Transcript VHE g-ray physics of active galactic nuclei & the

AGN Observations
in the GeV/TeV Energy Range
with the MAGIC Telescope
R. M. WAGNER
Max-Planck-Institut für Physik, München
on behalf of the MAGIC COLLABORATION
R. M. Wagner: AGN observations with MAGIC – p.1
Contents
Blazars & jets – how can TeV observations help?
MAGIC blazar observation activities
Blazars observed by MAGIC, some highlights
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Markarian 421
1ES 1959+650
1ES 1218+304
PG 1553+113
Markarian 501
Markarian 180
1ES 2344+514
BL Lacertae
Conclusions
R. M. Wagner: AGN observations with MAGIC – p.2
16 sources (incl M87) to date and counting
seen in VHE -rays
TeV Blazars | E>100 GeV
Jets observed under small angle
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Rapid variability at all wavelengths
Most violent and rapid often in VHE
High Doppler factors: amplified
emission, deep insight into jet
Mkn 501 HEGRA, Kranich 2001
How can TeV observations help?
-rays are crucial messengers:
• Dynamics of emission regions in the jets
• Study acceleration & energy loss timescales
• Decide: leptonic vs hadronic acceleration?
- Hadronic models challenged by observed
X/VHE correlations and by very rapid
-ray variability
- Variability needs to be explained: Matter
crossing the jet? sub-shocks? ...jet structure
• Decide SSC/EIC
R. M. Wagner: AGN observations with MAGIC – p.3
Hadronic
Kino et al. Inverse
synchrotron
peak
(Buckley 1999)
Compton
peak
The MAGIC Telescope
Major
Atmospheric
Gamma-ray
Imaging
Cherenkov
Telescope
• 17m  Imaging Air Cherenkov
Telescope: currently largest
single-dish instrument
• 3.5°  FOV
Optimized for extragalactic
point-like sources
• Trigger threshold: 50 – 60 GeV
Analysis thresh: 70 – 100GeV
• Energy resolution 30% at
150 GeV
• Sensitivity: 2.5% Crab Nebula
in 50 hours at E=250 GeV
• Enhanced duty cycle
(moon observations)
• 2nd telescope under construction
R. M. Wagner: AGN observations with MAGIC – p.4
MAGIC
| AGN & blazar observation activities
 Extensive blazar observation program:
approx. 500 hours/year
 Simultaneous optical monitoring during
observations
 MWL campaigns with Suzaku and
other satellite experiments (results: see ICRC’07)
 Numerous ToO agreements with optical; X-ray,
-ray satellites;  telescopes, and
 Global Network of Cherenkov Telescopes initiative
 simultaneous observations w/HESS: wider energy coverage
 sequential observations w/VERITAS: ext’d time coverage
 Ongoing blazar monitoring of known bright
sources: low state, flare statistics, blazar duty cycle
Mkn 421 | z=0.030 | Nov 2004 - Apr 2005
• 25.6 h observations, clear diurnal signal
• Energy threshold: 150 GeV
• Source-inherent cutoff 1.40.3 TeV
MAGIC
historical
TeV spectra
R. M. Wagner: AGN observations with MAGIC – p.5
ApJ 663 in press
astro-ph/0603478
Mkn 421 | z=0.030 | Nov 2004 - Apr 2005
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Variable fluxes on day-to-day scale,
0.5–2 Crab, but no flares shorter than 1h
ApJ 663 in press
astro-ph/0603478
Intra-night, 10 min bins:
6 nights, night-by-night
F(E>200GeV)
2-10 keV
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optical
R. M. Wagner: AGN observations with MAGIC – p.6
Clear TeV/X-ray correlation,
slope hardens with intensity: IC favored
Mkn 501 | z=0.034 | June/July 2005
ApJ submitted
astro-ph/0702008
• Clear signal each night: > 85 s
• Energy threshold 150 GeV
• No strong evidence for correlated optical/X/VHE emission
Clear variability in -rays
<F>Mkn501 ~ 0.5 Crab (‘low’)
June 30
July 09
Unprecedented
fast variations!
(<3 min)
Emission region
severely constrained!
June 30
July 09
Obs during moontime!
