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Aims. We study the distribution of the molecular gas in the Andromeda galaxy (M 31) and compare this with the distributions of the atomic gas and the emission from cold dust at λ175 µm. Methods. We obtained a new 12 CO(J = 1−0)-line survey of the Andromeda galaxy with the highest resolution to date (23 , or 85 pc along the major axis), observed On-the-Fly with the IRAM 30-m telescope. We fully sampled an area of 2• × 0.• 5 with a velocity resolution of 2.6 km s −1 . In several selected regions we also observed the 12 CO(2−1)-line. Results. Emission from the 12 CO(1−0) line was detected from galactocentric radius R = 3 kpc to R = 16 kpc with a maximum in intensity at R ∼ 10 kpc. The molecular gas traced by the (velocity-integrated) (1−0)-line intensity is concentrated in narrow arm-like filaments, which often coincide with the dark dust lanes visible at optical wavelengths. Between R = 4 kpc and R = 12 kpc the brightest CO filaments define a two-armed spiral pattern that is described well by two logarithmic spirals with a pitch angle of 7• -8• .The arm-interarm brightness ratio averaged over a length of 15 kpc along the western arms reaches about 20 compared to 4 for H iat an angular resolution of 45 . For a constant conversion factor X CO , the molecular fraction of the neutral gas is enhanced in the spiral arms and decreases radially from 0.6 on the inner arms to 0.3 on the arms at R 10 kpc. The apparent gas-to-dust ratios N(H i)/I 175 and (N(H i) + 2N(H 2 ))/I 175 increase by a factor of ∼20 between the centre and R 14 kpc, whereas the ratio 2N(H 2 )/I 175 only increases by a factor of 4. Conclusions. Either the atomic and total gas-to-dust ratios increase by a factor of ∼20 or the dust becomes colder towards larger radii. A strong variation of X CO with radius seems unlikely. The observed gradients affect the cross-correlations between gas and dust. In the radial range R = 8-14 kpc total gas and cold dust are well correlated; molecular gas correlates better with cold dust than atomic gas. The mass of the molecular gas in M 31 within a radius of 18 kpc is M(H 2 ) = 3.6 × 10 8 M at the adopted distance of 780 kpc. This is 7% of the total neutral gas mass in M 31.

Abstract. Eight optical and four radio observatories have been intensively monitoring the BL Lac object 0716+714 in the last years: 4854 data points have been collected in the UBVRI bands since 1994, while radio light curves extend back to 1978. Many of these data, which all together constitute the widest optical and radio database available on this object, are presented here for the first time. Four major optical outbursts were observed at the beginning of 1995, in late 1997, at the end of 2000, and in fall 2001. In particular, an exceptional brightening of 2.3 mag in 9 days was detected in the R band just before the BeppoSAX pointing of October 30, 2000. A big radio outburst lasted from early 1998 to the end of 1999. The long-term trend shown by the optical light curves seems to vary with a characteristic time scale of about 3.3 years, while a longer period of 5.5-6 years seems to characterize the radio long-term variations. In general, optical colour indices are only weakly correlated with brightness; a clear spectral steepening trend was observed during at least one long-lasting dimming phase. Moreover, the optical spectrum became steeper after JD ∼ 2 451 000, the change occurring in the decaying phase of the late-1997 outburst. The radio flux behaviour at different frequencies is similar, but the flux variation amplitude decreases with increasing wavelength. The radio spectral index varies with brightness (harder when brighter), but the radio fluxes seem to be the sum of two different-spectrum contributions: a steady base level and a harder-spectrum variable component. Once the base level is removed, the radio variations appear as essentially achromatic, similarly to the optical behaviour. Flux variations at the higher radio frequencies lead the lower-frequency ones with week-month time scales. The behaviour of the optical and radio light curves is quite different, the broad radio outbursts not corresponding in time to the faster optical ones and the cross-correlation analysis indicating only weak correlation with long time lags. However, minor radio flux enhancements simultaneous with the major optical flares can be recognized, which may imply that the mechanism producing the strong flux increases in the optical band also marginally affects the radio one. On the contrary, the process responsible for the big radio outbursts does not seem to affect the optical emission.

The exact location of the γ-ray emitting region in blazars is still controversial. In order to attack this problem we present first results of a cross-correlation analysis between radio (11 cm to 0.8 mm wavelength, F-GAMMA program) and γ-ray (0.1-300 GeV) ∼ 3.5 year light curves of 54 Fermi-bright blazars. We perform a source stacking analysis and estimate significances and chance correlations using mixed source correlations. Our results reveal: (i) the first highly significant multi-band radio and γ-ray correlations (radio lagging γ rays) when averaging over the whole sample, (ii) average time delays (source frame: 76 ± 23 to 7 ± 9 days), systematically decreasing from cm to mm/sub-mm bands with a frequency dependence τ r,γ (ν) ∝ ν −1 , in good agreement with jet opacity dominated by synchrotron self-absorption, (iii) a bulk γ-ray production region typically located within/upstream of the 3 mm core region (τ 3mm,γ = 12 ± 8 days), (iv) mean distances between the region of γ-ray peak emission and the radio "τ = 1 photosphere" decreasing from 9.8 ± 3.0 pc (11 cm) to 0.9 ± 1.1 pc (2 mm) and 1.4 ± 0.8 pc (0.8 mm), (v) 3 mm/γ-ray correlations in 9 individual sources at a significance level where one is expected by chance (probability: 4 × 10 −6 ), (vi) opacity and "time lag core shift" estimates for quasar 3C 454.3 providing a lower limit for the distance of the bulk γ-ray production region from the supermassive black hole (SMBH) of ∼ 0.8-1.6 pc, i.e. at the outer edge of the Broad Line Region (BLR) or beyond. A 3 mm τ = 1 surface at ∼ 2-3 pc from the jet-base (i.e. well outside the "canonical BLR") finally suggests that BLR material extends to several pc distances from the SMBH.

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