Synoptic VHE Gamma-Ray Telescopes

Gus SinnisPRC-US Workshop, Beijing June 2006

Synoptic VHE Gamma-Ray Telescopes

Gus Sinnis

Los Alamos National Laboratory


Outline

• Physics reach of gamma-ray astrophysics

• Description of current instruments

• New results from Milagro

• Sketch of future plans


Vela Jr.TeV &x-ray

HESS TeV image of Supernova Remnant

High Energy Particle AstrophysicsWhat do we know?• Nature accelerates

particles to >1020 eV• Gamma-ray sources

accelerate particles to >1014 eV– Galactic sources

• Pulsar winds• Supernova Remnants• Stellar Mass Black Holes

– Extragalactic sources• Supermassive Black

Holes in active galactic nuclei

HST Image of M87 (1994)

Black Hole producing relativistic jet

Pulsar powering a relativistic wind

Crab nebula x-ray


What Do We Want to Learn?• What are the origins of cosmic rays?

– Are the accelerators of hadrons different from electrons?– How high in energy can galactic sources produce particles?– What are the sources of the UHECRs?

• How do astrophysical sources accelerate particles?– What is the role of the extreme gravitational an magnetic

fields surrounding black holes and neutron stars?– How are particles accelerated within relativistic jets?

• Fundamental physics & cosmology– What is the EBL and how did it evolve?– What is the dark matter?– What are the tightest constraints on Lorentz invariance?– Are there primordial black holes?


What Measurements Required?

• Measure -ray flux due to cosmic-ray interactions• Observe multiple -ray sources of different classes of

astrophysical sources• Detect hadronic vs. leptonic signatures in energy spectra • Determine the highest energy particles accelerated in

different types of sources• Observe rapid variability to probe the closest regions to

the black hole in active galactic nuclei• Compare -ray images with images at other wavelengths


What Tools Do We Use?• Auger and HiRes measure the

highest energy cosmic ray flux, spectrum, and anisotropy

• ICECube searches for TeV neutrino sources – the most direct signature of hadronic accelerators

• GLAST will detect thousands of new GeV sources

• VERITAS, HESS, MAGIC, and CANGAROO image and measure spectra and variability of TeV sources

• Milagro, As, and ARGO image large-scale structures and searches for new and transient TeV sources


Active Galactic Nuclei ~108 Msun black hole Relativistic particle jets 1048 ergs/sec TeV emission is along jet Highly variable Open questions

– what is being accelerated?– how large is the bulk Lorentz factor

of shock?– B-field in shock?

Need multi-wavelength observations

– many objects– many flares– long-term monitoring


AGN Modeling

Relative sizes oflow and high energypeaks changes withjet axis orientation withrespect to us

Low energy peak dueto synchrotron.

High energy peak due to inverse Compton scattering of synchrotron photons (SSC) or external (ECR) sources (disk, clouds)AND/OR proton interactions with thesephotons


Gamma Ray Bursts• Most energetic objects in

universe ~1051 ergs• Rapid Variability• Unpredictable Direction• ~ 1 /day/ 4 sr


High Energy Component in GRBsCombined EGRET-BATSE observation shows a new high energy component with hard spectrum and more fluence. (Gonzalez, 2003 Nature 424, 749)

The highest energy gamma-ray detected by EGRET from a GRB was ~20 GeV and was over an hour late. (Hurley, 1994 Nature 372, 652)

Milagrito’s > 650 GeV observation implies a new mechanism with greater fluence than synchrotron. (Atkins, 2003, Ap J 583 824)

GRB940217

GRB970417

GRB941017


Gamma Ray Bursts ModelsCentral Engine:

hypernovaeneutron star - neutron star mergerblack hole - neutron star mergers

Emission Spectra:fireball - internal or external shocks convert energy into electromagnetic radiation.


Detectors in Gamma-Ray Astrophysics

High SensitivityHESS, MAGIC, CANGAROO, VERITAS

Large Aperture/High Duty CycleMilagro, Tibet, ARGO, miniHAWC, HAWC?

