UN/ESA/NASA/JAXA Workshop on Basic Space Science and IHY 2007, Daejeon, Korea

1. Are GRBs events the most violent events in the Universe? UN/ESA/NASA/JAXA Workshop on Basic Space Science and IHY 2007, Daejeon, Korea Ericson Lopez ObservatorioAstronomico de QuitoQuito,Ecuador

2. Quito AstronomicalObservatory • Founded in 1873 • Latitude:0º12'53.70'' • Longitude:78º30'9.20'' • Altitude:2 818,05 m

4. ASTRONOMICAL HERITAGE Instrumentos de paso

6. Big Telescopes focal distance 200cm, lens: 162mm. Focal distance: 319cm lens: 238mm

10. Outline of Talk: • Review of Gamma Ray Bursts • Fireball model for GRBs • Some Fundamental Problems • Relativistic Kinematic • Relativistic Model • Conclusions

11. Quick Review History of GRBs: • 1967- Discovery by American military Vela satellite of GRBs 1973 – Declassified for scientific community End of 1970s – `Konus’ experiments onboard Russian Veneras (E.P.Mazets et al) • 1991-2000 – `BATSE’ (CGRO) era. Largest homogeneous data (a few thousands) on GRBs. Debates on galactic vs extragalactic origin • 1997-… Afterglow era. Discovery of afterglows in X-ray (BeppoSAX, 1997), optical, radio. Triumph of cosmological model for (long) GRB origin. Multivawelength GRB astronomy • 1998 – possible association of GRB980425 with nearby peculiar type Ic SN1998bw. Start of hypernova era (?)

12. Observed: Duration: 0.1-1000 s Fluence: S~10^-7--10^-3 erg/cm2 Spectrum: nonthermal, 10keV-100 MeV Variability: high, 1-10 ms Rate: 1 per day Location: z=0.17-4.5, Associated events: X-ray (~100%), optical (~70%), radio (~50%) afterglows F(t)~t-αα~1-2 + Environment signatures: transient X-ray em./abs. lines, metal rich material Derived (for long GRBs only!): Isotropic energy release Eγ=4πdl^2/(1+z) ~10^51 -10^54 erg (but 980425 ~10^48) Evidence for jets from afterglow breaks θj~0.01-0.1 Points to ‘standard’ energy release ΔE~10^50-10^51erg equally shared in kinetic energy and radiation Photon energy correlations vFν~Eiso Association with SN Ib/c General properties

13. BATSE rate ~1 per day No repetions, full isotropy Light Curve: GRB 990123 BATSE Evidence for Cosmological Origin of GRBs

14. Classes of Gamma Ray Bursts 1. (Classical) Long-duration GRBs2. Short-hard class of GRBs3. X-ray rich/X-ray flashes4. Low Luminosity GRBsSoft Gamma Repeaters (SGRs)

15. FIREBALL MODEL FOR GRBs Rees & Meszaros (1992, 1994…) Recent review: Piran 2004 The problem of the high opacity for all photons about the pair-creation threshold. Fireball model by Piran (1993). Internal shocks  GRB itself External shock in ISM  X-ray, optical, radio emission of the GRB `afterglow” The optical thickness problem Initial interaction of GRB ejecta  Reverse shock propagating inward and decelerating fireball ejecta.

16. X-RAYS g-RAYS OPTICAL INTERNAL SHOCK RADIO EXTERNAL SHOCK Fireball Model 1000-2000 AU 1-6 AU G2 G1 ISM 20 km

17. FUNDAMENTAL PROBLEMS How the energy escape the compact region? How to produce 1054 erg?

18. RELATIVISTIC KINEMATICS • To resolve this fundamental problem of opacity… • In this context, we analyze the problem of large opacity as a relativistic illusion • Causes by the emitting plasma of gamma-rays, which is moving relativistically as a whole.

19. Relativistic Plasma Motion • Models involving the relativistic bulk motion of the of gamma-ray emitting plasma match the theory with high-energy photons observed to escape in theGRB events. • Krolik& Pier (1991) remarkable and clearly exposed the potential of relativistic bulk motion of the emitting plasma in order to provide an elegant solution to the problem of large opacity.

20. Doppler Aberration * We propose further considerations which must be taken into account in the relativistic moving models for GRBs. The moving plasma is considered as relativistic fluid The main physical parameters of the emitting material, must be reduced or boosted by a suitable potency of the Doppler Lorentz factor:

21. Relativistic Boosting Spherical blob in comoving frame rb=r´b G Doppler Factor Source size from temporal variability: Variability timescale implies maximum emission region size scale

22. Then, for the observer, the radiation is not more isotropic. G(x) 2qj And, now we must pay attention in deducing the corrected relation for transformed Flux density expression.

23. Usual model: Flux Distribution No evidence for anisotropy in GRB directions (Meegan et al. 1992) Therefore, for a moving source, the observed monochromatic flux density F is related to the Flux density in the commoving frame by: Relativistic model: This work is attempting to give a contribution in understanding the physics and origin of GRBs events, incorporing the relativistic motion of the jets and their geometry into the physical models. TOTAL FLUX:

24. RELATIVISTIC MODEL • In most of the proposed models the isotropic radiation can not provide the release of energy necessary for the appearance of a cosmological GRB. • Radiation must be affected by the Lorentz boosting factor . Therefore, we are detecting in the earth frame a flux F enhanced by: And the total intrinsic energy of the source at its rest frame can be derived from the previous relation: From here, we are available to obtain the total energy released by the source and computed at theobservedframe: the true energy released in a GRB event

25. Constrains on the GRBs energy • Considering that GRBs are located at distances around of : • Computing the energy released by the source for several probable values of observed fluxes and Doppler factor. • In the same way, we works also with sources located at a more far distance, around:

26. Energy released

27. We note that a GRB can be pretty transparent formildly cosmological distance (r ~ 1 GPc) and for mildly relativistic Lorentz factor (Γ ~ 300). → → We found that for all cases, the involved energy in a GRB event is appreciable less that the huge energy (10^52 ergs/cm2 s) required in anisotropicmodel.

28. CONCLUSIONS • We evidenced the fact that the energy released in a gamma-ray event could be over estimated, if the emission is considered isotropic. • The observations carried out on these explosive events suggest us that anisotropic models are also a good alternative and maybe a more realisticsugesstion. • We can process thinking in a relativistic beaming, where the observer see only a limited portion of emitted radiation. • Then the true gamma-ray energy is smaller than the isotropic energy under the consideration of relativistic beaming which makes the observed radiation to be anisotropic.

29. MAIN CONCLUSIONS • Therefore, the GRB events are not necessarily associated with the formation of stellar black holes or SN. • The values present in these paper are more compatible with the energies involved in AGNs events, where a fraction of a solar mass per year can be accelerated to , leading to powers of ergs/sec.

30. THANK YOU FOR YOUR KIND ATTENTION