1 / 56

VHE Gamma Ray Astronomy an overview

VHE Gamma Ray Astronomy an overview. John Learned University of Hawaii P711/A736 12 April 2005. Origins of the Field. Early ideas and attempts by Russians, English, particularly J.V.Jelly. CfA’s Trevor Weekes in 1970’s, Mt. Hopkins first dedicated (10m) telescope.

clodia
Download Presentation

VHE Gamma Ray Astronomy an overview

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. VHE Gamma Ray Astronomyan overview John Learned, A736/P711 12 April 2005 John Learned University of Hawaii P711/A736 12 April 2005

  2. Origins of the Field • Early ideas and attempts by Russians, English, particularly J.V.Jelly. • CfA’s Trevor Weekes in 1970’s, Mt. Hopkins first dedicated (10m) telescope. • Key idea from Micheal Hillas…. How to distinguish image of Gamma Shower from predominant proton (and nucleon) showers. • Marginalized, almost no support, and largely considered a failure through 80’s. • Blossoms in 90’s with first TeV sources (mainly the Crab Nebula), but really taking off now. John Learned, A736/P711 12 April 2005

  3. TeV Gammas • Lower energies (say <GeV) are observed with direct counting, few m2. Must be from balloons at few gm/cm2 or better satellites (or on moon). • Energies ~MeV can be nuclear. Higher E’s involve particle acceleration, peculiarly common in the universe. Must be there, since CRs known to exist, but what flux and what origin? • If seeking TeV energies, need areas in the range of >10,000 m2. Use showers. • Was soon (80’s) known that there were no huge point sources in cosmic rays. Protons stirred by gal mag field, so should not point. So, no huge gamma fluxes, re P’s, and thus need means to sort out gamma showers. John Learned, A736/P711 12 April 2005

  4. Aside: our UH role • No GR or any point sources detected. • Weekes at Mt. Hopkins, pursued imaging and we were involved a bit (Gorham thesis, etc. JGL built calibrator, Stenger did data analysis). Not making much progress. Imaging a flop. • Mid-80’s, we built GR telescope on Haleakala, with Wis, Purdue. • Bet on wrong horse: simulations showed handle on GR showers by fast timing. Did not work. • Finally, Weekes gets enough pixels, fast electronics and good calibrations…. Finds Crab. John Learned, A736/P711 12 April 2005

  5. Methods of Detection • Cost: counters ~>$1000/m2, if need ~105 m2, then ~$100M. • Detect showers: at ground their size is about 105 m2 (less in high mountains). • Use Cherenkov light in atmosphere. Too low an energy for air fluorescence (EeV). Sort showers by image Mt. Hopkins, VERITAS, Cangaroo, HESS, Magic, and around 6 others). • Use dense counter array, only water affordable (MILAGRO, HAWC). • Use RPCs (Tibet). • New technology ACT, ASHRA in Hawaii. John Learned, A736/P711 12 April 2005

  6. Following slides from Mori, of ICRR and Cangaroo collab CGRO/EGRET • Apr 1991 – Jun 2000 • 30 MeV – 30 GeV • 67%=5.85(100 MeV/E)0.534 John Learned, A736/P711 12 April 2005

  7. EGRET Allsky Map John Learned, A736/P711 12 April 2005

  8. Diffuse gamma-ray spectrum • Flatter than expected (E -2.75): why?⇒ Flatter proton/electron spectrum?? Nishimura et al. EGRET John Learned, A736/P711 12 April 2005 JACEE 0 Whipple Brems uniform IC ————————————— ——— S. Hunter, Heidelberg WS, 2000

  9. Third EGRET catalog John Learned, A736/P711 12 April 2005 R.C. Hartman et al., ApJS, 1999

  10. Pulsars 5 AGN (mostly blazars) 66 27 (marginal) Radio galaxy (Cen A) 1 (marginal) Unidentified (Some may be SNRs) 170 Large Magellanic Cloud 1 Solar flare 1 Total 271 EGRET point source summary John Learned, A736/P711 12 April 2005 R.C. Hartman et al., ApJS, 1999

  11. Pulsars Radio Princeton catalog (706 pulsars), 1995 John Learned, A736/P711 12 April 2005 MeV only (GeV candidates: 1046-58, 0656+14, J0218+4232) GeV Thompson, Heidelberg WS, 2000

  12. Gamma-ray pulsar light curves John Learned, A736/P711 12 April 2005 GLAST proposal

  13. BL Lac’s and EGRET AGNs RED EGRET 3rd catalog AGNs Green Padovani & Giommi MN 1995 John Learned, A736/P711 12 April 2005 TeV Whipple, HEGRA, CAT, 7TA, Durham