Low Energy ThresholdEGRET/GLAST

Large Effective Area

Good Background Rejection (~95%)

Excellent Angular Resolution (~0.07o)

Low Duty Cycle/Small Aperture

High Resolution Energy Spectra

Studies of known sources

Surveys of limited regions of sky

Space-based (small area)

“Background Free”

Good angular resolution (~0.4o)

Large Duty Cycle/Large Aperture

Sky Survey (<10 GeV)

AGN Physics

Transients (GRBs) <100 GeV

Moderate Area/Large Area (HAWC)

Good Background Rejection (~95%)

Good Angular Resolution (~0.5o)

Large Duty Cycle/Large Aperture

Unbiased Sky Survey (~1 TeV)

Extended sources

Transients (AGN, GRB’s)

Solar physics/space weather


First Generation EAS ArraysT

ibet

III

Mila

gro


Milagro

• 2600m asl• Water Cherenkov Detector• 898 detectors

– 450(t)/273(b) in pond– 175 water tanks

• 3.4x104 m2 (phys. area)• 1700 Hz trigger rate• 0.5o resolution• 95% proton rejection

10 m


Milagro Detector

175 Outrigger tanks (Tyvek lined – water filled)2.4m diameter, 1m deep1 PMT looking down


Event Reconstructione

Tim

e Pond only

w/outriggersMilagro PSF

Degrees


• Cosmic-ray induced air showers contain penetrating ’s & hadrons– Cosmic-ray showers lead to

clumpier bottom layer hit distributions

– Gamma-ray showers gives smoother hit distribution

Background Rejection in MilagroProton MC Proton MC

Data Data MC MC


Background Rejection (Cont’d)

• Parameterize “clumpiness” of the bottom layer hits– Compactness ( nb2/mxPE > 2.5)

• 50% gammas & 10% hadrons• Sensitivity improved by 1.6

– A4 ((nOut+nTop)*nFit/mxPE > 1600)• 20% gammas & 1% hadrons• Sensitivity further improved by 1.4

mxPE: maximum # PEs in bottom layer PMT

nb2: # bottom layer PMTs with 2 PEs or more

nTop: # hit PMTs in Top layer

nOut: # hit PMTs in Outriggers

nFit: # PMTs used in the angle reconstruction


Spectral Determination

A4 is related to energy2-20 TeV useful range

S/N increases with A4

No loss of statistical accuracy!

Sensitivity

improvement


Sky Survey (Milagro today)Crab Nebula ~14

Galactic Ridge clearly visible

Cygnus Region discovery ~12

Prelim

inary


Diffuse Emission from the Galactic Plane

EGRET data

• Diffuse emission from the Galaxy is due to– Proton matter interactions (

component)– Inverse Compton scattering of

high-energy electrons from CMB, IR, optical photons (ISRF)

• EGRET observations to 20 GeV– Indicate a GeV excess– Stronger IC component?– Unresolved point sources– Dark matter?

• Higher energy observations critical for understanding GeV excess


The Galactic Plane a TeV energies

Sig

nific

ance


Galactic Plane Analysis

• Strong & Moskalenko optimized model– Fit to EGRET– Increase 0 (2x) and IC

(5x) component throughout Galaxy

• TeV flux can not be fit with a pure component

• Requires large inverse Compton component

• Work in progress

EGRET

From A. Strong

Milagro


The Cygnus Region

• Complex region of Galaxy

• But simpler than Galactic Center

• 9 SNRs• >20 Wolf-Rayet stars• 6 OB associations• Shocked gas• Excellent Cosmic Ray

Laboratory

Canadian Galactic Plane Survey - Far IR


Cygnus Region Morphology

Contours are EGRET diffuse model

Crosses are EGRET sources TeV/matter correlation good Brightest TeV Region

– Coincident with 2 EGRET sources (unidentified)

– Possible Pulsar wind nebula (similar to Crab)

– Possible blazar (unlikely TeV counterpart)

– TeV extended ~0.35 degrees Diffuse region Energy Analysis in progress

Prelim

inary


Diffuse Emission from Cygnus Region

• Strong & Moskalenko optimized model– Fit to EGRET– Increase 0 and IC

component throughout Galaxy

– Milagro ~2x above prediction

– Unresolved sources?– Proton accelerators?

