Recent Results from the CANGAROO Observations

Transcription

1 Recent Results from the CANGAROO Observations Kyoshi Nishijima Department of Physics, Tokai University - Introduction of ground based observation of VHE gamma-rays - Our recent results with the CANGAROO-II 10 m telescope - Summary of the present status of VHE gamma-ray astronomy

2 Observation Technique of Gamma-Rays E 300 GeV IACT(Imaging Air Cherenkov Telescope) Large collection area Whiple, CANGAROO, HEGRA, Array of heliostats ( 50 GeV) CELESTE, STACEE, E 30 GeV Satellite OSO-3, SAS-2, COS-B, EGRET, AGILE, GLAST ( 100GeV) STACEE EGRET Whipple

3 Satellite vs Ground-based gamma-ray telescope Base Satellite Ground Gammaray detection Direct (pair creation) Indirect (atmospheric Cherenkov) Energy < 30 GeV ( 100 GeV) >300 GeV ( 50 GeV) Pros High S/N Large FOV Large area Good Cons Small area High cost Low S/N (CR bkgd.) (but imaging overcomes this!) Small FOV

4 Imaging Air Cherenkov Technique S eff = cm 2 4

5 Image Parameters D.J. Fegan, J.Phys.G, 1997 (Simulation)

6 CANGAROO Collaboration Collaboration of Australia and Nippon for a GAmma Ray Observatory in the Outback University of Adelaide Australian National University Ibaraki University IbarakiPrefectualUniversity Kanagawa University Konan University Kyoto University Nagoya University National Astronomical Observatory of Japan Osaka city University Institute of Physical and Chemical Research Shinshu University Institute for Space and Aeronautical Science Tokai University University of Tokyo Tokyo Institute of Tehnology Yamagata University Yamanashi Gakuin University

7 CANGAROO-II 10m Telescope 10m telescope m Focal length 80cm CFRP mirrors 8m Parabola 114 (57m 2 ) Mar m Number of PMTs Electronics Point image size 552 (1/2 ) FOV ~ 3 (4 ) TDC & ADC 0.20 (FWHM) (<0.15 ) May1999- Feb m

8 Why VHE Gamma-Rays? Origin of cosmic rays Characteristics of cosmic ray sources Physics of particle accerelation Something new...

9 Origin of Cosmic Rays Energetics of Cosmic Rays (<10 16 ev) Required Energy Supply ~10 40 erg/s (τ ~ 10 6~7 yrs, ρ CR ~ 1 ev/cm 3 ) Unique Candidate SNR E max ~ ev Extra Galactic Origin (>10 18 ev) E max ~10 20 ev Spectrum Index -2.5 ~ -3.0 Shock Acceleration Composition : Mainly Protons

10 TeV Gamma-Ray Processes E E 1. 6 E E 2.2 E 2.2 E 2.2 de dt de dt = 4 I.C. 3 Sync = σ 4 3 T σ T cγ cγ 2 U max photon 2 max 2 B 2

11 Why VHE Gamma-Rays? Origin of cosmic rays Characteristics of cosmic ray sources Physics of particle acceleration Something new...

12 TeV Gamma-Ray Sources Galactic Objects Pulsar/nebula: Young pulsar + synchrotron nebula Crab pulsar, PSR , Vela pulsar SNR: Synchrotron X-ray emission, SN1006, RX J , Cas A Other candidates: G.C., Micro quasar, pulsar/be star binary Extragalactic objects AGN: nearby blazars (z <0.1) Mkn421, Mkn501, PKS , 1ES , 1ES , 1ES Starburst galaxy: NGC253 Other candidates: Merging cluster of Galaxy UnID TeV source TeV J2032

13 Crab nebula: unpulsed spectrum synchrotron IC SSC(Synchrotron Self Compton) B=(170 30)µG (Aharonian et al. 2000) E max ev (De Jager & Harding 1992) Aharonian & Atoyan, astro-ph/ / Heidelberg WS, 2000 important tested and calibration source

14 PSR : Differential flux Differential Flux E -3.0 Period :102 ms Distance :1.8 kpc Age : yr Spin-down energy loss : erg/s Chandra ACIS ATCA image 10 arcsec = pc PSR vary around 1 TeV? steep above 1TeV IC scattering due to electrons?

