Download Gamma - Ray Observations of Olaf Reimer

Gamma-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
AGILE first gamma-ray detection of a GRB:
GRB 080514B
(Mereghetti et al., to be submitted)
SuperAGILE 1-D
SuperAGILE – Mars Odyssey annulus
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).
Gamma-ray Observations of
Supernova Remnants
EGRET sources and Supernova Remnants
A mixed blessing:
• Spatial coincidences of UNIDs and cataloged (radio-)SNRs
-23.0
W28
2.00
W44
-23.2
1.75
Declination
Declination
-23.4
-23.6
1.25
-23.8
1.00
270.4
γ Cyg
1.50
270.2
R.A.
270.0
269.8
269.6
284.75
284.50
R.A.
284.25
284.00
IC443
41.5
22.8
Declination
Declination
41.0
40.5
22.4
40.0
Esposito et al. 1996
22.6
306.0
305.5
305.0
R.A.
304.5
304.0
• No detections in cases like SN1006, Tycho & Kepler
94.6
94.4
R.A.
94.2
• multifrequency support, that several synchrotron nebulae in SNR harbour
magnetospherically active neutron stars (i.e. CTA1)
• GeV-measured gamma-ray source positions do not correlate well with Xray bright
rim/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
γCyg
IC443
Zhang & Cheng 98
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 J0008+73 / RX J0007.0+7302
G119.5+10.2 (CTA1)
2EG J2020+4026 / RX J2020.3+4026
SNR G78.2+2.1
74o00'
15'
41 o00'
23°00'
30'
HD 193322
30'
HD 229119
AGN
DECLINATION
DECLINATION
DECLINATION
RX J2020.3+4026
o
73 00'
RX J0007.0+7302
45'
30'
15'
o
40 00'
22°00'
30'
21°45'
30'
o
72 00'
h
20 25
m
h
m
20 20
RIGHT ASCENSION
h
20 15
m
h
00 15
m
h
00 05
m
RIGHT ASCENSION
h
23 55
m
06h 2 2m
20
18
RIGHT ASCENSION (2 000)
16
Nevertheless: statistical significant correlations with galactic objects found
Montmerle et al. 1979
Sturner & Dermer 1995
Esposito et al. 1996
Romero et al. 1999
•
•
•
COS-B, SNRs, OBs → "SNOB"
EGRET, SNRs → significant positional correlation
EGRET, SNRs (X-ray) → 14 associations
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
Torres, Romero et al. 2003
More than a single population of galactic γ-ray
sources present in the EGRET data.
SNR as prime candidate sources for Galactic Cosmic Rays
TeV electrons – YES! →
SN1006 as seen by ASCA
(Koyama et al. 1995)
But what about the hadrons?
Evidence for hadronic particle acceleration in SNRs?
“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 !
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 J1713.7-3946
as seen by H.E.S.S.
RA
6:17
8:52
14:42
17:13
18:00
23:23
SNR
IC 443
RX J0852-4622
RCW 86
RX J1713.7-3946
W28
Cas A
seen by
MAGIC, VERITAS
CANGAROO, HESS
HESS
CANGAROO, HESS
HESS
HEGRA, MAGIC, VERITAS
Particles accelerated in shock
On the scale of kyrs,
fields decay / are
damped and particles
diffuse out of the source
Particles are
confined to source
region by pre-existing
or dynamically generated
magnetic fields
X-ray / gamma ray correlation
H.E.S.S.
Porter et al. (2006)
Katz & Waxman (2007)
Plaga (2007)
…
electrons
X-rays
~
IC γ-rays
B ~ 10 μG
Key issue:
Strenght of
magnetic
field
protons + 10-4 electrons/proton
Berezkho & Völk (2006)
+ gas
→ B2 ~ ρ
B ~ 100 μG
Lucek & Bell
MNRAS 2000
Contour lines: ASCA X-rays
Y. Uchiyama et al. 2002
+ gas
→ πo → γ-rays
~
X-rays
Where are we now with RXJ1713.7-3946?
Archetypal SNR
protons
electrons
•
– 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
H.E.S.S.
Who will settle this quest?
