Transcript Diapositiva 1

Faint blazars potential target
for KaVA observations
F. Mantovani 1,2, M. Bondi 2, K.-H. Mack 2,
W. Alef 1, E. Ros 1, J.A. Zensus 1
1
2
Max-Planck-Institut für Radioastronomie, Bonn, Germany
Istituto di Radioastronomia - INAF, Bologna, Italy
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Blazars:
an extreme class of Active Galactic Nuclei
FSRQs (high luminosity radio galaxies)
BLLacs (low luminosity radio galaxies)
Characteristics:
high luminosity
rapid variability
high optical polarisation
Emission:
a broad continuum of non-thermal origin,
extending from the radio wavelengths
through gamma rays
Radio band:
flat (α < 0.5) radio spectra
core-dominated objects
apparent superluminal speeds
Gamma band:
vast majority of sources in the Fermi 2FGL catalogue
Interpretation:
based on bright and luminous sources discovered
in radio or X-ray surveys
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Any connection between radio and γ-ray emission ?
γ-ray emission:
low energy photons plus
relativistic beaming 
up-scattering of the photons
(Inverse Compton)
Radio emission:
synchrotron radiation
from relativistic electrons
Origin of gamma-ray
emission ?
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Fermi - Large Area Telescope
Single-Dish Monitoring Programmes
programme
freq. (GHz)
sampling
OVRO
Effelsberg
IRAM
APEX
UMRAO
Metsähovi
RATAN-600
15
2.6 – 43
86 – 270
345
4.8, 8, 14.5
37
1 – 22
2-3 weeks
monthly
monthly
monthly
15 days
monthly
2-4 weeks
size
> 1000
≈ 60
≈ 60
≈ 60
35
≈ 100
600
F-GAMMA
VLBI monitoring programmes
VLBA Monitoring at 43 GHz of EGRET blazars (Jorstad et al. 2001)
MOJAVE VLBA observations at 2 cm of 300 sources (Lister et al. 2009)
VISP
VLBA Imaging and Polarimetry Survey at 5 GHz and 15 GHz survey of ~1100 AGN
TANAMI Tracking AGN with AU-SA array, 80 sources at 8.4GHz and 22GHz
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Direct relation
between
the γ-ray and
parsec-scale
synchrotron
radiation
Average Fermi LAT 100 MeV-1 GeV photon flux (Abdo et al. 2009)
vs. quasi-simultaneous 15 GHz flux density.
Filled circles: total VLBI flux density. Open circles single-dish flux density.
(Kovalev et al. 2009 ApJ 696,L17)
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Integrated
0.1–100 GeV
Fermi photon flux
vs.
15 GHz VLBA
core flux density
(for data pairs in which the
VLBA flux density
measurement was taken
2.5 ± 0.2 months after the
LAT flux measurements)
MOJAVE flux density cut
(Pushkarev et al. 2010 ApJ 722, L7)
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Deep X-ray Radio Blazars Survey
(Perlman et al. 1998; Landt et al. 2001)
Cross-correlation ROSAT sources
WGCAT – White, Giommi, Angelini 1995
and radio sources with flat radio spectra
GB6 – Gregory et al. 1996
NORTH20CM – White and Becker 1992
PNM – Griffith and Wright, 1993
 flux density down to ~ 50 mJy at 5 GHz
 power down to
~ 10 24 W Hz ─ 1
 nearly complete optical identification
 includes both FSRQs and BL Lac sources
234 quasars, 181 FSRQs, 53 SSRQs
36 BL Lacs
28 NLRG
redshift distribution: < z > ≈ 1
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“Weak blazars sample”
87
sources selected from the “Deep X-ray Radio Blazars Survey”
Selection criteria: Dec > ─ 10 deg
Investigation:

Effelsberg multi-frequency
observations

European VLBI Network 5 GHz observations
Source coordinates derived from NVSS and FIRST images
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Main aims
 verify the spectral index classification
 make the first mas resolution observations
 do the observations while Fermi is making its survey
 make a comparison with samples of bright blazars
(MOJAVE, TANAMI, etc …)
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Effelsberg observations
(1-6 July 2009)

66 sources bona fide blazars (FSRQs)

