TeV gamma rays expected from supernova remnants in different uniform interstellar media

Calculations of the expected TeV gamma-ray emission, produced by accelerated cosmic rays (CRs) in nuclear collisions, from supernova remnants evolving in a uniform interstellar medium (ISM) are presented. The aim is to study the sensitivity of gamma-ray production to a physical parameter set. Apart from its general proportionality to N-H, it is shown that the gamma-ray production essentially depends upon the ratio of the CR diffusion coefficient kappa to a critical value kappa(crit) = 10(B-o/5 mu G)(N-H/0.3 cm(-3))(-1/3)kappa(B), where B-o and N-H are the magnetic field and hydrogen number density of the ISM, and kappa(B) denotes the Bohm diffusion coefficient. If kappa is of the same order or lower than kappa(crit), then the peak TeV gamma-ray flux in the Sedov evolutionary phase, normalized to a distance of 1 kpc, is about 10(-10)(N-H/0.3 cm(-3))photons cm(-2)s-(1). For a CR diffusion coefficient that is significantly larger than kappa(crit), the CR cut off energy is less than 10 TeV, and the expected gamma-ray flux at 1 TeV is considerably below the presently detectable level of 10(-12) photons cm(-2) s(-1). The same is of course true for a supernova remnant in the rarified, so-called hot ISM. (C) 2000 Elsevier Science B.V. All rights reserved.