Mathematics – Logic
Scientific paper
May 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998aas...192.7002w&link_type=abstract
American Astronomical Society, 192nd AAS Meeting, #70.02; Bulletin of the American Astronomical Society, Vol. 30, p.925
Mathematics
Logic
Scientific paper
Although unresolved AGNs (predominantly Seyfert galaxies) are believed to be the dominant contributors to the Cosmic gamma -ray Background (CGB) below E_gamma ~ 300 keV, and blazars explain the bulk of the CGB flux above 10 MeV, the origin of the CGB in the MeV region is perhaps less certain. The most promising candidates in this energy regime are cosmological supernovae (Clayton & Silk,ApJ,158,L43,1969, The et al.,ApJ,403,32,1993). The gamma -ray emission resulting from the decay chain \(56Ni \rightarrow \) \(56Co \rightarrow\) \(56Fe \) (847,1238,1770,2030,2599,3250 keV) produces a line spectrum plus a Compton scattering continuum. Although iron synthesis occurs in all types of supernovae, SNIa contribute predominantly to the CGB, due to larger Ni yields and higher photon escape probabilities. Estimates of the star formation history in the local universe yield a present-day rate density of =~ 3.7 x 10(-2) {em h}(3) \ {em Msun} \ {em Mpc}(-3) \ {em yr}(-1) (Cole et al.,MNRAS,271,781,1994) , but the star formation rate was about ten times higher at a redshift of ~ 1.5-2. The rate then decreases, reaching the present-day value near redshifts =~ 5 (Lilly et al., ApJ,460,L1,1996). In addition to gamma -rays from SNIa we also consider contributions to the CGB due to lines from SNII (such as (26) Al at 1.8 MeV, (44) Ti at 1.157 MeV, and (60) Co at 1.17 & 1.33 MeV). The gamma -ray spectrum of Model W10HMM (Pinto & Woosley, ApJ,329,820,1988) was time integrated to derive a template spectrum for Type II supernovae. For SNIa we also included the gamma -ray continuum, using the W7 model of Nomoto et al. (ApJ,286,644,1984), integrated over 600 days, as template. Lifetimes of SNIa progenitors ( ~ 1-2 Gyrs; Yoshii et al. 1996,ApJ,462,266) are taken into account. We discuss the resultant SNIa contribution to the CGB and compare the models to observations of COMPTEL, SMM, and earlier instruments. We discuss the use of the CGB as a powerful tool to constrain cosmological and galactic chemical evolution parameters.
Hartmann Dieter H.
Leising Mark D.
The Lih Sin
Watanabe Katsuhiro
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