Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO...
Transcript of Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO...
![Page 1: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/1.jpg)
Diffuse Gamma ray emission
P. SreekumarISRO Satellite CentreBangalore
![Page 2: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/2.jpg)
3C 279Vela Pulsar
Geminga
Crab
The Gamma Ray Universe - as seen by EGRET
Galactic plane
Galactic Center
![Page 3: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/3.jpg)
The gamma-ray sky - FERMI
Galactic plane
![Page 4: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/4.jpg)
1) Neutral pion decay from cosmicray nucleons interacting with nucleons in the interstellar gas
2) bremsstrahlung by cosmicray electrons,
3) Inverse Compton interaction of cosmicray electrons with ambient low energy interstellar photons.
Diffuse γ -rays
Production processes :
02/18/10
![Page 5: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/5.jpg)
03/23/09 5
Neutral pion Decay
03/23/09
Interaction between nuclei produces pions of all charge.
Neutral pions decay to gamma-ray:
p+p → π °
π ° → 2γ
![Page 6: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/6.jpg)
03/23/09 6
π 0 decay
Primary nucleon spectrum γ distribution from π o decay
![Page 7: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/7.jpg)
Electron Bremmstrahlung
• Use crosssections of Koch & Motz (1959)• Assume ISM=mostly H; 10% He; 1% heavy nuclei
qem(E) = 4.7E25 K(r) Ee−α / ( α −1)
α = index of electron spectrumK(r) = normalisation for electron spectrum
![Page 8: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/8.jpg)
Inverse Compton• CR electrons upscatter soft photons
(CMB, FIR, NIR, optical, & UV)
photon distribution (adapted from Chi & Wolfendale 1991)which used stellar model of Mathis, Mezger & Panagla (1983)
<Eγ > = 4/3 { Ee/Mc2 } <ei>
A 100 MeV γ ray arises from inv. Compton interaction between an electron of 1 300 GeV and a lowenergy photon.
electron E photon E
![Page 9: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/9.jpg)
Galactic diffuse emission
• CR + matter• CR + starlight
– Address distribution of matter in the Galaxy– Address distribution of starlight– Model CR distribution– Consistency check with gammaray distribution
Derive distribution of cosmic rays
![Page 10: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/10.jpg)
Interstellar medium constituents
• 99% is gas– 90% is hydrogen
• Atomic• Molecular• Ionised
– 10% helium
At visible wavelengths, dust plays a more important role than gas but not so at gammaray energies
![Page 11: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/11.jpg)
Tracing atomic hydrogen
• 21 cm line emission – hyperfine transition (1.4 GHz) – not blocked by dust !!
ground state
excited state
100 – 3000 K gas~ 3 billion solar mass of H in Galaxy
![Page 12: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/12.jpg)
Tracing molecular hydrogen
• Cannot directly trace molecular H2 in its cold phase - no permitted rotational transitions
• CO – most abundant heteronuclear molecule is used as a tracer of H2
• 2.6 mm line of the rotational transition J = 1 0 of CO• Brightness temperature of CO, integrated over velocity, WCO
approximately scales with total emitting gas in a given region.
XCO = N(H2) / WCO
Q : Is XCO uniform across the Galaxy?
![Page 13: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/13.jpg)
Distributing matter in space ….
![Page 14: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/14.jpg)
Structure of the Milky Way
A typical spiral
![Page 15: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/15.jpg)
Rotation curve
![Page 16: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/16.jpg)
Position in the Galaxy … Line-of-sight velocity distribution
41,3
2
50 0 + 50 + 100
4
3
2
1
sun
inte
nsity
Doppler shift (km/s)
GC
8.5
kpc
velocities are positive
velocities are negative
![Page 17: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/17.jpg)
Galactic rotation curve
Sun, v= 220 km/sDistance = 8.5 kpc
Keplerian rotation curveV = 1/ √ √ r
observed rotation curve
![Page 18: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/18.jpg)
H1 survey : LeidenDwingeloo 25 m radio survey in 21 cm
![Page 19: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/19.jpg)
Giant Molecular Clouds
~105 solar mass; cold ; mostly confined to the Galactic plane
![Page 20: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/20.jpg)
![Page 21: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/21.jpg)
(from Dame et al (CfA preprint 3952)
Radial profile of Atomic and Molecular Hydrogen
![Page 22: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/22.jpg)
Approach to diffuse emission analysis
• Ring-velocity boundaries are defined / adjusted for each line of sight to optimise ‘structures’ in the (l,b,v) phase space.
