1. Probing the TeV Emission and Jet Collimation Regions in M87
R. C. Walker
M. Beilicke, F. Davies, P.E. Hardee, H. Krawczynski, D. Mazin, R. Wagner, M. Raue, S. Wagner, C. Ly, W. Junor, and the VERITAS, MAGIC, and H.E.S.S. Collaborations

2. CONTEXT: M87 LARGE SCALE STRUCTURE
X-Ray
Optical
Radio
1 kpc scale
A dominant elliptical in the Virgo Cluster
Radio images
25 kpc = 5'
800 pc
0.8 pc
300 pc
400 pc
NM Symposium Jan. 15, 2010
Walker: TeV and VLBA Results from M87

3. M87 - THE BEST SOURCE FOR IMAGING A JET BASE
Large angular size black hole
Large black hole mass: ~6 X 109 Msun (Gebhardt and Thomas 2009)
Nearby: 16.7 Mpc (A central galaxy of the Virgo Cluster)
Scale: Rs = 120 au = 7.1 as; 1 c = 3.8 mas/yr
VLBA 43 GHz resolution; 210 X 430 as (~30 X 60 Rs)
Innermost stable orbit (spin dependent): 4 days to 1 month
Jet is bright enough to see significant structure
Core has about 0.7 Jy at 43 GHz - can self-calibrate VLBI data
Jet well resolved transversely very near core
Can be seen by northern hemisphere instruments
Sgr A* black hole 40% higher angular size but has no jet
Well studied at all wavelengths from radio to TeV
FERMI detection reported Monday (McConville )
1.3mm VLBI observations reported Monday, 4.3Rs beam (Schenck )
NM Symposium Jan. 15, 2010
Walker: TeV and VLBA Results from M87

4. PROSPECTS FOR COMPARISON OF THEORY AND OBSERVATION
Simulations of disk/jet systems are reaching observable scales
Models indicate the launch and collimation region extends over Rs
The observational goal of our VLBA project is to provide a data set that constrains the theory
Need the best possible resolution in gravitational units
VLBI just able to reach into that regime in M87
Max scale
40 c2/(GM) 1000
McKinney & Narayan 2007

5. Walker: TeV and VLBA Results from M87
M87 VLBI IMAGES
20 mas
15 GHz VLBA
Double sided, edge brightened jet
Wide opening angle base
“Counterjet” > 3mas long (420 Rs)
Super- and sub-luminal speeds seen
1 mas = arcsec = 0.081pc = 141Rs mas/yr = 0.26c
1 mas
Krichbaum global array
86 GHz
5 mas
VLBA 43 GHz
23 image average
NM Symposium Jan. 15, 2010
Walker: TeV and VLBA Results from M87

6. THE VLBA AND TEV PROJECTS
VLBA at 43 GHz:
Every 3 weeks for 1 year in 2007 followed by
Every 5 days for 70 days in 2008
Each epoch included 20 phase referencing scans between M87 and M84 (1.5º separation)
Resolution 30 X 60 Rs (0.21 X 0.43 mas)
TeV joint campaign
Imaging atmospheric Cerenkov telescopes VERITAS, MAGIC, and H.E.S.S. (E > 100 GeV)
>120 hours in early 2008
Resolution ~5X107 Rs (~0.1 degree)
Chandra
4 observations during the TeV campaign + others earlier
Resolution ~1.1X105 Rs (~0.8 arcsecond)
NM Symposium Jan. 15, 2010
Walker: TeV and VLBA Results from M87

7. THE VLBA MOVIE PROJECT: DYNAMICS OF THE INNER M87 JET
Preliminary movie is from the first 11 images Jan-Aug 2007
Apparent motions ~2 c
Analysis not finished - especially polarization processing
NM Symposium Jan. 15, 2010
Walker: TeV and VLBA Results from M87

8. Walker: TeV and VLBA Results from M87
TeV/RADIO FLARE
TeV
A series of large TeV flares seen during the late January to early February observing window
Windows set by Moon
Extra observations made after trigger
X-rays from core high in mid February
HST1 X-ray flux steady
Radio flare
Began at time of the TeV flares
Peaked near scheduled end of observations in early April
Larger flare than any seen before in M87 by the VLBA
Flux density increase mostly on the radio core
X-ray
HST-1
Nucleus
<1.2 mas
Radio
Peak
Jet >1.2 mas
2Apr2007
1Apr2008
Acciari et al 2009 Science 325, 444
NM Symposium Jan. 15, 2010
Walker: TeV and VLBA Results from M87

9. Walker: TeV and VLBA Results from M87
THE RADIO FLARE
A: Pre-flare average
B: Last flare image
C-F: Flare images with average subtracted
Core already above average at start
Inner jet was below average
Most of new flux remains on the core
New weak components moving at about ~1.1c
Slower than movie saw farther out - accelerating?
NM Symposium Jan. 15, 2010
Walker: TeV and VLBA Results from M87

10. Walker: TeV and VLBA Results from M87
SIMPLE BLAST MODEL
Radio from self-absorbed synchrotron emission from electrons injected into a slower outer sheath
Hollow cone geometry
Ring of radio emitting plasma
-ray flare at time of injection
Injection function proportional to TeV emission can match data
Modeled emission region remains unresolved to the VLBA
The new fast, weak components would be something else
Only a fraction of flare flux density
Radio from 1 injection
(plot 80 days full width)
Injection based on TeV data
NM Symposium Jan. 15, 2010
Walker: TeV and VLBA Results from M87

11. Implications of the TeV/Radio Flare
Coincidence in time of TeV and radio flares indicates they are related
Both events abnormally large for this source
Implies the TeV Emission region is near the black hole
Small size had been known because of rapid TeV variability
Position of TeV emission was unknown previously
Allowing for projection etc, TeV is within < 200 Rs of black hole
Assumes the black hole is near the radio core
HST1 is not the location of these TeV flares
2005 HST-1 X-ray flare had made it a candidate
Emission mechanism must work near the black hole.
Several candidates still viable
Radio emitting material injected near time of TeV flare
Optically thick
NM Symposium Jan. 15, 2010
Walker: TeV and VLBA Results from M87

12. STABILITY OF CORE POSITION
VLBA project included relative astrometry between M87 and M84
Separation 1.49º = 434 kpc
RMS scatter during flare 11 X 34 as = 1.6 X 4.8 Rs (Beam: 210 X 430 mas)

Elongated along beam
Implies the core position stable to a few Rs.
Reasonable if radio core is near the black hole
Might expect less stability if core is a shock far down the jet as in some models.
2001 data point suggests relative proper motion
~800km/s
Reasonable for Virgo Cluster
M84
M87
NM Symposium Jan. 15, 2010
Walker: TeV and VLBA Results from M87

13. Walker: TeV and VLBA Results from M87
SUMMARY
M87 allows VLBI observations in the jet collimation region
Edge brightened jet
Wide opening angle base
Jet shows ~2c motions
Rapid structure variations
“Counterjet” feature seen
Radio core nearly stationary
Radio/TeV flare implies the TeV emission region is close to the black hole
TeV emission mechanism must work close to the black hole
Several viable mechanisms have been proposed
Radio emitting plasma injected at time of TeV flare
Radio is likely synchrotron self-absorbed for around a month
NM Symposium Jan. 15, 2010
Walker: TeV and VLBA Results from M87