First detection of hotspot advance in a Compact Symmetric Object. Evidence for a class of very young extragalactic radio source

Original · EN

We present the results of multi-epoch global VLBI observations of the Compact Symmetric Object (CSO), 0710+439 at 5 GHz. Analysis of data spread over 13 years shows strong evidence for an increase in the separation of the outer components at a rate of 0.251 ± 0.029 h⁻¹c. Dividing the overall size of 86.8 h⁻¹pc by this separation rate implies an estimated kinematic age of only 1100 ± 100 yrs. After taking into account possible temporal variations in hotspot advance speeds due to cloud collisions or hydrodynamic instabilities we argue that the upper limit to the age of 0710+439 is most likely within a factor of 2 of this estimate and certainly within a factor of 10 (i.e. <11 000 yrs). This result therefore strongly supports the idea that Compact Symmetric Objects are very young radio-loud sources. Furthermore the large radiative efficiency we calculate for 0710+439 is consistent with strong negative luminosity evolution as CSOs grow in size and with them evolving into classical double sources.