The Role of Nuclei-Nuclei Interactions in the Production
of Gamma-Ray Lines in Some Solar Flares
Boris M. Kuzhevskij (1), Wei-Qun Gan (2),
and Leonty I. Miroshnichenko (3, 4)
(1) SINP, Moscow State University, Moscow, RUSSIA
(2) Purple Mountain Observatory (PMO), Nanjing, CHINA
(3) Instituto de Geofísica, UNAM, MEXICO, leonty@geofisica.unam.mx
(4) N.V. Pushkov Instiute IZMIRAN, Troitsk, Moscow, RUSSIA
Chinese Journal of Astronomy and Astrophysics,
2005, v.5, No.3, p.295-301
Abstract
• Dramatic extensions of experimental possibilities (spacecraft RHESSI,
CORONAS-F, INTEGRAL and others) in solar gamma-ray astronomy
call for urgent and detailed consideration of a set of physical problems
of solar activity and solar-terrestrial relationships that earlier may
have only been outlined.
• We undertake a theoretical analysis of issues related to the production
of gamma-radiation in the processes of interactions of SEPs - energetic
(accelerated) heavy and middle nuclei with the nuclei of the solar
atmosphere (the so-called heavy-heavy, or ij-interactions). We also
make an estimate of the contribution of these interactions to the
formation of nuclear and isotopic abundances of the solar atmosphere
in the range of light and rare elements.
• The analysis is curried out for SEP spectra in the wide range of their
spectral indices. We compare our theoretical estimates with RHESSI
observations for the flare of 23 July 2002. It was shown that the 24Mg
gamma-ray emission in this event was produced by the newly
generated 24Mg nuclei. With a high probability, the gamma-ray line
emission of 28Si from this flare was generated by the same processes.
Relative abundances of some elements in the solar
atmosphere and cross sections of i-j and p-k interactions
Variant (a), Aller (1963):
N(O)/N(Mg) = 36.4; N(C)/N(Mg) = 20.8;
Variant (b), Cameron (1973):
N(O)/N(Mg) = 22.2; N(C)/N(Mg) = 13.3
________________________________________________
Cross sections of i-j interactions (0.73-7.2 MeV/n):
250-300 mb (Dyer et al., 1981; Kuzhevskij, 1985).
Cross sections of p-k interactions (5.0-30 MeV):
300-550 mb (Dyer et al., 1981; Kuzhevskij, 1985).
Ratios of gamma-ray fluxes approach to ~1 for spectral
index S ≥3.
Table 1. Contribution of 12C and 16O Nuclei into
Gamma-Ray Flux from Excited 24Mg Nuclei
_______________________________________
S
2
3
4
5
6
7
_______________________________________
G(C)
0.016 0.20 1.70 15.4 25.90 154
G(C+O) 0.035 0.40 3.40 30.0 50.00 300
_______________________________________
G is a ratio of gamma-ray fluxes produced
by p-k and i-j interactions; S – power-law index.
Table 2. Ratios of Gamma-Ray Flux from 12C nuclei
to that from Other Nuclei
Ratios
•
Experiment
(23 July 2002)
Calculations for p-k and
alpha-k interactions
____________________________________________________
12C/24Mg
12C/20Ne
12C/28Si
12C/56Fe
1.01, max 1.90
1.34, max 2.47
1.67, max 3.31
3.81, max 8.02
10.40 (a);
2.65 (a);
31.0 (a);
30.00 (a);
4.40 (b)
1.53 (b)
12.0 (b)
2.60 (b)
____________________________________________________
Observational RHESSI data are taken from Smith et al.
(2003)
___________________________________
Conclusions
• Our analysis of the gamma-ray line fluences from the
RHESSI flare of 23 July 2002 confirms that i-j
interactions are very important for nuclei whose
initial abundances in the solar atmosphere are small.
Amongst them are light elements Li, Be, and B, as
well as some rare elements, e.g., Na, and even Mg, Si.
• The role of i-j interactions grows, especially, in cases
where the SEP has a soft spectrum (S≥3). Note that
such a situation is very often encountered in
processes of particle acceleration at/near the Sun.
Implications and Prospects
• The nuclei of 24Mg and 28Si may be effectively
produced in the solar active region during the flare
due to i-j interactions, e.g., between C-O and O-O.
• The contribution of C-O interactions to the generation
of 20Ne is small, and the 56Fe nucleus cannot be
created due to C-O and/or O-O interactions.
• Standard solar composition (Grevesse & Sauval,
1998) does not change our preliminary conclusion
about the role of i-j interactions in the production of
gamma-ray lines from 24Mg and 28Si nuclei.
ACKNOWLEDGEMENTS
This work was supported partly by the Russian
Foundation for Basic Research (RFBR, projects 0202-39032, 03-02-96026), Federal Purpose Scientific
and Technical Program Section I, Project 4), and
President’s Grant of Russian Federation (project
1445.2003.2). The work by W. Gan was supported by
the National Natural Science Foundation (NNSFC) of
China via grants 10173027, 10221001, 10333040 and
by grant G2000078402 from the Ministry of Science
and Technology of China.
Acknowledgements
• This work was greatly inspired by and
carried out due to enormous efforts of
Prof. Boris M. Kuzhevskij (SINP MSU,
Moscow) who drastically passed away on
28 February 2005. His contribution to the
investigation of different aspects of solar
gamma rays remains very significant.
Important references
• B.M. Kuzhevskij. Nuclear Processes in Solar
Atmosphere and Solar Cosmic Radiation.
Moscow, Energoatomizdat, 1985.
• N. Grevesse & A.J. Sauval. Space Sci. Rev.,
85, 161 (1998).
• B. Kozlovsky, R.J. Murphy, and R. Ramaty.
Ap. J. Suppl., 141, 523 (2002).
• D.M. Smith, G.H. Share, R.J. Murphy et al. (in
all 6 authors). Ap. J. Lett., 595, L81(2003).