  14. Gamma-ray blazars H(igh freq. peaked) BL  X(-ray selected) BL L(ow-freq. peaked) BL  R(adio-selected) BL • Mostly FSRQ and BL Lac’s John Learned, A736/P711 12 April 2005 Lin et al. ApJ 1999 Mukherjee et al. ApJ 1997

  15. Multiwavelength spectrum of AGNs • Double-peaked structure= synchrotron + inverse Compton Kataoka, Ph.D 2000 John Learned, A736/P711 12 April 2005 Mrk 421 (z=0.03, XBL) PKS0528+134 (z=2.1, FSRQ) ↑ νIC =γ2νsync ↑ νsync Kubo et al. ApJ 1998

  16. EGRET unidentified sources • Low vs High latitude • Persistent vs Variable • Geminga-like pulsars? • SNRs? • OB associations? • Gould belt? John Learned, A736/P711 12 April 2005 I. Grenier, GeV-TeV WS, 1999

  17. EGRET unIDs and SNRs RED EGRET 3rd catalog unID Green D.A. Green’s catalog TeV CANGAROO TeV HEGRA John Learned, A736/P711 12 April 2005 GeV Esposito et al. ApJ 461, 1996

  18. Extragalactic diffuse gamma-rays • Single power-lawE–2.100.03 (30 MeV-100 GeV) • Unresolved point sources (ex. Blazars etc.)?Upscattered CMB? John Learned, A736/P711 12 April 2005 E–2.100.03 P. Sreekumnar et al., ApJ 1998

  19. Whipple1968 John Learned, A736/P711 12 April 2005

  20. Imaging Cherenkov technique John Learned, A736/P711 12 April 2005

  21. Image parameters John Learned, A736/P711 12 April 2005 ● (Simulation) D.J. Fegan, J.Phys.G, 1997

  22. Example of image cut analysis • Hadron rejection power ～100 Whipple CANGAROO (Vela) John Learned, A736/P711 12 April 2005 M. Punch et al., Nature, 1992 T. Yoshikoshi et al., ApJ, 1997

  23. TeV catalog 2000 John Learned, A736/P711 12 April 2005 T.C. Weekes, Heidelberg WS, 2000

  24. TeV sky 2000 John Learned, A736/P711 12 April 2005

  25. TeV observations of AGNs John Learned, A736/P711 12 April 2005 (Detection of 1ES1426+428 (z=0.13) is claimed by Whipple but not published) Krennrich, astro-ph/0101120

  26. AGN: Mrk 421 variability • Time scale < a few hours • Correlation with X-ray flux John Learned, A736/P711 12 April 2005 Gaidos et al., Nature, 383, 1996 Takahashi et al. ApJ 542, 2000

  27. AGN: Mrk 421 spectrum z=0.031 • Synchrotron+ inverse Comptonmodel workswell⇒ e origin • Proton modelstill possible Takahashi et al. ApJ 542, 2000 John Learned, A736/P711 12 April 2005 synchrotron inverse Compton One-zone SSC model δ=14, B=0.14G

  28. AGN: TeV gamma-ray absorption by IR background Mean free path for e+e- pair production IR Background John Learned, A736/P711 12 April 2005 Protheroe et al. astro-ph/0005349

  29. AGN: Mrk 501 spectrum z=0.033 Crisis?↓ John Learned, A736/P711 12 April 2005 Protheroe et al. astro-ph/0005349 Aharonian et al. A&Ap 349, 1999

  30. Sensitivity of various detectors (2000) John Learned, A736/P711 12 April 2005

  31. e m g 6 meters 200 meters MILAGRO PrincipleHAWC: High Altitude Water Cherenkov • 200m x 200m water Cherenkov detector • Two layers of 8” PMTs on a 2.7 meter grid • Top layer under 1.5m water (trigger & angle) • Bottom layer under 6m water (energy & particle ID) • ~11,000 PMTs total (5,000 top and 5000 bottom) • Trigger: >50 PMTs in top layer • Two altitudes investigated • 4500 m (~Tibet, China) • 5200 m (Atacama desert Chile) John Learned, A736/P711 12 April 2005 Following Milagro/HAWC slides from Gus Sinnis, LANL

  32. Event Reconstruction John Learned, A736/P711 12 April 2005 Angular resolution ~0.75 degrees

  33. 30 GeV 70 GeV 230 GeV 270 GeV 20 GeV 70 GeV Background Rejection Bottom Layer Gammas John Learned, A736/P711 12 April 2005 Protons

  34. Gammas Protons Background Rejection Uniformity Parameter nTop/cxPE > 4.3 Reject 70% of protons Accept 87% of gammas 1.6x improvement in sensitivity John Learned, A736/P711 12 April 2005

