The TeV Gamma-ray Universe Trevor C. Weekes Harvard-Smithsonian Center for Astrophysics Motivation/Techniques The TeV Sky Future Prospects

Nu Vus of the Universe weekes A Lonely TeV Cosmic Ray

Nu Vus of the Universe weekes

The Lonely TeV Proton takes a mate and produces a family; many of the off spring go astray but dutiful gamma rays carry on the family tradition and relay its message.

Nu Vus of the Universe weekes The Relativistic Universe The Relativistic Universe is defined by the presence of high energy particles, the sites where the particles are accelerated, the mechanisms by which they are accelerated, and the regions through which they propagate. Their presence is indicated by the emission of TeV gamma rays.

Nu Vus of the Universe weekes EGRET

Nu Vus of the Universe weekes Simple Technique, Simple Detectors, Low Budget Collection Area = Size of Football Field

Nu Vus of the Universe weekes Development of GeV-TeV First Generation Systems 1960 – 1985 First Generation Systems 1960 – 1985 Weak or no discrimination Weak or no discrimination Lebedev, Glencullen, Whipple, Narrabri, Crimea Lebedev, Glencullen, Whipple, Narrabri, Crimea Second Generation Systems 1985 – 2004 Second Generation Systems 1985 – 2004 Atmospheric Cherenkov Imaging Telescopes Atmospheric Cherenkov Imaging Telescopes Whipple, Crimea, CAT, HEGRA, Durham, CANGAROO Whipple, Crimea, CAT, HEGRA, Durham, CANGAROO …… …… Third Generation Systems 2004 – 2010 Third Generation Systems 2004 – 2010 Arrays of Large ACITs Arrays of Large ACITs MAGIC, HESS, CANGAROO-III, VERITAS, MACE MAGIC, HESS, CANGAROO-III, VERITAS, MACE Fourth Generation Systems Fourth Generation Systems TBD TBD TeV Sources Zero ~ 12 > ? New Technology Increase in Scale New Technology?

Nu Vus of the Universe weekes Development of MeV-GeV First Generation Systems 1960 – 1972 First Generation Systems 1960 – 1972 Spark Chambers Spark Chambers Balloons Balloons Controversy Controversy Second Generation Systems Second Generation Systems Spark Chambers Spark Chambers Small Satellites Small Satellites SAS-II, COS-B SAS-II, COS-B Third Generation Systems Third Generation Systems Spark Chamber Spark Chamber Bigger Bigger EGRET on CGRO EGRET on CGRO Fourth Generation Systems Fourth Generation Systems New Technology: Solid State New Technology: Solid State AGILE, GLAST AGILE, GLAST 100 MeV Sources One 30 (15) ,000? New Technology Increase in Size New Technology What?

Early Expectations of TeV Gamma-ray Astronomy Find the Origin of the Cosmic Radiation: * Single source or class of sources * Unambiguous detection of the 70 MeV bump in the spectrum * Source(s) would be in the Galaxy Locate the “Smoking Gun” of Cosmic Ray Origins! The reality has been quite different! * Many different sources (too many!) * No unambiguous proton source detection * Many sources are Extragalactic

Nu Vus of the Universe weekes Atmospheric Cherenkov Imaging Technique (ACIT) Proposed in 1977 *Imaging systems came into operation 1984 (Whipple, Crimea) *First TeV Source detected (Crab Nebula/ Whipple Observatory) 1989  Standard Candle for TeV Gamma-ray Astronomy  Strongest Steady Source in TeV Sky

Nu Vus of the Universe weekes TeV Image of Crab (not resolved) Compton Synchrotron Model for TeV Gamma-ray emission (first proposed by Gould, 1964) Electron Progenitor Prototype Model for most TeV gamma-ray sources Synchrotron Compton

Detection of TeV Gamma-ray AGN Markarian 421 Weak Source in EGRET but strong at TeV energies Markarian 421 Cross = X-ray source Dotted line : EGRET error circle Contours: TeV source intensity (29 sigma) Variation in Nightly Rates from Markarian 421 Hours-days-months

