Very High Energy Gamma Ray Observations with the MAGIC Telescope (a biased selection)
Nepomuk Otte for the MAGIC collaboration • Imaging air shower Cherenkov technique – The MAGIC telescope
• Observation of the AGN 3c279
• Observation of Neutron Stars with MAGIC
• The Crab nebula and Pulsar (young pulsar) [astro-ph/0705.3244] • PSR B1951+32 (middle aged pulsar) [astro-ph/0702077] • PSR B1957+20 (millisecond pulsar) • LS I 61+303 [Science 2006]
• Where to go next?
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 2 The non-thermal universe in VHE gamma-rays
SNRs Pulsars Micro quasars AGNs and PWN X-ray binaries GRBs
Origin of Space-time cosmic rays Dark matter & relativity Cosmology
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 3 VHE gamma-ray sources status ICRC 2007
71 known sources
detections from ground
Rowell
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 4 Imaging Air Cherenkov Technique
Cherenkov light image of particle shower Gamma in telescope camera ray Particle ~ 10 km • fast light flash (nanoseconds) shower • 100 photons per m² (1 TeV Gamma Ray)
t h g o li ~ 1
v o k n e r e h C
reconstruct: ~ 120 m arrival direction, energy reject hadron background
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 5 CurrentCurrent generationgeneration CherenkovCherenkov telescopestelescopes
MAGIC Veritas MAGIC (Germany, Spain, Italy) VERITAS 1 telescope 17 meters Ø (USA & England) 4 (7) telescopes Montosa 10 meters Ø Canyon, Roque de Arizona los Muchachos, Canary Islands CANGAROO III Cangaroo(Australia III & Japan) 4 telescopes 10 meters Ø H.E.S.S. Windhoek, HESS Namibia (Germany & France) Woomera, 4 telescopes Australia 12 meters Ø
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 6 The MAGIC site
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 7 A recent view of MAGIC
MAGIC II
MAGIC I
counting house
picture by R.Wagner
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 8 Current Status of MAGIC
First telescope in regular observation mode since fall 2004 MAGIC-I – 236 m2 mirror area (17m Ø) – Fast repositioning (40 sec) for GRB follow-up observations – Upgrade: 2GSamples/s FADCs
– Trigger threshold: ~ 50 GeV – Sensitivity: 2 % Crab (5σ,50h) for E>200GeV – Using timing parameters after installation of new 2GSamples/s FADC: => Sensitivity improved to 1.5% Crab
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 9 Central Pixel for Optical Measurements
• Modified central pixel for optical measurements • simultaneous with Gamma-ray observations view from back
Crab pulsar in optical by MAGIC
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 10 Event Parameterization
gamma candidate hadron hadron muon ring
event parameterization with principal components
commonly known as Hillas parameters
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 11 Background Rejection
gamma shower
Main background: - cosmic ray (hadron) showers
->103 times more numerous than γ-ray showers
- reject based on shower shape (hadrons are broader)
hadron shower (background)
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 12 Gamma / Hadron Separation
differences between gammas and background events background compressed into one variable:
HADRONNESS
determined with the method gamma rays of Random Forests Breimann 2001
analysis for Sizes < 200 phe is difficult
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 13 Extragalactic Sources: Active Galactic Nuclei
Narrow Jet Line Region
Broad Black Line Region Hole
Obscuring Accretion Torus Disk
Urry & Padovani (1995) blazar
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 14 Attenuation of VHE γ-rays Cherenkov EBL Telescope
BL-Lac object
−+ 2 γγEBLHE → ee Eγγ ≈1.8*( 2mec )
2.7K
• Absorption leads to cutoff in AGN spectrum • Measurement of spectral features allows to constrain EBL Models Red shifted stellar light Red shifted dust light
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 15 known extragalactic VHE-sources (19)
Source Redshift Sp. Types Discovery Observation M 87 0.004 2.9 FR-I HEGRA HESS Mkn 421 0.031 2.2 HBL Whipple many Mkn 501 0.034 2.4 HBL Whipple many 1ES 2344+514 0.044 2.9 HBL Whipple MAGIC Mkn 180 0.045 3.3 HBL MAGIC 1ES 1959+650 0.047 2.4 HBL 7TA many PKS 0548-322 0.069 HBL HESS BL Lac 0.069 3.6 LBL MAGIC PKS 2005-489 0.071 4.0 HBL HESS PKS 2155-304 0.116 3.3 HBL Durham many 1ES 1426+428 0.129 3.3 HBL Whipple HEGRA 1ES 0229+200 0.139 HBL HESS H 2356-309 0.165 3.1 HBL HESS 1ES 1218+304 0.182 3.0 HBL MAGIC VERITAS 1ES 1101-232 0.186 2.9 HBL HESS 1ES 0347-121 0.188 HBL HESS 1ES 1011+496 0.212 4.0 HBL MAGIC 3C 279 0.538 FSRQ MAGIC
PG 1553 ? 4.0 HBL HESS/MAGIC A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 16 Detection of 3C279
Sky map around 3C279 80-220 GeV Preliminary Preliminary
Preliminary
E> 220 GeV Preliminary big jump into the deep universe
may deliver stringent constraint on EBL and acceleration models Preliminary
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 17 Pulsars and & pulsar nebulae
Exploring Extreme electrodynamics & GR Relativistic winds Acceleration in shocks The Pulsar Wind Nebula Complex on the example of the Crab massive object in center: magnetized, spinning neutron star (pulsar)
energy carried away by electromagnetic radiation and particles (~1038 erg/s)
particle acceleration in: 1. light cylinder 2. shock front
from Aharonian et al
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 19 The Crab Nebula resolved in X-Rays
rich and dynamic structure in X-rays:
•wisps •knots •jets
7 still images of Chandra observations taken NASA/CXC/ASU/J.Hester et al. between November 2000 and April 2001.
