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Scientific Report 2007-2009<br />
Theoretical physics<br />
T10. Gamma-Ray Bursts<br />
After the great discovery of the black holes in our<br />
galaxy, following the identification of Cygnus-X1 [1],<br />
one of the greatest challenges has been to try to identify<br />
the moment of gravitational collapse and the extraction<br />
of the gravitational and electromagnetic energy in the<br />
process of black hole formation. It was clear, from<br />
the early work on the mass formula of the black hole,<br />
that up to 50% of the black hole mass-energy could in<br />
principle be extractable. In this way, the black hole<br />
would become, as recalled by Christodoulou & Ruffini in<br />
1971, “the largest storehouse of energy in the universe”.<br />
Soon after the discovery of Gamma-Ray Bursts, in 1975<br />
Damour & Ruffini proposed that indeed vacuum polarization<br />
process occurring during a Kerr-Newmann black<br />
hole formation may lead to energy emission of ∼ 10 54<br />
ergs. The dynamics of the e + e − plasma formed in the<br />
dyadosphere and originating the GRB phenomenon can<br />
be divided into five fundamental phases: the self acceleration<br />
of the e + e − pair-electromagnetic plasma (PEM<br />
pulse); its interaction with the baryonic remnant of<br />
the progenitor star (PEMB pulse); the approach of the<br />
PEMB pulse to transparency, the emission of the proper<br />
GRB (P-GRB) and its relation to the “short GRBs”;<br />
the ultrarelativistic and finally the non relativistic<br />
regimes of the optically thin baryonic matter shell left<br />
over after the transparency and ballistically expanding<br />
in the Circumburst Medium (CBM). The best fit of<br />
the theory leads to an unequivocal identification of the<br />
“long GRBs” as extended emission occurring at the<br />
afterglow peak (see Fig. 1).<br />
Using the observed GRB data, we progress on the<br />
uniqueness of our theoretically predicted GRB structure<br />
as composed by a proper-GRB (P-GRB), emitted at<br />
the transparency of an electron-positron plasma with<br />
suitable baryon loading, and an extended afterglow<br />
comprising the so called “prompt emission” as due to<br />
external shocks (see Fig. 2). We can theoretically fit<br />
detailed light curves for selected energy bands on a<br />
continuous time scale ranging over 10 6 seconds. The<br />
theoretically predicted instantaneous spectral distribution<br />
over the entire afterglow is presented, confirming a<br />
clear hard-to-soft behavior encompassing, continuously,<br />
the “prompt emission” all the way to the latest phases<br />
of the afterglow.<br />
Luminosity (dE/(dtdΩ) (ergs/(s*sterad))<br />
2.0x10 51 1.2x10 -5<br />
GRBM observations in 40-700 keV band<br />
Afterglow light curve in 40-700 keV band with =10 -3 #/cm 3<br />
Afterglow light curve in 40-700 keV band with =1 #/cm 3<br />
1.5x10 51<br />
P-GRB light curve in 40-700 keV band<br />
8.0x10 -6<br />
1.0x10 51<br />
6.0x10 -6<br />
4.0x10 -6<br />
5.0x10 50<br />
2.0x10 -6<br />
0.0x10 0<br />
0.0x10 0<br />
-20 0 20 40 60 80 100<br />
Detector arrival time (t a<br />
d ) (s)<br />
Figure 2: The theoretical fit of the BeppoSAX GRBM observations<br />
of GRB970228 in the 40–700 keV energy band.<br />
The red line corresponds to an average CBM density ∼ 10 −3<br />
particles/cm 3 . The black line is the extended afterglow light<br />
curve obtained rescaling the CBM density to ⟨n cbm ⟩ = 1<br />
particle/cm 3 keeping constant its shape and the values of<br />
E tot<br />
e<br />
and B. The blue line is the P-GRB. Details in Ref. [4].<br />
±<br />
Observed flux (ergs/(cm 2 *s))<br />
References<br />
1. R. Giacconi, R. Ruffini, Physics and Astrophysics of<br />
Neutron Stars and Black Holes, Cambridge Scientific<br />
Publishers (2009).<br />
2. L. Caito et al., Astron. Astroph. 498, 501 (2009).<br />
3. R. Guida et al., Astron. Astroph. 487, L37 (2008).<br />
4. M.G. Bernardini et al., Astron. Astroph. 474, L13 (2007).<br />
Figure 1: The energy radiated in the P-GRB and in the extended<br />
afterglow, in units of the total energy of the plasma<br />
(Etot), e± are plotted as functions of the baryon loading B parameter.<br />
Also represented are the values of the B parameter<br />
computed for most of the GRBs we have analyzed.<br />
Authors<br />
A.G. Aksenov 6 , M.G. Bernardini, C.L. Bianco, L. Caito, P.<br />
Chardonnet 6 , M.G. Dainotti, G. De Barros, R. Guida, L.<br />
Izzo, F.A. Massucci, B. Patricelli, L.J. Rangel Lemos, R.<br />
Ruffini, G. Vereshchagin, S.-S. Xue<br />
http://www.icra.it/<br />
http://www.icranet.org/<br />
The relative intensities, the time separation and the<br />
hardness ratio of the P-GRB and the extended afterglow<br />
are used as distinctive observational test of the theory<br />
and the excellent agreement between our theoretical<br />
predictions and the observations are documented.<br />
<strong>Sapienza</strong> Università di Roma 33 Dipartimento di Fisica