Nu Vus of the Universe weekes TeV Catalog of AGN Catalog Name SourceDate/GroupTypeRedshift TeV Mrk /WhippleHBL0.031 TeV H /WhippleHBL0.129 TeV Mrk /WhippleHBL0.033 TeV ES /TAHBL0.048 TeV PKS /DurhamHBL0.116 TeV ES /WhippleHBL0.044 Horan, Weekes, 2003 HBL = High frequency BL Lac All confirmed sources Spectra measured Light-curves determined Multi-wavelength Correlations Only two in EGRET Catalog

Multiwavelength Results: Power Spectra Synchrotron Compton Mrk 501 Similar double peaked Power Spectra seen in other AGN

AGN Jet Emission Mechanisms Electron Progenitors: Synchrotron Self Compton External Compton Proton Progenitors: Proton Cascades Proton Synchrotron Electron Synchrotron Self Compton Models most consistent with TeV AGN…..but observations are complex and require more sophisticated Modelling of Jets.

Limitations of ACIT Telescopes Second Generation Telescopes successful but…. Second Generation Telescopes successful but…. Limited Flux Sensitivity Limited Flux Sensitivity Hitting the “Muon Wall” Hitting the “Muon Wall” Need Lower Energy for GLAST Overlap Need Lower Energy for GLAST Overlap Array Concept demonstrated by HEGRA Array Concept demonstrated by HEGRA

Nu Vus of the Universe weekes ARRAYS (Third Generation) Arrays of Cherenkov telescopes viewing the same shower and improving the energy threshold, the angular resolution and the energy resolution; muon background removed. FacFac Factor of improvement in flux sensitivity

The Big 5 TeV ACIT Observatories CANGAROO III, 4 tel., 2006 (Australia) HESS, (Namibia) 4 tel., tel., 2007 VERITAS, (Arizona) 4 tel tel. 2008? MAGIC (La Palma), 1 tel., tel., 2008 MACE (India) 2 tel. 2008

Iowa State University Adler Planetarium Iowa State University Adler Planetarium Leeds University Barnard College Leeds University Barnard College McGill University DePauw University McGill University DePauw University National University of Ireland, Dublin Grinnell College National University of Ireland, Dublin Grinnell College Purdue University U.C. Santa Cruz Purdue University U.C. Santa Cruz Smithsonian Astrophysical Observatory U. Mass. Smithsonian Astrophysical Observatory U. Mass. University of California, Los Angeles N.U.I., Galway University of California, Los Angeles N.U.I., Galway University of Chicago Cork I.T. University of Chicago Cork I.T. University of Utah Galway-Mayo I.T. University of Utah Galway-Mayo I.T. Washington University, Saint Louis Washington University, Saint Louis Funding from NSF/DOE/Smithsonian/PPARC/SFI/NSERC VERITAS: Very Energetic Radiation Imaging Telescope Array System First two 12 m telescopes of VERITAS now in operation at temporary site at Whipple Observatory Basecamp, December, 2005 Four telescopes in operation in 2006 Seven telescopes in 2008? The VERITAS Collaboration

Nu Vus of the Universe weekes 1 GeV100 GeV GLAST (2 Years) VERITAS-4 (3  in 50 hrs) Whipple 10 m (3  in 50 hrs) DiDi Differential Flux Sensitivity VERITAS, HESS and MAGIC will overlap and complement GLAST

Nu Vus of the Universe weekes HESS European Collaboration; M.P.I (Heidelberg) 4 x 12 m Telescopes Completed in Dec Located in NAMIBIA First of the Big 5 to come on-line Direction ~ arc-min Energy Resolution ~ 10% Background ~ 0

Nu Vus of the Universe weekes The TeV Sky H1426 Mrk501 1ES1959 1ES 2344 PKS 2155 Cas A RXJ 1713 CrabTeV 2032 M87 PKS 2005 PSR B1259 RXJ 0852 MSH SNR G0.9 HessJ1303 GC R.A.Ong Aug 2005 Pulsar Nebula SNR AGN Other, UNID H2356 1ES ES 1101 LS 5039 Vela X Cygnus Diffuse Diverse Categories of TeV Gamma-ray sources: AGN SNR (Plerion and Shell) Radio Galaxy Microquasar Galactic Plane Binary Extended Sources Dark Sources Galactic Center