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 20 The Crab-PWN: Broadband Emission
synchrotron emission Pulsar • little known at energies around the peak of the IC-emission
morphology? variability? Nebula spectrum? Synchrotron IC
pulsar? IC-emission
Aharonian & Atoyan (1998) studied with MAGIC at energies >60 GeV
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 21 Crab Nebula: Spectral Energy Distribution
• good agreement with other Cherenkov telescopes above 400GeV
• spectrum well described within SSC-framework
• first time determination of
the IC-peak at 77±47statGeV
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 22 Crab Nebula: Morphology
• emission region compatible with point-like source - emission region <2’ (1σ radius)
• center of gravity coincides with the position of the Crab pulsar (black dot) - systematic uncertainty in position ~1’
X-ray, optical composite picture
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 23 Crab Nebula: Variability
no variability (>200 GeV) on time scales of: • minutes (<20% Crab-flux) • days (<10% Crab-flux) • months (<5% Crab-flux)
10 min binning
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 24 The Crab Pulsar Wind Nebula Complex
turning to the central object
the pulsar
from Aharonian et al
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 25 Gamma-Ray Emission from Pulsars
magnetic dipole moment spin axis • three sites favored for particle acceleration
• emission appears pulsed; lighthouse model
• complex electrodynamics; challenging for theory
• no pulsar detected above ~100 GeV
Æspectral cutoff; Harding challenging for experiment
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 26 Crab Pulsar in Gamma-Rays
events with Size <300 photoelectrons significance of pulsed emission: no prior assumption about pulse profile: 1.2σ guided by EGRET >100 MeV profile: 2.9σ
Fierro, 1998 shaded: regions of pulsed emission defined by EGRET measurements above 100 MeV (P1, P2)
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 27 Upper limit on cutoff energy
1. assume EGRET spectrum with exponential cutoff
2. convolute spectrum with MAGIC response
3. calculate number of expected pulsed excess events
4. compare with upper limit on pulsed excess events MAGIC response after cuts (Size <300phe)
5. reiterate with different cutoff energy until match exponential cutoff <30 GeV super-exponential cutoff <60 GeV
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 28 Crab Pulsar II
• no detection/hints of pulsed emission in differential bins of energy
• upper limits compatible with results from other experiments
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 29 PSR B1951+32 / CTB 80
A different pulsar than Crab
• 100 times older (~105 years) optical • 10 times lower surface magnetic field (~5x1011 G) • moves 2 times faster through ISM (240km/s) • 100 times lower spin down luminosity (~1036 erg/s)
pulsar detected by EGRET up to 20 GeV
at 10 GeV similar luminosity as the Crab radio pulsar
radio and synchrotron nebula CTB80 + VHE gamma-ray predictions Æ a good candidate to observe with MAGIC
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 30 In the surroundings of PSR B1951+32
No displaced gamma ray emission level of few % Crab (point source 0.1° RMS radius)
reduced sensitivity for more extended emission region
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 31 PSR B1951+32 / CTB 80
• can exclude flux level predicted by Bednarek & Bartosik (2003)
• magnetic field larger than assumed Æ pulsar wind not particle dominated?
• model calculations do not take pulsar motion into account Æ emission smeared out over a larger volume?