Milagro

preliminary


Solar Physics

Coronal mass ejections are an ideal laboratory to study particle acceleration in the cosmos

By monitoring the singles rates in all PMTs we are sensitive to “low”-energy particles (>10 GeV)

Milagro has detected 4 events from the Sun with >10 GeV particles


X7-Class flare Jan. 20, 2005

GOES proton data– >10 MeV– >50 MeV– >100 MeV

Milagro scaler data– > 10 GeV protons– ~1 min rise-time– ~5 min duration

1.45E+07

1.47E+07

1.49E+07

1.51E+07

1.53E+07

1.55E+07

1.57E+07

1.59E+07

1.61E+07

1.63E+07

1.65E+07

45.0 47.0 49.0 51.0 53.0 55.0 57.0 59.0 61.0 63.0 65.0

Minutes after 18:00 UT

Counts/Sec in Muon layer


Future Instruments: ARGO-YBJ


Farther Future: miniHAWC Build pond at extreme altitude (Tibet 4300m, Bolivia 5200m, Mexico 4030m) Incorporate new design

– Optical isolation between PMTs– Larger PMT spacing– Deeper PMT depth (in top layer)

Reuse Milagro PMTs and electronics

e

150 meters

4 meters

~$4-5M for complete detector~10-15x sensitivity of Milagro

Crab Nebula in 1 day (4 hours) [Milagro 3-4 months]GRBs to z < 0.8 (now 0.4)


Farther Future: HAWC Build pond at extreme altitude (Tibet 4300m, Bolivia 5200m, Mexico 4030m) Incorporate new design

– Optical isolation between PMTs– Much larger area (90,000 m2)– Two layer design (2 m and 6 m below water surface)

Advanced electronics and DAQ (~200MBytes/sec)

~$40-50M for complete detector~60x sensitivity of Milagro

Crab Nebula in 30 minutes [Milagro 3-4 months]GRBs to z >1 (now 0.4)

e

300 meters

6 meters


Effective Areas: Future Detectors


Detector Sensitivity (Single Location)

miniHAWCHAWC

GLAST

EGRET

Crab Nebula

WhippleVERITAS/HESS

Current synoptic instruments


Survey Sensitivity

4 m

in/fo

v

7 m

in/fo

v1500 hrs/fov1500 hrs/fov


Conclusions EAS arrays have achieved sufficient sensitivity to detect known

TeV sources and discover new sources! All-sky view has lead to significant discoveries

– Diffuse g-ray emission from the Galactic plane – Diffuse emission from Cygnus region– Extended source coincident with 2 EGRET unidentified

objects• Some evidence for VHE emission from GRBs

– Constraints now VHE fluence < ~keV fluence Solar physics results study particle acceleration in well known

environment We are still understanding the performance of EAS arrays

– Significant improvement possible for low cost– miniHAWC <$5M ~10x Milagro sensitivity– HAWC ~$50M ~60x Milagro sensitivity



HAWC: Simulated Sky Map

C&G AGN

Hartmann IR model

known TeV sources

Milagro extended sources

1-year observation


Low energy threshold (300 GeV)Excellent angular resolution (0.07o)Good background rejection (95%)Small field of view (2 msr)Small duty cycle (< 10 %)

Moderate energy threshold (1 TeV)Good angular resolution (0.5o)Good background rejection (95%)Large field of view (~2 sr)High duty cycle (>90%)

Detecting TeV Gamma RaysAir Cherenkov Telescope Extensive Air Shower Array

100 GeV gamma ray 1 TeV gamma ray

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Synoptic VHE Gamma-Ray Telescopes