15 PSR1706: Multiwavelength Spectrum E 2 I(E) (erg cm -2 s -1 ) CANGAROO COMPTEL Radio(VLA) New RXTE Optical(VLT) OSSE Optical nebula EGRET pulsed Chandra pulsar EGRET unpulsed Chandra nebula Sync. Sync IC B=0.15µG B=3µG IC with 2.7K CMB X-ray sync. peak energy: higher than 10 kev Expected IC peak energy: higher than our results Energy (ev) TeV gamma-ray flux is difficult to be explained by Sync-IC model (2.7K CMB) in the nebula.

16 PSRJ pulsed TeV Gamma-ray sources of pulsars and candidates Crab Vela 10 arcmin. ASCA image unpulsed. E (erg/s)/4pd (cm) 2 PSRB arcsec=0.15pc Chandra ACIS(2000), PSR Vela 200arcsec=4.3pc Chandra ACIS(2000), Thompson, Heidelberg WS, 2000 Period [sec] Roberts,Romani,Johnston (2001) ApJ 561: L187 L190. PSRB

17 Supernova Remnant: SN1006 Radio:Shell, with two bright arcs X-ray:Thermal shell, with non-thermal limb-brightened arcs Distance:Optical spectra and proper motion indicate kpc, modeling spectra gives kpc Shock structure Chandra ACIS T. Naito

18 Observation by ASCA/SIS : SN1006 Non-thermal emission from NE rim existence of high energy electrons up to 100 TeV the possibility of TeV Gamma-Ray Emission Koyama et al.1995 `Power-law Synchrotron Rad. Several Peaks: Thermal Emission

19 Significance map: SN1006 We succeeded in detection of TeV signals from the northeast rim. Chandra ACIS 10m result. PSF ~0.25 deg radius. 3.8m result.

20 Multi-band Spectrum & Fitting:SN1006 Durham S = -2.2 B ~ 4 G E max ~50TeV TeV emission : IC scattering of CMB photons by high energy electrons. There is no evidence of proton acceleration. Naito et al. Astron. Nach. 320, 1999

21 Supernova Remnat: RXJ Discovered in ROSAT All Sky Survey Slane et al, ApJ, 525,1999 Galactic plane CO Image Adjacent clouds & HII region Density in SNR <<1atom/cm -3 Radio

22 Observation by ASCA/SIS : RX J (G ) Radio:Faint emission X-ray:Non-thermal, with limb-brightened, with central sources Distance:Association with molecular clouds, and HII region, suggests 6 kpc Synch. X-ray Emission (ASCA) Existence of multi TeV Electrons Tomida, Ph.D., 1999 Slane et al, ApJ, 525,1999

23 TeV gamma-rays expected from synchrotron inverse Compton model: RX J Naito et al 2001(CANGAROO) Ellison et al µG Synchrotron Rad. I.C. 3µG 5µG 3.8m 10µG 20µG 1TeV

24 Spectrum & Significance map: RX J E 2.8 Steeper sub-tev spectrum than expected from IC model X-ray TeV Infrared

25 Multiwavelength spectrum : RX J Sync. Bremsstrahlung I.C. TeV spectral shape does not show a good fit with simple IC model Detected gamma-rays are produced by π 0 decay rather than IC. π 0 decay Proton acceleration? Nature 416(2002) 823

26 Non-thermal shell type SNRs RCW86 Dist. a few Kpc Type II RX J Dist >1kpc? Bamba et al ASCA Results Slane et al. 2001

27 AGN: Mkn 421 Variability and Multiwavelength Observation Time scale < a few hours R<10-4 pc (10R Sch radii of a 10 8 Solar mass black hole) Correlation with an X-ray variability Gaidos et al., Nature, 383, 1996 The X-ray and the TeV photons arise from the same emission region, likely from the same population of synchrotron radiating electrons Takahashi et al. ApJ 542, 2000 the SSC mechanism is at least partially if not dominantly at work in the γ-ray production

