# Presentation: 116053

## Resolving Shocks Around Galaxy Clusters with GLAST

- Avi Loeb, Harvard University

**Collaborators:** ***Eli Waxman, Uri Keshet***

## Structure Formation in the IGM

- Density contrast of gas shocked between z=0.14-0.09

- Density contrast of gas at z=0 for a 100x100x10 Mpc^3 slice

## Collisionless Intergalactic Shocks

- For a shock compression factor

- For strong shocks:

- Examples: SN 1006, SN RX J1713.7-3946
- E_max= 100 TeV (from X-ray and TeV observations)
- v_sh ~ 1000-2000 km/s
- Energy fraction in relativistic electrons:

## IGM Acceleration Parameters

- Larmor radius =

- the magnetic field could have a short coherence length.
- The acceleration e-folding time:

- Cooling time:

- Maximum Lorentz factor:

- Scattered CMB:

## Spectrum of Scattered Radiation

- In young X-ray clusters:

- But note that if r~2 instead of 4:

- 10-15%

- infall

- virialization shock

- cluster

## Gamma-Ray Background

- Loeb & Waxman, Nature, 405, 156, 2000

- T=1 keV
- strong shocks

- T=0.3 keV
- strong +weak      shocks

- Simulations

## Cosmic Background Radiation

- Gamma-ray background

## EGRET All Sky Map (>100 MeV)

## Cosmological Simulations

- Motivation:

- Springel & Hernquist (2000)

## γ-ray images

- >100 MeV

- Δθ=42’

- Keshet et al. (2003)

## Gamma-Ray Clusters

- EGRET

- Flux Above 1 GeV From  a Simulated 16x16 degrees^2 Field

- GLAST

- Keshet et al. 2001

## Number Counts at 100 MeV From Simulations

- Keshet et al. (2002)

## Radio Clusters

- Feretti et al. 2001

- A2163

## Radio Surface Brightness

- Govoni et al. 2001

## Diffuse radio sources

- calibrated model

- Best fit

- Best fit:

- Keshet, Waxman & Loeb (2004b)

- Radio halos: association with structure formation

## Predicted Anisotropies

- Waxman & Loeb, ApJL,545, L11 (2000)

- Press-Schechter+self-similar accretion onto X-ray clusters

## Ultraluminous Infrared Galaxies (ULIRGs): Factories of High-Energy Neutrinos

- ULIRGs discovered by IRAS in mid 80’s
- LFIR > 1012 L >> Loptical (dusty)
- Disturbed Morphologies: Mergers
- Powered by nuclear starbursts** **&/or obscured AGN (much debated)
- Key phase in growth of elliptical    galaxies and massive black holes

**“****Accelerator Beam Dump” for collisionless shocks in galaxies**

## Physical Conditions:  Arp 220

- Condon et al. 1991

- Radio Emission; FIR-Radio
- Correlation + Radio SN 
- ~ 100 pc scale starbursts
-  with ~ 100 M/yr

- Smith, Lonsdale, Diamond

- Individual Radio SN detected w/ VLBI

**1” = 350 pc**

- The collisionless shocks of SNe are likely to inject relativistic electrons and protons (cosmic-rays) into their dense gaseous environment

## Fate of Injected Cosmic-Rays

- The energy loss time of a relativistic proton
- The starburst lifetime (a few dynamical times)
- SN injected protons will dissipate all their energy if

***Matches the minimum  surface density of starburst galaxies***!

## Synchrotron cooling time of e- is much shorter than e- escape time (Thompson et al. 2006).
Proton-nucleon loss time is much shorter than cosmic-ray proton escape time

*Proton*-nucleon loss time is much shorter than cosmic-ray *proton* escape time

- Injection of relativistic *e- & p+*

***Cosmic-ray production rate can be calculated from synchrotron luminosity of relativistic electrons***

## Starburst Contribution to the Gamma-Ray Background

- Thompson, Quataert, & Waxman 2006

## Cosmic Background of High-Energy Neutrinos

- Loeb & Waxman, astro-ph/0601695

***AMANDA, ANTARES, NESTOR***

***IceCube, ******NEMO, ANITA***

##    The predicted neutrino background at                            
   is                                              implying a detection rate of                                          in a terrestrial detector like IceCube

-    is                                              implying a detection rate of                                          in a terrestrial detector like IceCube

- neutrinomuon in Antarctica iceCerenkov lightoptical sensors

## Conclusions

- Collisionless IGM shocks accelerate electrons and protons to relativistic energies.
- The gamma-ray (IC) and radio (synchrotron) emission by the accelerated electrons could be a substantial fraction of the fluctuations in the low-frequency (<10 GHz) and gamma-ray backgrounds.
***X-ray clusters*** are ***radio**** *and* ****gamma-ray clusters**** *as well
- Starburst galaxies are efficient factories of high-energy gamma-rays and neutrinos.