Simulated GeV-Spectrum of RXJ1713? Yes (in b/w
perspective)
GLAST
GeV-Imaging of RXJ1713?
GLAST
Assumptions on 3EGJ1714 made, underlying: 5 year exposure, E > 3 GeV
(Funk et al. 2006)
If hadronic, do we see enough SNR, and at the right places? → GLAST
The remaining freedom in the interpretation of VHE data will be constraint by
E < 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, VERITAS
W28: HESS
IC443: MAGIC, VERITAS
↓
shellsize < instumental resolution: unresolved
↓
The “composite” SNR/PWN: e.g. G0.0+0.1, HESS J1813, …
Gamma-Rays from Pulsar Wind Nebulae
Energy Flux
Synchrotron
π0 decay
Inverse
Compton
Synchrotron:
Ex(keV) = 4 (B/1mG)(Ee/10TeV)2
Radio
IR/Optical X-rays
γ-rays
VHE γ-rays
Eγ(TeV) ~ (0.05Ee)2
Energy
Neutral pion decay:
〈Eγγ〉 ~ 0.15 Ep
X-ra
y
10 keV X-ray → 10 TeV e1 TeV γ-ray → 20 TeV e-
io
d
a
→ 6 TeV p
a
γ-r
R
y
Synchrotron
IC (on CMB):
IC on target:
Synch. (+CMB)
Gamma-Rays from Pulsar Wind Nebulae
The PWN Population
•
•
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
H.E.S.S. sources near energetic pulsars
435 pulsars in HESS survey region*
preliminary
Implied efficiency
Spin-down → TeV
~ 1%
Systematic studies
possible !
ATNF PSRs vs. TeV
Carrigan et al. 2007
GeV vs. TeV
Funk Reimer Torres Hinton 2008
random
coinc.
Spin-down energy flux
in ergs/kpc2
HESS J1825-137
•
•
•
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
PWN (numerically) most prominent class of identified
galactic γ-ray sources
Archetypal (before HESS): Crab
Now: diversity among the PWNs!
• often extended,
• displaced from PSR,
• energy dependend morphology change
Vela X
Horns 2006
The binary system
PSR B1259-63 / SS 2883
Periastron 7. March 2004
Be Star
10 M~
Discovery: H.E.S.S.,March 2004
First variable galactic TeV source.
First in a new source class in HE g-rays.
48 ms Pulsar
3.4 y period
Complex interaction
between pulsar and star
during periastron
Pulsar
Massive star
Shock front
PSR B1259-63
Johnston et al. 1992
Millisecond pulsar (T=48 ms)
Mass of ca. 1.4 solar masses
Massive Be-type companion star
of ca. 10 solar masses
Highly 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 outflow
Shocked electrons radiate in
synchrotron (X-rays) & IC
(TeV Gamma-rays)
Very plausible scenario, theoretically predicted.
Periastron
Flux >380 GeV [cm-2 s-1]
The PSR B1259-63 field of view
H.E.S.S.
Feb. 04
March 04
Apr./May 04
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
As in most accretion disk systems, this results in
the formation of collimated outflows:
Mildly relativistic jets: Γ ~ 2
Generally identified
as radio jets
X-ray binary spectra
typically consist of a
thermal disk
component plus a
hard power-law.
Gamma-ray binaries
• 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
LS I +61 303
PSR B1259-63
windpowered
Be
BH or
PSR ?
PSR
Be
0.7 au
10 au
26 d
3.5 yr
Cyg X-1
LS 5039
accretion
powered
O6.5V
BH
BH or
PSR ?
O9.7I
0.2 au
4d
0.2 au
obs.
5.6 d
© G. Dubus
γ-ray binaries: They are orbitally modulated!
H.E.S.S.: LS5039 (Aharonian et al. 2005)
MAGIC: LS I 61°303 (TeVPA 2007)
MAGIC
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
LS I +61o 303: MAGIC
(Albert et al. 2006)
→ Analogy to blazars!?
Controversy: microquasar or pulsar ?
Mirabel 2006
High-Energy Emission Model for Microquasar
Jets
Synchrotron
emission
Qe (γ,t)
νFν
Injection,
acceleration of
ultrarelativistic
electrons
Relativistic jet outflow with Γ ≈ 2
ν
Compton
emission
γ1
γ2 γ
Injection over finite
length near the
base of the jet.
