GammaGamma--Ray Observations of Ray Observations of

SLAC Summer Institute, August 4th - August 15, 2008

Olaf Reimer Hansen Experimental Physics Labs & Kavli Institute for Particle

Astrophysics and Cosmology, Stanford University

GRB 080514B has been localized jointly by SuperAGILE

and IPN

(GCN 7715)

and shows a significant gamma ray emission (GCN 7716). Follow-up by Swift (GCN 7719 and 7750)

provided the afterglow in X-rays. Many telescopes participated in the observation of the optical afterglow: Watcher (GCN 7718), GRON (GCN 7722), KPNO (GCN 7725) and NOT (GCN 7734).

SuperAGILE

–

Mars Odyssey annulus

SuperAGILE

1-D

AGILE first gamma-ray detection of a GRB: GRB 080514B (Mereghetti et al., to be submitted)

Gamma-ray Observations of Supernova Remnants

Esposito et al. 1996

W28 W44

γ Cyg IC443

269.6269.8270.0270.2270.4 R.A.

-23.8

-23.6

-23.4

-23.2

-23.0

Decl

inati

on

284.00284.25284.50284.75 R.A.

1.00

1.25

1.50

1.75

2.00

Decl

inati

on

94.294.494.6 R.A.

22.4

22.6

22.8

Dec

linati

on

304.0304.5305.0305.5306.0 R.A.

40.0

40.5

41.0

41.5

Dec

linati

on

EGRET sources and Supernova RemnantsA mixed blessing:

• Spatial coincidences of UNIDs

and cataloged (radio-)SNRs

• No detections in cases like SN1006, Tycho

& Kepler

• multifrequency

support, that several synchrotron nebulae in SNR harbourmagnetospherically

active neutron stars (i.e. CTA1)

•

GeV-measured gamma-ray source positions do not correlate well

with X-

ray brightrim/shell features (although hampered by angular resolution)

• GeV-cutoffs

already significant in EGRET-spectra

→ serious consideration of neutron star origin at GeV

SNR-associations

CTA1 W28

Zhang & Cheng 98

γCyg IC443

Cheng & Zhang 98

EGRET sources and Supernova Remnants –

the X-ray view on the associations

Cas

A : central X-ray point source (Chakrabarty

et al. 2001), unpulsed

IC443 : X-ray point source + PWN outside EGRET contour (Olbert

et al. 2001),

hard point source (Keohane

et al. 1997, Bykov& Bocchino

2001)

γCyg: complete identification of EGRET GeV-contour (Brazier et al. 1996) →

RX J2020.2+4026

However: Becker et al. 2005

CTA1: complete identification of EGRET GeV-contour (Brazier et al. 1998) →

RX J0070.0+7302

W44: association with PSR 1853+01 + PWN (Harrus

et al. 1997)

W28: associaton

with PSR 1801-23 ?

2EG J2020+4026 / RX J2020.3+4026SNR G78.2+2.1

RIGHT ASCENSION20 25

h m20 15

h m20 20

h m

40 00'o

30'

DEC

LIN

ATIO

N

41 00'o

30'

HD 193322

HD 229119

RX J2020.3+4026

2EG J0008+73 / RX J0007.0+7302G119.5+10.2 (CTA1)

DEC

LIN

ATIO

N

73 00'o

74 00'o

30'

30'

72 00'o

RIGHT ASCENSION00 15

h m23 55

h m00 05

h m

RX J0007.0+7302

AGN

21°45'

06h22m 20 18 16

22°00'

15'

15'

30'

45'

23°00'

RIGHT ASCENSION (2000)

DEC

LIN

ATIO

N

Nevertheless: statistical significant correlations with galactic

objects found Montmerle

et al. 1979 COS-B, SNRs, OBs → "SNOB"Sturner

& Dermer

1995 EGRET, SNRs

→ significant positional correlationEsposito et al. 1996 EGRET, SNRs

(X-ray) → 14 associationsRomero et al. 1999 EGRET, SNRs

(radio), OB, WR → 22 associations

•

overwhelming statistical evidence for SNR correlation•

significant evidence for OB association correlation•

marginal support for WRs

and/or Of stars

More than a single population of galactic γ-ray sources present in the EGRET data.

Torres, Romero et al. 2003

“The spectrum is a good match to that predicted by pion

decay, and cannot be explained by other mechanisms.”

(Enomoto

et al. 2002, Nature)

IC interpretation in conflict with data !

