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