Multifrequency observations of OV236 (1921–293) reveal an unusual spectrum

Abstract

As part of a programme of multifrequency single epoch observations of BL Lac objects and flat-spectrum radio sources we have examined the radio source OV236 (1921–293) which has been classified both as a quasar and a BL Lac object. Its polarization and variability at 2.2 µm¹ and generally featureless optical spectrum are consistent with it being a BL Lac object. Wills and Wills² measured its optical polarization, variability and emission line spectrum and find it to have a redshift z = 0.352. It is an extremely variable radio source, during the outburst reported by Dent and Balonek³ it was the brightest 10-cm quasar in the sky. The outburst was first measured at 3.3 mm and was increasingly delayed at longer wavelengths; there was also evidence for correlated optical/radio variability during this outburst⁴. We have obtained J, H, K, 10, 20, 800 and 1,100 µm flux measurements of 1921–293 over a period of four days from the same telescope, enabling us to present a ‘snapshot’ of its IR to millimetre spectrum. The continuum spectrum of 1921–293 is suggestive of a peak in the submillimetre region. This excess could be due to an injection of high-energy electrons into a synchrotron emitting region, although thermal emission from dust remains a possibility.