Very High Energy Gamma Ray Observations with the MAGIC Telescope (a biased selection) Nepomuk Otte for the MAGIC collaboration

Transcription

1 Very High Energy Gamma Ray Observations with the MAGIC Telescope (a biased selection) Nepomuk Otte for the MAGIC collaboration

2 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/ ] PSR B (middle aged pulsar) [astro-ph/ ] PSR B (millisecond pulsar) LS I [Science 2006] Where to go next? 2

3 The non-thermal universe in VHE gamma-rays SNRs Pulsars and PWN Micro quasars X-ray binaries AGNs GRBs Origin of cosmic rays Dark matter Space-time & relativity Cosmology 3

4 VHE gamma-ray sources status ICRC known sources detections from ground Rowell 4

5 Imaging Air Cherenkov Technique Gamma ray Particle shower ~ 10 km Cherenkov light image of particle shower in telescope camera fast light flash (nanoseconds) 100 photons per m² (1 TeV Gamma Ray) Cherenkov light ~ 1 o ~ 120 m reconstruct: arrival direction, energy reject hadron background 5

6 Current generation Cherenkov telescopes Veritas VERITAS (USA & England) 4 (7) telescopes 10 meters Ø Montosa Canyon, Arizona MAGIC (Germany, Spain, Italy) 1 telescope 17 meters Ø H.E.S.S. MAGIC Roque de los Muchachos, Canary Islands Windhoek, HESS Namibia (Germany & France) 4 telescopes 12 meters Ø CANGAROO III Cangaroo III (Australia & Japan) 4 telescopes 10 meters Ø Woomera, Australia 6

7 The MAGIC site 7

8 A recent view of MAGIC MAGIC I MAGIC II counting house picture by R.Wagner 8

9 Current Status of MAGIC First telescope in regular observation mode since fall m 2 mirror area (17m Ø) Fast repositioning (40 sec) for GRB follow-up observations Upgrade: 2GSamples/s FADCs MAGIC-I 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 9

10 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 10

11 Event Parameterization gamma candidate hadron hadron muon ring event parameterization with principal components commonly known as Hillas parameters 11

12 Background Rejection gamma shower Main background: - cosmic ray (hadron) showers ->10 3 times more numerous than γ-ray showers - reject based on shower shape (hadrons are broader) hadron shower (background) 12

13 Gamma / Hadron Separation differences between gammas and background events compressed into one variable: background HADRONNESS determined with the method of Random Forests Breimann 2001 gamma rays analysis for Sizes < 200 phe is difficult 13

14 Extragalactic Sources: Active Galactic Nuclei Jet Black Hole Narrow Line Region Broad Line Region Obscuring Torus Accretion Disk Urry & Padovani (1995) blazar 14

15 Attenuation of VHE γ-rays EBL Cherenkov Telescope BL-Lac object ( ) + γ HE γ EBL e e E γγ 1.8* 2m e c 2 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 15

16 known extragalactic VHE-sources (19) Source Redshift Sp. Types Discovery Observation M FR-I HEGRA HESS Mkn HBL Whipple many Mkn HBL Whipple many 1ES HBL Whipple MAGIC Mkn HBL MAGIC 1ES HBL 7TA many PKS HBL HESS BL Lac LBL MAGIC PKS HBL HESS PKS HBL Durham many 1ES HBL Whipple HEGRA 1ES HBL HESS H HBL HESS 1ES HBL MAGIC VERITAS 1ES HBL HESS 1ES HBL HESS 1ES HBL MAGIC 3C FSRQ MAGIC PG A. Nepomuk 1553 Otte? Max-Planck-Institut 4.0 HBL HESS/MAGIC für Physik / Humboldt Universität Berlin 16

17 Detection of 3C279 Sky map around 3C279 Preliminary GeV Preliminary Preliminary big jump into the deep universe E> 220 GeV Preliminary may deliver stringent constraint on EBL and acceleration models Preliminary 17

18 Pulsars and & pulsar nebulae Exploring Extreme electrodynamics & GR Relativistic winds Acceleration in shocks

19 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 (~10 38 erg/s) particle acceleration in: 1. light cylinder 2. shock front from Aharonian et al 19

