ (120 m) showed an unusual signal. ‘Occasionally’ = 15% of the occasions that part of sky observed

19. High-speed recording Centre trace shows pulsed nature of emission

20. The naming of pulsars Interviewed by Science Correspondent of The Daily Telegraph – Anthony Michaelis – shortly after the discovery What were we going to call them? He suggested pulsar – cf quasar 20

21. 21 Why then? Pulsars, quasars, CMB, molecules, masers…..

22. Possible factors Computers? No – arriving but not yet arrived Transistors? No – arriving but not yet arrived Post WWII technology kicking in? – Unlikely – it’s two decades since the end of the war. Space race, drawing attention to astro? Critical mass of radio astronomers? 22

23. Possible factors Computers? No – arriving but not yet arrived Transistors? No – arriving but not yet arrived Post WWII technology kicking in? – Unlikely – it’s two decades since the end of the war. Space race, drawing attention to astro? Critical mass of radio astronomers?  23

24. 24 Key factors in the discovery Our own telescope and receiver – I understood its behaviour. One of the first observations with a short time constant (new area of phase space). As a research student I had time/space to follow-up anomalies. ‘Imposter syndrome’.

25. 25 Key factors, contd If we had computerised the search, would the pulsars have been discovered? We had a good address – a reputable laboratory. Essential for getting published!

26. 26 The End