1
High energy evidence for past activity
from Sgr A* or its surroundings
Gabriele Ponti
Marie Curie Fellow at
University of Southampton
R. Terrier, A. Goldwurm, G. Belanger and G. Trap
Sgr A* today: a dormant AGN
Sgr A* low luminosity
MSgrA*
=4.4106
M Sun
LSgrA*~31033 - 1035 erg s-1
Ledd = 51044 erg s-1
Chandra
~10-9
Sgr A* today: in a broader context
Sgr A* low luminosity
MSgrA*
=3.6106
Image from Gallo 2010
Sgr A*
during normal flare
deep in quiescence!
M Sun
LSgrA*~31033 - 1035 erg s-1
Ledd = 51044 erg s-1
~10-9
How was the Sgr A* accretion
rate in the past?
Are we testimony of a
peculiar moment of Sgr A*?
The idea: Molecular clouds as mirrors of past activity
0
0
0
0
-100
Galactic plane from above
00
Sgr A* sits on the centre of the
Central Molecular Zone (CMZ)
107-108 MSun of MC in the
central 300 pc
-50
0
-50
-100
 MC are mirrors of the GC past
activity
0
0
0
Sgr A*
How do the Sgr A* light fronts
appears to us at infinity?
50
0
100
00
pc
Toward the Earth
Sunyaev et al. 1993; 1998
The idea: Molecular clouds as mirrors of past activity
Sgr A* sits on the centre of the
Central Molecular Zone (CMZ)
107-108 MSun of MC in the
central 300 pc
 MC are mirrors of the GC past
activity
Iso-delay light fronts are parabola!
Sunyaev et al. 1993; 1998
The idea: Molecular clouds as mirrors of past activity
Sgr A* sits on the centre of the
Central Molecular Zone (CMZ)
Galactic plane from above
107-108 MSun of MC in the
central 300 pc
nH
r
d
 MC are mirrors of the GC
past activity
Sgr A*
Light fronts appears to us as
Parabola
 Tool to study history of GC
emission
IFeK µ
n H ´ r 2 ´ LSgrA*
d2
Toward the Earth
Sunyaev et al. 1993; 1998
Reflection spectrum from neutral material
keV (Photons cm−2 s−1 keV−1)
0.01
0.1
1
2
Source
Link between source incident flux and reflection intensity
Direct source continuum
50
Fe Kα+β emission lines
Compton hump
FeK edge
Fe Ka+b
20
A reflection spectrum should contain:
Neutral reflection from MC
5
10
Energy (keV)
Slab of neutral reflecting material
Open problems:
Which is the origin of the Hard X-ray emission from MC?
GRANAT: Hard X-ray/MC
Sunyaev et al. 1993
ASCA: Fe K from some MC
Koyama et al. 1996
Are MC reflecting GC radiation?
Chandra: Fe K toward SgrA*
Murakami et al. 2001
Chandra: Sgr A cont. variability
INTEGRAL: MC - reflection
FeK: constant intensity!
Revnivtsev et al. 2004
Multi-instruments: Sgr B2 variability
Sgr B2 consistent with
reflection
But weak detection of
variability
Muno et al. 2007
Inui et al. 2009
Alternatives to reflection: Cosmic Rays
Cosmic ray electrons
Contours 850-micron; FeK map (red); 20 cm (green)
Yusef-Zadeh et al. 2002; 2007
Cosmic ray protons
Aharonian et al. (2006)
HESS TeV contours on FeK map
X-ray from MC: Reflection or Cosmic Rays?
 Low energy cosmic ray electrons or protons
Low energy cosmic ray electrons: Yusef-Zadeh et al. 02; 07 Valinia et al. 00;
Low energy cosmic ray protons: Dogiel et al. (2009)
Supernovae ejecta: Bykov 02
 Sgr A* flare ~1.51039 erg s-1 ~ 100 yr ago
Internal source
External source: Sgr A*, X-ray binary, Sgr A East
I will present the new results on the field based on:
~ 7 years (~20 Ms) of INTEGRAL monitoring of the GC region
 study of the high energy Sgr B2 emission - accurate light curve
~ 10 years (~1.2 Ms) of XMM-Newton monitoring of the 15’ region around Sgr A*
 study the time variability of MC in Sgr A
 disentangle the models
~ 5 years Suzaku
The INTEGRAL view of Sgr B2
FeK (xmm)
Terrier, Ponti et al. 2010
No point source
Decay time ~8.21.2 yr
~core light crossing time
variability 4.8 
The INTEGRAL view of Sgr B2
Terrier, Ponti et al. 2010
Spectral shape: both low energy cosmic ray electrons and reflection!
