Jordan Goodman University of Maryland Erice July 2004

Air Shower Gamma Ray Detectors

Outline• Air Shower Physics

– Extensive Air Showers– Gamma/Hadron sep.

• Why use EAS Detectors• Detecting showers on the ground

– Water Cherenkov - Milagro– RPCs – ARGO

• Recent Milagro Results– Known Sources– New Detections

• Future Detectors - HAWC

Milagro

Jordan Goodman University of Maryland Erice July 2004

Extensive Air Shower Development

Jordan Goodman University of Maryland Erice July 2004

From Ralph Engel

Jordan Goodman University of Maryland Erice July 2004

Effect of Altitude

Low Energy Threshold Requires High Altitude

Milagro

ARGO

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Cascade Development

ARGO Milagro

1 TeV

10 TeV

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Shower Content

NgammasNelectrons

Primary Energy (GeV)

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Photon Shower 2 Gamma (movies by Miguel Morales)

Blue – Electrons Muons – Yellow Pions – Green Nucleons – Purple

Jordan Goodman University of Maryland Erice July 2004

Proton Shower 2 TeV (movies by Miguel Morales)

Blue – Electrons Muons – Yellow Pions – Green Nucleons – Purple

Jordan Goodman University of Maryland Erice July 2004

Techniques in TeV Astrophysics

Low energy thresholdGood background rejectionSmall field of viewLow duty cycleGood for sensitive studies of known point sources.

High energy thresholdModerate background rejectionLarge field of view (~2sr)High duty cycle (>90%)Good for all sky monitor and for investigation of transient and diffuse sources.

Pointed instruments

Non-pointed instruments

Jordan Goodman University of Maryland Erice July 2004

Why Use EAS Detectors

• Transient Sources– GRB’s

• Don’t know when

or where to look• Some indications

of 2nd hard comp.

– Variable Sources• Diffuse Sources

– Galactic Plane– New Sources

Jordan Goodman University of Maryland Erice July 2004

Cherenkov Radiation

Boat moves throughwater faster than wavespeed.

Bow wave (wake)

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Cherenkov Radiation

Aircraft moves throughair faster than speed ofsound.

Sonic boom

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Cherenkov Radiation

When a charged particle moves throughtransparent media fasterthan speed of light in thatmedia.

Cherenkov radiationCone oflight

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Cherenkov Radiation

Jordan Goodman University of Maryland Erice July 2004

Milagro

Air Shower Layer

Hadron/Muon layer

2m

8" PMTs

Light-tight Cover

8 m

80m50m

450 Top Layer 8” PMTs

273 Bottom Layer 8” PMTs

Jordan Goodman University of Maryland Erice July 2004

The Milagro Collaboration

D. Berley, E. Blaufuss, J.A. Goodman,* A. Smith , G. Sullivan, E. Hayes, D. Noyes

University of Maryland At College ParkShoup, and G.B. Yodh

University of California, IrvineD.G. Coyne, D.E. Dorfan, L.A. Kelley D.A. Williams S. Westerhoff, W. Benbow, J. McCullough, M. Morales

University of California, Santa CruzA.I. Mincer, and P. Nemethy, L. Fleysher, R. Fleysher

New York University

R.W. Ellsworth

George Mason UniversityG. Gisler, T. J. Haines, C.M. Hoffman*, F. Samuelson, C. Sinnis

B. Dingus, Los Alamos National LaboratoryJ. Ryan, R. Miller, A. Falcone

University of New HampshireJ. McEnery, R. Atkins

University of Wisconsin*Spokesmen Students

Jordan Goodman University of Maryland Erice July 2004

Milagro

Jordan Goodman University of Maryland Erice July 2004

Inside Milagro

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Milagro Site

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Milagro Outriggers

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Shower hitting the pond at an angle

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2 Tev Proton Shower hitting the pond

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2 Tev E/M Shower hitting the pond

Jordan Goodman University of Maryland Erice July 2004

Angle Reconstruction

For large showers, the angle can be reconstructed to better than 0.50o. (However, there are systematics associated with core

location)

Jordan Goodman University of Maryland Erice July 2004

Events

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Shower Curvature

Jordan Goodman University of Maryland Erice July 2004

Operations

• Milagro has been operating since 2000 at 2650m– 0.22 Trillion Events

• Outriggers were finished in 2003• We run with ~96% on-time• Data rate is ~ 1700 Hz

– 8-9% deadtime• We reconstruct in real-time

– We look for GRBs and send out alerts– Three months of raw data saved for archival

analysis• Data is sent via network to LANL & UMD• Nearly total remote capability

Jordan Goodman University of Maryland Erice July 2004

Milagro Energy Response (before/after new trigger)

1 TeV1 TeV

Ratio of response to new trigger

New Trigger installed March 2002 – removes muon triggers at large angles to allow triggering on lower energy showers

Jordan Goodman University of Maryland Erice July 2004

Milagro Sensitivity

Our energy threshold increases with the zenith angle.