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 32 PSR B1951+32 Pulsar
special thanks to Andrew Lyne et al. for providing the radio ephemerides
• no pulsed emission detected
• constrain on the cutoff energy <30 GeV
• constrain predicted IC emission at TeV energies
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 33 Evolution of Pulsars in Binary systems
spin up of old pulsars by accretion of mass from companion star Æ millisecond period pulsars
Lower magnetic field: Æ reduced screening of Gamma-rays Æ lower acceleration voltage
Lorimer, 2005
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 34 PSR B1957+20: The black widow
• second fastest known pulsar (1.607 ms)
• recycled pulsar
• binary system (eccentricity <10-5)
• companion star (0.02 MO) in 9.17 h orbit around pulsar
• continuous mass flow from companion to pulsar
• observation “edge on”
VHE-γ rays expected from pulsar and interaction of pulsar wind with star wind
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 35 PSR B1957+20: search for steady gamma-ray emission
can not exclude predicted gamma-ray flux from pulsar [Bulik (2000)] more sensitive pulsed analysis not possible because of invalid ephemeris of the binary system
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 36 PSR B1957+20: Search in orbital phase
light curve flux limits
no evidence for gamma ray emission
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 37 LSI+61 303
LSI+61 303: • high mass x-ray binary • Be star companion with circumstellar disc • high eccentricity (~0.7) • radio and x-ray emission modulation: 26.5 days (orbit) •radio jets(100AU)
Massi et al 2004
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 38 LSI+61 303: MAGIC observations
Albert et al., SCIENCE 2006
• 54 h observation from November 2005 till March 2006 • 9 σ detection of point-like source (E > 200 Gev) • Spectral index = -2.6 ± 0.2 (stat) ± 0.2 (syst) • Flux clearly variable • Average emission has maximum (~16% Crab) at phase 0.6.
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 39 LSI+61 303: models
•Microquasar:rel. electrons (& hadrons) from accretion powered jets or • Binary Pulsar: rel. electrons from rotational energy of pulsar
Mirabel 2006
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 40 Summary and Conclusion
• MAGIC in full production
• ~1 new source every two month
• many exciting results like 3C279 or LSI 60+303
• detailed studies possible: Crab nebula in the energy range between 60GeV and 400GeV – within experimental resolution: • emission region is point like; <2’ radius of emission region • constant gamma ray flux; less than ~10% variability • could determine IC-peak at 77±47 GeV • spectrum well described by SSC models / no hint for hadronic component – hint of emission from pulsar or just a fluctuation? – Needs clarification / work in progress
• detection of pulsars remains an open task in VHE Gamma-Rays Æ
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 41 Outlook into the Future
• The gamma-ray window between 10 GeV and 100 GeV is still closed
• GLAST will be a pathfinder mission but can not answer all questions – the strength of Cherenkov telescopes is a large collection area (~104 m²) Æhigh sensitivity to transients • short time flaring in AGNs • test stability of pulsed emission at the highest energies •….
• Opening the 10 GeV - 100 GeV window from ground will be necessary Æ lower threshold Cherenkov telescopes are needed
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 42 Very near future: This Crab season
• trigger threshold of MAGIC is limited by accidental triggers caused by PMT afterpulses
• current trigger requires a 4 next neighbor coincidence
• investigate new trigger idea: – analog signals are clipped above ~6phe – analog sum of ~10 pixels – discriminate sum signal at ~20 phe
Æ First tests on MAGIC are very encouraging
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 43 Trigger tests on La Palma
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 44 midterm future (2008): MAGIC II
Aim: • Increase sensitivity (particularly below 100 GeV) • Lower energy threshold further second telescope: MAGIC-II MAGIC-II
”Improved clone” – Most fundamental parameters identical MAGIC-I to MAGIC-I – Use improved technology where available: • High QE photosensors • Fast sampling readout 85m
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 45 MAGIC II Monte Carlo Studies
Stereo Analysis: • observe shower simultaneously with 2 telescopes • 3D shower reconstruction • Additional shower parameters: – Impact parameter
– Shower maximum (hmax) – Eliminate ambiguity on arrival direction
