1. Signs of the Blandford & Znajek mechanism in GRB afterglow lightcurves
Antonios Nathanail
ITP Frankfurt, University of Athens
Geneva 2015

2. We want to argue that the rapid decay phase of the afterglow (X-rays), is nicely described as the spin down of a slowly rotating black hole (Blandford-Znajek mechanism)

3. ANATOMY OF A BURST

4. ANATOMY OF A BURST Central engine extended activity
Tagliaferi et al. 2005
Ghiselini et al. 2009
Zhang et al. 2014

5. ANATOMY OF A BURST Central engine extended activity Off-axis radiation
Tagliaferi et al. 2005
Ghiselini et al. 2009
Zhang et al. 2014
Off-axis radiation
Steep power law

6. Small Break for theory

7. Why not a slowly rotating black hole
Small Break for theory
Spin of BH …
Why not a slowly rotating black hole

8. Small Break for theory Loosing Energy as ……. Stellar mass black hole
slowly rotating
Ω angular
velocity
Strong magnetic fields expected
Loosing Energy as …….

9. Small Break for theory Loosing Energy as ……. Stellar mass black hole
slowly rotating
Ω angular
velocity
Strong magnetic fields expected
Loosing Energy as …….

10. Small Break for theory Loosing Energy as ……. magnetic flux
Blanford & Znajek 1977
……...
magnetic flux

11. Small Break for theory Loosing Energy as …
Nathanail & Contopoulos 2015
Nathanail, Strantzalis & Contopoulos 2015

12. Small Break for theory
Loosing Energy as …

13. Can This Be observed Luminosity?

14. ANATOMY OF A BURST

15. Zoom in the rapid decay phase
Nathanail, Strantzalis & Contopoulos 2015

16. From 343 Long GRBs 30% had this sign
Nathanail, Strantzalis & Contopoulos 2015

17. Duration of a GRB depends on the magnetic field strength
Nathanail, Strantzalis & Contopoulos 2015

18. Extraordinary duration ...
Easy to explain
Ultra Long GRBs
Extraordinary duration ...
Nathanail & Contopoulos 2015

19. magnetic field strength
From the timescale
we can estimate the
magnetic field strength
at the black hole
Nathanail & Contopoulos 2015
Nathanail, Strantzalis & Contopoulos 2015

20. The Rest 70%
The rapid decay
phase is not
entirely seen
sparse
data

21. Mass infall-Flaring Activity
Proga & Zhang 2006
magnetic barrier
X-rays
spin down mass infall again spin down (spin up)
in preparation . . .

22. 30% of Long GRBs show signs of Black Hole Spin Down
Summary
30% of Long GRBs show signs of
Black Hole Spin Down
Duration of a GRB depends on the magnetic field strength