Problematiche astrofisica VHE

Transcription

1 Istituto Nazionale di Fisica Nucleare Problematiche astrofisica VHE Antonio Stamerra Università di Siena & INFN Pisa JC - 10 febbraio 2010 Pisa antonio.stamerra@pi.infn.it

2 IACT detector IACT Imaging Atmospheric Cherenkov Telescope Atmosphere is opaque to γrays IACT detector = Atmosphere + telescope Satellite: direct detection of γray Ground-based: indirect detection 2

3 Electromagnetic atmospheric shower pair-production Bremsstrahlung R~9/7 X0~45g/cm2 (in air, 20oC) 3

4 17 m diameter reflecting surface (240 m2 ) MAGIC high reflective diamond milled aluminum mirrors Active mirror control Light weight Carbon fiber structure for fast repositioning Analog signal transport via optical fibers 2-level trigger system & 300 MHz FADC 4 system

5 MAGIC-II Florian Goebel Telescopes Stereoscopic mode: Improved sensitivity Better angular and energy resolution New technologies: Camera: Photo-detectors with higher QE (HPDs in near future) Faster Digitalization: 4 GHz Analogue to Digital Converts (Domino) 5

6 Imaging Air Cherenkov Telescopes Shower top N1,θ A telescope placed inside the Cherenkov light pool can obtain an image of the development of the shower above the night sky background (NSB) fluctuations C1 γ -ray direction Q uicktim eï¾ ª e un decom pressore sono necessari per visualizzare quest'im m agine. Shower tail Shower top n2>n1 θ C2> θ C1 Shower tail Distances in camera = Angular Distances on sky Direction reconstruction Particle-id Energy reconstruction 6

7 Background Cosmic-ray background γ-rays have a definite direction (source position on sky) CR are isotropically distributed ON-OFF selection? CR flux overwhelms γ-ray flux Night-Sky background (NSB, LONS) Field stars 7

8 Gamma/hadron separation gamma 300 GeV gamma proton 1 TeV proton 8

9 Modelli emissione adronica 9

10 Cosmic rays All-particle spectrum Power law spectrum (~E2.7 ) Particles decrease with energy Two breaks in the power law Knee ~3 PeV (3x1015 ev) Ankle ~1 EeV (1018 ev) Underlying physical processes? Acceleration mechanism? Acceleration sites? 10

11 Cascade shower By M. Hayashida 100GeV gamma ray 300GeV Proton 11

12 EAS simulation - uncertainties Reliability of simulation of hadronic interactions (extrapolation of accelerator data and/or theoretical assumptions) - partially solved by IACTs using real hadrons Forward physics unexplored (LHC? E.g. TOTEM) Physical Intrinsic shower fluctuations Enviromental Weather condition (Calima, high clouds, ) Night sky light (Bright stars, Moon, city, ) Instrumental Calibration (absolute QE, mirror aging, ) Background estimation (inhomogeneity, ) Telescopes condition (dead pixels, misspointing, ) Analysis Generally, IACTs claim Simulation (atmospheric model, trigger, )20% systematics! Analyzer choices (optimizations, binning, ) 12

13 Sensitivity Depends on the Effective area and CR Background rejection (and background uncertainty) Sensitivity in 50h 5σ & 10 evts For 5σ: Sensitivity 1/sqrt(time) For 10 evt: Sensitivity 1/time 13

14 MAGIC-II Overall sensitivity will be improved by a factor of 2-3 Energy resolution ~25% 15-20% Angular resolution Substantial improvement 14

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16 Sites of particle acceleration Hillas plot Compact sites and high B Diffuse objects and low B The acceleration site environment plays a key role A deeper (astrophysical) knowledge of candidate sites is mandatory 16

17 Exploring extreme accelerators with gamma-rays VHE γ-astronomy address diversity of topics related to the nonthermal Universe: acceleration, propagation and radiation of ultrarelativistic protons/nuclei and electrons generally under extreme physical conditions in environments characterized with huge gravitational, magnetic and electric fields, highly excited media, shock waves and very often associated with relativistic bulk motions linked, in particular, to jets in black holes (AGN, Microquasars, GRBs) and cold ultrarelativistic pulsar winds 17

18 Goal 0: Detection! Gammas are not for free Signal reconstruction Background rejection Sensitivity Minimum flux detectable Shortest time variation Rate Observation time S s » Rate g T B In the following we assume we are lucky and we always get gammas. We focus on goals 1, 2, 3. We ll tackle goal 0 later on (slide 35 ff). 18

19 Standard candle: Crab Nebula Crab broad-band spectrum 19

20 UV Flux MW X-Ray γ -ray Optical Radio sincrotrone e 100Mev-10GeV VHE - e >100GeV - B γ e- IC γ γ Energy 20

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22 Goals summary Spectrum #ph in E Lightcurve #ph in t Skymap #ph in Ω Energy reconstruction E energy resolution Time resolution Pulsar ms AGN min. Angular resolution PSF F.o.V. 22