Leptonic
Models
Additional contribution from → Include abs. by
γγ absorption along the jet companion star light!
νFν
γ-q
ν
Seed photons:
Synchrotron (SSC),
Accr. Disk + BLR (EC)
+ Companion star light
Orbital modulation of VHE γ-rays can be
explained by γγ absorption alone!
Pulsar Wind Nebula emission
9 Proven mechanism (Crab)
Proposed long ago for LS I+61 303 by Maraschi & Treves (1981)
9 Low steady emission
9 Radio pulse ? absorbed in strong stellar wind
(tighter orbits in LS 5039, LS I+61 303)
Modeling in a PWN model
[from G. Dubus]
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
SuperAGILE
1.61curve
+/- 0.13
SuperAGILE Γ~
light
Low/Hard State
LE (20-25 keV):
Yellow
Searching for transitions…
HE (25-50 keV): Cyan
GRID
…and gamma-ray emission
Del Monte et al., in preparation
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)
18-60 keV
gamma-ray U.L.
gamma-ray map
Galactic gamma-ray transients
EGRET: Seen one over mission life time. Never identified.
AGILE:
• Cygnus region
• Carina region
• Crux region
AGILE observes variability and detects new
transients on time scales of 1 day at flux levels of 106 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)
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
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
~85% of all γ in galactic diffuse
~15% in sources
CR propagation near sources or in molecular clouds
GLAPROP might give us a
prediction based on largescale consistency of nuclear
reactions, ISRF, gas
distributions, CR and γ-ray
measurements.
May or may not be correct for
→ CS used, avoiding opacity problems
a localized diffuse emission
problem!
for 12CO (Aharonian et al. 2006)
High-lat molecular clouds
often coincidences
yielding ambiguity
between expanding SNR
and molecular cloud
(Gabici & Aharonian ’07)
The TeV Galactic Centre
1 degree
• Two bright point-sources in the central part of the Galaxy
HESS
Diffuse Emission
1 degree
• After subtracting point-sources, diffuse emission is
seen extending along the galactic plane
Diffuse Emission
HESS
CS Line Emission
(dense clouds)
smoothed to match
H.E.S.S. PSF
1 degree
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 associations
Yadigaroglu & 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)
+ hint of confirmation* from Whipple
in massive Cygnus OB2 association
~2600 OBs estimated
final 237 h observations (!), 6.1σ,
extended 0.1° (compared 0.07° psf)
“highscore”: the deepest MWL follow-up for an UNID VHE source so far (55 ksec Chandra, 50 ksec XMM)
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 ??!
2006: H.E.S.S. observed the stellar cluster Westerlund 2
(seen here with SPITZER eyes)
• embedded in a giant
molecular cloud
• ongoing star formation
Westerlund 2
WR 20b
WR 20a
• 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)
1
r=
Ro
d ~ 51..53 Ro
orbital period: 3.686 d
9.3
Rauw et al. 2005
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
# excess events
-> HESS J1023-575 is an extended and constant source
point source
for H.E.S.S.
150
observed source extension
σ = 0.18° ± 0.02°
100
WR20a
WR20b
50
0
VHE γ-ray image
-50
0
0.05
0.1
0.15
0.2
0.25
θ2 (deg 2)
The “blister”
(Whiteoak & Uchida 1997):
indicative for rapid expansion into a ambient low-density
medium (superbubble?)
WR20a
WR20b
γ-ray image
radio: 843 MHz
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 (TenarioTagle 1979, Völk & Forman 1982, Cesarsky & Montmerle 1983) ?
Contribution to Cosmic Rays ? -> Need to see more := common phenomenon or not!
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)
WR20a
WR20b
843 MHz radio image
-> consider a new class of extreme particle
accelerators in our Galaxy
-> consequences for CRs: Will contribute, fraction unclear!
Milagro Pevatron?
GeV Sources Emit TeV Gamma-Rays ?
E. Ona-Wilhelmi, et al.,
ICRC 2007
•
•
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
Abdo, et al. ApJ Lett 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…