SNR as prime candidate sources for Galactic Cosmic Rays

SN1006 as seen by ASCA(Koyama et al. 1995)

TeV electrons –

YES! →

But what about the hadrons?

Evidence for hadronic particle acceleration in SNRs?

π0 decay interpretation in conflict with data, too !(Reimer & Pohl 2002)

The steepness of previously measured spectrum not confirmed by HESS(Aharonian et al. 2004, 2006)

And then there came H.E.S.S. – SNR seen by ground-based Cherenkov telescopes

Supernova Remnants seen –

primariy

particle distribution > 100 TeV

RX J1713.7-3946as seen by H.E.S.S.

RA SNR seen by6:17 IC 443 MAGIC, VERITAS8:52 RX J0852-4622 CANGAROO, HESS14:42 RCW 86 HESS17:13 RX J1713.7-3946 CANGAROO, HESS18:00 W28 HESS23:23 Cas A HEGRA, MAGIC, VERITAS

Particles accelerated in shock

Particles are confined to source region by pre-existingor dynamically generatedmagnetic fields

On the scale of kyrs,fields decay / are damped and particlesdiffuse out of the source

X-ray / gamma ray correlation

Contour lines: ASCA X-raysY. Uchiyama et al. 2002

H.E.S.S.electrons

X-rays ~ IC γ-rays

protons + 10-4 electrons/protonBerezkho & Völk (2006)

+ gas→ πo → γ-rays ~ X-rays

+ gas→

B2 ~ ρLucek & BellMNRAS 2000

Porter et al. (2006)Katz & Waxman (2007)Plaga (2007)…

B ~ 10 μG

B ~ 100 μG

Key issue:Key issue:StrenghtStrenght of of magnetic magnetic

fieldfield

–

Close correlation with X-rays [+electrons]–

Spectral shape [+protons]–

IC interpretation implies (too) low B-field [+protons]–

No tight correlation with molecular material [+electrons]•

Not yet clear…–

Need data at lower energies to be sure, e.g. GLAST

protons

electrons

Where are we now with RXJ1713.7-3946? Archetypal SNR

Who will settle this quest?

GeV-Imaging of RXJ1713?

H.E.S.S.

GLAST

Assumptions on 3EGJ1714 made, underlying: 5 year exposure, E > 3

GeV(Funk et al. 2006)

Simulated GeV-Spectrum of RXJ1713? Yes (in b/w perspective)

If hadronic, do we see enough SNR, and at the right places?

→ GLAST

GLAST

The remaining freedom in the interpretation of VHE data will be constraint byE < 100 GeV data –

and sensitive X-ray data (Uchiyama et al. 2007)

(a)

3EGJ1714 will be refined/disentangled from RXJ1713.→ Molecular Cloud interaction → improved (CfA & Nanten) CO surveys

(b) GeV emission from RXJ1713 will be detected or an u.l. will be truly sensitive → sanity check

for the leptonic models/hadronic models → SNR ACCELERATION SITE FOR HADRONS OR NOT ?

(c) Nature of 1WGA J1713.4-3949 ? Compact object? Progenitor??

1xx GeV to ~100 TeV – ground-based Cherenkov telescopes

Non-morphological resolved SNR-detections:

Cas

A: HEGRA, MAGIC, VERITASW28: HESSIC443: MAGIC, VERITAS

↓

shellsize

< instumental

resolution: unresolved

↓The “composite”

SNR/PWN: e.g. G0.0+0.1, HESS J1813, …

Energy

Energy Flux π0 decay

Inverse Compton

Synchrotron

Radio IR/Optical X-rays γ-rays VHE γ-rays

IC on target: Synch. (+CMB)

Radio

X-ray

γ-ray

Synchrotron

Synchrotron:

Ex

(keV) = 4 (B/1mG)(Ee

/10TeV)2

IC (on CMB):

Eγ

(TeV) ~ (0.05Ee

)2

Neutral pion

decay:

⟨Eγγ

⟩

~ 0.15 Ep

10 keV

X-ray → 10 TeV e-

1 TeV

γ-ray → 20 TeV e-

→

6 TeV p

Gamma-Rays from Pulsar Wind Nebulae

Gamma-Rays from Pulsar Wind Nebulae

•

Many known X-ray PWN now identified as TeV

emitters and almost all of the highest spin-down power radio pulsars have associated TeV

emission –

Efficient particle accelerators•

May be easier to detect in TeV

than keV

?–

Integration over pulsar lifetime for TeV

electrons (less cooling)–

TeV

instruments sensitive to more extended objects –

no confusion with thermal emission–

Many of our unidentified sources may be PWN

The PWN Population

H.E.S.S. sources near energetic pulsars

435 pulsars in HESS survey region*

randomcoinc.

