Fermi-LAT Constraints on UHECR Sources Marco Muzio (NYU) Glennys - - PowerPoint PPT Presentation

Marco Muzio (NYU)

Fermi-LAT Constraints

• n UHECR Sources

Marco Muzio (NYU) Glennys Farrar (NYU), Michael Unger (KIT)

1

Marco Muzio (NYU)

Motivation

• Liu et al. (2016) argued that there

must be a “local fog” of UHECR sources (cf. Taylor highlight talk)

• Used IGRB limits on diffuse

photon fluxes

• Considered a pure-proton

scenario

• Could a mixed-composition

scenario evade the IGRB limits without such a fog?

• YES!

2 Liu, et al., Phys. Rev. D 94, 043008 (2016)

Marco Muzio (NYU)

UFA Source Model

• UFA model explains the origin of ankle and light composition at

EeV energies

• Does so by taking into account photonuclear reactions in source

environment

3

cosmic ray

source environment EBL/CMB detection

• M. Unger, G.R. Farrar & L.A. Anchordoqui, Phys. Rev. D 92 (2015) 123001,

arXiv:1505.02153 e+ e- 𝛿

Marco Muzio (NYU)

UFA models give excellent fit to flux and composition

4

Escaping flux from source Flux at Earth Composition at Earth

UFA fiducial model

Marco Muzio (NYU)

Goal of CRtoEM

• Use Fermi-LAT data to constrain

viable CR source models

• Specify UHECR source model
• Injection spectrum and

composition

• Source evolution
• Create an efficient way to obtain the
• bserved flux of CRs and EM

particles predicted by various source models with high statistical quality

• Avoid redundant calculations!

5

UHECR Source model

dN/dE, dN/dz, composition

E

E2dN/dE

CRtoEM

Marco Muzio (NYU)

Methodology

• Average observed flux of CRs, EM

particles due to CR propagation depends

• n only:
• Particle type
• Initial particle energy
• Initial distance from observer
• Method:
• Tabulate the average fluxes due to CRs
• f a given type, energy, and distance
• Bin in energy and comoving distance
• Weight these fluxes to reflect a given

source model

6

Ei Dj

E

E2dN/dE

E

E2dN/dE

CRs

Photons

Z, A

Marco Muzio (NYU)

Building CRtoEM

• Tabulated fluxes based on CRPropa3 and

ELMAG

• Calculation is done in 3 parts:
• CRPropa3 is used to propagate CRs
• Observed CR flux (a)
• Distribution of EM primary

secondaries (b)

• ELMAG is used to cascade EM particles
• Observed flux of photons and e+/-’s

(c)

• Primary secondary distribution and
• bserved EM fluxes are combined to
• btain observed EM flux due to CRs

7

• Parameter space:
• CR: 0-6520 Mpc, 10

17

• 10

20

eV

• EM: 0-6520 Mpc, 10

8

• 10

20

eV

• 10 bins per decade of energy
• 20 Mpc wide bins in comoving distance

Marco Muzio (NYU)

Pure proton model with uniform evolution is in tension with Fermi-LAT

8

Note that pure proton model can fit spectrum, but not composition

Marco Muzio (NYU)

Pure proton model with SFR evolution is in conflict with Fermi-LAT

9

Note that pure proton model can fit spectrum, but not composition

Marco Muzio (NYU)

Mixed Composition (UFA fiducial) with SFR evolution is consistent with Fermi-LAT

10

Note that UFA fiducial model can fit spectrum and composition

Marco Muzio (NYU)

Realistic, mixed composition UHECR model is not in conflict with Fermi-LAT

• The UFA predicted photon flux

is compatible with IGRB limits

• A more realistic mixed-

composition scenario evades IGRB limits even with a SFR evolution

• Other UFA source scenarios

may further reduce the Fermi- LAT gamma-ray flux

11

UFA ~87% of limit

Marco Muzio (NYU)

(Sensitivity to Redshift Cutoff)

• 50 GeV energy bin is not particularly sensitive to high

redshifts in uniform or SFR evolution scenarios

12

SFR Uniform

Marco Muzio (NYU)

Summary

• UFA-like scenarios are able to

recreate the Auger spectrum and avoid photon flux limits even for SFR evolution*

• The need for a local fog of

UHECR sources evaporates in mixed-composition scenarios

13

Future: Explore sensitivity of gamma ray flux to source evolution and environment assumptions UFA *see also Globus talk @ 1:45 today