23 Gamma/Neutrino astronomy Fermi acceleration processes create secondary particles, among them neutral particles γ and ν bring direct information on the acceleration site But. Their emission, and propagation depends on the environment and source details A deep (astrophysical) knowledge of the source is B Charged particles p He Ions Accelerated π particles n µ e γ ν 23

24 γ-ray production e- Leptonic processes Synchrotron radiation Bremstrahlung ISM e- γ Inverse Compton Hadronic processes Annihiliation p/nuclei interaction with ISM (proton induced cascade) eγ eγ γ e- e+ γ P (RC) π + π0 Proton-synchrotron γ B γ γ 24

25 Hadronic or leptonic? Emissione γ ray emission from π0 decay and interaction with molecular clouds Signature: π0 decay spectrum 25

26 Hadronic or leptonic? modelli leptonici (IC) modelli adronici Yet no smoking gun evidence of γ -rays stemmed from hadronic acceleration and π0 decay! But many hints. 26

27 WHAT DO WE LEARN FROM GAMMA RAYS? courtesy P. Blasi 27

28 WHY IS IT INTERESTING: II. Large B observed? PICAL THICKNESS OF FILAMENTS: 10-2 pc e synchrotron limited thickness is: Dx 4D E t syn E » 4 pc B B»100 m Gauss 3/2 m courtesy P. Blasi 28

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30 RXJ1713 EFFICIENT ACCELERATION LARGE B FIELDS OBLEMS: 1. LARGE THERMAL X-RAYS (BUT ) 2. VERY LOW RATIO OF ELECTRONS AND PROTONS 30

31 INEFFICIENT ACCELERATION LOW B FIELDS EMS: 1. VERY HIGH PHOTON DENSITY FOR ICS 2. LOW B FIELDS (IGNORES X-RAY OBSERVATIONS) 3. BAD FIT TO HIGHEST-E HESS DATA POINTS courtesy P. Blasi 31

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33 Kep~0.01 Kep~0.1 33

34 AGN - blazars BL-Lac FR-I, FR-II Radio quasars Intense and variable emission up to ~10 TeV Observed structures: accretion disk; obscuring thorus Relativistic Jet Broad/Narrow line regions (NLR, BLR) TeV emitting zone: jet with high relativistic bulk motion Particle acceleration at shock boundaries bundled in a magnetic field (Fermi acceleration processes) Gamma-ray emission from accelerated electrons (synchrotron and inverse-compton scattering) or hadronic interactions Unified AGN model: different AGN classes depending on viewing angle FRI, FR-II, Radio quasars, BL-Lac (HBL-LBL) 34

35 Emitted power γ-ray emission from AGN: SSC a (minimal) standard model Relativistic electrons injection/acceleration/cooling Synchrotron e- IC Blazar: collimated emission from jet (relativistic amplification) γ B γ min Environment: B, δ, R eγ γ br γ max eγ γ br γ maxkn Observed emission (SED) well described by leptonic models, such as SSC and EC. Expected X-ray / Tev time correlation Synchrotron peak: IR to x-ray IC peak: UV to γ-rays LBL, IBL, HBL Energy Outbursts of e.m. radiation 35

36 Blazar Multiwavelength campaigns Extreme (~>1 order of magnitude in flux) and fast (~hours, minutes) i var ability Simultaneous Multifreq. Observations covering 15 decades in photon energy: VHE: H.E.S.S., MAGIC, VERITAS HE: Agile, Fermi X-ray: Suzaku, Swift, Chandra, Integral Optical: KVA Radio: Metsahövi, VLBI Methods: Monitoring (optical, x-ray, radio) Intensive planned campaigns Target of Opportunity (ToO): react to alerts (internal/external) MAGIC Monitoring program of bright blazars (Mrk421, Mrk501, 1ES1959, 1ES ) Some recent MWL campaigns: Mrk 421, Mrk 501, OJ287, PG , 1ES , 1H , M87 and other campaigns organized 36

37 Mrk activity MWL campaigns on Mrk421 in flaring state optical to TeV energies Simultaneous data strong SSC model constraints time evolution of the SEDs New 2009 campaign on Mrk421 and Mrk501 pr ary n i elim Bonnoli G. et al. (MAGIC Coll.) arxiv: Publication in preparation 37

38 Mrk campaign Fermi 4.5 months Jan 20th - June 1st ~20 instruments 2-day sampling Swift/XRT Complete coverage 0.1 GeV-10 TeV MAGIC D.Paneque, Fermi symposium preliminary 38

39 S IBL z=0.31(?) ApJ - accepted arxiv: MAGIC collab. 2008, Atel #1500 High redshift Nilsson,A&A 487(2008)L29 reports the detection of the host galaxy: z=0.31±0.08 Bright in optical trigger MWL campaign (opt-x-γ) Clear signal in 2.6 h: 6.9σ 1st VHE detection F(>400 GeV) =7.5x10-12 ph/cm²/s ( 9% Crab) Significance 6.8 σ SSC model predicts an unplausible IC γ -ray flux Spine-layer model Ghisellini et al. 2005, A&A, 432,