Nu Vus of the Universe weekes Catalog of TeV AGN c NamezClassDiscovery Markarian HBL Whipple (Punch, 1992) Markarian HBL Whipple (Quinn, 1996) 1ES HBL Whipple (Catanese, 1998) 1ES HBL T. A. (Nishiyama, 2000) BL Lacertae 0.069LBL Crimea (Neshpor, 2001) PKS HBL H.E.S.S. (Aharonian, 2005) PKS HBL Durham (Chadwick, 1999) H HBL Whipple (Horan, 2002) H HBL H.E.S.S. (Aharonian 2005) BL HBL MAGIC (MAGIC 2005) BL HBL H.E.S.S. (Aharonian 2005) 3C66A * LBL Crimea (Neshpor, 1998)

Nu Vus of the Universe weekes Gamma-ray Meets IR-Photon  -ray IR-photon e + e - Absorption: exp(-  )Source: dN/dE ~ E -2 Spectrum at earth: E -2 exp(-  ) Extragalactic Background Light (EBL) causes spectral distortion due to  +   e + + e - Optical depth depends on integral over the EBL spectrum from the threshold for pair creation up to higher energies

Nu Vus of the Universe weekes EBL Detections & Limits From Dwek & Krennrich 2004, ApJ

Nu Vus of the Universe weekes HESS Survey: New Sources HESS J HESS J HESS ° RX J HESS J HESS J HESS J ° HESS J HESS J HESS J LS 5039 HESS J Gal. Center HESS J G HESS J HESS J HESS J ° 0° Sources > 6 sigma (9 new, 11 total) Sources > 4 sigma (7 new)

Nu Vus of the Universe weekes Microquasar: LS sigma detection by HESS Identification based on position Consistent with EGRET Source No time variability Hard spectum Microblazar?

Nu Vus of the Universe weekes Relativistic Jets and TeV Sources

Nu Vus of the Universe weekes Galactic Center Galactic Center Hard spectrum  = 2.2. No evidence for variability on a variety of time scales. Unlikely to be dark matter because of energy spectrum. HESS and MAGIC Spectrum Good agreement between HESS and MAGIC.

Nu Vus of the Universe weekes RX J (1) HESS Gamma: color ASCA X-ray: Lines Hard spectrum  ~ 2 Not a simple power-law. CANGAROO detection ~7 . Shell Supernova Remnant HESS confirmation ~ 40  Extended Bright Source Close Correlation with X-rays Spectrum Cosmic Ray Source?

Nu Vus of the Universe weekes RX J (2) CO Distributions: Target Material? Weak Radio Progenitors: Electrons or Protons “No decisive conclusions can yet be drawn regarding the parent population dominantly responsible for the gamma-ray emission from RX J ” Not the Smoking Gun!

GLAST: the Next Generation Gamma-ray Space Telescope: Future of GeV/TeV Gamma-ray Astronomy Also smaller version: AGILE (2006) Not clear what GeV space telescope might come after GLAST

Nu Vus of the Universe weekes Future of GeV/TeV Gamma-ray Astronomy (ground-based) HESS-2: Add 28m telescope: improved sensitivity at lower threshold (50 GeV) in coincidence mode (stereo) Fourth generation Observatories under discussion (>2010) e.g. HE-ASTRO proposed by Vladimir Vassiliev Third generation Observatories coming on-line (<2008) It is easy to extend/scale-up ground-based observatories

Nu Vus of the Universe weekesHE-ASTRO Because the size of the HE-ASTRO, ~1 km 2, is much larger than the size of the Cherenkov light pool, ~10 8 cm 2, the number of telescopes required is > 200 A Coupling distance: d=80m