## Slide 25

## The radio sky

***The radio sky***

- CMB

- Galactic

- synchrotron

- IGM shocks

- Keshet, Waxman & Loeb (2004b)

- total

- _ERB estimates_

- ν [MHz]

- IGM: significant fraction of ERB

## Fluctuations for l=400⇔θ=00.5

**Fluctuations for ****l=400⇔θ=0****0****.5**

- CMB

**Bremsstrahlung from Ly****α clouds**

**IGM   shocks**

**Galactic synchrotron ****∝l****-**1/2

**discrete      sources ****∝l**

- Keshet, Waxman & Loeb (2004b)

- 1’-00.5: IGM fluctuations dominate

**~ const   ****for 400<****l****<4000**

**21**** ****cm tomography**

**LOFAR**

## Future radio telescopes

- LOFAR

- Northern Netherlands shore

- SKA

## Physical Conditions:  Arp 220

- HST Nicmos Image

- Sakamoto et al. 1999

- LFIR ~ 1012 L
- Double Nuclei ~ 350 pc apart
- 2 ~ 100 pc scale disks with ~ 109 M gas
-                (+ circumbinary disk)
- gas ~ 10 g/cm2 ~ 4000 MW
-              (optically thick to FIR)
- <n> ~ 104 cm-3 vs. <n>MW ~ 1 cm-3

## Surface Densities

- Thompson et al. **astro-ph/0601626**

- actual B

- minimizing energy-B

## Synchrotron  Emission by Secondary

- GeV          emit at a synchrotron frequency of ~1GHz (B/0.1mG)
- and cool faster than the starburst lifetime (Thompson et al. 2006)

- The local 1.4GHz energy production rate per unit volume in starbursts

- implies

## Cumulative Synchrotron Luminosity Density

***Yun, Reddy, & Condon 2001***

## Extrapolation to Neutrino Energies >>GeV

- In analogy with the Milky-Way power-law distribution of protons

- where s=0.5-0.6 characterises the confinement time

- If starbursts are characterized by the MW injection index then

- up to the “knee” at ~0.1PeV or higher

*An injection index of -2 is expected for Fermi acceleration in strong shocks*

## UHECRs

- Present-day energy production rate of relativistic protons in starburst galaxies
-    is comparable to the energy production rate of ultra high-energy cosmic-rays, potentially because the former applies to
-     and the latter to                           ,    with the two matching at

## Radio signal

- Model & simulation agree well

- Keshet, Waxman & Loeb (2004b)

## EGRB: lower than previously thought

***EGRB: lower than previously thought***

- Keshet, Waxman & Loeb (2004a)

**EGRB upper limit: 1/3 of previous estimate**

## Previous EGRB estimates

- Keshet, Waxman & Loeb (2004a)

- Previous estimates problematic

## Shock Identification

**Efficient shock extraction from SPH**

- Keshet et al. (2003)

## Detecting γ-ray signal

- F[ph s-1 cm-2]

- N(>F)

- Keshet et al. (2003); Keshet, Waxman & Loeb (2004b)

- Dozen GLAST sources for ξe=3%

- IC

- Waxman & Loeb 2000

- θ/fr

- 10-1

- 100

- 10-1

- Detecting γ-ray signal

- 100

- fr<δ2Iν(θ)>1/2/<Iν>

## Slide 40

## Inverse-Compton spectrum

- Keshet et al. (2003)

**Simulation and model agree! **

- simulation

- J ∝ ξe

## Radio signal: fr ?

## Conclusions

**Quantitative predictions for emission from IGM shocks, testable in the next few years**

## Galactic LF radio sky

- Keshet, Waxman & Loeb (2004b)

## Slide 45

## Gamma Ray Large Area Space Telescope

**20 MeV to 300 GeV**
**Wide-field imaging telescope**
**NASA cost is $326 M**
**http://glast.gsfc.nasa.gov/**

**Theme:****  ****Exploring Sites of Particle**
**Acceleration in the Universe**

## Mission Parameters

- Energy Range
- Energy Resolution (E/E)
- Effective Area (peak)
- Field of View
- Angular Resolution
- Sensitivity (> 100 MeV)*
- Mass
- Lifetime
- * 2 year survey at high latitudes

- EGRET
- 20 MeV - 30 GeV
- 0.1
- 1500 cm2
- 0.5 sr
- 5.8° @ 100 MeV
- 0.5° @ 10 GeV
- ~ 10-7 cm-2 s-1
- 1810 kg
- 1991 - 1997

- AGILE
- 30 MeV - 50 GeV
- 1
- 700 cm2
- ~ 3 sr
- 4.7° @ 00 MeV
- 0.2° @ 10 GeV
- 5  10-8 cm-2 s-1
- 60 kg
- 2002 - 2005

- GLAST
- 20 MeV - > 300 GeV
- 0.1
- 12000 cm2
- 2.5 sr
- ~ 3.5° @ 100 MeV
- ~ 0.1° @ 10 GeV
- ~ 2  10-9 cm-2 s-1
- 3000 kg
- 2005 - 2010

## Number of Extended Sources

## Results Based on a Numerical Simulation of Structure Formation in the IGM 

- Uri Keshet, Waxman, Loeb, Springel, & Hernquist 2002