Astrophysical Sources ofHigh Energy Radiation and Particles
in the Era of CTA and ASTRO-H	

Lukasz Stawarz (ISAS/JAXA)
Tadayuki Takahashi (ISAS/JAXA)
Yasunobu Uchiyama (KIPAC/SLAC)	

“Multiwavelength Astronomy and CTA: X-rays”
Takahashi et al., 2012,
APh, in press (arXiv:1205.2423)	

Outline of the Talk	

• ASTRO-H• Low-Power Blazars (BL Lacs)• High-Power Blazars (FSRQs)• Misaligned Blazars (Radio Galaxies)• Radio-Quiet AGN (Seyferts)• Clusters of Galaxies• Summary: X-ray/γ-ray synergy

ASTRO-H
ASTRO-H, to be launched in 2014, will carry the first focusing hard X-ray telescope with graded
multilayer reflecting surface operating in the energy range 5-80 keV. In addition to the Hard X-ray
Imager, ASTRO-H will carry two soft X-ray telescopes, one with a micro-calorimeter spectrometer
array with excellent energy resolution (Soft X-ray Spectrometer), and the other with a large area
CCD in their respective focal planes. In order to extend the energy coverage to the soft gamma-ray
regime, the Soft Gamma-ray Detector will be implemented as a non-focusing detector covering theenergy range 40-600 keV, and being capable of measuring polarization of bright (>10mCrab) sources.

HXI & SGD

Chandra/ACIS-S, Suzaku/HXD (PIN & GSO), Integral/IBIS, ASTRO-H/HXI & SGD:
3σ sensitivity curves for 100 ks exposures; ΔE/E = 0.5.
CGRO/COMPTEL & EGRET: all-lifetime all-sky survey.
Fermi/LAT: pre-launch sensitivity for the 5σ detection limit at high Galactic latitudes with 0.25decade ranges of energy in a one-year dataset.
MAGIC, H.E.S.S.: 5σ detection with >10 excess photons after 50h exposure.
CTA: simulated configuration C sensitivity curve for 50h exposure at a zenith angle of 20deg.

SXS
Imaging spectroscopy with an energy resolution<7 eV by the SXS of extended sources canreveal line broadening and Doppler shifts due
to turbulent or bulk velocities of the X-ray
emitting plasma, enabling the determination of
the level of turbulent pressure support inclusters, supernova ejecta dispersal patterns,
the structure of active galactic and starburst
winds, and the spatially dependent abundance
pattern in clusters and elliptical galaxies. 	

ASTRO-H/SXS
XMM/RGS (RGS-1 & RGS-2)
Chandra/LETG, MEG & HEG
The spectroscopic capability of X-ray
micro-calorimeters is truly unique!

Hard X-ray Sky	•All-sky-survey by BAT onboard SWIFT resulted in the detection of 1092 sources (at thesignificance level of ≥4.8σ) in the 58-month accumulation of the data within the photon
energy range 14-195 keV (Baumgartner et al. 2011). Majority of sources (730) have been
identified with extragalactic objects, and in particular with AGN (627).

GeV Sky• 2nd catalog of AGN detected by LAT (“2LAC”, 24 months of data collected in scientific operationmode) includes 1016 gamma-ray sources located at high Galactic latitudes (|b|>10°) that are detected
at high significance (≥5σ) and associated statistically with AGN (Ackermann et al. 2011).

885 AGN in a “clean 2LAC sample” comprising 395 BL Lacs, 310 FSRQs, 22 AGN of other types, and
156 AGN of unknown types (to be compared with ~100 AGN, mostly FSRQs, associated with EGRET
sources; Hartman et al. 1999).

TeV Sky• The extragalactic TeV sky is dominated by blazars as well, with BL Lacs constituting majority ofthe detected sources. Most of the objects were discovered during the last decade thanks to theoperation of modern Cherenkov Telescopes H.E.S.S., Magic, or VERITAS.

http://tevcat.uchicago.edu/	

Much more AGN are expected to be detected in a near future with CTA!

Active Galactic Nuclei
AGN are established sources of a broad-band emission.
In non-blazar objects, IR emission is dominated by the circumnuclear dust, optical-to-UV emission byaccretion disks, and X-ray emission by the accretion disk coronae.
In blazar sources, the entire radio-to-γ-ray continuum is due to the emission of relativistic jets. Rapidand large-amplitude variability of blazars points toward a very efficient and extremely rapid
acceleration of the jet particles to ultrarelativistic energies, typically ascribed to shocks.

