Class P Spectra $--$ Peaked Spectra

Radio sources with peaked spectra are basically objects having steep or optically thin spectra at high radio frequencies with turn over at low radio frequencies. The high frequency spectral index reflects the index of the distribution of synchrotron electron and the turn over frequency depends on it's size and magnetic field.

For the sources showing peaked spectra, since the turn over frequency can be measured, we assume typical angular size 1 milli-arcsecond, we can calculate the magnetic field in the source region using equation 5.7.

We subdivide this class of the peaked spectra into two :

• Class P1 : those having peak at meter wavelengths ($<$ 1 GHz), and
• Class P2 : those having peak at $cm$ wavelengths ($>$ 1 GHz), which is known as gigahertz peak sources.

We subdivide Class P1 spectra depending on the spectral index of the optically thin high frequency end of the spectra as :

• Class P1-A : steep peaked spectra, and
• Class P1-B : flat peaked spectra.

In the table 5.2, we give the list of the sources which fall in Class P1-A The figure 5.11 gives the plots a few example of Class P1-A sources. The table 5.3 gives the list of the sources which fall in Class P1-B. The figure 5.12 gives the plots a few example of Class P1-B sources. The table 5.4 gives the list of sources which fall in Class P2. The figure 5.13 gives the plots a few example of Class P2 sources.

For all the source in this category, we have examined the spectra to get the peak flux density and the frequency at which the peak occurs and, assuming an angular diameter of 1 milli-arcsecond and z=1, we have estimated the magnetic field in the source using equation 5.7. These fields are also given in the tables 5.2, 5.3 and 5.4. We note that for the Class P1-A sources (steep spectra sources with turnover at frequencies less than 1 GHz), the typical magnetic fields are typically much less than a micro-gauss. For the Class P1-B (flat spectrum sources with turnover frequencies less than 1 GHz), the magnetic field is of the order of a micro-gauss. However, for the Class P2 (sources with turnover greater than 1 GHz) the magnetic field is considerably larger and in some cases many milli-gauss. However this is not surprising given the 5th power dependence of the magnetic field on the turnover frequency. While it is possible that some of the Class P2 sources are misclassified, the more likely explanation would be that these sources could be smaller than the assumed 1 milli-arcsecond that has been assumed. Independent measurements of the angular size around the turnover frequency are required to make more accurate estimates of the magnetic fields.

Table 5.2: List of Sources with Class P1-A Spectra.

Sr. No.	Source Name	Mag. Field	Sr. No.	Source Name	Mag. Field
-	-	(micro-gauss)	-	-	(micro-gauss)
1.	0022+002	0.0709	17.	1248-199	0.0006
2.	0024-420	8.1040	18.	1323-448	0.0505
3.	0240-231	1.6008	19.	1347+122	0.0141
4.	0323+055	0.0008	20.	1400+621	0.0194
5.	0410+769	0.0149	21.	1435+760	0.2212
6.	0432+416	0.0001	22.	1513+236	0.1697
7.	0438+488	0.1697	23.	1924+334	0.0006
8.	0447-220	0.0016	24.	1944+548	0.2745
9.	0459+024	19.6098	25.	2035+189	0.1587
10.	0632+103	0.1186	26.	2130+050	0.0439
11.	0837-198	0.0005	27.	2212+018	0.0476
12.	0834+555	0.0002	28.	2214-385	0.1033
13.	0943-083	0.0553	29.	2254+247	0.1334
14.	1035+564	0.2444	30.	2314-449	0.0908
15.	1120+143	0.0657	31.	2344+824	0.0289
16.	1154-350	0.0003	-	-	-

Figure 5.11: Sources with Class P1-A Spectra.

Table 5.3: List of Sources with Class P1-B Spectra.

Sr. No.	Source Name	Mag. Field	Sr. No.	Source Name	Mag. Field
-	-	(micro-gauss)	-	-	(micro-gauss)
1.	0029+349	0.2521	11.	0735-175	0.1026
2.	0059+001	0.0694	12.	0746+258	360.1791
3.	0119+321	0.0683	13.	1130-148	0.0279
4.	0155-408	0.1314	14.	1351-148	0.4243
5.	0321+123	0.1614	15.	1845+401	0.6348
6.	0329+279	35.3841	16.	1939-100	1.3172
7.	0414+343	0.2128	17.	2007-445	0.9483
8.	0424+020	0.4742	18.	2035+109	0.5763
9.	0604+442	0.4545	19.	2355+498	0.1098
10.	0614+607	0.3970	-	-	-

Figure 5.12: Sources with Class P1-B Spectra.

Table 5.4: List of Sources with Class P2 Spectra.

Sr. No.	Source Name	Mag. Field	Sr. No.	Source Name	Mag. Field
-	-	(micro-gauss)	-	-	(micro-gauss)
1.	0403+260	21.9846	15.	1609+266	2.7235
2.	0503+020	11.0305	16.	1751+096	292274.2602
3.	0555+398	9380.8453	17.	1751-253	37.5950
4.	0713+438	16.0439	18.	1923-210	49464.9786
5.	0745+101	2807.3034	19.	1937-399	298016.2762
6.	0842+185	32.4161	20.	2005+778	57695.9511
7.	0921-263	52531.8592	21.	2025+337	210.0350
8.	1111+199	37.5950	22.	2052+365	2.3770
9.	1146-247	37.5950	23.	2101-423	32.4161
10.	1150-003	8.1040	24.	2136+006	350.8771
11.	1227+365	14.4072	25.	2151+058	34389.4667
12.	1354-021	42456.1317	26.	2202+422	1.7244
13.	1445+099	9.3988	27.	2236+284	8597.3667
14.	1522-275	9232.3194	-	-	-

Figure 5.13: Sources with Class P2 Spectra.