Extragalactic 1 millimeter sources: Simultaneous observations at centimeter, millimeter, and visual wavelengths

Abstract

Observations simultaneously made at visual (B, V, and R) wavelengths, at 1, 1.4, and 3.4 mm and at 1.3, 2, 6, and 20 cm of 9 QSOs and BL Lac objects are reported. The range of the millimeter visual spectral index ɑ_(mv) was only 0.65-0.82, typical of optically thin synchrotron emission. This may indicate that the electrons radiating synchrotron emission in this portion of the spectrum are not subjected to large radiative losses, and therefore relativistic bulk motion with Doppler factors ~10 are required. The visual spectral index is much more broadly distributed and typically larger than ɑ_(mv). The spectral energy distributions have not changed much in the last 2-5 years except for 2251 + 15 and perhaps 0235 + 164. Only 1749 +09 shows a sharp spectral break shortward of 1 mm. Sixteen other sources were observed at 1 mm, of which seven were detected.

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