6 objects show an inverted spectra


27 sources show a steep spectrum
9 sources show a GPS type spectral index

43 % show variability on a time scale of 20 years

36 sources are polarised at 5 GHz

7 of them have │RM│> 200 rad m-2
Mantovani et al. 2011 A&A 533, 79
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EVN observations
Frequency
Stations
Recording
Strategy
5 GHz
12
512 Mbits, 2 bit sampling (~ 2.5 TBytes/station)
5 scans, 6 minutes long each per source
Observations
EM077A
EM077B
EM077C
EM077D
EM077E
EM077F
EM097A
EM097B
Correlation
22 Oct 2009
30 May 2010
31 May 2010
23 Nov 2010
(e-VLBI correlation at JIVE)
15 Dec 2010
(e-VLBI correlation at JIVE)
31 May 2011
24 Feb 2013
27 May 2013
MPIfR DiFX software correlator
1 sec integration time  field of view ~ 11”
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Results from the EVN observations
 All sources (87) detected
 SEVN / SEF median ≈ 0.36 +/- 0.8
 Structure: 45 core-jet
39 point-like
3 triples
 Tb in the range 107 - 1012 K
13 sources Tb > 1011 K
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Peak flux = 0.4 mJy
rms noise = 0.03 mJ/beam
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Classification according to spectral index
Flat Spectra:
56 FSRQs (blazars)
2 NLRG
Steep Spectra:
10 SSRQs
10 Compact Steep-spectrum Sources
3 BLLacs
Convex Spectra:
6 Giga-Peaked Sources
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List of SSRQs, CSSs and GPSs
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CSSs and GPSs
X-ray ROSAT observations
< LX > ≈ 5 x 1044 ergs/sec
LX similar for CSSs and GPSs quasars
Column density (1 – 15) x 1020 nH cm2 ≈ Galactic nH
CSSs and GPSs quasars are not obscured by
large column of cold gas surrounding their nuclei
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DXRBS sources associated to Fermi objects
50% are BL Lacs
BL Lacs are the 13% of DXRBS sources
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J0448.2-2110
J1231.7+2848
Fermi detection limit
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External Compton Model
(Dermer 1995 ApJ 446, L63)
Lister M.L. 2010
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Target sources for high frequency observations
with the
 Korean VLBI Network
or
 KaVA (KVN plus VLBI Exploration of Radio Astrometry)
A comparison sample of faint blazars
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Flat Spectrum Radio Quasars
EVN at 5 GHz:
11 sources with Score > 100 mJy
22 sources with Score > 50 mJy
 Flux density and polarisation measurements
at 22 GHz and 43 GHz
 Source-Frequency Phase Referencing method
(M. Rioja & R. Dodson 2011 AJ 141, 114)
 Map the innermost structure
 Comparison with bright blazars
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KaVA Sensitivity
Sensitivities (1σ) in mJy
Integration time 120 seconds for baseline sensitivities
Integration time 4 hours for images sensitivities
Total bandwidth of 256 MHz for continuum emission
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Sources with “inverted” spectral index
Name
SEF
SEVN
[mJy]
[mJy]
J0535.1-0239
86.4
49.4
p
J0937.1+5008
110.5
257.6
p
J1028.5-0236
132.4
318.6
p
J1105.3-1813
34.7
J1359.6+4010
266.5
267.0
cj
J1648.4+4104
499.9
392.6
p
J2329.0+0834
293.6
43.8
p
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Struct.
High Frequency Peakers candidates ?
Sources with inverted spectral index
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Giga-Peaked Sources
Name
SEF
SEVN
Struct.
[mJy]
[mJy]
J0227.5-0847
109.5
40.5
p
J0434.3-1443
387.9
J0435.1-0811
91.8
37.9
cj
J0931.9+5533
55.7
1.8
cj
J1116.1+0828
397.8
742.5
p
J1406.9+3433
278.1
216.9
cj
J1427.9+3247
60.5
17.4
cj
J2159.3-1500
68.2
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Are they true GPS ?
Giga-Peaked Sources
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J0204.8+1514
(0202+149; 4C +15.05)
 Included in the MOJAVE programme
(classified as FSRQ)
 SSRQ associated to a γ-ray object
 Classified as CSS: LS = 4.7 kpc
(1.58 arcsec x 1.42 arcsec at PA -40.5 deg)
 Faint extended emission detected
(Cooper et al. 2007).
 Radio variability (Mantovani et al. 2011)
 γ-ray variability
(Nolan et al. 2012 )
Rather peculiar in a CSS
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Sources with very high γ to radio ratio
J0448.2-2110 (PKS 0446-212)
FSRQ, z = 1.971
S5GHz = 227 mJy
log FX/FR = ─12.25
J1231.7+2848 (B2 1229+29)
BL Lac, z ?
Core-jet structure
Score ≈ 20 mJy
log FX/FR = ─11.14
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Summary
• All 87 target sources detected by the EVN at 5GHz
•
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•
•
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•
•
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Brightness temperature ranges from 107 to 1011 K
56 Blazars
2 NLRGs
29 CSSs plus GPSs
CSSs and GPSs quasars are not obscured by large
column of cold gas surrounding the nuclei
15 DXRBS sources are associated to γ-ray LAT objects
50% of the associated objects are BL Lacs
Correlation between Score and γ-ray photon flux confirmed
External Compton model ruled out
Many objects are good candidates for KaVA observations
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Many thanks for your attention
This work was supported by the:
- European Community Framework Programme 7 (2007-2013)
under grant agreements no. 227290 and no. 283393
- COST Action MP0905 Black Holes in a Violent Universe
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Fermi and the “Faint blazars sample”
~ 13 % of the DXRBS objects has been possibly detected by Fermi
Are they too few or are they too many ?
EGRET  130 blazars detected
Number counts are Euclidean: N(>S)
α
S ─ 1.5
Fermi ~30 times more sensitive than EGRET
≤ 0.5 objects / deg 2

20,000 expected detection
≈ surface density in the Deep X-ray Radio Band Survey
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External Compton model (Dermer 1995)
γ-ray emission boosted by a higher power of the
Doppler factor than their radio emission ?
Synchrotron radiation beaming pattern
α δ 3+α
External Compton-scattered photon
α δ 4+α
(accretion disk photon field)
It implies lower radio / gamma for higher Doppler factor
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