2 min bins
2 min bins
<F>Mkn 501
R. M. Wagner: AGN observations with MAGIC – p.7
Mkn 501 | Intra-night flares
ApJ submitted
astro-ph/0702008
• Two flares behave rather differently
• June 30 flare: No high (>600 GeV) energies
• July 09: all energies, “pre-flare“?
June 30
July 09
150-250 GeV
250-600 GeV
600-1200 GeV
1200 GeV
and above
R. M. Wagner: AGN observations with MAGIC – p.8
Mkn 501 | Spectral variations
ApJ submitted
astro-ph/0702008
Flux-Spectral index correlation
SED
MAGIC
Spectrum hardens with increasing flux
Constant fit : c2/ndf = 76.6/25 (P=4×10-7)
Peak in VHE distribution clearly observed in high-flux nights
EBL corrected
(Kneiske et al. 2004 “low IR”)
EBL corrected
(Kneiske et al. 2004 “low IR”)
measured
measured
Peak
R. M. Wagner: AGN observations with MAGIC – p.9
Peak
Peak location
seems to depend
on the source
luminosity
1ES 2344+514 | z=0.044 | Aug 2005 – Dec 2005
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Discovery: Whipple, Flare Dec 1995,
F(>350GeV) = 63% Crab Catanese et al. 1997
UL from Whipple (1997, 2000), HEGRA
(1998-2002), TACTIC (2004-2005)
MAGIC: observation Aug-Dec 2005
F(>350GeV)=6% Crab
11 s - Clear detection
Only marginal hints of variability
First time-resolved observation
of the low blazar emission state
R. M. Wagner: AGN observations with MAGIC – p.10
ApJ 663 in press
astro-ph/0612383
Energy spectrum
PG 1553+113 | z>0.09
ApJL 654 (2007) 119
Blazar at unknown distance
• No emission lines: Jet outshines core?
Very close alignment of jet axis to observer?
• High z? Small host galaxy?
• Discovery by H.E.S.S. & MAGIC
• Steepest observed –ray spectrum:
spectral slope a=4.2±0.3
– how much absorption is intrinsic?
• Light curve: No correlation with optical flare. Time lag?
MAGIC VHE
2005
2006
KVA optical
2005
2006
R. M. Wagner: AGN observations with MAGIC – p.11
SSC modeling:
• Models based on different z:
Disfavor z>0.56 on 4.5s level
BL Lacertae |
ApJL submitted
astro-ph/0703084
z=0.069 | Aug – Dec 2005
LBL-type blazar:
Synchrotron peak in the optical:
Expect steep slope at VHE
 profit from low energy threshold!
 First LBL discovered in VHE –rays!
O/VHE correlation?
Sky map
Epeak=250 GeV
216 Excess events
Significance: 5.1s
 Relatively steep –ray spectrum:
spectral slope a=3.6±0.5
 Leptonic model, no EIC components necessary
as required to explain 1997 flare seen by EGRET
Ravasio et al. 2002
R. M. Wagner: AGN observations with MAGIC – p.12
Summary & Conclusions
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There are now 16 blazars observed in -rays above 100 GeV with more
observations & detections in the pipeline
VHE observations are crucial for modeling non-thermal emission regions in
jets, but...
Will need full time-dependent modeling & MWL observations
Increased instrumental sensitivity helps precision observations of
bright blazars Mkn 421, Mkn 501, 1ES 2344.
• Leptonic nature of acceleration?
flux-hardness correlation, IC peak detected
• Fast blazar flaring: First time minute-scale variability in VHE!
• Low blazar emission state was mostly elusive before:
• now removing observational bias
towards flaring sources in the VHE regime
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Many new sources discovered with interesting properties:
• Mkn 180: source detected upon optical trigger
• 1ES 1218: high redshift (now confirmed by VERITAS)
• PG 1553: probably very close alignment to jet axis
• BL Lacertæ: First LBL -ray source
R. M. Wagner: AGN observations with MAGIC – p.13
Backup slides
R. M. Wagner: AGN observations with MAGIC – p.14
Detection of E>100 GeV -rays
, 100 GeV
• Cosmic rays initiate
extensive air showers
Proton, 100 GeV
• Cherenkov light is emitted by
relativistic particles in the shower
• Showers induced by -rays and
hadronic cosmic rays (104 times
more numerous) develop differently
in the atmosphere
• Image parametrization
• Background suppression:
Cuts in image parameters
 showers
hadronic showers
• Narrow images
• Spread images
• Aligned towards
candidate
events
source
direction
• Isotropic arrival
direction

from pointing direction
R. M. Wagner: AGN observations with MAGIC – p.15
Acceleration and VHE  production
Primary acceleration by
diffusive shock acceleration in jets
Power law
Typical Spectral Energy Distribution

• Electrons emit synchrotron radiation
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Electron
Kino et al.