• NH1 and WCO are then calculated for each region
![Page 23: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/23.jpg)
Cosmic rays
• Cosmic rays – Composition– Spectrum– Origin and acceleration
Composition
• 98% protons• rest are electrons, alphas,• heavier particles • (includes anti-particles)
![Page 24: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/24.jpg)
CR spectrum
dN/dE = a E −γ
![Page 25: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/25.jpg)
Supernova remnant : site for CR acceleration
Cas A Crab
Solar flare
![Page 26: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/26.jpg)
Origin & Acceleration
• SNR as sites for CR origin and acceleration
• Shock acceleration (SNR / ISM shocks)
SNR ush
D(p)
shock
pdtdp sh
3u∇−=avg. gain in
momentum
Emax ~ 1014 Z eV in the Bohm limit
Maxwell – Boltzmann distribution∆ E/E α v/c
1st order Fermi acceleration
![Page 27: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/27.jpg)
Cosmic ray models
• Many radially symmetric models models– SN distribution (Case & Bhattacharya 1998)
– Pulsar distribution (Strong et al 2004) in GALPROP code
![Page 28: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/28.jpg)
Cosmic ray models (contd)
• radially asymmetric models – not based on multiparameter fits
– Based on density distribution of matter itself – equipartition arguments
– Hunter et al (1997) – with EGRET data
– Need to examine the role for such models using FERMI results
A possible way to derive more realistic distribution of Cosmic rays in the Galaxy
![Page 29: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/29.jpg)
Observed γ -ray emission
+ point sources
![Page 30: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/30.jpg)
03/23/09
Components of galactic diffuse emission
π 0 decay
electron bremsstrahlung
Inv. Compton
Models from FERMI team
![Page 31: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/31.jpg)
(Strong et al 1999)
Pion decay “bump” is visible
OSSE + COMPTEL + EGRET diffuse γ ray spectrum
Conventional CR spectrum Hard proton spectrum
![Page 32: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/32.jpg)
Radial dependence of γ ray emissivity
SNR distribution: Case & Bhattacharya (1998)
Derived CR density distribution
![Page 33: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/33.jpg)
Diffuse emission beyond the milky way …
• Nearby galaxies– LMC– SMC
• Starburst galaxies (enhanced cosmic ray densities)– NGC251– M82
![Page 34: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/34.jpg)
LMC in γ rays FERMI
• Fermi’s Large Area Telescope (LAT) shows that an intense star-forming region in the Large Magellanic Cloud named 30 Doradus is also a source of diffuse gamma rays. Brighter colors indicate larger numbers of detected gamma rays. Credit: NASA/DOE/Fermi LAT Collaboration
30 Doradus
Large Magellanic Cloud ( 50 kpc away)
LMC – γ ray model(Fichtel et al 1992)
![Page 35: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/35.jpg)
Extragalactic gamma-ray background
![Page 36: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/36.jpg)
The gamma-ray sky - FERMI
![Page 37: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/37.jpg)
03/23/09 37
What is meant by Extragalactic gamma-ray background ?
Extragalactic γ -ray Background
= Observed highlatitude emission { Instrumental
+ resolved point sources + Galactic diffuse emission}
03/23/09
![Page 38: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/38.jpg)
03/23/09 38 03/23/09
Extragalactic Diffuse Emission
Truly Diffuse Processes
• Large scale structure formation• BlackHole evaporation• Exotic particle annihilation• UHE CR interactions• …..
Unresolved Point Sources
3. AGNs2. Normal Galaxies3. Starburst Galaxies4. Cluster of Galaxies
![Page 39: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/39.jpg)
03/23/09 39
What is implied by diffuse emission?
Emission that is perceived given the detector angular resolution
Emission that seems to possess fairly uniform characteristics (not strongly location dependent, not strongly time-dependent)
![Page 40: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/40.jpg)
03/23/09 40
‘diffuse emission’ from poor angular resolution
Images with increasing poor angular resolutions - increasing size of PSF
‘Diffuse’ emission
poor angular resolutionbetter angular resolutionstill better angular resolution
Truly Diffuse emission
Point sources
highest angular resolution
![Page 41: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/41.jpg)
03/23/09
So how does one estimate the EGRB component of
diffuse emission ?
