4 Comments on individual sources

In the context, the apparent brightness temperature is given by Gopal-Krishna et al. (1984),

$$T_{\rm app}\geq \frac{2c^{2}\bigtriangleup S}{\pi \kappa \nu^{2}\theta_{\rm app}^{2}}~{\rm K},$$ (1)

when transforming to the co-moving frame of the source it becomes,

$$T'_{\rm app}\geq T_{\rm app}(1+z)^{3}\delta^{-3}~{\rm K},$$ (2)

where $\bigtriangleup S$ is the flux change during a period $\tau$, $\theta_{\rm app} \leq 2c\tau/D_{\rm a}$ the apparent diameter of the variable component based on the causality argument, $D_{\rm a}$ (Lang 1974) the angular distance of the source, and $\delta$ the Doppler factor.

• 0016+734: This quasar (z=1.781, in which highly superluminal motion is observed, SLM hereafter) shows a monotonic flux decrease at 6, 3.6 and 2.8 cm. Its modulation index is 38% at 6 cm. It belongs to a complete sample of flat spectrum sources in the S5 survey (S5 sample hereafter);

• 0134+329 (3C 48): This quasar (z=0.367) shows no flux variations as expected. It has been used as a primary flux calibrator;

• 0153+744: In this quasar (z=2.338, showing highly SLM), the modulation index is 3.8% at 6 cm. It belongs to the S5 sample;

• 0212+735: In this quasar (z=2.367, highly SLM), the modulation index increases with decreasing wavelength from 6.5% at 6 cm to 9.1% at 2.8 cm. Its spectrum at 6 and 2.8 cm has been inverted since around late 1996. It belongs to the S5 sample;

• 0235+164: In this BL Lac object (z=0.940, highly SLM), a pronounced outburst started at early 1997 and lasted to the end of our monitoring period at all observing wavelengths. Its modulation index increases with decreasing wavelength at 11, 6 and 2.8 cm. It is a IDV source discussed recently by Kraus et al (1999a). Its angular-diameter distance $D_{\rm a}$ is $1.72 \ 10^{3}$Mpc. Because of the flux change $\bigtriangleup S$ = 2.88Jy at 2.8cm during $\tau\sim 229$ days (which corresponds to the fastest flux change in the lightcurve), this corresponds to an apparent brightness temperature in the co-moving frame of the quasar, $T'_{\rm app}\geq 1.59\ 10^{14}\delta^{-3}$K. If the large excess of the brightness temperature over the inverse Compton limit of 10¹²K (Kellermann & Pauliny-Toth 1969) is due to a relativistic bulk motion (as suggested by Rees 1966b and by Woltjer 1966) of the variable component, a Doppler factor $\delta\geq 5.4$ is needed. The resultant $\delta$ is well within the "canonical'' value of 10, derived from VLBI and X-ray observations (see Ghisellini et al. 1993; Zensus 1997; Wagner & Witzel 1995);

• 0316+413 (3C 84): This galaxy (z=0.017, showing subluminal motion, Sub-LM hereafter) mostly shows a slow, monotonic flux decrease (with an exception at 21 cm where it is not variable), but with an increase in the middle of 1998 at 3.6 cm and a significant increase at 7 mm since 1994. Its modulation index at the level of 5 - 13% varies irregularly with wavelength;

• 0420-014: In this quasar (z=0.915), two outbursts cover the whole monitoring period at all observing wavelengths. Its modulation index decreases firstly from 11.5% at 6 cm to 9.3% at 2.8 cm, then increases to 12.9% at 1.3 cm;

• 0454+844: This BL Lac object (z=0.112, SLM), shows firstly a monotonic flux increase till the middle of 1995, then a monotonic decrease. Its modulation index at the level of 17 - 21% varies up and down with decreasing wavelength. It belongs to the S5 sample;

• 0518+165 (3C 138): This quasar (z=0.759) shows no flux variations as expected. It has been used as a primary flux calibrator;

