5 Individual sources

Here we list briefly specific properties for the individual flat-spectrum sources observed. The optical identifications and redshifts are taken from Kühr et al. (1981) and Stickel et al. (1994).

• 0153+744: This quasar (z=2.338) was observed in October 1992. There are some indications of variability on the 1%-level, but these are not strong enough to pass the $\chi^2$ test.

• 0235+164: This BLLac object (z=0.940) was observed in October 1992. Strong short-timescale variations have been found, especially an event which is unusual in that it appears to be faster and stronger at 20cm than at shorter wavelengths. Possible models for these peculiar variations have been discussed in detail by Kraus et al. (1999b).

• 0333+321: Observed only at $\lambda = 6$cm in October 1992. This source (a quasar, z=1.258) was included as phase calibrator for the radio star UXAri, and showed IDV on the 3%-level.

• 0336-019: This quasar (z=0.852) was measured only at $\lambda = 6$cm in October 1992, as phase calibrator for V711Tau. It showed IDV on the 5%-level.

• 0716+714: Observed in all three campaigns, this source (a BLLac object with unknown redshift) shows pronounced variations at all frequencies and in linear polarization. There seems to be a correlation between the flux density at various frequencies (except for $\lambda = 20$cm), and between total and polarized flux density.

• 0804+499: In Effelsberg data obtained in April 1990 this quasar (z=1.433) showed the highest variability amplitude observed so far in sources of the northern hemisphere (Quirrenbach et al. 1992). Therefore, it was included in the October 1992 VLA campaign, in which it showed rapid variability, although "only'' on a level of a few percent.

• 0836+710: No variations are seen in this quasar (z=2.172) which is not surprising because this source is characterized by a pronounced, long jet (e.g. Otterbein et al. 1998; Lobanov et al. 1998). Therefore it can be (and was) used as secondary calibrator; it is particularly useful as a polarization calibrator because of its high degree of polarization ($\sim 9\%$ at 6 cm).

  
  

   

   

  Table 4: Observations in February 1990, total intensity

  $\lambda$ = 20cm TOT T = 25 d m0 = 0.70%
  Source	N	I[Jy]	m[%]	$\chi^2_{\rm r}$	Y[%]	type
  0716+714	186	0.87	3.58	14.52	10.54	I
  0917+624	330	1.22	4.43	23.63	13.13	I
  0954+658	373	1.03	4.19	25.49	12.40	I

  
  
  

  $\lambda$ = 6cm TOT T = 25 d m0 = 0.50%
  Source	N	I[Jy]	m[%]	$\chi^2_{\rm r}$	Y[%]	type
  0716+714	209	0.57	5.44	22.39	16.25	I/II
  0917+624	378	1.46	3.66	38.19	10.88	II
  0954+658	416	1.23	1.52	7.57	4.31	I

  
  
  

  $\lambda$ = 3.6cm TOT T = 25 d m0 = 1.00%
  Source	N	I[Jy]	m[%]	$\chi^2_{\rm r}$	Y[%]	type
  0716+714	186	0.54	3.96	8.79	11.48	I
  0917+624	330	1.53	2.55	6.13	7.04	II
  0954+658	359	1.19	1.78	3.13	4.41	II

  
  
  

  $\lambda$ = 2.0cm TOT T = 25 d m0 = 2.00%
  Source	N	I[Jy]	m[%]	$\chi^2_{\rm r}$	Y[%]	type
  0716+714	138	0.64	6.33	7.57	18.01	I/II
  0917+624	268	1.53	2.19	0.95		0
  0954+658	299	1.16	2.24	1.05		0

  
  
  

  
  

  
  

   

   

  Table 5: Observations in October 1992, total intensity

  $\lambda$ = 20cm TOT T = 22 d m0 = 0.70%
  Source	N	I[Jy]	m[%]	$\chi^2_{\rm r}$	Y[%]	type
  0153+744	102	1.81	0.74	0.40		0
  0235+164	121	1.57	7.41	153.8	22.14	I
  0716+714	229	0.75	2.51	3.87	7.23	I
  0804+499	134	1.00	3.10	14.04	9.06	I
  0836+170	218	3.60	0.54	0.72		0
  1749+701	222	0.73	1.39	4.34	3.61	I
  1803+784	219	1.81	1.12	4.11	2.64	I
  2007+777	218	1.12	4.44	39.69	13.16	I

  
  
  

  $\lambda$ = 6cm TOT T = 22 d m0 = 0.70%
  Source	N	I[Jy]	m[%]	$\chi^2_{\rm r}$	Y[%]	type
  0153+744	107	1.32	0.78	1.07		0
  0235+164	117	4.05	4.77	77.35	14.14	I
  0333+321	59	1.84	1.50	5.61	3.99	II
  0333-019	58	2.49	2.45	11.56	7.05	II
  0716+714	215	0.77	5.13	58.90	15.24	II
  0804+499	157	1.13	1.94	11.79	5.44	II
  0836+170	229	2.13	0.49	0.56		0
  1749+701	226	0.66	2.27	13.69	6.49	I
  1803+784	227	2.06	2.80	30.06	8.15	I
  2007+777	231	2.55	2.72	21.97	7.90	I

  
  
  

  $\lambda$ = 3.6cm TOT T = 22 d m0 = 0.80%
  Source	N	I[Jy]	m[%]	$\chi^2_{\rm r}$	Y[%]	type
  0153+744	97	0.77	0.80	0.78		0
  0235+164	108	5.23	2.01	6.13	5.54	II
  0716+714	216	0.84	8.24	53.37	24.60	I
  0804+499	139	1.16	2.08	6.57	5.77	II
  0836+170	217	1.93	0.72	0.69		0
  1749+701	204	0.64	1.34	2.04	3.21	II
  1803+784	219	2.20	2.25	7.37	6.32	II
  2007+777	210	2.61	0.82	0.97		0

  
  
  

  
  

• 0917+624: One of the most strongly variable sources (a quasar, z=1.446) in total flux density and linear polarization (P and $\chi$; e.g. Quirrenbach et al. 1989b; Kraus et al. 1999c). It was observed in May 1989 and February 1990, and showed pronounced IDV which seems to be correlated at wavelengths $\lambda \leq 6$cm. The variations at $\lambda = 20$cm are somewhat slower. The polarized flux density seems to be anti-correlated with the total flux density. Both intrinsic variations (Qian et al. 1991) and propagation effects in the interstellar medium (Rickett et al. 1995) have been explored as potential explanations of IDV in this source.

• 0954+658: A BLLac object (z=0.367) showing variability on a level of a few percent, somewhat stronger at $\lambda = 20$cm in February 1990. Except at $\lambda = 20$cm it showed no significant variability in the linear polarization.

• 1642+690: This quasar (z=0.751) was observed in May 1989, and showed IDV at $\lambda = 20$cm and 6cm.

• 1749+701: One of the first sources in which IDV was discovered (Heeschen et al. 1987). This BLLac object (z=0.770) showed weak variations in May 1989 and stronger IDV in October 1992.

• 1803+784: This source (classified variously as BLLac object or quasar, z=0.684) showed only slow variability (type I) in most observations. At $\lambda = 20$cm strong variability of the polarization angle has been found.

• 1928+738: A quasar (z=0.302) which has a pronounced jet structure similar to 0836+710. Correspondingly, it did not show any IDV in total intensity. Only in linear polarization weak variability has been seen.

• 2007+777: A BLLac object (z=0.342) showing mostly slow variations.