I Obs
NH
I Obs = I EGRB + B * (NH)
Sreekumar et al. 1998
I EGRB
Approach 1
Approach 2
Directly from pixel-by-pixel ML fit of FERMI all sky data
![Page 42: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/42.jpg)
03/23/09 42 03/23/09
2Radio galaxy
~170unidentified
1Normal galaxy
9(?)
9
SNRs
5Pulsars
66+27AGNs
No. of srcs(271)
(
SourceclassGammaray source catalog
FERMI – 1400 srcs and counting ….
![Page 43: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/43.jpg)
03/23/09 43
How to find the contribution to EGRBfrom a source population
flux from a source of luminosity L
F = L/(4π d2(z))
)
All sources have the same luminosity L.Total flux observed =
F = Σ Fi
F = (L/4π ) ∗Σ ( 1/(di2(z))
(
![Page 44: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/44.jpg)
03/23/09 44
So if one knows the distribution of sources with distance (f(z) =dN/dz),One can find the contribution
F = (L/4π )∗∫ {1/d2(z)}f(z)dz
Now Luminosity of sources are also different. So one has to find the distributionof sources with luminosity andredshift.The distribution functionφ (L,z) = dN/(dL dV)
�
φ (L,z) Luminosity Function
![Page 45: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/45.jpg)
03/23/09 45
Luminosity function
The luminosity function is defined as the number of sources per unit co-moving volume of the Universe.
dN = φ (L,z) dL dV(z)
f
co-moving volumeLuminosity function
The contribution to the diffuse extragalactic emission is
diffuse
03/23/09
Observed Flux
dLDzL
zLdzdzdV
FzL
L L
z
∫∫−+×=
)lim(
min
max
2
)1(
0 4)1(
),(41
πφ
π
α
![Page 46: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/46.jpg)
03/23/09 46
Approach
Derive details of individual source class distributions from observational data
Source flux Luminosity
Luminosity function
Integrate over luminosity and redshift space
For every source class
![Page 47: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/47.jpg)
catalog
impose selection criteria
< V / Vmax> = 0.5 ?
pureDensity
evolution
pureLuminosityevolution
density +Luminosityevolution
Noexhibits evolution
Yesno evolution
LuminosityFunction
averagespectral index
Evolutionfunction
Exponential Power law
Deevolvedluminosity
filtered source list
![Page 48: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/48.jpg)
V / Vmax test• Schmidt (1968) – test for examining uniformity of quasars
– Limitations from sensitivity – truncated dataset
• Procedure :– For each source, find
• redshift• the maximum redshift within which the
object is observable (above min detectable limit)
Imp question : Is the catalog list of sources drawn from a uniform distribution in space ?
![Page 49: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/49.jpg)
03/23/09 49
flim zmaxVmax
z V(z)
V
Consider a source of luminosity L at redshift zLimiting flux of the survey = flim
Move source to max distance zmax such that f decreases to flim
For uniform source distribution V/Vmax is expected to be uniformly distributed between 0 and 1
z
zmax
Concept of Vmax
CalculateVVmax
< >
![Page 50: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/50.jpg)
03/23/09 50
∫ ∫
∫ ∫>=<
max
min
max
min
)(
0
)(
0 max
max )(),(
)(),()(
L
L
Lz
L
L
Lz
m
m
zdVzLdL
zdVzLVV
dL
VV
φ
φ
21
)()()(
)()()()(
max
min
max
min
1
0 maxmax
1
0 maxmaxmax
max
=>=<
∫ ∫
∫ ∫L
L
L
L
VV
dLVLdL
VV
dVV
LVLdL
VV
φ
φ
If φ (L) is independent of z
![Page 51: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/51.jpg)
03/23/09 51
<V/Vmax test>
03/23/09
For source population without any evolution < V/Vmax > = 0.5;
For < V/Vmax > ≠ 0.5 indicates some evolution.
< V/Vmax > < 0.5 fewer srcs at high z< V/Vmax > > 0.5 more srcs at high z
![Page 52: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/52.jpg)
03/23/09
So if there is evidence for evolution …..
![Page 53: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/53.jpg)
03/23/09 53
Evolution of Luminosity Function
03/23/09
Luminosity & number density distribution of a population can be expressed as
Φ (L,z) = Φ (L, z=0)ρ (L,z)
Φ (L, z=0) - Local luminosity functionρ (L,z) Evolution function
![Page 54: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/54.jpg)
Luminosity evolution
![Page 55: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/55.jpg)
03/23/09 55
Pure Luminosity Evolution
03/23/09
The number of sources in co-moving volume remain same.
