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Session 84 - QSOs and BL Lacs.
Display session, Wednesday, January 17
North Banquet Hall, Convention Center

[84.11] Difference between X-Ray-Selected and Radio-Selected BL Lacertae Objects in EGRET Observations

Y. C. Lin, P. F. Michelson, P. L. Nolan, T. D. Willis (Stanford), D. L. Bertsch, C. E. Fichtel, R. C. Hartman, S. D. Hunter, D. J. Thompson (NASA/GSFC), B. L. Dingus, J. A. Esposito, R. Mukherjee (USRA/GSFC), C. von Montigny (NAS/NRC/GSFC), D. A. Kniffen (Hampden-Sydney), G. Kanbach, H. A. Mayer-Hasselwander (MPE), E. J. Schneid (Northrope/Grumman)

In the course of the Compton Observatory mission, the EGRET telescope has detected 12 BL Lac objects in high-energy gamma rays. According to the BL Lac sample in Ciliegi, Bassani, and Caroli (1995, ApJ, 439, 80) [CBC95], 3 of these 12 sources are X-ray-selected (XBL), 8 are radio-selected (RBL), and 1 is not listed in this sample. At 5 GHz, the average radio flux of the 3 XBL is \sim 0.7 Jy, the lowest value being 0.31 Jy, compared to an average value of \sim 3.0 Jy for the 8 RBL, according to the radio fluxes quoted in Véron-Cetty and Véron (1993, ESO Scientific Report No. 13) [VV93]. But at 3 keV and in the units of 10^-29 erg cm^-2 s^-1 Hz^-1, the average X-ray flux of the 8 RBL is \sim 0.2, the lowest value being 0.02 and with 4 values below 0.1, compared to an average value of \sim 3.2 for the 3 XBL, as quoted in [CBC95]. Thus while the radio fluxes of the EGRET detected BL Lac's are at least moderately strong, there does not seem to be a similar correlation between the high-energy gamma-ray fluxes and the X-ray fluxes for these sources. Furthermore, for the BL Lac objects listed in [CBC95] that are not detected by EGRET, co-adding of the EGRET data for the undetected RBL, in a way that the source positions coincide with each other, yields a flux excess at a 3-\sigma significance level. But similar co-adding of the EGRET data for the undetected XBL yields no flux excess. These results will be discussed in the paper.

Program listing for Wednesday