1 Introduction

Since the detections of high-frequency variability (Kellermann & Pauliny-Toth 1968) and low-frequency variability (e.g. Hunstead 1972), many extragalactic sources have been found to show significant variability at various frequencies, on time scales of months to a few years (e.g. Dennison et al. 1981), and even of a day (Witzel et al. 1986; Heeschen et al. 1987). Both relativistic bulk motion (Rees 1966a; Jones & Burbidge 1973; Burbidge et al. 1974; Blandford & Königl 1979) and refractive interstellar scintillation (e.g. Rickett 1986) are commonly invoked to explain the various variability phenomena detected.

In order to study the long-term variability behavior of extragalactic radio sources over a range of wavelengths, several monitoring programs have been carried out (Spangler & Cotton 1981; Aller et al. 1985; Padrielli et al. 1987; Salonen et al. 1987; Bregman et al. 1990; Teräsranta et al. 1992; Bloom et al. 1999). We have carried out flux monitoring of selected sources over a wide range of wavelengths with the Effelsberg 100 m radio telescope since 1994. Here we present the results of this long-term monitoring for 40 sources at several wavelengths. Among them, 13 compact extragalactic radio sources, with a declination $\delta \geq 70^{\rm o}$, a galactic latitude $\vert b^{\rm II}\vert \geq 10^{\rm o}$, flux density at 5 GHz $S_{\rm 5GHz} \geq 1$ Jy, and spectral index (between $\lambda =11$ cm and $\lambda =6$ cm) $\alpha_{6}^{11} \leq 0.5$ ( $S \sim \nu^{-\alpha}$), form a complete sample of flat spectrum sources from the S5 Survey (Kühr et al. 1981).

In the following section, we briefly introduce the observations and data reduction. In Sect. 3 the results for all 40 extragalactic radio sources are presented, including light curves, spectra and statistics. Subsequently, we make brief comments on individual sources. Observational findings are summarized in Sect. 5. Throughout the paper the radio spectral index is defined by $S_{\nu} \propto \nu^{-\alpha}$, a deceleration parameter q₀=0.5 and a Hubble constant of H₀=50kms^-1Mpc^-1 are used.

 

 

Table: Source properties: Opt. Id. denotes the optical identification, $b^{\rm II}$ the galactic latitude, z the redshift, $\alpha$ ( $\alpha _{6}^{11}, \alpha _{2.8}^{6}$) spectral indices, $\beta _{\rm a}$ apparent superluminal speed (in unit of speed of light c), Ref. reference for $\beta _{\rm a}$, and IDV or not

