BL Lac天体Mkn 421的MERLIN图像

MERLIN MAPS OF BL LAC OBJECT MKN421

本文介绍BL Lac天体Mkn 421在频率408MHz(λ73cm)和5GHz(λ6cm)上的MERLIN图像.它们填补了角分尺度的VLA图像和高分辨率的毫角秒尺度的VLBI图像之间的空缺.两频率上的图像均呈略分解状态:408MHz的MERLIN图像在朝东和朝西北方向有延伸的趋势,两个延伸方向与1.5GHz(λ20 cm)的VLA图像上的延伸方向一致;5GHz的MERLIN图像包括一个致密核和一个围绕核的低表面亮度的晕。晕呈椭圆状,其长轴方向与5GHz的VLBI图像中的喷流方向相同。Mkn421具有较弱的BL Lac天体的特征.一般认为这类天体的射电核的特殊性质是由于物质沿视线方向的相对论性运动而形成,所以它们的观测角应当较小.但是,VLA、MERLIN和VLBI的观测结果表明Mkn421可能有较大的观测角.

For getting arcsec scale and subarcsec sca e structures of Mkn421, its MERLIN data of 408 MHz and 5 GHz were processed. This paper presents their maps. On the 408-MHz MERLIN map, there are two extensions, which coincide with the directions of extension shown on the 1.5-GHz VLA map, towards the East and the Northwest respectively. The 5-GHz MERLIN map consists of a core surrounding by a low brightness, elliptic halo. The direction of long axis of ellipse is about the same as that of the jet shown on the 5-GHz VLBI maps. A commonly held belief is that the radio cores of BL Lac objects are generated by relativistically moving material along the line of sight. So, their viewing angle should be narrower. The results of VLA, MERLIN and VLBI observations suggest that it is possible to have a wider viewing angle for Mkn421 which could come into conflict with the assumption described above.