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The connection between millimeter and gamma-ray emission in AGNs
Marcello GirolettiINAF Istituto di Radioastronomia
BOHEME, 24-25 maggio 2012
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
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
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)
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)
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
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
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
Locating the black hole in M87
Hada et al. 2012, Nature
to BH, via ALMA/VLBI
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
Extra stuff
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
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
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
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
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)
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
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
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
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)
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