The Galactic Centre

● Sgr A*: a not so quiet SMBH

● The GC region across the ray band

● The GC source

● CR accelerators in the inner 200 pc

R. Terrier (APC CNRS/Univ. Paris 7)

AstroGam 2nd workshop, March 2015

The central 200 pc in X-rays

100 pc

Chandra, Muno+09

Starburst activity in the central 200 pc

100 pc

A superbubble candidate?Thermal energy ~ 1051 erg/s

Mori+09, Heard+13

Tidal Capture remnant?Ponti+15

Total kinetic power from SN in the GC ~ 1.4 x 1040 erg/sCrocker et al. (2011)

A SNR candidate with a 34 pc long outflowTsuru+10

soft X-ray plasma kT~ 0.8 keVChandra, Muno+09

Multiple SNe from the Quintuplet cluster

Ponti+15

A SNR candidate with a 34 pc long outflowTsuru+10

Genzel et al (2010)

Lbol

~ 1036 erg/s

Sgr A*: a SMBH in quiescent state

Accretion driven by massive stars wind: accretion rate at Bondi radius: 10-5 Mo/yr

(Baganoff+03)Accretion rate at the SMBH: 10-9 M

o/yr < M

dot < 10-7 M

o/yr

(Marrone+07)Advected power (outflows) ~ 1039 erg/s

(Wang+13)

Sgr A*

Chandra

Chandra XVPWang+13

M

0.5 pc

•

A not so dormant black hole!

2000-2005

2012

Large scale variations of non-thermal hard X-ray & 6.4 keV Fe K emission:

Past 1039 erg/s flares reflected in the ISM!

Ponti+10, Terrier+10, Nobukawa+11, Clavel+13, Soldi+14

100 pcXMM, 6.4 keV FeK lineSoldi+13

• Nakashima+13 have discovered large region of recombining plasma emission 1.5° south of Sgr A*

••••••

•

•••••

A relic of a 100 kyr old event?

Nakashima+13

Thermal energy content:1.6 x 1051 erg

Relaxation timescale ~ 100 kyr

Origin?:● Past star forming activity?

● Bipolar outflow from Sgr A*?

● Photo-ionization by jet emission from Sgr A*?

100

pc

200

pc

1045

Lum

inos

ity(e

rg s

-1)

107 now

Time (years)

LSgrA*

=LEdd

LSgrA*

=10-10 LEdd

Quiescence

Normal flares

Hard X-ray echoes

High latitude plasma?

Fermi bubbles?

From Ponti+13

Sgr A* past activity ?

106 105 104 103 102 10

1043

1041

1039

1037

1035

The central 200 pc harbor the closest SMBH to Earth and the one of the most active star forming region in the Galaxy.

What is the duty cycle of the not so dormant SMBH and how is it affecting its environment?

What triggers changes in accretion rate? What are the effects of recurrent planetisimal and stellar captures?Is it accelerating particles? What is the impact on the ambient medium?

Cosmic-ray acceleration and propagation in the region?Is there an overdensity of low energy CR (LECR) in the central 200pc?What are the CR acceleration sites?What powers the Fermi bubbles?

Some Key Questions related to GC physics

Hard X-ray emission from the central 200 pc

•

••• Emission dominated by accreting compact objects•• IBIS/Isgri detected hard X-ray emission consistent with the GC position

• (Bélanger et al, 2004)

GC hard-X-ray emission dominated by a population of faint CVs?Extrapolation of ridge emissivity explains at least a part of GC source spectrum(Revnivtsev et al 2005, Krivonos et al 2007)

See also Perez+15

20-30 keV 60-85 keV

100 pc 0.7°

> 1 GeV emission from the central 200 pc

Fermi excess image >1 GeV

100 pc

Fermi > 1 GeV

Emission from molecular clouds

Bright GC source

On larger scales: GeV GC excess

HESS > 380 GeV

Dominant stable GC source

Diffuse emission > 380 GeV

An over abundance of TeV CR in the central 200 pc

HESS collab (2006)

100 pc

Yusef-Zadeh+13

SF2A 2004

GC source spectral energy distributionGC source spectral energy distribution

From HESS collab.( 2009)

Sgr A* quiescent

Sgr A* flare ~1 hour

IBIS Fermi

HESS

?

This is due to Sgr A*

Unresolved emission of faint sources

SF2A 2004

Origin of the GeV-TeV emission: Sgr A*?Origin of the GeV-TeV emission: Sgr A*?

Is Sgr A* accelerating TeV emitting particles?(Liu+04, Liu+06, Aharonian+05)

If TeV hadrons are produced in the vicinity of the SMBH, they have to diffuse away before producing photons

3pc

Circum Nuclear Ring M ~ 2 105 M

O

At high energy: mean free path

λ ~ RCNR

Energy dependent propagation regime

SF2A 2004

Origin of the GeV-TeV emission: Sgr A*?Origin of the GeV-TeV emission: Sgr A*?

