Indications of electron-to-proton mass ratio variations in the Galaxy. II. 3 mm methanol lines toward Sgr B2(N) and (M)

Abstract

Differential measurements of the fundamental constant mu = m_e/m_p (the electron-to-proton mass ratio) for two sources near the Galactic Center - the Sgr B2(N) and B2(M) molecular clouds - suggest that mu is lower in these clouds than its laboratory value. Based on observations of methanol (CH3OH) emission lines in the 80-112 GHz range (data from the IRAM 30-m telescope), a weighted mean value (Delta mu/mu) = (mu_obs - mu_lab)/mu_lab = (-2.1 +/- 0.6)*10^(-7) (1 sigma) was obtained for Sgr B2(N) at the sample size n = 9. This value of (Delta mu/mu) has the same sign as the result of recent measurements of methanol lines in the higher frequency range of 542-543 GHz (data from the Herschel space telescope) for Sgr B2(N): (Delta mu/mu) = (-4.2 +/- 0.7)*10^(-7) (sample size n = 2).