Spin-down energy fluxin ergs/kpc2

preliminary

Systematic studies possible !

ATNF PSRs

vs. TeVCarrigan

et al. 2007

GeV

vs. TeVFunk Reimer Torres Hinton 2008

Implied efficiency Spin-down → TeV

~ 1%

•

PSR J1826-1334–

3×1036

erg/s spin-down power, ~2×104

years old•

5’

X-ray PWN–

G 18.0-0.7 (Gaensler et al 2002)•

1°

TeV

γ-ray source–

HESS J1825-137 (Aharonian et al 2005)

–

Energy dependent morphology•

A first at TeV

energies–

Cooling of electrons away from pulsar? (tcool

∝

1/E)[ 2 keV synchrotron emission comes

from 200 TeV electrons (if B ≈ 10 μG)…, γ-rays come from lower energy electrons ]

HESS

HESS J1825-137

Archetypal (before HESS): Crab

Horns 2006

Now: diversity among the PWNs!• often extended, • displaced from PSR, • energy dependend

morphology change

Vela X

PWN (numerically) most prominent class of identified galactic γ-ray sources

The binary system PSR B1259-63 / SS 2883

Discovery: H.E.S.S.,March

2004

First variable galactic TeV

source.

First in a new source class in HE g-rays.

48 ms Pulsar3.4 y period

Be Star10 M

Periastron 7. March 2004

Complex interaction between pulsar and star during

periastron

PSR B1259-63Johnston et al. 1992

Millisecond pulsar (T=48 ms)Mass of ca. 1.4 solar massesMassive Be-type companion star of ca. 10 solar massesHighly eccentric orbit (T= 3.4year)Closest impact is ~1013 cm or ~20 stellar radii

Electron wind from a pulsar terminates onto the strong Be-star outflowShocked electrons radiate in synchrotron (X-rays) & IC (TeV Gamma-rays)

Pulsar

Massive star Shock front

Very plausible scenario, theoretically predicted.

The PSR B1259-63 field of view

March 04 Apr./May 04Feb. 04

H.E.S.S.

Per

iast

ron

Flux

>38

0 G

eV[c

m-2

s-1

]

X-Ray Binaries as Gamma-Ray Sources

Binary systems of a compact object (neutron star or black hole) and a stellar companion

Matter is flowing over from the stellar

companion onto the compact object.

Angular momentum conservation

=> Formation of an accretion disk

Matter in the accretion disk heats up to ~ 106 K

=> X-ray emission

…more on X-Ray Binaries

Generally identified as radio jets

As in most accretion disk systems, this results in the formation of collimated outflows:

Mildly relativistic jets: Γ

~ 2

X-ray binary spectra typically consist of a

thermal disk component plus a hard power-law.

•

Similarities–

massive star (O, Be) e≠0

–

TeV

emission ~ 1033-34

erg/s

–

Low, ~ stable radio and X-ray emission (periodic radio outbursts in LS I+61 303 and PSR B1259-63)

–

Spectral energy distributions

Gamma-ray binaries

O6.5V

LS 5039

0.2 au

Be

LS I +61 303

0.7 au

26 d

4 d

O9.7I

0.2 au5.6 d

Cyg X-1

BH orPSR ?

BH

BH orPSR ?

© G. Dubusobs.

accretionpowered

Be

PSR B1259-63

10 au

3.5 yr

PSR

wind-powered

MAGICTeVPA 2007

γ-ray binaries: They are orbitally modulated!

H.E.S.S.: LS5039 (Aharonian

et al. 2005)MAGIC: LS I 61°303 (TeVPA

2007)

VERITAS: LS I 61°303 (TeVPA

2007)

γ-ray binaries: They flare!

•

Small FoV

telescopes depend on alerts or luck !

•

NEW: Contemporaneous data will always be there!

allsky

capability/high duty cycle: SWIFT/MAXI/GLAST

vs.

small FoV/low duty cycle but high sensitivity/angular resolution: VHE

→ Analogy to blazars!?

LS I +61o

303: MAGIC

(Albert et al. 2006)

Controversy: microquasar or pulsar ?