Urry & Padovani 1995	

“Standard” Blazar Models	
High-power blazars: FSRQs (3C454.3)
Low-power blazars: BL Lacs (Mrk 421)	

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Sikora et al. 1994	

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Single well-defined and homogeneous emission zone at >102 Rg ~ 1016 cm distances from the central
SMBH – clearly a huge oversimplification, justified in the EGRET era, but not anymore.
Most of the radiatively dissipated power of blazars is emitted in either X-ray or γ-ray domains.

BL Lacs
The correlated variability in the X-ray and TeV bands established for many BL Lacs (e.g., Mrk 421)
proves the inverse-Compton origin of the observed gamma-rays.
The exact correlation patterns
emerging from detailed analysis
revealed a picture which is much
more complex than that expectedin the “standard’” models,assuming a single homogeneousemission zone and a simplified
prescription for the shock
acceleration of the radiating
particles.
LS: it is not clear if moresophisticated models involving
multiple or inhomogeneousemission zones are necessarily
more realistic. The crucial
problem seems to be related tohardly understood particle
acceleration processes involved.
Fossati et al. 2008	

Highest Energy Electrons
Kataoka et al. 2001	
An exciting and unique possibility
for constraining particle acceleration
processes taking place in blazar jets
is the detection of the polarization in
hard X-rays by SGD during
particularly strong flaring states ofthe brightest BL Lacs, like that of
Mrk 501 in 1997 when thesynchrotron continuum of thesource extended up to the >100 keV
photon energy range.

X-ray domain carries information regarding the >TeV energy electrons directly involved in
shaping the gamma-ray properties of BL Lacs.
Instruments HXI and SGD onboard ASTRO-H will enable us, for the very first time, totrack the spectral evolution of several bright BL Lacs above 10 keV photon energies in
100 ks (or even shorter) exposures.

MWL Campaigns
Truly MWL and simultaneous
observations of Mrk 501 with the best(up to date) spatial and temporal
coverage (Abdo et al. 2010; CAs:
Paneque & LS).
Hard X-rays: Swift/BAT
VHE γ-rays: MAGIC & VERITAS
Abdo et al. 2010

Hard X-ray and soft gamma-ray regimes
are the least explored!
“Typical” behavior of Mrk 501: only modest
and rather long-timescale flux changes

Ultrafast Variability

Variability in the TeV range for PKS 2155-304 is seen
up to ~600 sec in the Fourier power spectrum, andwell-resolved bursts varying on time scales of ~200 sec
are observed. There are no strong indications forspectral variability within the data. The shortest
observed flux doubling timescale, tvar ~ 200 s, implies
linear size of the emitting region R < c tvar δ. For themass of the black hole MBH ~ 109 Msun, this gives R ~(δ/100) × Rg suggesting that the blazar zone is locatedin the closest vicinity of the black hole, and that thewhole outflow is already extremely relativistic thereby(Aharonian et al. 2007, 2009)

Giannios et al. 2009	FSRQsIn FSRQs the X-ray observations probe the low-energy segment of the high-energy emission
component. This high-energy component dominates energetically over the synchrotron one, reachingapparent gamma-ray luminosities as large as ~1049 erg/s during the flaring states.
The low-energy tail of the high-energy emission components of FSRQs is produced via the IC process
involving the lowest-energy electrons, down to the mildly-relativistic regime. Hence these are the
combined gamma-ray and X-ray observations which constrain the jet energetics in FSRQs.

Sikora et al. 2008	Very	
  ﬂat	  	
  X-­‐ray	  spectra!	

Ghisellini &Tavecchio 2009	Heavy Jets

Γ2

Lack of bulk-Compton
features in soft-X-ray
spectra of blazars indicatesthat there are not enoughcold electrons to carry bulkof the jet kinetic power.
This indicates a dynamicalrole of (cold) protons(Begelman & Sikora 1987,
Sikora et al. 1997, Sikora &Madejski 2000, Celotti et al.
2007, Celotti & Ghisellini
2008, Kataoka et al. 2008)

GeV Spectral Breaks	
Fermi/LAT discovered that gamma-ray spectra of luminous FSRQs are typically of a broken
power-law form, with spectral breaks located around a few GeV (e.g., PKS 1222+216).