40 S IBL z=0.31 Rotation of positional angle of polarization (EVPA) during maximum (60deg/day) Larionov et al.,atel #1502 propagation of a polarized knot spiraling down the jet, following helical magnetic field QuickTimeﾪ e un decompressore H.264 sono necessari per visualizzare quest'immagine. (e.g. BLLac, Marscher et al., 2008, Nature, 452, 966) Similar behavior (degree of polarization) during Fermi campaign on 3C279: polarization degree a good precursor of γ-flares? X-ray spectrum shows synchrotron component: transition between LBL-HBL states? E.g. reported on PKS Y.H.Zhang, ApJ,682(2008)789 40

41 BL Lacertae MAGIC detection in flare end October 2005 ~MJD MAGIC Coll., ApJL 666 (2007) L17 A. Marscher et al., Nature 452 (2008)

42 M87 RG z=0.0043, 16.7 Mpc misaligned blazar (15-25o); 17 Mpc HEGRA hint; HESS/VERITAS detection Candidate nearby CR site (hadronic emission?) Variability? Site for TeV emission (core/hst-1)? Harris+07 Radio VLBA 8 GHz HST-1 knot D nucleus knot A X-rays Chandra 42

43 MAGIC coll. Science, 325 (2009) 444 M87 Joint paper MAGIC-VERITAS-HESS-VLBI-Chandra ApJL, 685 (2008) MWL campaign jan-feb 2008 (triggered by MAGIC detection on 1st February flare) 9.9σ detection; 8.0σ single night 1st-feb First spectrum at E>100 GeV VHE Marginal hint of spectral hardening Clear <~daily variability at E>350GeV Chandra observations core/hst-1 contribution (core active / HST1 dim) Nucleus radio brightening HST-1 X-ray nucleus radio Nucleus ~100Rs jet Apr07 Jul07 Oct07 Jan08 Apr08 43

44 Mrk 501 Goal 2: lightcurve TeV AGN, µqso days, minutes Pulsar ms #ph / T Time resolution Crab pulsar LS I TeV TeV TeV X-ray 26 days 4 min lag 20 minutes 33 ms TeV 44

45 Crab pulsar Cutoff depends on the acceleration and radiation process (outer gap/polar cap) Absorption in magnetosphere (magnetic/photon pair production) Maximum acceleration energy First hint at E~>60 GeV Albert et al. 2008, ApJ, 674,

46 Crab pulsar M. Teshima et al. 2008, Atel #1421 MAGIC coll., Science 322 (2008) 1221 Lower trigger threshold: new trigger system (sumtrigger) 46

47 electrons LS I Relativistic from accretion powered o High Mass X-ray Binary (2kpc) o Be star orbiting unknown object (NS-BH) o P=26.5d; e=0.72 Relativistic Jet radio structures: µ-qso nature? (Massi et al. 2004) Cometarylike radio structure: interaction of pulsar/jet o X-ray emissionwind at o Φ~0.5 o GeV-emitter (3EG ) jet Relativistic electrons from rotational energy of pulsar Mirabel 2006 Massi et al mas 10 mas Candidate for TeV emission M. Massi et al., A&A 414, L1 (2004) J.Albert et al., ApJ, 684, 1351 (2008) 47

48 LS I MAGIC Coll. 2006, Science, 312, 1771 MAGIC observations (54 hrs, 6 orbits) 8.7 sigma; point-like; max at Φ~

49 LS I campaign) F (E > 400 GeV) 2nd campaign - sep-dec 2006; 112 hrs Hint of X-ray/TeV emission correlation No time correlation with radio Highest emission at Φ=0.65 Periodicity: 26.8±0.2 days Phase spectral No significant changes Phase Phase (1st with phase MAGIC coll. 2009, ApJ, 693, 303 P.Esposito et al 2007 Swift/XRT kev MAGIC 1stcampaign E>400GeV Periastron 49

50 LS I Simultaneous MWL campaign, single period XMM, Swift, MAGIC - sep 2007; Clear X-ray/TeV emission correlation No radio-tev(x-ray) correlation Highest emission at Φ=0.65 No significant spectral changes with phase TeV X-ray MAGIC coll. 2009, ApJ Lett. 706, L27 50

51 Energy flux Emitted spectrum EHEε Energy 2 2 EBL=3.6(mec ) o b se rv e d E γ Î Eg m m 1 z 1T e V λ Ï u n a b so rb e d Ee γ Î E γ τ (E,z): Optical Depth Gamma Ray Horizon (GRH): τ =1 High absorpti on EBL Interaction with Extragalactic Background Light (EBL) Energy observed spect. energy dependent γ -ray absorption modification of original spectrum Low absorption Energy 51,z

52 Cosmic backgrounds 52

53 CIB: modelli Primack (2005) 53

54 /wwwmagic.mppmu.mpg.de/ 54