Mirabel 2006

High-Energy Emission Model for Microquasar

Jets

Injection, acceleration of ultrarelativistic

electrons

Qe

(γ,t)

γ

Synchrotron emission

νFν

ν

Compton emission

νFν

ν

γ2γ1

γ-q

Seed photons:

Synchrotron (SSC), Accr. Disk + BLR (EC)

Injection over finite length near the base of the jet.

Additional contribution from γγ

absorption along the jet

Leptonic Models

Relativistic jet outflow with Γ

≈

2

+ Companion star light→ Include abs. by companion star light!

Orbital modulation of VHE γ-rays can be explained by γγ

absorption alone!

Pulsar Wind Nebula emission

Proven mechanism (Crab)Proposed long ago for LS I+61 303 by Maraschi

& Treves (1981)

Low steady emission

Radio pulse ? absorbed in strong stellar wind (tighter orbits in LS 5039, LS I+61 303)

[from G. Dubus]

Modeling in a PWN model

Conclusions: gamma-ray binaries as compact PWN

•

Interpretation as pulsar / stellar wind interaction

explains similarities between VHE emitting binaries.

•

VHE emission occurs close to pulsar/star (γγ

absorption should modulate TeV

flux in LS 5039).

•

Large scale emission can be explained by comet-like shocked material, radio morphology depends on orbit.

AGILE: Micro-QSO observations

•

Cyg X-1•

GRS 1915+105

Cyg X-1

the longest continuous hard X-ray monitoring of Cyg

X-1

Total Observation Time: ~ 4.5 Ms

(1196 Orbits)

1 Month~1.3 Crab Flare

(see also INTEGRAL ATels

#1533,1536)

Cyg

X-1

Del Monte et al., in preparation

SuperAGILE

GRID

SuperAGILE light curve

LE (20-25 keV): Yellow

HE (25-50 keV): Cyan

Γ~ 1.61 +/-

0.13

Low/Hard State

Searching for transitions…

…and gamma-ray emission

GRS 1915+105

GRS 1915+105

15 April 2008

Recent reactivation of the microquasar

GRS 1915+105

GRS 1915+105

(Trushkin

S. et al., ATel

#1509)

gamma-ray U.L.

18-60 keV

gamma-ray map

Galactic gamma-ray transients

•

Cygnus region•

Carina region

•

Crux region

AGILE observes variability and detects new transients on time scales of 1 day at flux levels of 10-6 cm-2s-1 , even in crowded, high diffuse emission Galactic plane regions.NO detectable simultaneous hard X-ray emission (F < 20-30 mCrab, 18-60 keV, 1-day integration)

EGRET: Seen one over mission life time. Never identified.AGILE:

GLAST: Expectations translated into full-scale transient trigger and follow-up program, in place by now.

Gamma-Ray Emission from active and passive Molecular Clouds

~85% of all γ

in galactic diffuse

~15% in sources

The most prominent GeV source is our Milkyway itself!

The diffuse γ-ray emission is observational evidence of CR interactions in the interstellar medium via Bremsstrahlung, IC, π0-decay

CR propagation near sources or in molecular clouds

GLAPROP might give us a prediction based on large-

scale consistency of nuclear reactions, ISRF, gas distributions, CR and γ-ray measurements.

May or may not be correct for a localized diffuse emission problem!

→ CS used, avoiding opacity problems

for 12CO (Aharonian et al. 2006)

High-lat molecular clouds

often coincidences yielding ambiguity

between expanding SNR and molecular cloud

(Gabici

& Aharonian ’07)

1 degree

The TeV Galactic Centre

•

Two bright point-sources in the central part of the Galaxy

Diffuse Emission

•

After subtracting point-sources, diffuse emission is seen extending along the galactic plane

1 degree

HESS

Diffuse Emission

1 degree

CS Line Emission (dense clouds)smoothed to match

H.E.S.S. PSF

HESS

Diffuse Emission

•

Molecular clouds are ‘glowing’

in TeV

γ-rays after being bombarded by cosmic ray protons and nuclei!

•

Energy spectrum harder than local cosmic ray spectrum (proximity to accelerator?)

SNR/cloud interactions?

•

Correlations with available target material–

IC 443 and W 28, Old (>104

yr) SNRs

near mol. Clouds–

Both have associated GeV

sources

pp → π0

→ γγ

?

Have we spoken lately about the role of stellar winds in the quest for Cosmic Ray acceleration?

early 80s: COS-B and the “SNOBs“Montmerle 1979: no 1:1 between SNRs (as a class) and gamma-ray

sources, rather linked with young objects

early…late 90 – EGRET era: more g-ray sources, more coincidences (sic!)