• Better reconstruction of energy and arrival direction • Improved background rejection
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 46 Improved Reconstruction
• Energy resolution –MAGIC-I: ~25% – MAGIC-II: 14-20% (2 telescopes)
• Angular resolution – Substantial (~50%) improvement since source position is obtained from intersection point of both showers
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 47 Improved Sensitivity
using Stereo Analysis • better background rejection down to low energies • increase sensitivity by up to factor 3 => reduce observation time by factor 9 • Large gain in sensitivity at low energies (< 100 GeV)
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 48 New photon detectors: The G-APD
a promising photon detector concept invented in Russia in the 80’s
advantages
• sensors with ~60% efficiency become available • internal gain ~105 -106 • compact and robust •…
disadvantages
• small sizes (<5x5mm²) • optical crosstalk (10%) •… P. Buzhan et al. http://www.slac-stanford.edu/pubs/icfa/fall01.html
Otte et al., IEEE TNS. 53 (2006) 636. SNIC-2006-0018, Apr 2006
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 49 Test on La Palma with MAGIC
MAGIC Pixel Size 4 MPPC-33-050C from Hamamatsu:
sensor size: 3x3mm² single cell size: 50x50µm² nominal bias: 70.4V dark rate at nominal bias: ~2MHz gain at nominal bias: 7.5*105 crosstalk at nominal bias: 10%
Array of 4 MPPCs: light catchers with factor 4 concentration; 6x6mm² onto 3x3mm²
peak photon detection efficiency 55% needs to be confirmed
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 50 Array mounted onto the MAGIC camera entrance window for two nights
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 51 position of MPPC array
1 phe 2 phe 4 phe 1 phe MPPCs
70 phe 35 phe 35 phe 15 phe PMTs
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 52 Shower Signals: MPPC vs PMT
event selection: two PMTs next to MPPCs with more than 15 photoelectrons in each tube
~300 events from ~30 min data
signals are correlated counts on average MPPCs detect 1.6 times more light
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 53 End
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 54 Light recorded from Calibration Runs
Pedestal
UV-LEDs 375nm 1 phe
single phe-resolution degraded due to light 2 phe from night sky background 3phe
…
easy calibration
some recorded showers Æ
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 55 Key technological elements for MAGIC
17 m diameter parabolic reflecting surface (236 m2 ) high reflective diamond milled aluminum mirrors Light weight Active mirror control Carbon fiber (PSF: 90% of light in structure for fast 0.1o inner pixel) repositioning
-3.5o FOV camera - 576 high QE PMTs (QEmax= 30%)
Analog signal transport via optical fibers IPE 2-level trigger system IPE & FADC system NETIPECE A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 56 Data Set
• October – December 2005
• 16 hours ON source / 19 hours OFF source
• zenith angle <23°
skymap for energies >500 GeV
alpha plot for energies >200 GeV
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 57 The Crab Pulsar Wind Nebula
• standing reverse shock
• acceleration of electrons up to 1016 eV
• synchrotron emission (radio to gamma -rays) downstream of shock
• inverse Compton scattering (VHE gamma-rays)
other possible VHE gamma-ray components are pi0-decay or bremsstrahlung
influence on VHE gamma-ray spectrum, morphology and variability
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 58 3C 279
• EGRET brightest AGN – Gamma-ray flares in 1991 and 1996 – Apparent luminosity ~ 1048erg/s – First time variation △T ~ 6hr in 1996 flare • Typical OVV quasar (Optically violent variable) – Categorized as a FSRQ (Flat Spectrum Radio Quasar) • Superluminal motion, γ~ 20~30
• z = 0.538, Ld ~ 3Gpc
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 59 3C 279 Flare in 1996
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 60 SSC+EC / Hadronic
MAGIC
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 61 EBL Absorption
+ - Pair Creation; γHE＋γEBL Æ e + e
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 62 MAGIC Telescope
New technologies to lower the threshold energy
17m diameter world largest cherenkov tel. 0.1°High resolution camera Hemispherical PMT with enhanced QE Analogue signal fiber transmission
Current MAGIC-I Performance
Fast rotation for GRB < 40secs Trigger threshold ~50GeV Sensitivity ~2% of Crab (50hrs) Angular resolution ~0.1 degrees Energy Resolution 20-30%
MAGIC-II is under construction and will be 85m completed in the fall of the next year
Improve sensitivity by a factor of three Effectively lower the threshold energy A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 63 Observation of 3C 279 with MAGIC
