On some weaknesses of the standard afterglow model:

1. In this theory the size of the region where the GRB prompt emission arises must be ~ 1015 - 1017 cm, if it is supposed that radiation (with 100 MeV and 10 GeV photons) is generated by ultrarelativistic jets moving with huge Lorentz factors ~ 100 -1000.

2. On some weaknesses of the standard afterglow model: The study of the physics of relativistic collisions shocks is still at its infancy, and the standard afterglow model simply parametrizes our ignorance.

3. arXiv:0811.1657v1 [astro-ph]: From Abstract:

4. Some weaknesses of the standard afterglow model: The most puzzling for afterglow theory are the chromatic breaksin Swift X-ray light curves which are not seen in the optical at the same time… (On the prediction of jet breaks: Piran et al, 1993, …, …, 2004 and more.) These new observations challenge traditional afterglow theory and call for new ideas.

5. The X-ray and optical may arise in separate physical components, which would naturally account for their seemingly decoupled light curves. However, this type of explanation also introduces a new ingredient (with its associated degrees of freedom) into the model, and unless it can be tested against other independent data it is hard to constrain such an option or reach any definitive conclusions. One might ask: are we just adding epicycles to a fundamental flawed model?

6. arXiv: 0811.2997, Y. Zou, Y. Fan, and T. Piran:

7. arXiv:0705.1061v1, M. Battelino, F. Ryde, N. Omodei and F. Longo – On the Black-body component and GeV(?)

8. The GRB light cuvres are composed by a sequential superposition of many pulses. The spectral and temporal characteristics of these pulses are key ingredients for understanding the prompt emission mechanisms of GRBs (e.g., Ryde & Petrosian 2002). Unfortunately, the narrow spectral range of the Swift BAT detector limits and makes difficult the spectral analysis.

9. The strong GeV emission? Kumar & Panaitescu (2008) and Racusin et al. (2008b) explained the prompt emission of GRB 080319B. As a direct consequence, they predicted a remarkably strong GeV emission component, whose luminosity is about 10 times higher than the observed MeV one. In contrast to this prediction, for several bright GRBs detected by EGRET on CGRO, the GeV fluence is not higher than that in the MeV energy band detected by BATSE (e.g. Sommer et al. 1994; Hurley et al 1994). This prediction could be further tested by GLAST/Fermi…

10. If this is not a fireball, then what is it? Maybe our “standard” theoretical models are based on prejudices = inaccurate knowledge, and the latter is connected with the observational selection, i.e. the data sample is not complete yet/always for the theory to become “standard”. So, now it is still rather popular than a real standard physical model of GRB sources.

11. The popular conception of the relation between long-duration GRBs and core-collapse SNe (the picture from Woosley and Heger , 2006) 56Ni synthesized behind the shock wave Shematic model of asymmetric explosion of a GRB/SN progenitor …a strongly non-spherical explosion may be a generic feature of core-collapse supernovae of all types. …Though while it is not clear that the same mechanism that generates the GRB is also responsible for exploding the star. astro-ph/0603297 Leonard, Filippenko et al. The shock breaks out through the wind The wind envelope of size ~1013 cm Though the phenomenon (GRB) is unusual, but the object-source (SN) is not too unique. The closer a GRB is, the more features of a SN.

12. On GRB luminosityindicators and a compact GRB model. (The Amati correlation and a compact GRB model.) V. V. Sokolov

13. Соотношение Амати в компактной модели источника гамма-всплесков. В.В.Соколов

14. Several GRB luminosity indicators or GRB luminosity relations have been proposed in recent years. GRB luminosity/ energy relations are connectionsbetween measurable properties of the prompt γ-ray emission with the luminosity or energy. The most famous of these relations is the peak of the spectrum and the isotropic bolometric energy:(Ep - Eiso) relation or so-called Amati relation (Amati et al., 2002). Ep is the peak energy in GRB spectra, Eiso is the total isotropic energy of the prompt GRB emission.

15. В последнее время предложено несколько эмпирических соотношений междунаблюдаемыми свойствами (prompt)излучения гамма-всплесков GRB.Наиболее известно соoтношение Амати (Amati et al., 2002) --- это связьмежду между пиковой энергией в спектре GRB (Epeak) и его полнымэнерговыделением (Eiso), если считать что источник светит изотропно.