Kaaret & Cottam – correlation EGRET <-> OB associationsYadigaroglu & Romani – OB associations, (open clusters, HIIs, PSRs, SNRs)Romero et al. – associations of individual SNR, OB associations

…but got stuck at 3σ

conficence level (compared to the 5-6σ

for SNRs)

2002 onwards – TeVs scored: HEGRA TeVJ2032+4130

inital detection report (112 h obs, 4.6σ)

final 237 h observations (!), 6.1σ, extended 0.1°

(compared 0.07°

psf)

+ hint of confirmation* from Whipple

in massive Cygnus OB2 association

~2600 OBs estimated

Possibility of -

at least two -

explanations–

Faster diffusion of higher energy hadrons and subsequent interaction in molecular clouds yielding a source a bit separated from the accelerator

-

Particle acceleration by stellar winds itself

–

GRB-remnants in our Galaxy ?!–

photo-de-exitation of PeV CRs after photodesintegration on UV-photons ??!

“highscore”: the deepest MWL follow-up for an UNID VHE source so far (55 ksec

Chandra, 50 ksec

XMM)

2006: H.E.S.S. observed the stellar cluster Westerlund

2 (seen here with SPITZER eyes)

WR 20aWR 20b

Westerlund

2

•

embedded in a giant molecular cloud

• ongoing star formation

•

stellar winds blow cavities around massive Wolf-Rayet

(WR) stars

•

WR 20a itself is known as the most massive binary star in our Galaxy (two stars of ~80 Msolar

in a 3.8 day orbit)

Therein: young, hot & massive stars

-> 8 evolutionary earlier then O7, 2 WRs, and in particular WR20a, the most massive measured

stars in our Galaxy (WN6+WN6 binary)

r=19.3 R o

d ~

51..5

3 R o

Rauw

et al. 2005

orbital period: 3.686 d

The H.E.S.S. observations:

• detection of a new very-high-energy gamma ray source, probably associated with the stellar cluster Westerlund

2

based on 14h data, at Ethres

= 380 GeV, Γ=2.53 ±0.16stat

±0.1syst

• origin of energetic γ-rays unlikely the WR stars itself -> HESS J1023-575 is an

extended

and constant

source

)2 (deg2θ0 0.05 0.1 0.15 0.2 0.25

# ex

cess

eve

nts

-50

0

50

100

150

point source for H.E.S.S.

observed source extensionσ

= 0.18°

±

0.02°WR20a

WR20b

VHE γ-ray image

The “blister”

(Whiteoak

& Uchida 1997):

indicative for rapid expansion into a ambient low-density medium (superbubble?)

Shock acceleration at the boundaries of the blister Analogy with SN-driven expansions with expanding stellar winds.

Outbreak phenomenon from winds of hot and massive star ensembles

(Tenario-

Tagle

1979, Völk

& Forman 1982, Cesarsky

& Montmerle

1983) ?

Contribution to Cosmic Rays ? -> Need to see more := common phenomenon or not!

radio: 843 MHz γ-ray image

WR20aWR20b

Implications of the H.E.S.S. findings:

• intriguing new type of VHE gamma-ray source• archetypal for other young massive clusters ?

• if this association is confirmed and further stellar clusters will be detected in γ-rays (by ground-based γ-telescopes,or GLAST)

-> consider a

new class of extreme particle accelerators in our Galaxy

-> consequences for CRs: Will contribute, fraction unclear!

WR20aWR20b

843 MHz radio image

Milagro Pevatron?

Abdo, et al. ApJ Lett 2007

GeV Sources Emit TeV Gamma-Rays ?

•

Milagro has discovered

3 new sources

& 4 candidates in the Galaxy.•

5/7 of these TeV sources have GeV counterparts.

Only 13 GeV counterparts in this region -

excluding Crab. Probability = 3x10-6

E. Ona-Wilhelmi, et al., ICRC 2007

Milagro TeV “spectrum” of MGRO J1908+06 & HESS J1908+063

Median energy for this angle and α=-2.0 is 50 TeV Cut on A4> 4 & 9 gives median E of 60 and 90 TeV

60 90

Things to come?

•

Abundance of sources, many different types

•

Need more sensitivity, better (spatial / temporal) resolution and better MWL

to probe

underlying physics•

Many highly interesting source types just (?) below current sensitivity–

Starburst galaxies

–

Clusters of galaxies–

GRBs

–

…

One γ-ray eye is always on now…