1. On the nature of the Long-duration radio transients Eran Ofek CALTECH Collaborators: B. Breslauer, A. Gal-Yam, D. Frail, S.R. Kulkarni, P. Chandra, M. Kasliwal, E. Waxman, N. Gehrels Einstein Fellows symposium October 2009

2. Talk Layout Summary of observational facts New observations What are they? Speculations… A new class: Long-duration radio transients

3. Bower et al. (2007) 944 epochs, 1/week, for 22 years @ 5GHz 7 transients, fluxes: 0.3-1.7mJy Time scale 20 min Optical counterparts: g>27.6, R>26.5, K>18 No X-ray in ROSAT Galactic latitude: b~37 o Circular polarization <30%

4. Long-duration radio transients Lack of counterparts Ofek et al. 2009 K>20.4 mag

5. A Search for Radio transients Comparison of the NVSS and FIRST radio surveys Area: ~2500 sq. deg Flux limit: 6mJy @ 1.4 GHz Levinson et al. (2002) Gal-Yam et al. (2006) The FIRST-NVSS survey 1 transient candidates (SN in NGC4216)

6. Yet, some more… Kida et al. (2008)… 6 bright (>1 Jy) transients detected by the Nasu Pulsar Observatory, No localization Similar time scales (~<1 day)

7. Long-duration radio transients Rates

8. Long-duration radio transients Log N – Log S Ofek et al. 2009

9. Long-duration radio transients Surface density of progenitors 7 events within ~8’ in Bower et al. (2007) Sky surface density  >60 deg -2 (@95% CL) If repeaters If catastrophic Number of progenitors in the Universe >4x10 16 @ b~37 o rate

10. Progenitors – Extragalactic? Ovaldsen et al. (2007) analytic

11. Progenitors? - Galactic Many Galactic progenitors are ruled out: Flare stars, X-ray binaries, pulsars, magnetars, Evaporating BHs, microlensing, Floating planets, solar flares reflected from asteroids…

12. Isolated-old NSs? Large population in the Galaxy: 10 8 -10 9 Large energy reservoir: rotational, magnetic, accretion High velocities @ birth Large scale height Abundant at high Galactic latitudes

13. Isolated-old NSs? Ofek 09, Ofek et al. 09 All Birth rate Init. Vel. Dist.

14. Isolated-old NSs? Distance distribution at the direction of the Bower et al. field

15. Energetics – NSs? Ofek et al. 2009 Repetition time scale: Mean luminosity: 10 25 erg s -1 Total energy: 10 43 erg Magnetic: ~10 41 erg Rotational: ~10 44 erg Accretion: ~10 45 erg NSs Energy reservoir

16. Isolated-old NSs? Fireball model – Incoherent synchrotron radiation

17. Isolated-old NSs? Fireball model – Incoherent synchrotron radiation

18. New observations 30 VLA hours (August 2008) Target: 150 fields at low Galactic latitude 11 epochs Ofek et al., in prep.

19. New observations 30 VLA hours (August 2008) Target: 150 fields at low Galactic latitude 11 epochs Followup: VLA + Swift/XRT + P60/P200/Keck Excpectation: ~1 event, detect: 0 (above 2 mJy) Several fainter events still under investigation. For 3 most promising - no optical counterparts i~24 + for one source - no XRT source within 2 days

20. Predictions If transients are NSs… Repetition time scale ~ 3 month Spectral slope – syn. Self absorption More abundance towards the Galactic center, but details depends on flux limit and distance Pulsations? – search for pulsars at 5 GHz Linear polarization, if incoherent syn. radiation

21. End