the connection between millimeter and gamma-ray emission ...baselines) and two 12-m antennas (for...
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The connection between millimeter and gamma-ray emission in AGNs
Marcello GirolettiINAF Istituto di Radioastronomia
BOHEME, 24-25 maggio 2012
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The Atacama Large Millimeter Array (ALMA)
• At least 50x12m Antennas
• Frequency range 30-1000 GHz (0.3-10mm)
• 16km max baseline (<10mas)
• ALMA Compact Array (4x12m and 12x7m)
• Main drivers:
• Detect and map CO and [C II] in a Milky Way galaxy at z=3 in less than 24 hours of observation
• Map dust emission and gas kinematics in protoplanetary disks
• Provide high fidelity imaging in the (sub)millimeter at 0.1 arcsec resolution
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Short gamma-ray variability time scales
2155-304, HESSAbramowski et al. 2010
TeV, doubling timescale ~2min
3C454.3, Fermi-LATTavecchio et al. 2010doubling timescale ~6hr
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From gamma-rays to mm-wavelength
Log Frequency
Log
Flux
den
sity
self-abs.
opt. thin
radiation losses
• Gamma-ray variability implies compactness, compactness implies low frequency self-absorption
• Fermi sources call for millimeter observations. Indeed, some interesting results were obtained by Planck, but due to sensitivity limitations we are far from a clear understanding of radio spectra and broad-band SED
Planck collaboration et al. (2011, XV)
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Current ALMA status
• ALMA Cycle 1 Early Science Call for Proposals will be published on 31 May 2012, and that the proposal submission deadline will be 12 July 2012.
• ALMA Early Science Cycle 1 observations will start in January 2013 and span 10 months (800 hours of array time anticipated)
• ALMA Early Science Cycle 1 anticipated capabilities:
• Thirty two 12-m antennas in the main array, and nine 7-m antennas (for short baselines) and two 12-m antennas (for making single-dish maps) in the Atacama Compact Array (ACA)
• Receiver bands 3, 6, 7 & 9 (wavelengths of about 3, 1.3, 0.8 and 0.45 mm)
• Baselines up to 1km
• Both single field interferometry and mosaics
• Mixed correlator modes (both high and low frequency resolution in the same observation)
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ALMA sensitivity for Fermi sources
• let’s assume α = 0.5 (S∝ ν−α), this correspond to high significance detections for tens of Fermi blazars - note that the most intriguing sources have even flatter observed spectra
• still, no structural information
• need VLBI for that...
Bonnoli et al. (2010)
Planck collaboration et al. (2011)
ALMA
Band 3 6 7 9
Freq. (GHz) 100 230 345 675
1min rms (mJy beam-1)
0.2 0.3 0.6 5.3
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VLBI with ALMA?
• At present, Global Millimeter VLBI Array (GMVA)
• ~14 participating telescopes (6 Europe, 8 VLBA) - Noto, SRT in the future(?)
• 2 sessions per year
• Baseline sensitivity 50-350 mJy
• Angular resolution 40 μas
Courtesy of A. Marscher
http://www.mpifr-bonn.mpg.de/div/vlbi/globalmm/
mm-VLBI current with ALMA
sensitivity 100 mJy 10 mJy
resolution 50 µas 10 µas
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Angular and spatial resolution of mm-VLBI
• for nearby sources, these scales correspond to 1–100 Schwarzschild radii, depending on distance and black hole mass!
• linear size: 103Rs (log MBH=9), 30-100 Rs (log MBH=9), 1-5 Rs (log MBH=6)
• mm-VLBI is able to directly image the vicinity of SMBHs!
