1. 2nd Zwicky Workshop - Transients - 05may25 INTRODUCTORY REMARKS D. C. Backer Astronomy Department & Radio Astronomy Laboratory, UC Berkeley

2. 2nd Zwicky Workshop - Transients - 05may25 As we know, There are known knowns. There are things we know we know. We also know There are known unknowns. That is to say We know there are some things We do not know. But there are also unknown unknowns, The ones we don't know We don't know. Department of Defense news briefing Feb. 12, 2002 THE UNKNOWN

3. 2nd Zwicky Workshop - Transients - 05may25 Sources & Time Scales -- Generic Gravitational collapse – (G rho) -0.5 : e.g., star core ~ 1 s Nuclear – L/V s : e.g., NS accretion layer ~ 1 km/0.1 c?? Electromagnetic – L/c : e.g., PSR GP ~ 1 m/c ~ 3 ns Magnetic – L/V B : e.g., magnetar ~ 1 km/? Electrostatic – L/c : e.g., lightning, EMP Spin/Orbit? – gravity again? – Kepler time Mechanical – L/c s : e.g., neutron star crust Sites: factories for exotica in globular clusters & MBH galaxy cores, and also more prosaic environs of compact binaries

4. 2nd Zwicky Workshop - Transients - 05may25 Calculus Density, n = Birth Rate/Volume * Life Time Luminosity Function, dn/dL Flux = Luminosity / 4 pi Distance 2 Detections = 4/3 pi Distance 3 Density(Flux)

5. 2nd Zwicky Workshop - Transients - 05may25 Pulsars "We did all the work ourselves and cheerfully sledgehammered all one summer." Burnell and the antenna. THE FIRST FOUR While pursuing her PhD at Cambridge University, Jocelyn Bell’s advisor was Antony Hewish, a radio astronomer. Hewish and his graduate students in 1967 completed a radio telescope specially designed to observe the scintillation (twinkling) of stars, particularly quasars. That summer, she observed an unusual signal at a wavelength of 3.7m -- unusual in that it corresponded to a sharp burst of radio energy at a regular interval of about one second. These were not like signals from other known sources such as stars, galaxies, or solar wind. While continuing with her actual Ph.D. research, Bell identified a second piece of 'scruff' close to Cassiopea A (itself a supernova remnant) and managed to capture the regular pulses about 1 second apart. This significantly reduced the possibility of distant life, and Bell went back through the miles of chart data that she had accumulated looking for more 'scruff'. She identified two more lots of 'scruff' and several other potential anomalies. These additional discoveries confirmed to Hewish and Bell that this was neither man-made interference, nor was it (probably) alien life, but was some form of emission from these stars.

6. 2nd Zwicky Workshop - Transients - 05may25 Crab : Staelin & Reifenstein 1968 (Science) PSR B0531+21 - CrabPSR B0525+21 P-ALFA: 1/11 found via single pulses Parkes MB: ~20/800 M31/M33: “tantalizing” – J. Cordes

7. 2nd Zwicky Workshop - Transients - 05may25 Crab Giant Pulses Tip detectable out to Virgo cluster!

8. 2nd Zwicky Workshop - Transients - 05may25 Nature 422, 141 - 143 (13 March 2003) Nanosecond radio bursts from strong plasma turbulence in the Crab pulsar T. H. HANKINS, J. S. KERN, J. C. WEATHERALL & J. A. EILEK ns 2 ns resolution at 5 GHz; periodic frequency structure

9. 2nd Zwicky Workshop - Transients - 05may25 4C 21.53 – A Millisecond Pulsar – B1937+21 End of 19 th Century – photoelectric effect: small anomaly amidst grand edifice of Physics; takeoff point for Einstein & quantum world. Compact, steep-spectrum (high T B ) “weird” source in Crab Nebula (Hewish & Okoye c. 1960). “Calibrator” for DB’s MSc project – 20- km, 38-MHz interferometer – summer 1967. Pulsar 9 months later. Hewish scintillation array discovers zone of avoidance for IPS objects along plane – Readhead et al. Anomaly stood out: 4C 21.53. Tony R. told me about this in Fall 1979 at 1d astrophysics mtg at Caltech. I followed up and even wrote a speculative paper about confusing data. Westerbork image at 610 MHz in 1982 confirmed speculations and triggered Arecibo campaign starting with Shri K and Mike D observations in Sep 1982. Seen early as interstellar scintillator.

10. 2nd Zwicky Workshop - Transients - 05may25 Interstellar Scattering 101 Lesson 1: basic physical optics Lesson 2: source at finite distance D and screen at xD 6.5. Critical Size, Theta_c<l_o/D