Multiwavelength Monitoring of the BL Lacertae Object PKS 2155−304 in 1994 May. I. The Ground‐based Campaign

Abstract

Optical, near-infrared, and radio observations of the BL Lac object PKS 2155[304 were obtained simultaneously with a continuous UV/EUV/X-ray monitoring campaign in 1994 May. Further optical observations were gathered throughout most of 1994. The radio, millimeter, and near-infrared data show no strong correlations with the higher energies. The optical light curves exhibit Ñickering of 0.2È0.3 mag on timescales of 1È2 days, superposed on longer timescale variations. Rapid variations of D0.01 mag minute~1, if real, are the fastest seen to date for any BL Lac object. Small (0.2È0.3 mag) increases in the V and R bands occur simultaneously with a Ñare seen at higher energies. All optical wave bands (UBV RI) track each other well over the period of observation, with no detectable delay. For most of the period the average colors remain relatively constant, although there is a tendency for the colors (in particular, B[V) to vary more when the source fades. In polarized light, PKS 2155[304 showed strong color dependence (polarization increases toward the blue, and the highest optical polariza-P U /P I \ 1.31) tion (U \ 14.3%) ever observed for this source. The polarization variations trace the Ñares seen in the UV Ñux. For the fastest variability timescale observed, we estimate a central black hole mass of [1.5 ] 109(d/10) consistent with UV and X-ray constraints and smaller than previously calculated for M _ , this object.

Multiband Optical Polarimetry of the BL Lacertae Object PKS 2155−304: Intranight and Long‐Term Variability

“…For the uncertainties on the data points, see Table 2. (Brindle et al 1986 ;Mead et al 1990 ;Smith & Sitko 1991 ;Smith et al 1992 ;Allen et al 1993 ;Jannuzi et al 1993b ;Courvoisier et al 1995 ;Pesce et al 1997). be wavelength dependent because its spectrum should be signiÐcantly redder than that of the nucleus. In fact, given the measured magnitudes of the host galaxy (M H \ [26.8 ;Kotilainen, Falomo, & Scarpa 1998 and M I \ [24.2 ;Falomo et al 1991), using the color indices of a typical elliptical galaxy reported by Fukugita, Shimasaku, & Ichikawa (1995), Kotilainen et al (1998), andBertone et al (2000), we calculated the host galaxy Ñux in the F host UBV RI bands.…”

“…The BL Lac object PKS 2155[304 is a nearby blazar (z \ 0.116 ; see Falomo, Pesce, & Treves 1993), one of the brightest at optical to X-ray frequencies, and its polarized optical light has been observed over many years by Brindle et al (1986), Mead et al (1990), Smith & Sitko (1991), Smith et al (1992), Allen et al (1993), Jannuzi et al (1993b), Cour-voisier et al (1995), and Pesce et al (1997). The main results are a polarization fraction P varying from 2% to 10%, a position angle P.A.…”

Long-term optical variability of PKS 2155-304

“…(1) Griffiths et al (1979); (2) Griffiths et al (1979), (3) Miller & McAlister (1983), (4) Brindle et al (1986), (5) Hamuy & Maza (1987), (6) Pica et al (1988), (7) Treves et al (1989), (8) Mead et al (1990), (9) Smith & Sitko (1991), (10) Carini & Miller (1992), (11) Smith et al (1992), (12) Jannuzi et al (1993) and (13) Urry et al (1993) as collected in Zhang & Xie (1996); (14) Campbell (2004), (15) Courvoisier et al (1995) and (16) Pesce et al (1997) as collected in Osterman et al (2007); (17) Tommasi et al (2001). Table 1 shows statistics of the data on PKS 2155-304.…”

Astrophysics in 1997

“…Several papers estimated or limited central black hole masses using indirect methods, including the shape of the big blue bump in the continuous spectrum (Wang & Zhou 1996), timescale of variability (Pesce et al 1997 and two following papers), rising central rotation curves (Keneko et al 1997), total luminosities (Di Matteo & Fabian 1997), velocity profiles (van den Bosch & de Zeeuw 1996), line asymmetries (Nandra et al 1997), and polarization (Lee & Blandford 1997). Possibly these tell us more about the opinion of the authors than about the galactic centers in question, but also that said opinion is overwhelmingly pro-black hole.…”