![Page 56: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/56.jpg)
03/23/09 56
L(z) = L(z=0) × f(z); Comoving number density does not change with redshift.
Evolution function used: è f(z) = (1+z)β , f(z) =exp(T(z)/τ )T(z) Look back time
![Page 57: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/57.jpg)
03/23/09 57
Pure Density Evolution
03/23/09
Only the co-moving number density of sources changes with z. ρ (L,z) is independent of L.
Φ (L,z) = Φ (L)ρ (z)
(
![Page 58: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/58.jpg)
03/23/09
catalog
impose selection criteria
< V / Vmax> = 0.5 ?
pureDensity
evolution
pureLuminosityevolution
density +Luminosityevolution
Noexhibits evolution
Yesno evolution
LuminosityFunction
averagespectral index
Evolutionfunction
Exponential Power law
Deevolvedluminosity
filtered source list
![Page 59: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/59.jpg)
03/23/09
Finally ….
Using the final luminosity function. One can estimate the individual source contributions to the diffuse emission (beyond the source catalog limit)
Residuals beyond the estimated source contributions point to contributions from truly diffuse processes – a result of great interest.
![Page 60: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/60.jpg)
Spectral indices: BL Lac--> 1.99 ± 0.22, FSRQ -> 2.40 ± 0.17
BL Lac does not show any evolution: (similar findings from EGRET - Bhattacharya, Sreekumar, Mukherjee 2009)
Slope of luminosity function is 2.17± 0.05. FSRQ shows positive evolution.
Some preliminary results from FERMI (Abdo et al 2009)
![Page 61: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/61.jpg)
Comparison with EGRET results
Considerably steeper than the EGRET spectrum by Sreekumar et al.
No spectral features around a few GeV seen in re-analysis by Strong et al.
2004
2.37 +/- 0.05
2.13 +/- 0.03
2.41 +/- 0.05
spectral index
x 10-5 cm-2 s-1 sr-1
1.19 +/- 0.18
1.11 +/- 0.10
1.45 +/- 0.05
1.03 +/- 0.17
Flux, E>100 MeV
EGRET (Sreekumar et al., 1998)
LAT + resolved sources below EGRET sensitivity
EGRET (Strong et al. 2004)
LAT (this analysis)
PRELIMINARY
Slide from Ackermann et al 2009
![Page 62: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/62.jpg)
SED of the isotropic diffuse emission (1 keV – 100 GeV)
Slide from Ackermann et al 2009
![Page 63: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/63.jpg)
Unresolved source contribution (Debbijoy Bhattacharya thesis)
![Page 64: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/64.jpg)
Potential contributions to the isotropic diffuse continuum gamma-ray emission in the LAT energy range (100 MeV-300 GeV):
unresolved point sources• Active galactic nuclei• Star-forming galaxies• Gamma-ray bursts
diffuse emission processes• UHE cosmic-ray interactions with
the Extragalactic Background Light• Structure formation• large Galactic electron halo• WIMP annihilation
The isotropic diffuse gamma-ray emission
Dermer, 2007
Isotropic diffuse flux contribution from unresolved sources depends on LAT point source sensitivity
Contribution expected to decrease with LAT observation time
Slide from Ackermann et al 2009
![Page 65: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/65.jpg)
• Galactic diffuse emission model depends on a multitude of observational inputs (H1, CO, starlight models, CR models)
• Adequate models exist for typical point source analysis (of course - systematic errors could creep in through uncertainties in the diffuse model – as pointed out by Benoit)
• Detailed modeling with FERMI provides significant scope for improvements in understanding the origin, acceleration and distribution of cosmic rays.
• A more extensive source catalog permits much improved estimation of luminosity function, evolution and determination of contribution of unresolved sources to the extragalactic diffuse emission.
• FERMI data may provide evidence or place useful limits on a truly diffuse extragalactic component
Concluding remarks
![Page 66: Diffuse Gamma ray emission - Raman Research …Diffuse Gamma ray emission P. Sreekumar ISRO Satellite Centre Bangalore 3C 279 Vela Pulsar Geminga Crab The Gamma Ray Universe - as seen](https://reader035.fdocuments.us/reader035/viewer/2022070810/5f08ffc17e708231d424be87/html5/thumbnails/66.jpg)
We await detailed results from FERMI
Thankyou