But low energy cosmic ray electrons  huge cosmic ray electron
luminosity (~91039 ergs s-1)
Parallax measurement
120 pc in front of Sgr A*
Reid et al. 09
LSgrA*=2-51039 erg s-1
~75-150 years ago
Fe K emission in the GC:
CS emission in the GC to locate MC
nH CS= (7.51011Tex  TMB dv) /10-2
Where are the MC?
Which Fe K emitter are associated to a MC?
Molecular lines as tracers:
MC in GC have high densities, CO auto-absorbed
Uniform and complete scan of the CMZ
 CS Tsuboi et al. (1999)
Problems:
i)
Projection - depth in the line of sight
ii) MC velocity field not Newtonian
BUT
Coherent structures  similar velocities
TMB = 2.85 K km s-1  1.31022 cm-1
TMB = 75 K km s-1  3.41023 cm-1
X-ray spectra of MC
Model: wabs*(apec+edge*(PL+Ga+Ga))
Model: wabs*(apec+edge*(PL+Ga+Ga))
the bridge
Fe K+: E=6.411±0.002 keV, =28±5
eV, norm=7.5±0.510-5 ph cm-2 s-1
EW=955 eV; PL=1.9±0.4,
nH~741022 cm-1, =0.030.05
Fe K+: E=6.409±0.002 keV, =28±4 eV,
norm=4.7±0.310-5 ph cm-2 s-1
EW=750 eV; PL=1±0.4;
nH~431022 cm-1, =0.260.12
G0.11-0.11
G0.11-0.11
3,8 
4,8 
Decay time ~few yr
~core light crossing time
Inferring Sgr A*’s luminosity
Sgr B2
NH= 81023 cm-2
Dproj= 100 pc but 130 pc in front of
Galactic plane from above
Sgr A* (Reid et al. 2009)
Radius = 7 pc
normFeK= 1.710-4 ph cm-2 s-1
L2-10 keV SgrA* ~ 1.41039 erg s-1
Sgr A*
(Revnivtsev et al. 2004)
t = 100 yr
G0.11-0.11
NH=21022 cm-2 (Amo-Baladron et
al. 2009)
Dproj=25 pc
Radius=3.7 pc
normFeK=0.910-4 ph cm-2 s-1
LSgrA* > 1039 erg s-1
t > 75 years
Toward the Earth
Assuming FlareSgr A* = 1.41039 erg s-1
10 pc behind Sgr A*
100 yr ago
d 2 ´ IFeK
LSgrA* µ 2
r ´ nH
Other constraints on Sgr A* activity
50 km s-1
NH=91022 cm-2
Dproj=6 pc
Radius=4.7 pc
normFeK<1.110-5 ph cm-2 s-1
LSgrA* < 81035 erg s-1
t < 60-90 years
Galactic plane from above
Toward the Earth
Coil et al. (2000)
The bridge
Bridge
Bridge51
Bridge 6
Bridge 2
Bridge 7
Bridge 3
Bridge 4
11,3
9,1
2,6
8,6
13,3
0,8 
0,5 
0,4 
Super-luminal
motion?
Direction toward Sgr A*
Bridge 1
Bridge 2
Bridge 3
Bridge 4
Regions causally disconnected!!
 No propagation of single event
 Cosmic ray - internal source excluded!
 Many un-correlated variations
 Similar variation - distant source
 L15pc~1.31038 erg s-1 - Binary in
peculiar position close to bridge
 Flare Sgr A* (Sunyaev & Churazov 1998)
How can a superluminal echo happen?
Wall
Projector
Velocity of the variation observed on the screen = 1 m/s
To change slide 1 s
Wall distant 1 m from the projector
How can a superluminal echo happen?
Wall
Projector
To change slide 1 s
If the wall is distant 600000 km from the projector
The variation appears on the screen at v=2c!
Because the real “physical” variation happens at the level
of the projector and not of the wall
Possible past activity of Sgr A*
Bridge
NH=91022 cm-2
Dproj=15 pc
Radius=1.1 pc
normFeK=1.110-5 ph cm-2 s-1
Galactic plane from above
LSgrA* ~ 1.31038 erg s-1
Assuming L~1.41039 erg s-1
 60 pc
 Sgr A* activity 400 yr
Basic unknown: MC distance!