•Observation – In the period of January - April 2006 – Observation of 9.5hrs – Zenith angle range is between 32 and 40 degrees Î relatively high threshold of 80GeV
•Analysis – 4 independent analyses have been done – Standard analysis and standard quality cut
A. Nepomuk– Preliminary Otte Max-Planck-Institut results für Physikwill /be Humboldt presented Universität Berlin here 64 Sky-map and alpha plot on 23rd Feb 2007
80-220 GeV Preliminary
Sky map around 3C279
Preliminary Preliminary
E> 220 GeV Preliminary
Preliminary
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 65 3C279 VHE gamma-ray light curve
Intra-night LC Preliminary
Preliminary
Optical light curve
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 66 Extragalactic VHE-sources (19)
Observatio Source Redshift Sp. Types Discovery n M 87 0.004 2.9 FR-I HEGRA HESS Mkn 421 0.031 2.2 HBL Whipple many Mkn 501 0.034 2.4 HBL Whipple many Big progress in AGN study 1ES 0.044 2.9 HBL Whipple MAGIC 2344+514 from z ~ 0.2 to z = 0.538 Mkn 180 0.045 3.3 HBL MAGIC 1ES 0.047 2.4 HBL 7TA many 1959+650 PKS 0548- 0.069 HBL HESS 322 BL Lac 0.069 3.6 LBL MAGIC PKS 2005- 0.071 4.0 HBL HESS 489 PKS 2155- 0.116 3.3 HBL Durham many New HBL 1ES1011+496 304 1ES 0.129 3.3 HBL Whipple HEGRA See the presentation 1426+428 1ES 0.139 HBL HESS 0229+200 by D. Mazin H 2356-309 0.165 3.1 HBL HESS 1ES 0.182 3.0 HBL MAGIC VERITAS 1218+304 1ES 1101- 0.186 2.9 HBL HESS 232 1ES 0347- 0.188 HBL HESS 121 1ES 0.212 4.0 HBL MAGIC 1011+496 3C 279 0.538 FSRQ MAGIC
PGA. 1553 Nepomuk Otte ? Max-Planck-Institut4.0 HBL HESS/ fürMAGIC Physik / Humboldt Universität Berlin 67 Summary
• VHE gamma-ray emission from 3C 279 was discovered by MAGIC – New class of source FSRQ, OVV-quasar
• The VHE flare at 100GeV was observed on 23 February in 2006 – 6 sigma below 220GeV, and 5 sigma above 220GeV
• The survey distance is extended up to z = 0.538 by MAGIC telescope – Big jump toward the deep Universe!
• Study of Energy spectrum – may deliver a stringent constraint on EBL and acceleration model – Analysis is ongoing; We need very careful understanding of A. Nepomuksystematic Otte Max-Planck-Institut uncertainties fürin Physikthe energy / Humboldt determination Universität Berlin 68 Crab nebula emission region in VHE gamma-rays
• emission region determined by: • confinement of electrons by magnetic fields • synchrotron cooling times
lower energies Æ more extended emission region (few tens of arcseconds) Atoyan & Aharonian
possible hadronic component (pi0 decay) could result in a more extended emission region
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 69 Crab Nebula: Differential Energy Spectrum
• gamma-ray emission measured over two decades of energy 60 GeV – 9 TeV
• simple power-law behavior disfavored; χ²: 24/8
• spectrum is well described by a curved power law fit; χ²: 8/7
−− ( 300/log26.031.2 GeVE) dF ⎛ E ⎞ 1 ⋅= 106 −10 ⎜ ⎟ dE ⎝ 300GeV ⎠ 2 ⋅⋅ TeVscm
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 70 Crab pulsar in optical
verifies analysis chain
main pulse offset by -252±64 µs to position of main pulse in radio
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 71 Search for pulsed Gamma-ray emission
Excess Q = Background
Assuming exponential cutoff of the pulsar at 30 GeV
highest sensitivity for pulsed emission if events Q vs. upper Size cut with Size <300 (<180 GeV) are selected for analysis
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 72 Pulsar: Broadband Emission
MAGIC radiation processes
• synchrotron radiation •curvature radiation • inverse Compton scattering
Thompson et al. 1999 • no pulsar detected above ~100 GeV
Æspectral cutoff; challenging for experiment spectroscopy of the cutoff would help to distinguish between theories
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 73 The GeV excess
EGRET observed Gamma- GeV excess ray flux >1GeV can not be described by SSC
possible explanations:
•DC gamma-ray SSC-model component from the pulsar
• enhanced Bremsstrahlung emission
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 74 The GeV excess explained by Bremsstrahlung
amplified Bremsstrahlung in denser regions of the nebula (knots)
can explain the GeV excess Atoyan & Aharonian 1996
could result in modified spectrum between 100 GeV and several TeV
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 75 Crab Nebula: Spectral Index
• observation of energy dependent spectral index
• no deviation from SSC predictions (blue line)
• disfavor A&A 1996
• model A&A 1998 in agreement with measurement
A. Nepomuk Otte Max-Planck-Institut für Physik / Humboldt Universität Berlin 76