28 AGN: Mkn 421 multiwavelength spectrum Synchrotron + inverse Compton model works well e ± origin Takahashi et al. ApJ 542, 2000 Proton model still possible synchrotron inverse Compton One-zone SSC model =14, B=0.14G

29 CANGAROO Observation of Mkn421 in 2001 Observation:10 nights during extremely strong flare periods Large zenith angle observation:( 70 ) Energy threshold : 10TeV effective area: more than ten times larger than the case of vertical showers

30 Attenuation of TeV Gamma-rays with CIB Hauser & Dwek, 2001 Energy spectrum in multi TeV absorption of TeV gamma-rays due to cosmic infrared photon background(cib) E>10TeV gamma-rays from Mkn421 suppressed interaction with mid- to far-infrared photons

31 Energy spectrum: Mkn421 dn de = (3.3 ± 0.9 stat. ± 0.3 syst. ) E 10TeV ( stat. ± 0.3 syst. ) ph / cm 2 / sec/ TeV assuming power law ApJ. 579 (2002) L9 Energy spectrum steeper than that observed E<10TeV However, marginally significant excess (4σ) observed at E>20TeV Cut off energy: 8TeV

32 PKS Energy Spectrum CANGAROO has not succeeded in detection of VHE gamma-rays from other blazars. - Durham group reported the detection from PKS in 1997 correlated with a strong X-ray flare - This is the only TeV blazar detected in southern sky Integral Flux (cm -2 sec -1 ) preliminary - We have observed, but only upper limits are obtained

33 NGC253 distance : 2.5 Mpc Enhanced star formation rate High SN rate : /yr Higher CR production by factor Gamma-ray signals (0.5TeV) are detected at a high confidence level(>10σ) The emission region is: - much broader than the PSF of our telescope - somewhat larger than the optical image of the galaxy.

34 NGC253: differential flux df de = ( 2.85 ± 0.71) df 1.5 E / b E E / b de = ae 0 E 0 e 1 E TeV 3.85± 0.46 (1) (a=6 10-5, E 0 =200MeV, b=0.25±0.01) New TeV gamma-ray source! (2) (2) Crab (1) (2) Accepted in A&A Lett.

35 Summary of Galactic Sources Pulsar/nebula Unpulsed TeV gamma-ray emission from young pulsars with synchrotron nebula are detected. Crab, Vela, PSR seem to be well explained by IC with CMB or SSC by e? SNR Shell type SNRs with non-thermal X-ray emission are detected in TeV region. SN1006, RXJ , Cas A seem to be well explained by IC with CMB by e, or by π 0 decay produced by proton(cosmic Ray Origin)? Other candidates G.C., Micro qusar, pulsar/be star binary...

36 Summary of Extragalactic Sources AGN (still not well-understood!) 6 nearby blazar, HBLs, Strongly time variable, Mrk421, Mkn501, PKS , 1ES , 1ES , 1ES Leptonic models are preferred SSC(Synchrotron Self Compton) model? EC(External Compton) model? accretion disk?, BLR clouds? Hadoronic models are not ruled out photo-meson production? photo-pair production? proton synchrotron? Starburst Galaxy NGC253:the first normal spiral galaxy other than our own where TeV cosmic rays exit Other candidates EGRET unid, GRBs, SUSY particles, Merging clusters,g.c., Diffuse,..., and more?

37 Summary of VHE Gamma-ray Astronomy Experimentally, great progress has been made last decade. Source count is increasing steadily, however it is still a handful. We need more sources and better data. With the advent of CANGAROO-III, HESS, MAGIC, (VERITAS), we are entering a new era for observations Broadband simultaneous observations are essential!

38 CANGAROO-III (Stereo Observation) Array of four 10m telescopes(~2004) Full Imaging: Angular Res. : ~0.1 deg. Energy Threshold: ~100GeV

39 Third generation ground-based IACTs MAGIC 1 17m, Canary Island, VERITAS 7 10m, Arizona, HESS 4 12m, Namibia, CANGAROO-III 4 10m, Australia, 2000-

40 TeV sky 2000

41 2002

42 Sensitivity of future detectors

43 Third EGRET catalog R.C. Hartman et al., ApJS, 1999