• best candidates: Sgr A*, M87
λ ν θ z=1 z=0.01 d= 8 kpc
3 mm 86 GHz 45 µas 0.36 pc 9.1 mpc 1.75 µpc
2 mm 150 GHz 26 µas 0.21 pc 5.3 mpc 1.01 µpc
1.3 mm 230 GHz 17 µas 0.13 pc 3.4 mpc 0.66 µpc
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Locating the black hole in M87
Hada et al. 2012, Nature
to BH, via ALMA/VLBI
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Summary and outlook
• ALMA sensitivity and operating wavelength are ideal to access regions were gamma rays are most likely produced in AGNs
• As an element of a mm-VLBI array, ALMA will allow us to directly image the SMBH vicinity
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Extra stuff
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A near candidate for BH horizon: the radio galaxy M87
• d=16 Mpc
• low power but bright FR1 radio galaxy
• most massive black hole in nearby universe: MBH=109 Msun
• Schwarzschild radius RS=3.7 μas
• optical and X-ray jet with superluminal motions
• source detected at GeV/TeV energy
VLBA, VERITAS, HESS, MAGIC collaborations
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Coordinated VHE and MWL variability
• 2008: bright, fast TeV flare detected from all TeV telescopes (Acciari et al. 2009)
• VLBA 43 GHz radio core flux density increase
• (...but other TeV event show different MWL/radio characteristic, e.g. Harris et al. 2006, Giroletti et al. 2012)
]-1
s-2
cm
-12
[10
VHE
Φ
0
10
20VHE instruments
VERITASMAGICH.E.S.S.
]-1 s-2
cm
-12
[10
VHE
Φ 0
10
20
Time29 Jan 05 Feb 12 Feb
A
[keV
/s]
X-
ray
Φ
0
2
4
Chandra (2-10 keV)
knot HST-1
nucleus
B
[Jy]
radi
oΦ
0.5
1
1.5
2
Time02 Apr 2007 02 Jul 2007 01 Oct 2007 01 Jan 2008 01 Apr 2008
[Jy]
radi
oΦ
0.5
1
1.5
2 VLBA (43 GHz)nucleus (r = 1.2 mas)peak flux densityjet w/o nucleus (1.2-5.3 mas)
C
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M87 with present mm-VLBI
size of the jet base: 197x54 µas = 21x6 light days = 69x19 Rs
transverse width of jet at 0.5 mas: ~174 Rsclear transverse structure, counter-jet feature?
Krichbaum et al. 2008
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16/11/2009 M. Giroletti – Approaching the black hole horizon with mm-VLBI
230 GHz VLBI of Sgr A*Doeleman et al. (2008)10 & 11 April 2007 @3.84 Gbit/s
908 km230
4630 km
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Fitting and resolving the size of Sgr A* with 1.3 mm VLBI
Ring ("doughnut") outer diameter: 80 μas, inner diameter:
35 μas
HHT-Carma
HHT-JCMT
Carma-JCMT
Gaussian size: 43 μas
Doeleman et al. (2008)
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mm-VLBI observations of SgrA*
(Falcke et al. 2000)
General Relativity
calculation VLBI at 0.6 mm VLBI at 1.3 mm
maximally rotating BH
non rotating BH
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r=0.47, n=390 p<1e-7 r=0.42, n=248 p<1e-7 r=0.62, n=116 p<1e-7
r=0.42, n=209 p<1.3e-6 r=0.52, n=26 p<0.01 r=0.73, n=68 p=3.0e-7
Results: Ackermann et al. 2011, ApJ 741 30
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Radio-VHE correlation?
• Fermi lesson: (1) hard blazars correlate better but (2) correlation is not much stronger (certainly not more significant) at high energy
• Radio and VHE radiation may come from the same population, but certainly from very different parts of the electron energy distribution
• Little contamination from other components
• Variability is pronounced at VHE, much lower in radio
• VHE observations are biased towards flaring states
• Topic worth of study... maybe CTA will help?
HSP
Correlation coefficient vs energy band, divided by blazar type
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The Large Area Telescope (LAT) onboard Fermi
• Since 2008, Fermi-LAT is continuously monitoring the gamma-ray sky in the energy range ~100 MeV-100 GeV.
• After 2 years, Fermi has detected 1017 gamma-ray sources located at high galactic latitude that are associated statistically with AGNs (2LAC, Ackermann et al. 2011 ApJ 743)