Transcript Тонкие акценты

Special Astrophysical Observatory of RAS, Nizhnij Arkhyz
Multifrequency study of Gigahertz Peaked
Spectrum (GPS) sources and candidates with
RATAN-600
Mingaliev M.G., Sotnikova Yu.V., Erkenov A.K.
Torniainen I., Tornikoski M.
what is GPS (Gigahertz Peaked Spectrum)?
spectral peak (500 MHz - 10 GHz in observer’s frame);
homogeneous self-absorbed synchrotron source;
powerful (log P1.4 ≥ 25 WHz-1);
compact (≤1 kpc);
bright radio source population (~10%);
● young radio sources (< 104 yr) [Fanti 1995; Readhead 1996; O’Dea & Baum
1997]
● dense environment [O'Dea 1991, Gopal-Krishna 1991]
● recurrent activity [Baum 1991]
why GPS?
 contaminated GPS-sources sample
 galaxy type 0.1 ≤ z ≤ 1; quasar type 1 ≤ z ≤ 4
 different properties but similar spectrum’s shape
 GPS quasars are considerably “contaminated” by variable
sources
 variable or not?
long-term multifrequency monitoring
goals, tools, sample, observations
2006-2010
simultaneous radio spectra
variability
spectral properties
count of sources
RATAN-600: 1.1, 2.3, 4.8, 7.7, 11.2 and 21.7 GHz
1) 12 observing campaigns (5 years of monitoring):
76 quasar-type and 29 galaxy-type; 17 – unidentified; total
number - 122 sources
2) complete sample (1999-2010): 75° ≤ δ ≤ 88°,
S1.4GHz ≥ 200 mJy: 4-5 candidates
fluxes and radiospectra
fluxes and radiospectra
proposed class
N sources
max
max1
max2
max12
rising
flat
complex
steep
48
10
11
1
14
19
9
10
all
122
type of spectra
maximum at cm range
flat plateau at low frequencies
variable (≥25%)
flattering and variable
α≥0
0 ≥α ≥ -0.5
two or more minimum
α ≤ -0.5
candidates in GPS
only 25% candidates in GPS (using parameters of spectrum for
homogeneous self-absorbed synchrotron source with a power law
electron energy distribution:
α1≥ 0.5 and α2 ≤-0.7 (below and above spectral peak)
FWHM ≤ 1.2 frequency decades (full width at half maximum)
Var ≤ 25%
spectral properties
The average spectral index of the optically thin part:
-0.90(0.07) - galaxies, -0.75 (0.04) – quasars, -0.7(0.11) – unidentified
the difference is about 0.15
electron energy distribution* for GPS galaxies
is steeper than for GPS quasars; index (γ) for GPS galaxies differs by 0.3
*dN(E)
α1 = (γ1 - 1) /2;
= kE-γdE
α2 = (γ2 - 1)/2
Δα = (α1 - α2)= 0.15;
Δγ = 0.3
selection effect ???
variability
11.0(±1.4)% QSO
8.4 (±3.2)% G
QSO, z=2.37
G, z=0.08
QSO, z=0.68
QSO, z=1.13, var = 70%
QSO, z= 1.45, c
n, c
width of the spectra (FWHM)
there are sufficiently few sources with narrow spectra
narrowest reasonable spectrum,
assuming homogeneous self-absorbed
synchrotron source with a power law
electron energy distribution = 0.77
(+0.8)
using observational data FWHM = 1.2
Is the lack of sources with narrower spectra a real effect? …
statistics
4-5 candidates selected; 3 of them for the first time
(S1.4GHz ≥ 200 mJy, Dec 75º - 88º)
The percentage of sources
0.8 Jy at 1.4 GHz – 450
(AGNs) with identical and
0.8 Jy at 4 GHz – 225
increasing spectra is about
10% sources, 0.2 sterad
25% at the studied flux level.
[(225/10)*0.2]=4.5 sources
This means that GPS sources
are about 40% of the total
number of AGNs or about
10% of all bright sources
[0.25*0.4=0.1].
conclusions
The 5-year monitoring of 122 GPS source and candidates revealed a small
number of such sources - 25% of the initial sample. Only about 45% of candidates
to GPSs remained as early as in the first RATAN-600 observational set (2006).
Averaged instantaneous spectra at several epochs were obtained at
frequencies 1.1, 2.3, 4.8, 7.7, 11.2 and 21.7 GHz
The shape of the spectra remained clearly convex for only a fraction of sources
of the sample. Most of the sources are variable flat-spectrum sources with
inverted spectral shape only during flares (most of them - quasars). According to
various study the genuine quasar-type GPS sources seem to be very rare.
Spectral properties of galaxies and quasars differ: in optically thin part the
average spectral index of galaxies is less than for quasars (~0.15 ???).
There is a correlation between the high-frequency variability index and the
high-frequency spectral index (99.5%).
There are sufficiently few sources with narrower spectra in our sample (25%).
Studying spectral properties of complete sample in the polar region 4-5
candidates to GPSs were selected (full sample of objects of this class in this area);
3 of them are considered as GPSs for the first time.
Thank you for attention!
G
QSO
only 20% QSO
α2= -0.75 (0.04)
spectral
index
variability
50% G
α2= -0.90(0.07)
FWHM
25% of the sample
50% galaxies and 20% quasars (from the sample)