16. arXiv:0805.0377 Amati et al. Figure 1. Location in the Ep,i – Eiso plane of the 70 GRBs and XRFs with firm estimates of redshift and Ep,obsincluded in our sample (Eiso computed following Amati (2006) and assuming a cosmology with H0 = 70 km s−1 Mpc−1, ΩM = 0.3 and ΩΛ =0.7). Red dots are Swift GRBs. Black dots are GRBs discovered by other satellites. The best-fit power-law is the continuous line (±2σext region).

17. arXiv:0804.1675 Ghirlanda et al. Figure 1. The 76 GRBs with known redshifts and well measured spectral properties (updated to September 2007) in the rest frame plane. Bursts are divided in four redshift bins (as labelled). The lines are the best fit obtained with the least squares method (dotted, short–dashed, long–dashed, dot–dashed from small to high redshift values, respectively). The insert represents the slope as a function of the 4 redshift bin. The slope of the correlation defined with the entire sample of 76 bursts is also shown (cyan symbol in the insert).

18. arXiv:0710.5864 Tsutsui et al.

19. arXiv:0802.3428v1 [astro-ph] 23 Feb 2008

20. arXiv:0705.1061v1, M. Battelino, F. Ryde, N. Omodei and F. Longo – On the Black-body component and GeV(?)

21. It is difficult to understand this relation and all similar ones in the popular model of the relativistic fireball with a GRB source of size > 1015sm (Nakar & Piran, 2005).

22. arXiv: 0809.5206

23. arXiv: 0809.5206

24. Now about a compact model: The main purpose is to show that a GRBs are connected with compact (<108 cm) and massive (> 3M⊙) objects (collapsars)

25. In the compact GRB model the e-e+ pair is produced by two photons with energies E1and E2, which in sum are above the threshold energy (E1+E2> 2 Eth, Eth= √ E1E2) and where product E1E2 is E1E2 ≥ 2 (mec2)2/(1 – cos θ), 2(mec2)2 = 2(511кэВ)2, and θ is an angle between directions of the two photons/rays.As a result of the pair birth the photon previously moving along the observer’s line of sight disappears...

26. For the threshold of e-e+ pair production Eth= √ E1E2 , E1E2 ≥ 2 (mec2)2/(1 – cos θ) E2 e-e+ E1 511 keV • e-e+ E1 722 keV • E2 • e-e+ E1 >> 1MeV θ at smallθ E2

27. In the compact model of GRB (Aharonyan & Ozernoy, 1979; Carrigan & Karz, 1992; Sokolov et al., 2006) the relation Epeak-Eiso(the more distant a burst is, the more quanta with high energies are in its spectrum) can be a consequence of: 1)the dependence of the threshold of electron-positron pairs birth on an angle between momemta of colliding photons in a source, and 2) anisotropy of the source radiation, which can be connected with magnetic field on or near the surface of the compact source --- a GRB source of size < 108sm.

28. If γ-rays are collimated right in a GRB source (with a size c δT < 3000 km), then: The cones (with the opening angle θ) contains the more and more hard radiation (as θdecreases) along some selected direction (or a selected axisin GRB source) with energy of quanta E > Eth. The length of arrows is proportional to the threshold energy Eth. The red circle denotes the isotropic and the softestcomponent of radiation with total energy of ~/<1049 erg. The hardest quanta of a GRB spectrum are concentrated in the narrowest cone. They are observable only along the axis of a GRB/SN explosion…

29. In such a model the degrees of collimation of hard and soft radiation components in GRB spectra are different: photons of higher and higher energies in the spectrum (1 – 10 – 100… MeV) are more and more collimated. Only soft X-ray quanta (~/< 10 keV) are radiated isotropically with the total energy release not more than 1049 erg. As a result, the total (bolometric) energy of GRB can be of the same order.

30. So, the off-axis scenario is based on the assumption that we observe normal GRBs in (or very nearby to) the axis of the GRB beam, while XRFs are observed off-axis.

31. If γ-rays are collimated right in a GRB source (with a size c δT < 3000 km), then: The cones (with the opening angle θ) contains the more and more hard radiation (as θdecreases) along some selected direction (or a selected axisin GRB source) with energy of quanta E > Eth. The length of arrows is proportional to the threshold energy Eth. The red circle denotes the isotropic and the softestcomponent of radiation with total energy of ~/<1049 erg. The hardest quanta of a GRB spectrum are concentrated in the narrowest cone. They are observable only along the axis of a GRB/SN explosion.

