Two X-Ray--selected BL Lacertae Objects Observed with the HEAO 1 Scanning Modulation Collimator
Abstract
We have discovered two 16th magnitude BL Lac objects, H1101-232 and H1426+428, during an ongoing program to identify the optical counterparts of X-ray sources from the HEAO 1 survey. Each is a persistent and relatively bright X-ray source that was also detected by the Uhuru and Ariel 5 surveys. Our classifications are based on the combined observations of featureless optical continua, compact radio emission, and images of the underlying host galaxies. In addition, we have measured 2.7% linear polarization in the optical emission of H1101-232. We have confirmed the X-ray identification of H1426+428 in an observation with EXOSAT. The EXOSAT X-ray spectrum is well modeled by a power law with an energy index of 1.19. Both BL Lac objects exhibit high f_x_/f_opt_ ratios, and they show a distinct resemblance to other X-ray-selected BL Lac objects. The host galaxies are ~ 18th mag with angular diameters ~ 20", and each may be the dominant member of a cluster of galaxies. Additional wide-slit spectroscopy reveals faint absorption features with redshifts of 0.129 for H1426+428 and 0.186 for H1101-232. The implied X-ray and optical luminosities exceed 10^45^ ergs s^-1^ for both BL Lac nuclei, assuming isotropic emission. The optical brightness of H1101-232 faded by 0.3-0.6 mag during most of 1987. The HEAO 1 survey continues to identify BL Lac objects at a rate ~ 15% of the total number of active galactic nuclei, in sharp contrast with the statistics of the Einstein serendipitous sources at lower X-ray flux. Since the percentage of measurable redshifts is high among HEAO 1 BL Lacs (14 of 24, currently), the flux-limited subset of HEAO 1 LASS-MC identifications may clarify this problem by constraining the luminosity function of nearby, X-ray-selected BL Lac objects.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 1989
- DOI:
- 10.1086/167888
- Bibcode:
- 1989ApJ...345..140R
- Keywords:
-
- Active Galactic Nuclei;
- Bl Lacertae Objects;
- Sky Surveys (Astronomy);
- X Ray Sources;
- Astronomical Photometry;
- Heao 1;
- Linear Polarization;
- Radio Emission;
- Red Shift;
- Visible Spectrum;
- Astrophysics;
- BL LACERTAE OBJECTS;
- GALAXIES: CLUSTERING;
- GALAXIES: NUCLEI;
- X-RAYS: SOURCES