Assuming a luminosity of 1039 erg s-1
 MC distance
Consistent with unique outburst
Nothing special about 1039 erg s-1 if
MC are more distant  higher Sgr A*
luminosity
Toward the Earth
The in-glorious past of Sgr A*
The projected distance between Sgr A* and MC1, MC2 and the bridge are unknown
HOWEVER
their physical properties indicate that they are within the CMZ (~300 pc from Sgr A)
Assuming they are illuminated by Sgr A*, it is possible to pose a limit to its recent
luminosity
nH
r
d
d ´ IFeK
LSgrA* µ 2
r ´ nH
153 pc
2
Sgr A*
307 pc
460 pc
1041
ergs s-1
1040
If the CMZ is filled with “similar” MC
Sgr A* never reached L>1041 ergs s-1,
since the end of the Roman Empire
 Sgr A* barely exited from the
quiescent state, since the Romans
1039
1038
Phot on Index
Normalizat ion
Abs2(N H )
Cont inuum
Γ
1.87 ± 0.04
9.6+− 1.6
1.3
12.0 ± 1.1
10 Ca,
cm
Suzaku detection of Ar,
Cr, Mn Kα emission
22
−2
*
T he uncert aint ies indicat e t he 90% confidence levels.
A bsorpt ion-correct ed line int ensity in t he unit of 10− 6 phot on s− 1 cm − 2 .
‡ Observed equivalent widt hs of t he neut ral lines t o t he power-law cont inuum in equat ion 4.
§ Calculat ed equivalent widt hs in t he X RN and L ECEe scenarios.
3 phot ons keV − 1 s− 1 cm − 2 .
at 1 keV Kα
in t he
unit of 10−from
et Normalizat
al. 2010ion
discover
emission
Ar, Ca, Cr and Mn in the MC X-ray
†
Nobukawa
T ab l e 2. Fit t ing result s of P l asma.∗
Cr X X I I I K α
Mn X X IV K α
5.68 ± 0.02
22 ± 6
6.19 ± 0.02
39 ± 6
* T he
uncert aint ies indicat e t he 90% confidence levels.
Emission measure 10− 12 / (4πD 2 ) n e n H dV , where D is t he dist ance t o t he source (cm), n e and n H are t he elect ron and hydrogen
density (cm − 3 ), respect ively.
†
are more precise t han t he previous work (K oyama et al.
2007b). T he abundances of light er element s, Si and S,
(Ar, Ca), were respect ively det ermined t o be 2.3–2.6 and
1.8–2.0 solar, for t he first t ime. T he highly ionized Cr
100
1000
X−ray
Electron
10
Abundances
Value
6.75 ± 0.13
1.01+− 0.01
0.02
12 ± 1
7.0 ± 0.1
1.3 ± 0.1
2.52+− 0.09
0.17
1.87 ± 0.07
1.16+− 0.07
0.04
1.64 ± 0.37
1
AP E C2
Paramet er
Unit
22
NH
10 cm− 2
kT1
keV
Norm
†
kT2
keV
Norm
†
Si
solar
S, Ar, Ca
solar
Fe
solar
Ni
solar
Gaussian Lines
energy
(keV)
EW
(eV)
energy
(keV)
EW
(eV)
Equivalent Width
Equivalent Width (eV)
Component
Abs1
AP E C1
spectrum
Ar
Ca
Cr
Mn
Element
Fe
Ni
F i g. 5. Equivalent widt hs of K α line of various neut ral
at oms. Black and red lines are t he calculat ed values for t he
Reflection:
elements
withrespect
~2 Solar
X -ray (X RN)all
and
elect ron (Lconsistent
ECRe) scenarios,
ively.
T he dat a point s marked wit h t he open circles are t he observed value
in our work.
Errors were
est imat
at t he 90%
Cosmic
electrons:
consistent
but
~4 ed
Solar
confidence level. T he black and red dashed lines are t o guide
eyes, which are X RN and L ECRe scenarios in 1.6 solar and
4.0 solar abundances, respect ively.
T he phot on index, Γ of t he cont inuum (power-law) is
Can irradiation from external sources explain
the emission from ALL MC?
Fukuoka et al. 2009
G0.174-0.233  EW FeK = 950 eV  Reflection
G0.162-0.217  EW FeK = 360 eV  LECRE
Summary:
Study of the past activity of Sgr A*
Observe Fe K/Gamma-ray fading of Sgr B2
Observe another MC (G0.11-0.11) reflecting the same flare (~100 years ago)
50 km s-1 has no Fe K line
 Sgr A* luminosity < 81035 erg s-1 in the last 60-90 years
Observe an apparent superluminal motion (in the bridge MC)
 Cosmic rays or Internal source  excluded
 the illuminating source has to be far from the arm ( >2-4 times the apparent displacement)
 Sgr A* activity - best interpretation (but luminosity required is few1039 erg s-1  binary not
excluded)
Kα emission lines require abundances 2 Solar
MC emission consistent with a single Sgr A* period of activity of few hundreds
years and lasted until ~100 years ago
 As observed 1/3 of MC should be FeK bright
New questions:
Which is the mechanism that produces such outbursts? 106 times quiescence for >20 yr
Partial stellar capture? (Yu et al. 2011)
What is going to happen if Sgr A* goes to Eddington? To the GC surrounding material? To the Earth?