20 The Crab Nebula resolved in X-Rays rich and dynamic structure in X-rays: wisps knots jets 7 still images of Chandra observations taken between November 2000 and April NASA/CXC/ASU/J.Hester et al. 20

21 The Crab-PWN: Broadband Emission little known at energies around the peak of the IC-emission synchrotron emission Pulsar morphology? variability? spectrum? pulsar? Nebula Synchrotron IC-emission IC studied with MAGIC at energies >60 GeV Aharonian & Atoyan (1998) 21

22 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±47 stat GeV 22

23 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 23

24 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 24

25 The Crab Pulsar Wind Nebula Complex turning to the central object the pulsar from Aharonian et al 25

26 Gamma-Ray Emission from Pulsars spin axis magnetic dipole moment three sites favored for particle acceleration emission appears pulsed; lighthouse model complex electrodynamics; challenging for theory Harding no pulsar detected above ~100 GeV spectral cutoff; challenging for experiment 26

27 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) 27

28 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 5. reiterate with different cutoff energy until match MAGIC response after cuts (Size <300phe) exponential cutoff <30 GeV super-exponential cutoff <60 GeV 28

29 Crab Pulsar II no detection/hints of pulsed emission in differential bins of energy upper limits compatible with results from other experiments 29

30 PSR B / CTB 80 A different pulsar than Crab 100 times older (~10 5 years) 10 times lower surface magnetic field (~5x10 11 G) moves 2 times faster through ISM (240km/s) 100 times lower spin down luminosity (~10 36 erg/s) optical pulsar detected by EGRET up to 20 GeV at 10 GeV similar luminosity as the Crab pulsar radio radio and synchrotron nebula CTB80 + VHE gamma-ray predictions a good candidate to observe with MAGIC 30

31 In the surroundings of PSR B No displaced gamma ray emission level of few % Crab (point source 0.1 RMS radius) reduced sensitivity for more extended emission region 31

32 PSR B / CTB 80 can exclude flux level predicted by Bednarek & Bartosik (2003) magnetic field larger than assumed pulsar wind not particle dominated? model calculations do not take pulsar motion into account emission smeared out over a larger volume? 32

33 PSR B 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 33

34 Evolution of Pulsars in Binary systems spin up of old pulsars by accretion of mass from companion star millisecond period pulsars Lower magnetic field: reduced screening of Gamma-rays lower acceleration voltage Lorimer,

35 PSR B : The black widow second fastest known pulsar (1.607 ms) recycled pulsar binary system (eccentricity <10-5 ) companion star (0.02 M O ) 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 35

36 PSR B : 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 36

37 PSR B : Search in orbital phase light curve flux limits no evidence for gamma ray emission 37

38 LSI LSI : 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

39 LSI : MAGIC observations Albert et al., SCIENCE h observation from November 2005 till March 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

40 LSI : models Microquasar: rel. electrons (& hadrons) from accretion powered jets or Binary Pulsar: rel. electrons from rotational energy of pulsar Mirabel

41 Summary and Conclusion MAGIC in full production ~1 new source every two month many exciting results like 3C279 or LSI 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 41

42 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 (~10 4 m²) high sensitivity to transients short time flaring in AGNs test stability of pulsed emission at the highest energies. Opening the 10 GeV GeV window from ground will be necessary lower threshold Cherenkov telescopes are needed 42

43 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 First tests on MAGIC are very encouraging 43

44 Trigger tests on La Palma 44

45 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 to MAGIC-I Use improved technology where available: High QE photosensors Fast sampling readout MAGIC-I 85m 45

46 MAGIC II Monte Carlo Studies Stereo Analysis: observe shower simultaneously with 2 telescopes 3D shower reconstruction Additional shower parameters: Impact parameter Shower maximum (h max ) Eliminate ambiguity on arrival direction Better reconstruction of energy and arrival direction Improved background rejection 46

47 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 47

48 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) 48

49 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 ~ compact and robust disadvantages small sizes (<5x5mm²) optical crosstalk (10%) P. Buzhan et al. Otte et al., IEEE TNS. 53 (2006) 636. SNIC , Apr

50 Test on La Palma with MAGIC MAGIC Pixel Size 4 MPPC C 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*10 5 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 50

51 Array mounted onto the MAGIC camera entrance window for two nights 51

52 position of MPPC array 1 phe 2 phe 4 phe 1 phe MPPCs 70 phe 35 phe 35 phe 15 phe PMTs 52