• 0528+134: In this quasar (z=2.060, SLM), two pronounced outbursts covered the whole monitoring period at most of the observing wavelengths, but measurements were not available at 11 and 1.3 cm during the outbursts. The modulation index increases with decreasing wavelength at 11, 6 and 2.8 cm, but decreases by about 2% at 1.3 cm. The angular distance $D_{\rm a}$ is $1.63\ 10^{3}$Mpc. The flux change $\bigtriangleup S$ = 2.18Jy at 6cm during $\tau\sim 167.8$ days (the fastest flux change in the lightcurve) corresponds to an apparent brightness temperature $T'_{\rm app}\geq 3.48\ 10^{15}\ \delta^{-3}$K in the co-moving frame of the quasar. A Doppler factor $\delta\geq 15$ is needed in terms of a relativistic bulk motion, which is higher than the "canonical'' value of 10. However this agrees well with the suggested Doppler boosting (Krichbaum et al. 1995) and the observed superluminal motion (Krichbaum et al. 1995; Britzen et al. 1999) in this source, which is one of the strongest gamma-active blazars (Britzen et al. 1999);

• 0538+498 (3C 147): This quasar (z=0.545) shows no flux variations as expected. It has been used as a primary flux calibrator;

• 0615+820: In this quasar (z=0.710, SLM), the modulation index is 4.2% at 6 cm. It belongs to the S5 sample;
• 0716+714: In this BL Lac object (at uncertain redshift z=0.30, SLM), (quasi-)periodic flux variations appear simultaneously at all observing wavelengths. Remarkably, its modulation index at the level of about 25 -61% increases with decreasing wavelength, but has the same value at both 1.3 cm and 9 mm. It belongs to the S5 sample, showing close radio-optical IDV correlations (Quirrenbach et al. 1992; Wagner et al. 1996). Rapid variations on time scales of a few hours have been observed at 5 GHz (Quirrenbach et al. 1989). It is the only blazar showing the IDV phenomenon throughout the entire wavelength regime;

• 0735+178: In this BL Lac object (z=0.424, highly SLM), a monotonic flux decrease appears with a modulation index of 18.3% at 6 cm;

• 0804+499: In this quasar (z=1.433), a pronounced outburst started at early 1997 and continued to the end of the monitoring period at all observing wavelengths. Its modulation index increases by about 18% interval at wavelengths 11, 6 and 2.8 cm, then decreases by about 14% at 1.3 cm;

• 0835+580: This quasar (z=1.534, sub-SLM) shows no flux variations at all. Therefore it can be used as a secondary flux calibrator;

• 0836+710: In this quasar (z=2.172, highly SLM), a few outbursts appear with time delays at increasing wavelengths of 7 mm, 1.3, 2.8 and 6 cm. Its modulation index increases with decreasing wavelength till 2.8 cm, then decreases to about 20.2% at 7 mm. VLBI monitoring observations during 1993-1996 revealed the ejection of a new jet component, and gamma to radio variations of the flux density were observed in the first half of 1992, indicating a correlation of the jet activity with the variability of the broad-band electromagnetic spectrum of the source (Otterbein et al. 1998). It belongs to the S5 sample, and once showed weak IDV at a very low level (Kraus 1997). No variations were seen by Quirrenbach et al. (2000), and it has been further suggested to serve as a polarization calibrator because of its high degree of polarization;

• 0851+202 (OJ287): In this BL Lac object (z=0.306, SLM), significant variations appear. Its modulation index increases with decreasing wavelength till 2.8 cm, then decreases to 16.3% at 1.3 cm;

• 0917+624: In this quasar (z=1.446, SLM), smooth variations appear. Its modulation index varies with wavelength. It is an IDV source with a change in the variability properties (Kraus et al. 1999b);

• 0923+392 (4C 39.25): In this quasar (z=0.698, SLM), smooth flux variations appear with a wavelength-independent modulation index of 3.3%;

