October 21, 2005UCLA Gamma Ray Workshop

Wide Field of View surveying in Next Generation GeV/TeV

Observatories

D. KiedaUniversity of Utah

October 21, 2005UCLA Gamma Ray Workshop

Milagro Cygnus Arm Detection

R. Atkins et al, 22nd Texas Symposium on Astrophysics, Stanford (2004)

•Significance is 5.5 (Crab is 5.9)•Source extent is ~5o

•Implied source flux is several Crab

October 21, 2005UCLA Gamma Ray Workshop

Whipple Follow-up

● No Strong point source evident (given # of trials)●Typical point source flux limit~300 mCrab ● Quoted for E > 400 GeV , angular resolution ~ 0.05o.●Milagro source diameter >> f.o.v. of Whipple camera

G. Walker, Ph.D Thesis, U of Utah (2004)

October 21, 2005UCLA Gamma Ray Workshop

Source Detectability

source resolution

Source Size < Angular resolution

= Point Sources: CrabAGNM87

KA

A

FF

TA

A

FF

TNS

peff

eff

resolutioncrpeff

eff

resolutioncr

141

),,,,,( crresolutionpeffeff FAATKfF

constant

October 21, 2005UCLA Gamma Ray Workshop

Source Detectability

source resolution

'14

1 KA

AFF

TA

AFF

TNS

peff

eff

sourcecrpeff

eff

sourcecr

Source Size > Angular Resolution

= Diffuse Sources: SNRTibet-Milagro UIDMolecular Cloud

sourceF

n.b. if Source has internal structure you will do better 1;' KNS

October 21, 2005UCLA Gamma Ray Workshop

HESS Diffuse Sources

Many sources appear to have internal structure:

Ability to resolve a diffuse source is a key to determining its astrophysical processes

(HESS , 2005)

October 21, 2005UCLA Gamma Ray Workshop

Source Resolvability

source resolution

Source Size > Angular Resolution

Just need some factor >1 more S/Nto resolve internal source structure

KA

AFF

TA

AFF

TNS

peff

eff

sourcecrpeff

eff

sourcecr

14

1

sourceF

October 21, 2005UCLA Gamma Ray Workshop

Source Resolvability

resolution

Source Size < Angular resolution

As F increases, tails of Gaussian become detectable->resolve source size

resolutiond

source resolution

F

K

22

2

2121

source

resolution

r

sourcepeff

effeff

sourcecr

erdrA

A

FF

TK

2

2

2)( source

resolution

eKgF source

October 21, 2005UCLA Gamma Ray Workshop

Source Detect/Resolve

Detected(both)

DetectedMilagro only

Whipple

Increased Milagro sensitivityfor extended source

•longer exposure•Wider fov

Excellent Point Source sensitivity of IACT does not help here

Note that this plot neglects energy threshold benefits of IACTs

X

October 21, 2005UCLA Gamma Ray Workshop

Newer Arrays

Extended Sources:Molecular cloudsSNRPoint Sources:AGNPulsar

Diffuse Sources:Galactic PlaneGalactic Arm

Next Gen is 1 km2 IACT, 5 deg f.o.v, 1 mCrab/50 hours

October 21, 2005UCLA Gamma Ray Workshop

Larger SourcesImaging Source diameters > IACT f.o.v requires multiple pointing

4 pointings: 200 hours: about the most one can do per year

Larger areas require reduced time/pointing, thereby reducing sensitivity

Intersect at(Fx, x)

HF0NF0

October 21, 2005UCLA Gamma Ray Workshop

Larger Sources vs. Wider f.o.v IACTs

NfovH

resolution

Nresolution

N

H

x FF

0

0

NfovN

Nresolution

Hresolution

H

x FFF

0

2

0

H=HawkN=Next Gen

Typical

Nfovx 5.2

Nfovx millCrabF )/(125

October 21, 2005UCLA Gamma Ray Workshop

Source sensitivity depends on source diameter

If Cyg Arm is truly diffuse source, it is barely accessible to current IACTNext Gen area 100 x HAWC can compensate for 10% on-time efficiency

Next Gen ( 1 km2) IACT superior forNext Gen needs fov > 100 in order to resolve 250 diffuse sources Next Gen better for resolving sources, point sources, looking deeperHAWC-type better for large diffuse sources (ignoring energy threshold differences)

Summary

fovsource 5.2

October 21, 2005UCLA Gamma Ray Workshop

HAWC All-sky: Monitor + large scale structureLarge IACT Next Gen looks deep, low E (followup), spectral/time evolutionLimited energy range above 10 TeV-200 TeV: probe with km2 array of small (1 m class) dedicated imagers

Strategy

Study/design phase: Next year?Pursue Modular design:

• quick test/low cost•allow deploy/test subsystem at high altitude?•Site testing?•Easy final deployment, cheaper fabrication/maintenence