53 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 counts signals are correlated on average MPPCs detect 1.6 times more light 53

54 End 54

55 Light recorded from Calibration Runs Pedestal UV-LEDs 375nm 1 phe single phe-resolution degraded due to light from night sky background 2 phe 3phe easy calibration some recorded showers 55

56 Key technological elements for MAGIC 17 m diameter parabolic reflecting surface (236 m 2 ) high reflective diamond milled aluminum mirrors Active mirror control (PSF: 90% of light in 0.1 o inner pixel) Light weight Carbon fiber structure for fast repositioning -3.5 o FOV camera high QE PMTs (QE max = 30%) Analog signal transport via optical fibers IPE IPE NET IPE CE 2-level trigger system & FADC system 56

57 Data Set October December hours ON source / 19 hours OFF source zenith angle <23 skymap for energies >500 GeV alpha plot for energies >200 GeV 57

58 The Crab Pulsar Wind Nebula standing reverse shock acceleration of electrons up to 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 58

59 3C 279 EGRET brightest AGN Gamma-ray flares in 1991 and 1996 Apparent luminosity ~ erg/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, L d ~ 3Gpc 59

60 3C 279 Flare in

61 SSC+EC / Hadronic MAGIC 61

62 EBL Absorption Pair Creation; γ HE +γ EBL e + + e - 62

63 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% 85m MAGIC-II is under construction and will be completed in the fall of the next year Improve sensitivity by a factor of three Effectively lower the threshold energy 63

64 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 relatively high threshold of 80GeV Analysis 4 independent analyses have been done Standard analysis and standard quality cut Preliminary results will be presented here 64

65 Sky-map and alpha plot on 23 rd Feb GeV Preliminary Sky map around 3C279 Preliminary Preliminary E> 220 GeV Preliminary Preliminary 65

66 3C279 VHE gamma-ray light curve Preliminary Intra-night LC Preliminary Optical light curve 66

67 Extragalactic VHE-sources (19) Source Redshift Sp. Types Discovery Observatio n M FR-I HEGRA HESS Mkn HBL Whipple many Mkn HBL Whipple many 1ES HBL Whipple MAGIC Mkn HBL MAGIC 1ES HBL 7TA many PKS HBL HESS 322 BL Lac LBL MAGIC PKS HBL HESS 489 PKS HBL Durham many 304 1ES HBL Whipple HEGRA ES HBL HESS H HBL HESS 1ES HBL MAGIC VERITAS ES HBL HESS 232 1ES HBL HESS 121 1ES HBL MAGIC C FSRQ MAGIC PG A Nepomuk Otte? Max-Planck-Institut 4.0 HBL HESS/MAGIC für Physik / Humboldt Universität Berlin Big progress in AGN study from z ~ 0.2 to z = New HBL 1ES See the presentation by D. Mazin 67

68 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 sigma below 220GeV, and 5 sigma above 220GeV The survey distance is extended up to z = 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 systematic uncertainties in the energy determination 68

69 Crab nebula emission region in VHE gamma-rays emission region determined by: confinement of electrons by magnetic fields synchrotron cooling times lower energies more extended emission region (few tens of arcseconds) Atoyan & Aharonian possible hadronic component (pi0 decay) could result in a more extended emission region 69

70 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 df = 6 10 de E 300GeV ( E / 300GeV ) log cm s TeV 70

71 Crab pulsar in optical verifies analysis chain main pulse offset by -252±64 µs to position of main pulse in radio 71

72 Search for pulsed Gamma-ray emission Q = Excess Background Assuming exponential cutoff of the pulsar at 30 GeV highest sensitivity for pulsed emission if events with Size <300 (<180 GeV) are selected for analysis Q vs. upper Size cut 72

73 Pulsar: Broadband Emission radiation processes MAGIC synchrotron radiation curvature radiation inverse Compton scattering no pulsar detected above ~100 GeV Thompson et al spectral cutoff; challenging for experiment spectroscopy of the cutoff would help to distinguish between theories 73

74 The GeV excess EGRET observed Gammaray flux >1GeV can not be described by SSC GeV excess possible explanations: DC gamma-ray component from the pulsar SSC-model enhanced Bremsstrahlung emission 74

75 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 75

76 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 76