• 0951+699: This galaxy (z= 0.001) shows no flux variations at all. It can be used as a secondary flux calibrator;

• 0954+658: In this BL Lac object (z=0.367), a pronounced outburst appears. Its modulation index increases with decreasing wavelength till 3.6 cm, but decreases to 28.4% at 2.8 cm;

• 1039+811: In this quasar (z=1.254, highly SLM), a flux increase appeared since early 1997 at 6 and 2.8 cm. Its modulation index is almost the same at 6 cm and 2.8 cm. It belongs to the S5 sample;

• 1150+812: In this quasar (z=1.250, SLM), a monotonic flux increase appears at 21, 11, and 6 cm since 1994. Its modulation index is 8% at 6 cm. It belongs to the S5 sample;

• 1226+023 (3C 273): In this quasar (z=0.158, highly SLM), smooth flux variations appear. Its modulation index is 6% at 6 cm;

• 1253-055 (3C 279): In this quasar (z=0.536, highly SLM), smooth flux variation appears with a modulation index of 21% at 6 cm.

• 1328+307 (3C 286): This quasar (z=0.849) shows no flux variations as expected. It has been used as a primary flux calibrator;

• 1409+524 (3C 295): This galaxy (z=0.461) shows no flux variations as expected. It has been used as a primary flux calibrator;

• 1458+718 (3C 309.1): This quasar (z=0.905, highly SLM) has modulation indices of 5% at 6 cm and 7.6% at 2.8 cm;

• 1641+399 (3C 345): In this quasar (z=0.594, highly SLM), smooth flux variations appear. Its modulation index increases with decreasing wavelength;

• 1652+398: In this BL Lac object (z=0.034), very slow and weak flux variations appear. Its modulation index is 3% at 11 cm, then increases with decreasing wavelength;

• 1739+522: In this quasar (z=1.379), two (adjacent) continuous outbursts appear at 6 and 2.8 cm. Its modulation index varies with wavelength;

• 1749+701: In this BL Lac object (z=0.770, SLM), a pronounced outburst appeared at 6 cm since mid-1996. But there were no measurements available at other wavelengths during the outburst. Its modulation index is about 9% at 6 cm. It belongs to the S5 sample;

• 1803+784: In this superluminal source, classified variously as a BL Lac object or quasar (z=0.684), significant flux variations appear at 6 cm. Its modulation index decreases from 11.5% to 5.6% between wavelengths of 11 cm and 1.3 cm, but is almost the same at 6 and 3.6 cm. It belongs to the S5 sample;

• 1823+568: In this BL Lac object (z=0.664, SLM), a monotonic flux decrease appears at both 6 and 2.8 cm. Its modulation index is 21% at 2.8 cm;

• 1928+738: In this quasar (z=0.302, highly SLM), weak flux fluctuations appeared at most wavelengths since 1994. Its modulation index mostly increases with decreasing wavelength. It belongs to the S5 sample, sometimes showing weak IDV (Heeschen et al. 1987; Kraus 1997), but no variations were seen by Quirrenbach et al. (2000);

• 2007+777: In this BL Lac object (z=0.342, SLM), outbursts appeared at wavelengths longer than 2.8 cm. Its modulation index at the level of about 9 - 16% varies irregularly with wavelength. It belongs to the S5 sample. Simultaneous variability on time scales of a few days was found at radio, infrared and optical regimes (Peng et al. 2000);

• 2105+420 (NGC 7027): This planetary nebula (denote PN in Table 1), shows no flux variations as expected. It has been used as a primary flux calibrator;

• 2200+420: In this BL Lac object (z=0.069, SLM), a long-term (of more than 4 years at least) outburst on which many small flares are superimposed appeared. Its modulation index goes up by about 6% from 11 to 6 cm, then appears almost wavelength-independent at shorter wavelengths;

• 2251+158 (3C 454.3): In this quasar (z=0.859, highly SLM), two small outbursts appeared since 1994. Its modulation index increases with decreasing wavelength.