Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 1976
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1976apj...207..359m&link_type=abstract
Astrophysical Journal, vol. 207, July 15, 1976, pt. 1, p. 359-363. NSF-supported research;
Astronomy and Astrophysics
Astronomy
11
Astronomical Photometry, Extragalactic Radio Sources, Quasars, Spaceborne Astronomy, X Ray Sources, Brightness Temperature, Oao 3, Photographic Plates, Proportional Counters, Size (Dimensions)
Scientific paper
Results are reported for X-ray observations and nearly simultaneous photographic photometry of four BL Lacertae objects (BL Lac, W Com, ON 325, and AP Lib). The X-ray data were obtained in the band from 2.5 to 7.5 keV using a collimated proportional counter aboard OAO-C. Although none of the sources was detected above background at a statistically significant level, two-sigma upper limits on the X-ray flux incident at earth are given for each object. The photometric data indicate that all four objects were near the faint end of their visibility ranges during the time of the X-ray observations. The X-ray upper limits and B magnitudes are employed to calculate upper limits on the brightness temperatures and angular sizes of the radio synchrotron sources; upper limits on the distances to the objects are obtained from limits on the physical source sizes deduced from the radio variabilities. The strictest distance limit is 240 Mpc for BL Lac. Substantial evidence is noted for variability of ON 325 on a timescale of hours.
Bowyer Stuart
Davidsen Arthur
Jones Thomas W.
Margon Bruce
Mason Keith O.
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