Is Sgr A* accelerating TeV emitting particles?(Liu+04, Liu+06, Aharonian+05)

GeV-TeV spectrum: energy dependent CR propagation?(Chernyakova+11, Linden+12)

Ballisticpropagation

Diffusive propagation

SF2A 2004

Origin of the GeV-TeV emission: Sgr A*?Origin of the GeV-TeV emission: Sgr A*?

Is Sgr A* accelerating TeV emitting particles?(Liu+04, Liu+06, Aharonian+05)

GeV-TeV spectrum: time dependent CR injection following Sgr A* activity?(Chernyakova+11, Ballantyne+11)

Possible connection between CR injection and past hard X-ray flares Chernysov+14

300 yrs oldburst

Continuous injection

SF2A 2004

Origin of the Origin of the -ray source at the GC?-ray source at the GC?

Acceleration site: at ~105 Rs: A black hole plerion?

Acceleration at termination shock of a convective outflow in the ADAF(Atoyan+04)

Massive star wind collisions from central stellar disk (Quataert+05)

A Pulsar Wind Nebula (PWN) : G359.95-0.04a candidate PWN at 7'' (0.3pc) of SgrA* L

X ~ 1034 erg/s

(Wang+06, Hinton+07)

Population of millisecond pulsars in the central cluster:IC e± accelerated by MSP winds TeV emissionUnresolved MSP : GeV emission

(Bednarek+13)

Electrons accelerated during Sgr A* flaresGeV emission

(Kusunose+12)

GeV emission from SNR Sgr A East (interaction with 50 km/s cloud)Similarity with other SNR interacting with MoC (e.g. W44)

TeV

GeV

SF2A 2004

GC source above a a few MeV?GC source above a a few MeV?

From HESS collab.( 2009)

Sgr A* quiescent

Sgr A* flare ~1 hour

IBIS Fermi

HESS

?

Can we resolve the Comptel source in the GC region?l=358.5° b=-0.5°

Microquasar 1E1740.7-2942 , GC, or?Strong+01

SF2A 2004

GC source spectral energy distributionGC source spectral energy distribution

From HESS collab.( 2009)

Sgr A* quiescent

Sgr A* flare ~1 hour

IBIS Fermi

HESS

?

Can we resolve the Comptel source in the GC region?l=358.5° b=-0.5°

Microquasar 1E1740.7-2942 , GC, or?Strong+01

SF2A 2004

Evidences for CR excess in the central 200 pc Evidences for CR excess in the central 200 pc

Intense CR injection from GC starburst activity? (P ~ 1039 erg/s)- SN rate in the GC >~ a few 10-4 yr-1

Crocker+11, Crocker12, Yoast-Hull+14

Massive burst-like particle injection from the SMBH?e.g. Macias+14

Resolve GC diffuse emission < few 100 MeV to constrain CR distribution and origin

Up to 10 times local CR densties ~ 10 TeV

HESS coll. 06

< a few times local CR density ~ 10 GeV

Yang+14Yusef-Zadeh+13

150 pc, 1°

LECR in the Galactic Centre region?

Look for Low Energy CR ions injected in the central regions

Injected by local CR accelerators or SMBH

Typical signatures: C* (4.44 MeV) and O* (6.2 MeV) lines

Dogiel et al 2009

e.g. Estimation of LECR injection by tidal disruption of stars by SMBH

Flux integrated over a few degrees:

4.44 MeV and 6.2 MeV: 10-5 cm-2s-1

Typical width: 3-4%

Flux below 8 MeV: 10-4 cm-2s-1

Intense hard non-thermal X-ray emission (~1.6 up to 30 keV) around the Arches cluster

Capelli+10, Tatischeff+12, Krivonos+13

Inverse bremstrahlung emission of subrelativistic ions? Required power in CR ions:

PCR

= (0.5 – 1.8)×1039 erg s-1

Possibly powered by collision (200 km/s) between the Arches cluster and ambient cloud Clarkson+12

Kinetic power processed in the collision:

• Pkin

= 2 x 1040 erg/s

••••••••••

The Arches cluster: an accelerator of CR ions?

Archescluster

•

⇒

• CR energy density: ~ 1000 eV cm-3 The Arches cluster: an extreme

CR dominated region?

Tatischeff+12

••••••••••

The Arches cluster: an accelerator of CR ions?

Look for time variability of 6.4 keV and continuum emission over 13 yrs

•

A 30% flux variation observed in 2011-2013

Most of the non-thermal X-ray flux from Arches cluster surroundings is due to reflection of Sgr A* past flare

Clavel+14

Summary

••• Some key questions for ASTROGAM related to GC physics:

–

– - Nature of the -ray source at the GC?

• Particle acceleration by the BH? Sgr A east? Point source confusion?• ASTROGAM will resolve the GC Comptel source and constrain the origin of

GC soft -rays

•

– - Origin of CR in the inner 200 central pc? (& GeV GC excess)

– Starburst activity? SMBH bursts?

– ASTROGAM will constrain the distribution of < few 100 MeV -rays

–

– - Search for low energy cosmic-rays in the central 200 pc• Origin: Young stellar clusters? Recurrent stellar accretion by the SMBH?

• ASTROGAM will search for degree scale 4.4 and 6.2 MeV lines

–•