Nu Vus of the Universe weekes Array of 217 telescopes Array of 217 telescopes Elevation 3.5km Elevation 3.5km Telescopes’ coupling distance 80m Telescopes’ coupling distance 80m Area ~1.0km 2 (~1.6km 2 ) Area ~1.0km 2 (~1.6km 2 ) Single Telescope Field of View ~15 o Single Telescope Field of View ~15 o FoV area ~177 deg 2 FoV area ~177 deg 2 Reflector Diameter ~7m Reflector Diameter ~7m Reflector Area ~40 m 2 Reflector Area ~40 m 2 QE 50% ( nm) QE 50% ( nm) Trigger sensor pixel size o Trigger sensor pixel size o Trigger Sensor Size ~31.2cm Trigger Sensor Size ~31.2cm NSB rate per Trigger pixel ~3.2 pe NSB rate per Trigger pixel ~3.2 pe per 20 ns Single Telescope NSB Trigger Rate 1KHz Single Telescope NSB Trigger Rate 1KHz Energy Range 20–200 GeV Energy Range 20–200 GeV Differential Detection Rate Peak Differential Detection Rate Peak ~30 GeV Single Telescope CR trigger rate Single Telescope CR trigger rate ~30 kHz HE-ASTRO (specifications) Image pixel size – o Image pixel size – o Readout image – 128 x 128 pixels Readout image – 128 x 128 pixels Readout Image size – Readout Image size – o x o NSB per pixel – (20 nsec gate) NSB per pixel – (20 nsec gate) ADC – 8 bit (S/N improved, ADC – 8 bit (S/N improved, 10– >8) Pixel dimension 12mm x 12mm Pixel dimension 12mm x 12mm Sensor area – 12.3 mm x 12.3 mm Sensor area – 12.3 mm x 12.3 mm Shutter exposure – a few msec Shutter exposure – a few msec Image integration time - 20 ns Image integration time - 20 ns Optical system TBD Optical system TBD Array trigger protocol TBD Array trigger protocol TBD Data Rates ~80 Mb/secper node Data Rates ~80 Mb/secper node Online data processing TBD Online data processing TBD TeV Astrophysics Workshop, Palaiseau, April, 2005 (Vassiliev) TeV Astrophysics Workshop, Palaiseau, April, 2005 (Vassiliev)

Nu Vus of the Universe weekes Science coming soon (from a TeV Source near you) Astronomy and Astrophysics > 300 sources Old: SNR, AGN, Microquasars, Binaries, Dark Sources New: Clusters, Starburst, Pulsars, Others Cosmological Questions EBL Measured Magnetic Fields Distant Transients detected Lorentz Invariance Origin of Cosmic Rays Sources (ACIT Observatories) UHE Sources Distribution (EAS Arrays) Galactic Plane Physics Dark Matter?? GRBs ?? Prompt: ( Arrays EAS) PBHs Delayed: (ACIT Observatories)

Summary (1): The TeV Sky (present) No Smoking Gun for Origin of the Cosmic Radiation …but Cosmic Particle Acceleration is Ubiquitous Diverse Categories of TeV Gamma-ray sources: AGN SNR (Plerions and Shell) Radio Galaxies Microquasar Galactic Plane Binary Extended Sources Dark Sources Galactic Center but no confirmed detections (yet!) of: Pulsars Clusters of Galaxies GRBs Starburst Galaxies UHE Sources

Summary (2): The TeV Sky (future) Within a few years there will be five major ground-based gamma-ray observatories using the ACIT in operation. The Next Generation of TeV Gamma-ray Observatories using the ACIT are now under discussion: (lower energy, wider fields, large collection area) Watch this space! These will be complemented by: Space Telescopes: AGILE, GLAST (lower E, wide field) Air Shower Arrays: Milagro, Tibet(high E, wide fields) Neutrino Telescopes: IceCube, KM3

Nu Vus of the Universe weekes Why study TeV Gamma-rays? Why are Elephants the most popular animals in the zoo? They are easy to see and they tell us much!

Nu Vus of the Universe weekes Cosmological studies of High Energy Transient Phenomena to determine: Redshift evolution of these objects Redshift evolution of these objects Population properties of AGN and GRBs Population properties of AGN and GRBs Redshift evolution of EBL (z=0-6) Redshift evolution of EBL (z=0-6) Major contributors to EBL (stars, dust, AGN, Population III objects, relic particles, SFR, GFR, IMF, BH accretion histories, supernovae feedback, merger history) Major contributors to EBL (stars, dust, AGN, Population III objects, relic particles, SFR, GFR, IMF, BH accretion histories, supernovae feedback, merger history) Cosmological magnetic fields and their evolution Cosmological magnetic fields and their evolution High energy properties of space-time High energy properties of space-time

Nu Vus of the Universe weekes