1. The Transient Universe: AY 250 Spring 2007 Existing Transient Surveys: Radio II: Interferometric Surveys Geoff Bower

2. The Transient Universe: AY 250 Spring 2007

3. Radio Variability From AGN Aller, Aller & Hughes 1985

4. The Transient Universe: AY 250 Spring 2007 Variability Drives Jet Structure Bower et al 1997 NRAO 530

5. The Transient Universe: AY 250 Spring 2007 Activity Decreases with Timescale Hughes, Aller, & Aller 1992

6. The Transient Universe: AY 250 Spring 2007 Intra-day Variability 0917+624 Wagner & Witzel 1995 % change in flux

7. The Transient Universe: AY 250 Spring 2007 Brightness Temperature Representation of intensity (flux density per solid angle) –Tb ~ Flux Density * Lambda^2 / Omega Tb ~ Te ( 1 – e^-tau ) –  Tb ~ Te when optical depth is large

8. The Transient Universe: AY 250 Spring 2007 Intrinsic Origin for IDV Fluctuations in the small scale structure of the source Time scale  Size –1 hour  10^14 cm ~10 AU ~ 10^-4 pc –Theta ~ r/d ~ 10^-4/10^9 ~ 10^-13 ~ 0.01 microarcsec –Tb ~ 10^19 K (S/1 Jy) * (lambda/1cm)^2

9. The Transient Universe: AY 250 Spring 2007 But…

10. The Transient Universe: AY 250 Spring 2007 Inverse Compton Catastrophe B e- As source is compressed, IC increases exponentially. Radiation runs away at temperature 10^12 K.

11. The Transient Universe: AY 250 Spring 2007 Relativistic Beaming Effects of relativistic beaming can enhance Tb by D^3  Tb_intrinsic ~ 10^16 K Still strongly inconsistent with IC catastrophe and observed distribution Blandford & Konigl

12. The Transient Universe: AY 250 Spring 2007 Extrinsic Origin for IDV Refractive interstellar scintillation –Wave samples different zones in the turbulent interstellar medium, interferes with itself –Theta_source < Fresnel Zone ~ sqrt(lambda/D) ~ 10 microarcsec –  Tb ~ 10^13 K (for earlier example)

13. The Transient Universe: AY 250 Spring 2007 J1819+3845 Dennett-Thorpe & deBruyn

14. The Transient Universe: AY 250 Spring 2007 J1819+3845

15. The Transient Universe: AY 250 Spring 2007 J1819+3845 Observed delay of -100 sec to +100 sec Earth radius delay: 20 msec Earth+Sun motion delay: 3 sec  Delay must be in changing interstellar path length  Frozen fringe is sweeping over the Earth Delay & baseline implies fringe velocity –Removing Earth+Sun gives 10s km/s Characteristic time scale of variations & fringe velocity gives size scale of fringe –10^5 km

16. The Transient Universe: AY 250 Spring 2007 Annual Variations PKS 1257-326 Bignall et al 2003

17. The Transient Universe: AY 250 Spring 2007 Quenching in Annual Variations

18. The Transient Universe: AY 250 Spring 2007 Microarcsecond Frequency Structure Model corresponds to 10^4 km separation at distance of ISS At 10 pc,  10 microarcsec resolution Or… a refractive effect

19. The Transient Universe: AY 250 Spring 2007 MASIV A systematic VLA search for IDV 700 sources 1min/2hr – 5 subarrays Lovell et al 2003

20. The Transient Universe: AY 250 Spring 2007

21. Fraction of Sources with IDV 15%