Tanaka, LS et al. 2011	

Aleksic et al. 2011	

The mosr recent studies reveal variety of particle spectra resulting from 1st-order (diffusive) Fermi
acceleration at relativistic shocks, depending on the magnetic field configuration (subluminal orsuperluminal shocks), and turbulence spectrum (e.g., Niemiec & Ostrowski 2006, Lemoine et al 2006,
Spikovsky et al. 2010). There is no universal spectral shape of shock-accelerated particles!

Problems!	
Hayashida et al. 2012	
Boettcher et al. 2009	

No GeV/X-ray correlations, no obvious GeV/radio correlations,surprising and unexpected very fast TeV flares…

Cosmology

Ghisellini 2012	

Albert et al. 2008	

TeV detections of distant (z>0.2) FSRQs are interesting in the context of constraining
the cosmological evolution of EBL.
Deep hard X-ray observations may be the most efficient way of studying SMBHs andrelativistic jets in high-redshift (z>2) blazars of the FSRQ type.

Radio Galaxies
Radio galaxies are believed to constitute the parent population of blazar sources. Unlike inblazar sources, the observed X-ray emission of radio galaxies is significantly contributed, orsometimes even entirely dominated by the emission of the accretion disks and disk coronae.
This constitutes an opportunity to investigate the jet-disk coupling, and hence the jet
launching processes, by means of joint X-ray and gamma-ray observations.
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Growing Population

Not including Local Group Galaxies (SML, LMC, M31, MW)Low-Power, Nearby
Abdo et al. 2010	

Morganti 2010	

Centaurus A:
giant low-power (FR I) radio galaxy, only 3.7 Mpc away, detected by all the instruments
onboard CGRO, by Fermi/LAT, and HESS in the 100 keV - 10 TeV range.

Giant Lobes
Fermi/LAT

WMAP

Abdo et al. 2010
(CAs: Cheung, LS,Fukazawa, & Knodlseder)	
Fermi/LAT (similarly as WMAP) resolved giant
lobes of Centaurus A radio galaxy(~8 deg on the sky, ~1Mpc physical size).
X-ray and TeV mapping of the giant halo
awaits future observations.

Jet/Disk Connection
The long-term monitoring of 3C 120
at X-ray and radio frequencies
suggested that the dips in the X-ray
emission are followed by ejections ofbright superluminal knots along theradio outflow. The proposedinterpretation involved X-ray dips dueto the disappearance of the inner partsof the accretion disk leading to theejection of the excess matter along thejet axis, analogous to what is observedin the Galactic jet sources.
The possibility that the related
phenomenon may be also observed
at gamma-rays, with the gamma-ray
flares following the dips in theaccretion-related X-ray emission,
awaits the operation of CTA andASTRO-H.
Marscher et al. 2002	Seyfert Galaxies
absorption

fluorescent
Fe Kα linereflection
component(thermal) Compton
continuum

thermal plasmakTe ~ 100 keV?
non-thermal tail
δ ~ 0.01-0.1?

High energy (X-ray/soft γ-ray) emission of Seyfert galaxies is widely believed to be dominated by theaccreting matter (e.g., Zdziarski 1999, Poutanen 1998)

Strictly Thermal?
NGC 4151

Sy 1s

Sy 2s

Non-thermal models for
X-ray/soft γamma-ray spectraof Seyferts were widely
discussed in the 80s/90s.
However, OSSE observations
suggesting cut-offs in the
spectra of Seyferts around
100 keV implied that thermal
models are more likely. Still,
OSSE sensitivity was rather
limited, and the number of
OSSE-detected Seyferts wasrather low.
δ < 0.1 on average.

Zdziarski et al. 2000

Non-thermal Coronae
Galactic source Cygnus X-1
detected at 1-10 MeV photon energies(particularly in its “low hard” state),
and also (possibly?) at TeV energies.

TeV emission of Cygnus X-1 modeled
as produced by non-thermal particles
accelerated by turbulence andreconnection within the accretion flow
(disk coronae) and heavily absorbed by
the surrounding photon fields (leading
to the formation of a cascade
emission; Zdziarski et al. 2009).

What If … ?

Inoue et al. 2008	

Extragalactic MeV background may be explained by radio-quiet (Seyfert-like) AGN, assuming apresence of non-thermal electrons in hot and highly magnetized coronae of their accretion disks(acceleration to ultrarelativistic energies driven by magnetic reconnection), at the level δ ~ 0.01-0.1.