Energy threshold is not well defined.Even though our peak sensitivity isat a few TeV, we have substantial sensitivity at lower energies.

GLAST

Milagro Effective Area

EGRET

Jordan Goodman University of Maryland Erice July 2004

P

Gamma – Hadron Separation

Jordan Goodman University of Maryland Erice July 2004

Gamma / Hadron Separation in Milagro

Gammas (MC)

Data

Proton (MC)

This cut removes 90% of the protons and keeps 50% of the gammas

Q is improvement of signal to root BG which equates to sigma

This gives a Q of ~1.5 (same signif in ½ the time)

Jordan Goodman University of Maryland Erice July 2004

Tibet – 4300m

• ARGO

Jordan Goodman University of Maryland Erice July 2004

Jordan Goodman University of Maryland Erice July 2004

ARGO Technique

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Limited Streamer Tubes

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ARGO Design

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ARGO Building

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Inside the ARGO Building

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ARGO Event

ARGO will be a very capable detector when completed in several years!

Jordan Goodman University of Maryland Erice July 2004

Recent Milagro Results

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Milagro Point Sources

Data taken in the Crab Nebula region with 6.4 at the position of the Crab (2000-2002)

Signal map of Mrk 421 during the 2001 flare (1/17/01-4/26/01). The circle shows the position of Mrk 421 with our angular bin. The center corresponds to ~5

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Milagro All Sky Survey

Crab Mrk 421

Hot Spot

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Effect of the Outriggers

This improved ang. resolution give us an increase in Q factor of ~1.7

This means we see the same signal ~ 3 times faster!

More improvement (~1.5 – 2 in Q) is expected with better /h separation

With outriggers

With outriggers

Before outriggers 0.75o

Before outriggers

Core Error

Jordan Goodman University of Maryland Erice July 2004

Effect of the Outriggers

12 months of recent data on the Crab

~3 times faster to get same signal

Another factor of ~1.5 - 2 is expected from /h sep

Andy/Tony will provide a new plot

Jordan Goodman University of Maryland Erice July 2004

EGRET Observation of the Galactic Plane

Note that their coordinates run opposite from ours…

•Black is EGRET Diffuse Flux > GeV

•Red is Milagro Exposure (TeV)

Cygnus region

Inner Galaxy

Outer Galaxy

Jordan Goodman University of Maryland Erice July 2004

Milagro Galactic Plane

5 excess for the “inner galaxy” - Flux fraction ~ 4 x 10-5 of CR

This is the first detection of the galactic plane at these energies (~TeV)

Cygnus regionPre

liminary

Jordan Goodman University of Maryland Erice July 2004

Milagro Galactic Plane

Cygnus region

Prelim

inary

Inner Galaxy

Outer Galaxy

Jordan Goodman University of Maryland Erice July 2004

Galactic Plane

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The Cygnus Region

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3EG_J0520+2556 – Milagro Hot Spot

Jordan Goodman University of Maryland Erice July 2004

3EG_J0520+2556 – Milagro Hot Spot

This source is now ~6 and appears to be ~0.8deg wide!

This will be hard for an ACT to see!

When we reported a 3 source - Whipple looked, but didn’t see it…

Jordan Goodman University of Maryland Erice July 2004

GRB970417a

● 18 signal events with an expected background of 3.46 -> Poisson prob. 2.9e-8 (5.2). Prob. after correcting for size of search area: 2.8e-5 (4). Chance prob. of this excess in any of the 54 GRB examined for TeV emission by Milagrito: 54x2.8e-5 = 1.5e-3 (3).

Evidence for a TeV signal from GRB970417 was seen by Milagrito (a smaller, single layer prototype of Milagro)

Jordan Goodman University of Maryland Erice July 2004

Luminosity of GRB970417a

More luminosity at TeV energies than MeV energies.But the GRB must be close due to TeV-IR absorption, so the total energy released is not unusually large.