  35. D.C. Sensitivity: Galactic Sources • Crab Spectrum: dN/dE = 3.2x10-7 E-2.49 • Milagro 0.002 (0.001) Hz raw (cut) rate • HAWC 0.220 (0.19) Hz raw (cut) rate • Whipple 0.025 Hz • Veritas 0.5 (.12) Hz raw (cut) rate • Background rate 80 (24) Hz raw (cut) • 4 s/sqrt(day) raw data • 6 s/sqrt(day) cut data • 120 s/sqrt(year) • 40 mCrab sensitivity (all sky) in one year • Whipple: 140 mCrab per source • VERITAS: 7 mCrab per source (15 sources/year) John Learned, A736/P711 12 April 2005

  36. 3EG J0520+2556 Crab Excess Coincident with EGRET source 3EG J0520+2556 Source Reported twice before by Milagro: 1) APS Meeting: April 2002 Reported as a Hot Spot. A Larger than optimal bin size was used in that initial survey. 2) Location of one of the top excesses in our published point source All Sky search. John Learned, A736/P711 12 April 2005 5.5 s detection at (79.8o, 42o) using binsize= 2.9o

  37. Distribution of Excess in the Cygnus Region: Gaussian Weighted Excess 2 regions of excess give rise to the observed signal. John Learned, A736/P711 12 April 2005 b=+5 l=85 l=80 Cyg OB2 field l=75 b=0 b=-5

  38. Existing Arrays Milagro Dense sampling Moderate altitude (2650m) Background rejection John Learned, A736/P711 12 April 2005 Tibet Array Sparse sampling High altitude (4300m) No background rejection

  39. EAS Arrays • Provide synoptic view of the sky • See an entire hemisphere every day • Large fov & high duty cycle • Gamma ray bursts • Transient astrophysics • Extended objects • New sources • Excellent complement to GLAST • With >1000 sources need an all-sky instrument in VHE • Current EAS arrays lack sensitivity to complement GLAST • What can be done? • Need low threshold (GLAST overlap) < 100 GeV • High sensitivity John Learned, A736/P711 12 April 2005

  40. EAS Arrays in the GLAST Era John Learned, A736/P711 12 April 2005

  41. z = 0.0 z = 0.03 z = 0.1 z = 0.2 z = 0.3 Effect of EBL on Distant Sources John Learned, A736/P711 12 April 2005

  42. Detection principle:Stereoscopic imagingof Cherenkov light from air-showers • Large collection area • Multiple views of the shower • improved direction • improved energy • improved rejection of background (cosmic rays!) John Learned, A736/P711 12 April 2005

  43. Crab Nebula @ 45 degree zenith angle 3-Telescope data (2003) 54 , (27 /hr0.5) 10.8 +/- 0.2 /minute Preliminary John Learned, A736/P711 12 April 2005

  44. Official detections by H.E.S.S. so far… • Crab Nebula (2003, 3 Tel.) - 54 sigma • PKS 2155 (2003, 2 Tel.) - 45 sigma • Mrk 421 (2004, 4 Tel.) - 71 sigma • PSR B1259 (2004, 4 Tel.) - 8 sigma • RX J1713 (2003, 2 Tel.) - 20 sigma • Sagittarius A* (2003. 2 Tel.) - 11 sigma John Learned, A736/P711 12 April 2005 Very confident detections – all but Mrk 421 and PSR B1259 were confirmed independantly in datasets from two hardware configurations

  45. The Galactic Centre • -rays detected by CANGAROO and Whipple but: • Very complex region - lots of potential sources of -rays • Sagittarius A* - supermassive black hole - curvature radiation of accelerated protons? • Several SNR, including Sag-A East, 'standard' CR acceleration? • Dark matter annihilation? • To resolve the ambiguity we need • precise spectrum • well determined position John Learned, A736/P711 12 April 2005

  46. Sagittarius A* • -ray candidates (hard cuts) • H.E.S.S. 2003 • 2 telescopes, 16 hours • Ethresh = 160 / 250 GeV(2 data sets) • 11 significance Good source localisationHard energy spectrum John Learned, A736/P711 12 April 2005

  47. Chandra GC survey NASA/UMass/D.Wang et al. CANGAROO (80%) H.E.S.S. Whipple (95%) Contours from Hooper et al. 2004 Sagittarius A* - Source Location John Learned, A736/P711 12 April 2005

  48. H.E.S.S. 95% 68% Chandra F. Banagoff et al. • Point-like emission from Sgr A* direction John Learned, A736/P711 12 April 2005

  49.  Sgr-A East not ruled out H.E.S.S. limit on rms source size Sgr A East Chandra & Radio NASA/G.Garmire (PSU) F.Baganoff (MIT) Yusef-Zadeh (NWU) John Learned, A736/P711 12 April 2005

  50. DM annihilation: ? Curvature radiation: ? SNR Shocks: ? Shocks in winds: ? Sagittarius A* - Spectrum John Learned, A736/P711 12 April 2005

More Related