Título

Modelo de emisión de rayos gamma de la galaxia de Andrómeda

Autor

JUAN NOE SUAREZ PEREA

Colaborador

ALBERTO CARRAMIÑANA ALONSO (Asesor de tesis)

WILLIAM FRANK WALL (Asesor de tesis)

Nivel de Acceso

Acceso Abierto

Resumen o descripción

A model of diffuse gamma-ray emission is presented. The diffuse

gamma-ray emission is directly related to the distribution of gas and radiation in

an object and to its star formation. The relationship with star formation is due

to supernovae behaving as cosmic-ray accelerators. To model this emission from

M31, I have used the HI map of Brinks & Shane (1984) to represent the atomic

gas content and the CO map of Nieten et al (2006) to represent the molecular

hydrogen content. To represent the radiation field, I have used maps of M31 in

different bands, from infrared to ultraviolet. These images have been normalized to

the spectral energy distribution of M31. The cosmic-ray spectrum is a power law

whose indices are p = 2.76 for electrons and k = 2.71 for protons; heavier nuclei

are not currently included. These two spectra have been normalized assuming

energy equipartition between cosmic-rays and the magnetic field and a protonto-

electron ratio of 100. In these calculations I used the values for the magnetic

field strength given by Beck (1981) of 3.2 ± 0.9μG in the ring and 2.4μG in the

disk. The gamma-ray mechanisms that are used in this model are neutral pion

decay, bremsstrahlung and inverse Compton scattering. Production functions that

express the number of gamma-rays produced per unit of time per unit of nucleon

energy were obtained from Berstch et al (1993) and Haung et al (2007). The

model uses maps of gas derived from HI and CO emission lines, and maps of the

radiation field, and production functions as inputs. This gives a map of emission

in gamma-rays of M31. The integrated flux above photon energies of 100MeV is

2.11 × 10−8 photon s−1cm−2. A maximum likelihood analysis was applied to the

model map and the all-sky maps observed by EGRET. With this analysis I found

an upper limit of 7.9×10−9photons cm−2s−1 to the gamma-ray flux above 100MeV

for M31, implying a modification of the input parameters to the model. The most

probable error in the input was adopting a magnetic field strength a factor of ∼ 2

too high. A field strength of ∼ 2μG is the most appropriate value on large scales

in M31. The results of this model have been compared with flux estimates of

M31 in the same energy range made by other authors. ¨Ozel & Berkhuijsen (1987)

estimated a flux of 2.4×10−8ξ photons cm−2s−1 with ξ < 5 and Pavlidou & Fields

(2001) calculated 1×10−8photons cm−2s−1 respectively.

Editor

Instituto Nacional de Astrofísica, Óptica y Electrónica

Fecha de publicación

agosto de 2010

Tipo de publicación

Tesis de maestría

Versión de la publicación

Versión aceptada

Formato

application/pdf

Idioma

Español

Audiencia

Estudiantes

Investigadores

Público en general

Sugerencia de citación

Suarez Perea J.N.

Repositorio Orígen

Repositorio Institucional del INAOE

Descargas

1939

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