Astron. Astrophys. 347, 419-423 (1999)

1. Introduction

Blazars are AGNs characterized by compact radio core, high and variable radio and optical polarization, superluminal radio components. The continuum emissions are rapidly variable at all frequencies with amplitude of variability increasing with frequency (see Kollgaard 1994, Urry & Padovani 1995 and Scarp & Falomo 1997). Blazars include BL Lac objects, optically violently variable quasars (OVVs), highly polarized quasars (HPQs), flat spectrum radio quasars (FSRQs), and core dominated quasars (CDQ). All those objects are basically the same thing (Fugmann 1989; Impey et al. 1991; Valtaoja et al. 1992; Will et al. 1992; Scarpa & Falomo 1997).

3C 279 (PKS 1253-055, 4C-05.55) and 4C 29.45 (QSO 1156+295, Ton 599) are blazars. These two objects have some interesting observation properties. They are QSOs showing properties similar to those of a BL Lacertae object: Large amplitude variation and high and variable polarization. 4C 29.45 is classified as a BL Lac object (see Fan et al. 1993 and references therein), but its line spectrum looks like that of a normal QSOs when the continuum is faint (B 18) (Wills et al. 1983). 3C 279 occupies the same place as radio selected BL Lacertae objects (RBLs) in the polarization-Doppler factor diagram and is more like an RBL than a QSO (Fan 1998).

Before -ray observations were available, Impey & Neugebauer (1988) found that the infrared emission (1-100 ) dominates the bolometric luminosities of blazars. The infrared emission is also an important component for the luminosity even when the -ray emissions is included (von Montigny 1995). The high energetic -ray emission mechanism is still an open problem (see Fan et al. 1998a, and references therein). Recently, Xie et al. (1997) found that the high energy -rays are correlated with the near-IR emissions suggesting that the soft photons scattered to the -rays region are from the dust. So, study of the infrared will throw some lights on the understanding of the emission mechanisms in AGNs, particularly temporal correlation.

Blazars have been observed in the infrared region for more than 20 years, but there are no available long-term infrared variations in the literature for all these objects. In this paper, we present the long-term infrared (J,H, and K bands) light curves for 3C 279 and 4C 29.45 and discuss the variation properties in these wavebands. The paper has been arranged as follows: In Sect. 2, we present the literature for the data and the light curves; in Sect. 3, we discuss them and give a brief conclusion.

© European Southern Observatory (ESO) 1999

Online publication: June 30, 1999
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