• Inverse Compton scattering on
different possible target photon fields
synchrotron
peak
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Electron

• In particular in blazars:
Synchrotron Self-Compton model:
synchrotron photons target field
for IC process
• Natural explanation of X-ray / -ray
correlated variability
R. M. Wagner: AGN observations with MAGIC – p.16
Inverse Compton
peak
(Buckley 1999)
Hadronic acceleration models:
• Protons: 0 decay from photo-pion production
or synchrotron emission from protons
• Difficult to accomodate X-ray / -ray
correlations
• Should observe simultaneous -emission
Low-level blazar emission
ApJ in press
astro-ph/0612383
• Up to now VHE -ray observations biased towards flaring states:
• What are the properties of blazars at non-flare times?
1ES 2344+514
Discovery: Flare during the
night of 1995/12/21
MAGIC 2005
VHE -ray light curve
• MAGIC: Clear 11 s signal
from 23 observation nights
• Integral flux 5.7
times lower than
during 1995 flare
• Light curve well
compatible with
low emisson state
of the source
• and with previous
<5sobservations
• Profit from MAGIC’s
higher sensitivity
R. M. Wagner: AGN observations with MAGIC – p.17
1995 flare
All-time VHE -ray light curve
MAGIC
significance well below 5s
1995 flare data & 2005 MAGIC low emission data
could be modeled using a one-zone SSC model.
Attenuation of VHE -rays in the universe
PG 1553+113
blazar with unknown distance
• Simultaneous discovery by MAGIC, H.E.S.S.
• MAGIC: 8.8 s signal from 19 h observations
• Steepest observed –ray spectrum:
spectral slope a=4.20.3
Modification of spectrum due to
Extragalactic Background Light (EBL)
VHE + EBL e+e–
VHE is “lost” to observer
MAGIC
H.E.S.S.
PG
1553 redshift
probably
Possibility to
constrain
by assumptions
on EBL and acceleration
mechanism:
distant source!
z < 0.42 (Mazin & Goebel 2007)
Once distance is known: Source probably
decisive for EBL determination!
R. M. Wagner: AGN observations with MAGIC – p.18
Peak in
Vis
IR
(starlight)
(dust)
s e +e – 
GeV energies probe a
specific energy range
of the EBL spectrum
Net effect in the >100 GeV range:
Steepening of (power-law) spectra
Mkn 180 | z=0.045 | 2006 March 23-31
ApJL 648 (2006) 105
New sources discovered by IACT:
Mkn 180
• Successful optical trigger
• 11.1 h, 5.5 s,
F(>200GeV) = 11% Crab,
spectral slope a=3.3 ± 0.7
rather hard spectrum
• Earlier UL at comparable level
• No significant variability
• Need to understand whether
O/VHE correlation
SED
Model: FO98
Model: CG02
R. M. Wagner: AGN observations with MAGIC – p.19
1ES1218+304 | z=0.182
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ApJL 642 (2006) 119
Whipple: F(>350GeV)<8% C.U.
HEGRA: F(>750GeV)<12% C.U.
MAGIC: DISCOVERY!
Jan 2005, 8.2 h
6.4 s, F>120GeV = 13% C.U.,
spectral slope a=–3.0 ± 0.4
2 plot
R. M. Wagner: AGN observations with MAGIC – p.20
sky map
SED
MAGIC blazar observations
• High-peaked BL Lac objects
Cycle-I: 181 hours, 13 source candidates
Cycle-II: 99 hours
• Low-peaked BL Lac objects
Cycle-I: 76 hours
Cycle-II: 86 hours
• Monitoring of TeV-bright blazars
Cycle-II: 38 hours (70% done)
• Time-of-Opportunity observations (externally triggered)
Cycle-II: 11 hours
Upper limit publication of cycle-I HBLs upcoming...
R. M. Wagner: AGN observations with MAGIC – p.21