32. z = 6.3 arXiv:0805.0377 Amati et al. One can see that at least the sufficient condition of our description of the Epeak-Eiso correlation is fulfilled: the most distant GRB 050904 with z=6.29 has the largest Ep,i = 3178 keV (just the highest point in this figure).

33. Thus, in the compact GRB model the collimation for hard and for soft γ-quanta is different: the hardest quanta have the strongest collimation. XRF = X-Ray Flashes likeXRF/GRB060218/SN2008aj, XRR GRB = X-Ray Rich GRBs like GRB030329/SN2003dh, GRB = classical GRBs with Eiso >/~1051 erg (up to GRB050904 with z = 6.3).

34. Astro-ph/0408413 Friedman & Bloom Amati law X-ray flashes, X-ray-rich GRBs and classical GRBs arise from the same phenomenon

35. Astro-ph/0312634 D. Q. Lamb, T. Q. Donaghy, and C. Graziani

37. Astro-ph/0312504 D.Q.Lamb et al.

38. В компактной модели GRB эта связь (закон Амати) может быть "простым" следствием как формулы для Eth = √E1E2, так и анизотропии излучения,связанной (скорее всего) с магнитным полем наили вблизи поверхности компактного объекта. Анизотропия, может быть связана с переносом излучения в среде с сильным (регулярным, ~1014 - 1016Гс) магнитным полем, когда поглощение для фотонов, поляризованных поперек магнитного поля (необыкновенная волна), оказывается очень маленьким (B. Paczyński, 1992; V.G. Bezchastnov, G.G. Pavlov, Yu.A. Shibanov, V.E. Zavlin,1996). Тогда наблюдение сильной линейной поляризации излучения GRB должно быть еще одним следствием компактной модели.

39. In the compact model of GRB this relation (the Amati law) can be a “simple” consequence of both the formula for Eth = √E1E2 and the radiation anisotropy which is most probably related to magnetic field on or near the surface of a compact object. Anisotropy may be related to the radiation transfer in a medium with strong (regular, ~1014 – 1016Gs) magnetic field when absorption for photons polarized across magnetic field (the extraordinary wave) turns out to be very small (B. Paczyński, 1992; V.G. Bezchastnov, G.G. Pavlov, Yu.A. Shibanov, V.E. Zavlin,1996). Then observation of strong linear polarization of GRB radiation must be another consequence of the compact model.

40. Thank you.

41. Still…

42. arXiv:0802.3428v1 [astro-ph] 23 Feb 2008

43. GRB luminosity indicators and a compact GRB model. The Amati correlation and a compact GRB model. V. V. Sokolov and G. S. Bisnovatyi-Kogan

44. Several GRB luminosity indicators or GRB luminosity relations have been proposed in recent years. GRB luminosity/ energy relations are connections between measurable properties of the prompt γ-ray emission with the luminosity or energy. The most famous of these relations is the peak of the spectrum and the isotropic bolometric energy:(Ep - Eiso) relation or so-called Amati relation (Amati et al., 2002). Ep is the peak energy in GRB spectra, Eiso is the total isotropic energy of the prompt GRB emission.

45. If we take into account that the threshold for e-e+ pair production in GRB source depends on an angle between photon momenta, andif the ?-rays are collimated right in GRB source,then another model of GRB source is possible.Namely, the dependence of the threshold for e-e+ pair productionon the angle between photon momenta, a photon collimation in the sourceand (as a consequence) the dependence of this collimation on GRB photon energy must be taken into account.

46. arXiv:0811.1657v1 [astro-ph] From Abstract:

47. In the compact GRB model the collimationfor hard and for soft γ-quanta is different: the hardest quanta have the strongest collimation. In the compact model of GRB this relation (the Amati law) can be a ”simple” consequence of both the formula for Eth =and the radiation anisotropy which is most probably related to magnetic field on or near the surface of a compact object. Such a model can explain easily and naturally both the Amati law and all similar ratios (Yanetoky et al.) for prompt gamma-ray emission.

48. Some weaknesses of the standard afterglow model The study of the physics of relativistic collisions shocks is still at its infancy, and the standard afterglow model simply parametrizes our ignorance.

49. The X-ray and optical may arise in separate physical components, which would naturally account for their seemingly decoupled light curves. However, this type of explanation also introduces a new ingredient (with its associated degrees of freedom) into the model, and unless it can be tested against other independent data it is hard to constrain such an option or reach any definitive conclusions. One might ask: are we just adding epicycles to a fundamental flawed model?

50. arXiv: 0811.2997, Y. Zou, Y. Fan, and T. Piran