Publication Date:
2014-05-14
Description:
The exact location of the -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 programme) and -ray (0.1–300 GeV) ~3.5 yr 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 multiband radio and -ray correlations (radio lagging rays) when averaging over the whole sample, (ii) average time delays (source frame: 76 ± 23 to 7 ± 9 d), systematically decreasing from cm to mm/sub-mm bands with a frequency dependence r, () –1 , in good agreement with jet opacity dominated by synchrotron self-absorption, (iii) a bulk -ray production region typically located within/upstream of the 3 mm core region ( 3mm, = 12 ± 8 d), (iv) mean distances between the region of -ray peak emission and the radio ‘ = 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/-ray correlations in nine 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 -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 = 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 parsec distances from the SMBH.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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