1517+656: a BL Lac in its Birth-Throes

O'Dowd, Matthew; Urry, C. Megan; Scarpa, Riccardo
Referencia bibliográfica

Quasar Cores and Jets, 25th meeting of the IAU, Joint Discussion 18, 23-24 July 2003, Sydney, Australia

Fecha de publicación:
0
2003
Número de autores
3
Número de autores del IAC
0
Número de citas
0
Número de citas referidas
0
Descripción
The BL Lac 1517+656 is an extreme example of its class. Not only is it the most optically luminous BL Lac known but this extreme emission extends to both radio and X-ray frequencies. In our WFPC2 snapshot survey we discovered a series of arcs describing a 2 arcsecond ring surrounding the object. Follow-up observations with additional WFPC2 bands and the STIS longpass filter have revealed this structure to be the remnants of a very recent galaxy merger. Population synthesis modelling has shown that regions of the arcs have stellar populations with age <0.02 Gyrs. Additionally the circularity of the arcs indicates that the plane of the collision and hence accretion is very close to the plane of the sky. If activity in this source was sparked by the current interaction then this constraint on the accretion plane gives an independent indicator of the jet angle: less than 20 degrees from line of sight. Alternately if we assume a priori that BL Lac jets are very close to the line of sight then this observation indicates that jet angle is defined by the plane of collision. Regardless all evidence suggests that 1517+656 is a BL Lac in its birth-throes.