Search

A widely accepted model for BL Lac objects is that they are radio galaxies with a relativistic jet pointing almost directly towards us. But we need a clear trigger mechanism for these jets. One possibility is the close interaction between the BL Lac host and the closeby galaxies (e.g. Heckman et al. 1986). This interaction has been seen many times in the case of quasars (Hutchings et al. 1989) but not so much is known about the close surroundings of the BL Lac objects although there has been some pioneer work like Stickel et al. (1993). The problem has usually been that the images are not deep enough and that the seeing has not been so good. To clarify the situation we have started an observing program to get very deep images in the sub-arcsecond seeing conditions from the whole 1 Jy sample (Stickel et al. 1991) of BL Lac objects. The aims of this study are: 1. to search for very close companions to the BL Lacs, 2. to study the large scale galaxy clustering around the BL Lacs and 3. to study the BL Lac hosts themselves.

Blazar OJ 287 is one of the best observed extragalactic objects. It's historical light curve goes back to 1890′s. Based on the historical behaviour Sillanpää et al. (1988) showed that OJ 287 displays large periodic outbursts, with a period of 11.7 years. We have monitored OJ 287 intensively for two years, during the OJ-94 project. This project was created for monitoring OJ 287 during its predicted new outburst in 1994. In the data archive we have over 7000 observations on OJ 287, in the radio, infrared and optical bands. This data archive contains the best ever obtained light curves for any extragalactic object. The optical light curve shows continuous variability down to time scales of tens of minutes. The variability observed in OJ 287 can be broken down to (at least) four different categories

We present high-resolution imaging of the BL Lac objects 1ES 0229+200 (z = 0.14), Markarian 421 (z = 0.031) and the prototype BL Lac (z = 0.069). Our goal is to study the properties of the host galaxies of this enigmatic sources and to compare them with their non-actice counterparts. The observations were carried out with the Nordical Optical Telescope (NOT) at La Palma under sub-arcsecond seeing conditions (FWHM < 0.″8). The surface brightness profiles of the host galaxies were analyzed as described in Bender and Möllenhoff (A&A, 177, 71 (1987)). After masking the disturbing field stars/galaxies isophotes were fitted by ellipses down to 20.5 mag/arccsec2 in Markarian 421, 23.5 mag/arcsec2 in BL Lac and 25.5 mag/arcsec2 in 1ES 0229+200. Additionally, we analyzed the surface brightness profile of the companion of Markarian 421.The surface brightness profiles of the host galaxies were analyzed as described in Bender and Möllenhoff (A & A, 177, 71 (1987)). After masking the disturbing field stars/galaxies isophotes were fitted by ellipses down to 20.5 mag/arccsec2 in Markarian 421, 23.5 mag/arccsec2 in BL Lac and 25.5 mag/arccsec2 in 1ES 0229+200. Additionally, we analyzed the surface brightness profile of the companion of Markarian 421.