1. Radio Astronomy The 2nd window on the Universe:
The atmosphere is transparent in the centimeter & meter bands
< 5 mm mostly absorbed by molecular bands
>15 m or so, absorbed or reflected by the ionosphere
Draw picture for AM and FM and show plasma frequency formula:

2. Summary History of Radio Astronomy
Karl Bell Labs was researching noise in “short wave” radio communication.
Aside from thunderstorms, he found (1932) a steady hiss, peaking with sidereal, not solar, time
Localized to Sagittarius (center of galaxy) 20.5 MHz
Grote Reber -- working at home, made a dish 160 MHz: confirmed Milky Way origin
Also detected the Sun and Jupiter
WWII led to development of radar; afterwards many of these physicists and electrical engineers became
RADIO ASTRONOMERS: US, England, Netherlands, Australia, Germany & Russia

3. Astronomical Emitters of Radio Waves
Symbiotic stars (LR/LO < 10-6 for most stars!)
“Microquasars”: some X-ray binaries
Pulsars
Supernova Remnants
Radio Galaxies
Quasars (and other AGN)

4. Big Advantages of Radio Astronomy
Can observe DAY & NIGHT
Can penetrate clouds
Only stopped by strong winds, thunderstorms and snow!
Radio interferometry can produce better resolution than optical astronomy!

5. Disadvantages of Radio Astronomy
Powers received are very low, since each photon has a small h
 need big collectors (dishes)
Angular resolution is poor: /d
Optical: to get ~0.5 arcsec, =500nm
 d~50 cm (but can’t do much better w/o AO or optical interferometry)
Radio: to get ~0.5 arcsec, =5cm
 d~50 km
Thus, radio astronomers need interferometers

6. Radio Telescopes NRAO Very Large Array NRAO Very Long Baseline Array
NRAO Green Bank Telescope
TIFR Giant Metrewave Radio Telescope
MPIfRA Effelsberg Radio Telescope
NAIC Arecibo Radio Dish

7. VLA in Closest Array

8. More VLA photos
27 antennas, each 25 m diameter
Maximum baseline 36 km

9. VLBA: 10 25m dishes, 8000km baseline

10.  GBT: largest steerable RT: 110x100 m 
Asymmetric design keeps feeds off to side: no struts and diffaction from them
Works from 3m down to 3mm
Best for pulsar studies and molecular lines

11. GMRT: largest collecting area
Mesh design, good enough for long wavelengths
30 telescopes, 45 m aperture, maximum baseline: 25 km

12. Effelsberg: 2nd largest steerable dish
100 m aperture
Good for 800 MHz to 96 GHz

13. Arecibo: 305m fixed dish

14. Some Basics of Radio Telescopes
Key considerations:
Effective area  Gain (so antenna patterns are important)
Beam width  Resolution
Bandwidth, : different feeds at different 
Wider  gives stronger signal, but narrower gives better spectral resolution
Antenna temperature: TA = P / (kB )
Sizes of sources compared to beams
Fluxes: Sun: 4 MHz  GHz
SNR: Cas A: 2 MHz
1 Jansky = Jy = W/m2/Hz = erg/s/cm2/Hz
Diagrams and equations on the board

15. Radiographs Colors usually indicate fluxes: red is brightest
Images of supernova remnants
Pulsars and nearby shocks and jets
Black holes: jets in microquasars
Star forming regions
Galactic structure
Radio galaxies
Quasars

16. Tycho’s SN remnant

17. Crab SNR and Pulsar

18. W50, SNR home of microquasar SS433

19. Cas A: SN1680?: Inner ejecta crossing swept up shell

20. SN 1993J in M81 from some VLBA+ VLA+ EVN+ NASA

21. SN 1993J from VLBA

22. Pulsars in Globular Cluster M62

23. “The Duck”, pulsar moving at ~500 km/s

24. Sco X-1: jets from pulsar in binary: VLBA + APT + EVN

25. SS 433: bullets at 0.26c

26. X-ray Nova GRO J1655-40: microquasar
Apparent v=1.3 c from actual speed of about 0.9c
Approaching jet also has Doppler enhanced flux
WRITE ON BOARD EQUATIONS FOR

27. Superluminal Motion? Vapp=Vsin/[1-(V/c)cos]
=1/(1-2)1/2 , with =V/c
=1/ (1- cos)
Sobs=Sem n+ , with n=2 for smooth jet and n=3 for knot or shock
For large  and small  (~1/ ) this boosting factor can be > 10000!

28. Microquasar GRS 1915+105 Apparent v = 1. 25 c from v = 0
Microquasar GRS Apparent v = 1.25 c from v = 0.92 c BH mass about 16 Suns

29. Star Wind Interaction w/VLBA
Both O star and
Wolf-Rayet star (evolved O star) eject strong winds and when they collide they form a curved hot region which radiates and accelerates charged particles

30. W49A: from VLA Ultracompact HII regions around newly forming hot stars using 7mm wavelength for high resolution

31. M17: star forming region w/ GBT
Omega nebula
3.6 cm or 8.4 GHz
image

32. Atomic H in Our Galaxy: GBT et al.

33. M33: Doppler shifts show rotation
Used VLA measuring H 21cm spin-flip line to map atomic hydrogen, with spatial resolution of 10”
Color coded to blue approaching and red receding: velocity resolution km/s,
Includes Westerbork data for total intensity

34. 3C31: FR I Radio Galaxy

35. 3C 130 & 3C 449: FR I’s

36. 3C75 in A400: Two Merging Cores of cD

37. M87 Jet to Bubble Montage

38. Compact Symmetric Source: 4C31.04

39. Canonical FR II: Cygnus A

40. Quasar: 3C 175

41. 3C 227: RG, z=0.086 w/ Polarization Map
From Black et al., MNRAS, 256, 186

42. Quasars 3C215 (weird) & 3C263 (normal)

43. 3C353: Peculiar FR II

44. VLBA + Space antenna HALCA: 1156+295

45. VLBA of 3C279: Apparent Superluminal Motion with Vapp=3.5c: really V=0.997c at viewing angle of 2 degrees