If z~0.1 => E < 700 GeV so L < 5 x 1051 ergsIf z~0.03 => E < 10 TeV so L < 1 x 1049 ergs

Atkins, 2003, Ap J 583 824

Jordan Goodman University of Maryland Erice July 2004

GRB 941017 (pre-Milagro)

• M.M. González, B.L. Dingus, Y. Kaneko, R.D. Preece, C.D. Dermer and M.S. Briggs, Nature, 424, 749 (14 Aug 2003)

• This burst is the first observation of a distinct higher energy spectral component in a GRB

• Lower energy component decays faster than higher energy component

• Peak of higher energy component is above the energy range of the detector

• Power released in higher energy component is more than twice the lower energy component

-18 to 14 sec

14 to 47 sec

47 to 80 sec

80 to 113 sec

113 to 200 sec

Jordan Goodman University of Maryland Erice July 2004

Theories of the High Energy Component of GRB941017

• Requires GRBs to more energetic phenomena

• Different timescale of low and high energy implies an evolving source environment or different high energy particles

• Shape of high energy component applies tight constraints to ambient densities and magnetic fields

• Or evidence of origin of Ultra High Energy Cosmic Rays

• More and Higher Energy observations are needed

Pe’er & Waxman (astroph/0310836) constrain source parameters for Inverse Compton emission of GRB941017

Milagro Sensitivityz=0.2

z=0.02

Jordan Goodman University of Maryland Erice July 2004

Operations in the Swift era

Swift will be launched in September 2004

It will detect ~100-150 bursts per year with redshift information

Milagro observes ~ 1/6 the sky with some reasonable efficiency

Therefore we should expect ~20 GRBs per year in our FOV with redshift information

This will improve our sensitivity by ~ factor of 3

And allow us to put limits on bursts we don’t detect

Note: EGRET saw 6 bursts in 9 years!

Jordan Goodman University of Maryland Erice July 2004

Milagro Summary

• Running well with outriggers• Q factor is improving steadily• Improved sensitivity to GRBs• Two recent “discoveries”

– The galactic plane + Cygnus Region– A new diffuse source in the crab region

• More to come– Spectral information, etc.

Jordan Goodman University of Maryland Erice July 2004

HAWC – The Next Generation

Jordan Goodman University of Maryland Erice July 2004

HAWC Requirements

• Low Energy Threshold < 50 GeV• GRBs visible to redshift ~1• Near known GRB energy• AGN to redshift ~0.3

• Large fov (~2 sr) / High duty cycle (~100%)• GRBs prompt emission• AGN transients• Time domain astrophysics

• Large Area / Good Background Rejection– High signal rate– Ability to detect Crab Nebula in single transit

• Moderate Energy Resolution (~40%)– Measure GRB spectra (inter-pulse spectra)– Measure AGN flaring spectra

Jordan Goodman University of Maryland Erice July 2004

Effect of Altitude

Low Energy Threshold Requires High Altitude

Jordan Goodman University of Maryland Erice July 2004

HAWC Strawman Design

• 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)– ~10,000 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

Jordan Goodman University of Maryland Erice July 2004Reconstructed events

Jordan Goodman University of Maryland Erice July 2004

Effect of EBL on Distant Sources

z = 0.03z = 0.1z = 0.2

z = 0.3

z = 0.0

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Energy Distribution After EBL

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Point Source Sensitivity

Jordan Goodman University of Maryland Erice July 2004

Gam

mas

Pro

tons

Background Rejection: Bottom Layer

30 GeV 70 GeV 230 GeV

20 GeV 70 GeV 270 GeV

Jordan Goodman University of Maryland Erice July 2004

HAWC Conclusions

• A large area, high altitude all sky VHE detector will:– Detect the Crab in a single transit– Detect AGN to z = 0.3– Observe 15 minute flaring from AGN– Detect GRB emission at ~50 GeV / redshift ~1– Detect 6-10 GRBs/year (EGRET 6 in 9 years)– Monitor GLAST sources– Perform Time Domain Astrophysics in VHE Regime

• Extreme States of Extreme Systems• Continuing work

– Improve background rejection & event reconstruction• Increase sensitivity by ~50% - 100%? • Develop energy estimator

– Detailed detector design (electronics, DAQ, trigger, infrastructure)– Reliable cost estimate needed (~$30M???)– Site selection (Chile, Tibet, White Mountain)

• Time Line– 2004 R&D proposal to NSF & DOE (LANL & UNM)– 2006 full proposal to NSF & DOE– 2007-2010 construction

Jordan Goodman University of Maryland Erice July 2004

Conclusions on Air Shower Detectors

• They are complimentary to ACTs• Their features of wide field of view and continuous

observation gives them the ability to:– Observe transient sources– Observe diffuse objects– Discover new objects