Infrared Variation of Radio‐selected BL Lacertae Objects

Abstract

In this paper, the historical infrared (JHK) data compiled from the published literature are presented in electronic form for 40 radio selected BL Lacertae objects (RBLs) for the first time. Largest variations are found and compared with the largest optical variation. Relations between color index and magnitude and between color-color indices are discussed individually. For the color-magnitude relation, some objects ( 0048-097, 0735+178, 0851+202, 1215+303, 1219+285, 1749+096, and perhaps 0219+428, show that color index increases with magnitude indicating that the spectrum flattens when the source brightens while some other objects ( 0754+100, 1147+245, 1418+546, and 1727+502) perhaps show an opposite behaviour, while remaining objects do not show any clear tendency; For color-color relation, it is found common that (J-K) is closely correlated with (J-H) while (J-H) is not correlated with (H-K).Subject headings: Variability-Infrared-BL Lacertae Objects 10, the uncertainty in Col. 9 and 10 is the one sigma deviation. The infrared variations are very large for some objects. The color indices are also variable and associated with the magnitude for some objects, indicating that the spectrum flattens when the source brightens while some objects show different behaviours. For variation, it is reasonable for larger variation to correspond to shorter wavelength, but this paper shows that some objects do show a different behaviour. The objects showing large optical variation also show large infrared variations and high polarizations. Large variation and high polarization are associated. For the color-indices, it is common that there is a correlation for (J-K) and (J-H) while there is almost no correlation for (J-H) and (H-K) although some objects show different properties. But, when the averaged color indices are taken into account, there are mutual correlations between any two color indices of (J-H), (J-K) and (H-K) with the correlation between (J-H) and (H-K) being not so close as compared with other two correlations. (J-K) = 2.26(J-H) -0.28 with correlation coefficient r = 0.90 and the probability of chance correlation p = 6.3 × 10 −11 , (H-K) = 1.44(J-H) -0.41 with r = 0.80and p = 4.4 × 10 −7 , and (J-K) = 1.62(H-K) + 0.33 with r = 0.93 and p = 6.1 × 10 −13 . The (J-H) and (H-K) relation is shown in Fig. 1. In the next section, individual objects are discussed. Remarks PKS 0048-097, OB − 081, MC3, P HL856There is no redshift available for this polarized ( P 3.7cm = 9.3%, Wardle 1978;P opt =1%-27 %, CH(84); Brindle et al. 1986 ) object. Very faint infrared fluxes have been observed by Gear (1993), which leads the object to have the largest infrared variation among the objects discussed in the present paper. The infrared variations are ∆J = 6.55, ∆H = 6.23, and ∆K = 6.07 while that in the optical band is 2.7 mag (Angel & Stockman 1980). We can expect that the optical monitoring should get a similar amplitude. For color-color indices, there are correlations for (J-K) and (J-H) and for (J-K) and (H-K):(J-K) = 1.20(J-H) +...

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