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Astron. Astrophys. 345, 414-418 (1999)

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Simultaneous multifrequency observations of the BL Lac MS 0205.7+3509

D. Watson 1, L. Hanlon 1, B. McBreen 1, N. Smith 2, M. Tashiro 3, A.R. Foley 4, L. Metcalfe 5, V. Beckmann 6, S.F. Sánchez 7 and H. Teräsranta 8

1 Department of Experimental Physics, University College Dublin, Belfield, Dublin 4, Ireland
2 Department of Applied Physics and Instrumentation, Cork Institute of Technology, Cork, Ireland
3 Department of Physics, University of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
4 Netherlands Foundation for Research in Astronomy, Dwingeloo, The Netherlands
5 ISO Science Operations Centre, Villafranca del Castillo, Madrid, Spain
6 Hamburger Sternwarte, Gojenbergsweg 112, D-21029 Hamburg, Germany
7 IFCA-Departament de Física Moderna, CSIC-Universitat de Cantabria, Santander, Spain
8 Metsähovi Radio Research Station, Kylmälä, Finland

Received 15 October 1998 / Accepted 3 February 1999


Radio and optical observations of the possible microlensed BL Lac source MS 0205.7+3509 were obtained simultaneously with ASCA x-ray measurements in February 1997. A single power law model, with a photon index of 2.61, is an adequate fit to the ASCA data, once hydrogenic absorption in excess of the Galactic value is permitted, confirming a previous ROSAT measurement. On the basis of our simultaneous data we have determined MS 0205.7+3509 to be a typical x-ray selected BL Lac, with [FORMULA]. There is no indication of an inverse Compton (IC) component in the ASCA spectrum up to 10 keV. No evidence for variability on hour-long timescales is present in either the x-ray or the optical data. We discuss these results in the context of a gravitational microlensing scenario for MS 0205.7+3509.

Key words: X-rays: galaxies – cosmology: gravitational lensing – galaxies: BL Lacertae objects: individual: MS 0205.7+3509

Send offprint requests to: dwatson@bermuda.ucd.ie

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© European Southern Observatory (ESO) 1999

Online publication: April 19, 1999