Source	Other name	Opt. Id.	$b^{\rm II}$	z	$\alpha _{6}^{11}$	$\alpha _{2.8}^{6}$	$\beta _{\rm a}$	Ref.	IDV
0016+731	*	QSO	$+10.7^{\rm o}$	1.781	$+0.06\pm 0.94$	$-0.07\pm 0.62$	16.6	S92	+
0134+329	3C 48	QSO	$-28.7^{\rm o}$	0.367	$+0.89\pm 0.02$	$+1.02\pm 0.02$
0153+744	*	QSO	$+12.4^{\rm o}$	2.338	$+0.72\pm 0.06$	$+0.97\pm 0.05$	29.4	W88	+
0212+735	*	QSO	$+12.0^{\rm o}$	2.367	$-0.26\pm 0.18$	$-0.04\pm 0.14$	36.8	W88	-
0235+164		BLL	$-39.1^{\rm o}$	0.940	$+0.16\pm 1.39$	$-0.57\pm 1.31$	54.0	Chu	+
0316+413	3C 84	GAL	$-13.3^{\rm o}$	0.017	$+0.28\pm 0.25$	$+0.19\pm 0.18$	0.4	R84	-
0420-014		QSO	$-33.1^{\rm o}$	0.915	$-0.26\pm 0.19$	$-0.24\pm 0.19$			?
0454+844	*	BLL	$+24.7^{\rm o}$	0.112	$-0.05\pm 0.42$	$+0.18\pm 0.35$	>3.2	S92	?
0518+165	3C 138	QSO	$-11.3^{\rm o}$	0.759	$+0.68\pm 0.02$	$+0.78\pm 0.02$
0528+134		QSO	$-11.0^{\rm o}$	2.060	$-0.74\pm 0.53$	$-0.16\pm 0.67$	12.4	B99	?
0538+498	3C 147	QSO	$+10.3^{\rm o}$	0.545	$+0.88\pm 0.02$	$+0.91\pm 0.03$
0615+820	*	QSO	$+26.0^{\rm o}$	0.710	$+0.21\pm 0.09$	$+0.37\pm 0.10$	<4.4?	S92	-
0716+714	*	BLL	$+28.0^{\rm o}$	0.30?	$-0.05\pm 0.76$	$-0.13\pm 0.86$	4.6	S92	+
0735+178		BLL	$+18.1^{\rm o}$	0.424	$+0.30\pm 0.29$	$+0.58\pm 0.39$	>14.4	M90	+
0804+499		QSO	$+32.6^{\rm o}$	1.433	$+0.03\pm 0.50$	$-0.13\pm 0.70$			+
0835+580		QSO	$+36.9^{\rm o}$	1.534	$+1.09\pm 0.03$	$+1.20\pm 0.06$	-0.7	H93	?
0836+710	*	QSO	$+34.4^{\rm o}$	2.172	$+0.34\pm 0.20$	$+0.14\pm 0.38$	21.6	O98	+
0851+202	OJ 287	BLL	$+35.8^{\rm o}$	0.306	$-0.27\pm 0.33$	$-0.15\pm 0.32$	6.4	M90	+
0917+624		QSO	$+41.0^{\rm o}$	1.446	$-0.15\pm 0.17$	$+0.02\pm 0.16$	7.8	S96	+
0923+392	4C 39.25	QSO	$+46.2^{\rm o}$	0.698	$-1.01\pm 0.08$	$-0.23\pm 0.06$	7.1	S87	-
0951+699		GAL	$+40.6^{\rm o}$	0.001	$+0.69\pm 0.02$	$+0.76\pm 0.02$			-
0954+658		BLL	$+43.1^{\rm o}$	0.367	$-0.07\pm 0.58$	$-0.05\pm 0.49$	12.4	G96	+
1039+811	*	QSO	$+34.7^{\rm o}$	1.254	$-0.04\pm 0.19$	$-0.41\pm 0.14$	35.6	W88	?
1150+812	*	QSO	$+35.8^{\rm o}$	1.250	$+0.07\pm 0.21$	$-0.01\pm 0.10$	7.0	W88	+
1226+023	3C 273	QSO	$+64.4^{\rm o}$	0.158	$+0.23\pm 0.12$	$+0.19\pm 0.17$	16.1	C87	-
1253-055	3C 279	QSO	$+57.1^{\rm o}$	0.536		$-0.62\pm 0.43$	18.4	C79	-
1328+307	3C 286	QSO	$+80.7^{\rm o}$	0.849	$+0.59\pm 0.02$	$+0.68\pm 0.02$
1409+524	3C 295	GAL	$+60.8^{\rm o}$	0.461	$+1.05\pm 0.02$	$+1.21\pm 0.02$
1458+718	3C 309.1	QSO	$+42.1^{\rm o}$	0.905	$+0.57\pm 0.09$	$+0.48\pm 0.11$	13.1	K90	-
1641+399	3C 345	QSO	$+40.9^{\rm o}$	0.594	$-0.03\pm 0.07$	$+0.08\pm 0.11$	18.9	BM	-
1652+398		BLL	$+38.9^{\rm o}$	0.034	$+0.13\pm 0.07$	$+0.17\pm 0.05$			+
1739+522		QSO	$+31.7^{\rm o}$	1.379	$-0.13\pm 0.83$	$-0.04\pm 0.69$			+
1749+701	*	BLL	$+30.7^{\rm o}$	0.770	$+0.05\pm 0.17$	$+0.06\pm 0.23$	4.7	M90	+
1803+784	*	BL?	$+29.1^{\rm o}$	0.684	$-0.18\pm 0.24$	$-0.05\pm 0.15$	7.8	S92	+
1823+568		BLL	$+26.1^{\rm o}$	0.664	$-0.23\pm 0.21$	$-0.02\pm 0.31$	5.1	G89	+
1928+738	*	QSO	$+23.5^{\rm o}$	0.302	$-0.01\pm 0.09$	$+0.06\pm 0.10$	14.1	E85	+
2007+777	*	BLL	$+22.7^{\rm o}$	0.342	$-0.04\pm 0.32$	$+0.05\pm 0.27$	4.7	M90	+
2105+420	NGC 7027	PN	$-3.5^{\rm o}$		$-0.67\pm 0.02$	$-0.12\pm 0.02$
2200+420	BLLAC	BLL	$-10.4^{\rm o}$	0.069	$-0.08\pm 0.47$	$-0.04\pm 0.36$	7.5	M90	+
2251+158	3C 454.3	QSO	$-38.2^{\rm o}$	0.859	$-0.14\pm 0.19$	$+0.29\pm 0.27$	17.7	PT	-

Notes for columns in Table 1 - for Other name, a $\star$ marks the source which belongs to the S5 survey; for Opt. Id., PN stands for Planetary Nebulae; for z and $\alpha _{6}^{11}$, blank if it is not available; for IDV, + if it shows at least once IDV, - if not, ? if unclear yet, blank if it is a primary flux calibrator source.

Notes for references in Table 1 - BM: Biretta et al. 1986, B99: Britzen et al. 1999, C87: Cohen et al. 1987, C79: Cotton et al. 1979, Chu: Chu et al. 1996, E85: Eckart et al. 1985, G89: Gabuzda et al. 1989, G96: Gabuzda et al. 1996, H93: Hough et al. 1993, K90: Kus et al. 1990, M90: Mutel 1990, O98: Otterbein et al. 1998, PT: Pauliny-Toth et al. 1987, R84: Romney et al. 1984, S87: Shaffer et al., 1987, S92: Schalinski et al. 1992, S96: Standke et al. 1996, W88: Witzel et al. 1988.