John Learned, A736/P April 2005 VHE Gamma Ray Astronomy an overview John Learned University of Hawaii P711/A April 2005

John Learned, A736/P 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. 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/P April 2005 TeV Gammas Lower energies (say <GeV) are observed with direct counting, few m 2. Must be from balloons at few gm/cm 2 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 m 2. 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/P April 2005 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/P April 2005 Methods of Detection Cost: counters ~>$1000/m 2, if need ~10 5 m2, then ~$100M. Detect showers: at ground their size is about 10 5 m 2 (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/P April 2005 CGRO/EGRET Apr 1991 – Jun MeV – 30 GeV  67% =5.85  (100 MeV/E) Following slides from Mori, of ICRR and Cangaroo collab

John Learned, A736/P April 2005 EGRET Allsky Map

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

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

John Learned, A736/P April 2005 EGRET point source summary Pulsars5 AGN (mostly blazars)66 27 (marginal) Radio galaxy (Cen A)1 (marginal) Unidentified (Some may be SNRs) 170 Large Magellanic Cloud1 Solar flare1 Total271 R.C. Hartman et al., ApJS, 1999

John Learned, A736/P April 2005 Pulsars GeV Thompson, Heidelberg WS, 2000 Radio Princeton catalog (706 pulsars), 1995 (GeV candidates: , , J ) MeV only

John Learned, A736/P April 2005 Gamma-ray pulsar light curves GLAST proposal

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

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

John Learned, A736/P April 2005 Multiwavelength spectrum of AGNs Double-peaked structure = synchrotron + inverse Compton Kubo et al. ApJ 1998 PKS (z=2.1, FSRQ) Mrk 421 (z=0.03, XBL) Kataoka, Ph.D 2000 ↑ ν sync ↑ ν IC =γ 2 ν sync

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

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

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

John Learned, A736/P April 2005 Whipple 1968

John Learned, A736/P April 2005 Imaging Cherenkov technique

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

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

John Learned, A736/P April 2005 TeV catalog 2000 ClassificationObjectGroupRemark Grade A (>5σ, multiple) Crab PSR Mrk 421 Mrk 501 Many CANGAROO, Durham Many Plerion AGN (BL Lac) Grade B (>5σ) SN1006 Vela RXJ PKS ES BL Lac CANGAROO Durham Utah7TA Crimea SNR Plerion SNR AGN (BL Lac) Grade C (strong but with some qualifications) Cas A Cen X-3 1ES C66A Geminga B HEGRA CT Durham Whipple Crimea CANGAROO SNR X-ray binary AGN (BL Lac) AGN (z=0.44) Pulsar Plerion T.C. Weekes, Heidelberg WS, 2000

John Learned, A736/P April 2005 TeV sky 2000

John Learned, A736/P April 2005 TeV observations of AGNs Krennrich, astro-ph/ (Detection of 1ES (z=0.13) is claimed by Whipple but not published)

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

John Learned, A736/P April 2005 AGN: Mrk 421 spectrum Synchrotron + inverse Compton model works well ⇒ e  origin Proton model still possible Takahashi et al. ApJ 542, 2000 One-zone SSC model δ=14, B=0.14G synchrotroninverse Compton z=0.031

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

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

John Learned, A736/P April 2005 Sensitivity of various detectors (2000)

John Learned, A736/P April 2005 MILAGRO Principle HAWC: 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) 6 meters e  200 meters Following Milagro/HAWC slides from Gus Sinnis, LANL

John Learned, A736/P April 2005 Event Reconstruction Angular resolution ~0.75 degrees

John Learned, A736/P April 2005 Gammas Protons Background Rejection Bottom Layer 30 GeV70 GeV230 GeV 20 GeV70 GeV 270 GeV

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

John Learned, A736/P April 2005 D.C. Sensitivity: Galactic Sources Crab Spectrum: dN/dE = 3.2x10 -7 E –Milagro (0.001) Hz raw (cut) rate –HAWC (0.19) Hz raw (cut) rate –Whipple Hz –Veritas 0.5 (.12) Hz raw (cut) rate Background rate 80 (24) Hz raw (cut) 4  /sqrt(day) raw data 6  /sqrt(day) cut data –120  /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/P April 2005 Excess Coincident with EGRET source 3EG J 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. Crab 3EG J  detection at (79.8 o, 42 o ) using binsize= 2.9 o

John Learned, A736/P April 2005 Distribution of Excess in the Cygnus Region : Gaussian Weighted Excess l=80 l=8 5 l=75 b=0 b=-5 b=+5 2 regions of excess give rise to the observed signal. Cyg OB2 field

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

John Learned, A736/P April 2005 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/P April 2005 EAS Arrays in the GLAST Era

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

John Learned, A736/P April 2005 Detection principle: Stereoscopic imaging of 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/P April 2005 Crab Nebula Preliminary 3-Telescope data (2003) 54 , (27  /hr 0.5 ) /- 0.2  45 degree zenith angle

John Learned, A736/P April 2005 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* ( Tel.) - 11 sigma Very confident detections – all but Mrk 421 and PSR B1259 were confirmed independantly in datasets from two hardware configurations

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

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

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

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

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

John Learned, A736/P April 2005 Galactic Centre – Dark Matter Neutralino annihilation? – Use DarkSusy – Expect two lines and continuum Power law index Cut off at roughly m  / 3 We see no lines and no cut off – exponential cut off is limited to < 4 TeV Which implies m  > 12 TeV

John Learned, A736/P April 2005 RX J1713 H.E.S.S. smoothed gamma-candidate map after image size cuts (> 800 GeV) - no background subtraction or acceptance correction – Only two telescopes – 18 hours – 20 sigma c.f. ASCA (1-3 keV) Flux = 70% of Crab

John Learned, A736/P April 2005 THE MAGIC TELESCOPE E. LORENZ, for the MAGIC COLLABORATION COLLABORATION:IFAE BARCELONA,UA BARCELONA,U. BERLIN, UC-DAVIS,U.LODZ, UC MADRID,MPI MUNICH INFN PADOVA, U. POTCHEFSTROOM, INFN SIENA, TUORLA OBSERVATORY, INFN UDINE, U. WUERZBURG, YEREVAN PHYSICS INST., ETH ZURICH. 3 CANDIDATES, IN TOTAL 120 MEMBERS 17 mtr

John Learned, A736/P April 2005 MUON ARC IMAGES THE MAGIC TRIGGER SUPPRESSES FULL MUON RINGS (EX. CLOSE TO THRESHOLD) LIGHT YIELD FROM MUON ARCS AGREES WITHIN 10% WITH OTHER METHODS (F-FACTOR ANALYSIS OF LIGHT PULSER SIGNAL) FROM MC SIMULATION: RESIDUAL MUON BG ONLY A FRACTION OF HADRONIC BG. IMPORTANT: MUONS DO NOT PEAK AT SMALL ALPHA AND DO NOT FAKE A SOURCE MC SIMULATION OF MUON IMPACT ON GAMMA ANALYSIS AFTER STANDARD CUTS GAMMAS HADRONIC BACKGROUND CONTRIBUTION FROM MUONS

John Learned, A736/P April 2005 ECO STUDY OF A 1000 m 2 CHERENKOV TELESCOPE 34 m 17 m

John Learned, A736/P April 2005 Summary VHE Gamma Ray Astronomy blossoming An interesting future with new telescopes and techniques Moving rapidly from explorations to regular observational astronomy. UH may have a role in ASHRA all sky observations.