Gamma-ray Quiet?

No statistically significant gamma-ray excess coincident with any hard X-ray
brightest Seyfert galaxy, with possible exceptions of ESO 323–G077 and NGC
6814. The Fermi–LAT upper limits probe the ratio of gamma-ray to X-ray
luminosities < 10%, and even < 1% in some cases(Ackermann et al. 2012; CAs: Hayashida, LS, Madejski, & Bechtol).

Clusters of Galaxies
Merging processes leading to the formation of clusters of galaxies release huge amounts ofgravitational energy (≥1064 erg) on timescales of the order of ~Gyr.
While much of this energy is contained in thermal plasma with temperatures 10 keV emitting X-ray
photons via the bremsstrahlung process, part of it may be channelled to accelerate a small fraction ofparticles from the thermal pool to ultrarelativistic energies (e.g., on giant accretion shocks), and toform in this way an energetically relevant hadronic CR population within the ICM.	

Bullet cluster	Giant Radio Halos
Non-thermal activity in the ICM manifests clearly in the phenomenon of giant (~Mpc-scale) radio halos.
These are roughly spherical and low-surface brightness structures centered at the position of thepeaks in galaxy distributions, which are found in about 10% of the systems.
Are these due to the electrons formed as secondaries from hadronic CR interactions, electrons
produced via DM annihilation/decay processes, or electrons accelerated as primary CRs directly fromthe thermal pool of the ICM by the magnetic turbulence (stochastic processes)?

Coma cluster	DM, Shocks, Turbulence…
A variety of choices regarding the candidates for the DM particles, not fully constrained particle
acceleration mechanisms, and hardly known turbulence conditions within the ICM due to theinsufficient knowledge regarding the kinematics of the cluster gas and the structure of thecluster magnetic fields, all affect the model predictions regarding the spatial distribution andthe energy spectra of the non-thermal emission of clusters of galaxies.	

Xu et al. 2009: Isocontours of baryon density (left), magnetic field strength (middle), andmagnetic field lines at z = 0. The field of view is 6 Mpc. The color ranges are 1e-10 (blue)
to 2e-6 (red) G for magnetic fields. 	

Coma Cluster
Swift & Suzaku hard X-ray upper limit: Wik et al. 2011.
Fermi/LAT upper limit: Ackermann et al. 2011 (point source, King profile, 2D Gaussian 0.8deg).
HESS upper limits: Aharonian et al. 2009 (source region radius 0, 0.2 and 0.4deg).
Solid curves: turbulence/leptonic model for cluster magnetic field 2, 5 μG (Brunetti & Lazarian 2011).
Dashed curves: DM-induced emission for the neutralino mass of 60 GeV (Colafrancesco et al. 2011).
Thick line: shock/hadronic model (Pfrommer 2008, Pinzke et al. 2010).	

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ICM Spectroscopy
Detailed insight into the kinematics of the ICM, and hence into the various energy dissipation
processes involved, thanks to spectrometric observations probing bulk plasma velocities and/or
turbulence at a resolution corresponding to a speed of a few times 100km/s, together with anarcmin imaging system in the hard X-ray band with a sensitivity of orders of magnitude better
than previous missions	Simulated SXS spectra around the iron K line complex for 100 ks ASTRO-H observations of Perseus
Cluster. Line profiles assuming σ=0, 100 and 200 km/s turbulence. Simulated broad-band spectra
for hot plasma with three different temperatures of 0.6, 2.6 and 6. keV (Takahashi et al. 2010).	

Summary	
A very important synergy between the X-ray and VHE γ-ray
observations of astrophysical sources of high energy radiation andparticles with modern (future) instruments.
• Low-Power Blazars (BL Lacs)
probing particle acceleration with synchrotron X-rays and γ-rays• High-Power Blazars (FSRQs)
probing jet energetic with inverse-Compton X-rays and γ-rays• Misaligned Blazars (Radio Galaxies)
probing jet production with thermal X-rays and γ-rays• Radio-Quiet AGN (Seyferts)
probing SMBH and accretion disk physics with X-rays and γ–rays• Cluster of Galaxies
probing ICM dynamics and CR production with X-rays and γ–rays•

All the Galactic sources… (SNRs, PWNe, XRBs, Sgr A*,…)