Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Indication of a Local "Fog" of Sub-Ankle UHECR   During their propagation through intergalactic space, ultrahigh energy cosmic
rays (UHECRs) interact with the background radiation fields. These interactions
give rise to energetic electron/positron pairs and photons which in turn feed
electromagnetic cascades, contributing to the isotropic gamma-ray background
(IGRB). The gamma-ray flux level generated in this way highly depends upon the
UHECR propagation distance, as well as the evolution of their sources with
redshift. Recently, the Fermi-LAT collaboration reported that the majority of
the total extragalactic gamma-ray flux originates from extragalactic point
sources. This posits a stringent upper limit on the IGRB generated via UHECR
propagation, and subsequently constrains their abundance in the distant
Universe. Focusing on the contribution of UHECR at energies below the ankle
within a narrow energy band ($(1-4)\times 10^{18}$eV), we calculate the diffuse
gamma-ray flux generated through UHECR propagation, normalizing the total
cosmic ray energy budget in this band to that measured. We find that in order
to not over-produce the new IGRB limit, a local "fog" of UHECR produced by
nearby sources may exist, with a possible non-negligible contribution from our
Galaxy. Following the assumption that a given fraction of the observed IGRB at
820GeV originates from UHECR, we obtain a constraint on the maximum distance
for the majority of their sources. With other unresolved source populations
still contaminating the new IGRB limit, and UHECR above the ankle invariably
contributing also to this background, the results presented here are rather
conservative.

21
The categories of this paper are: adap-org
28
The categories of this paper are: alg-geom
12
The categories of this paper are: nucl-th
0
The categories of this paper are: hep-ph
1
The categories of this paper are: cs
30
The categories of this paper are: q-alg
19
The categories of this paper are: eess
25
The categories of this paper are: patt-sol
18
The categories of this paper are: econ
15
The categories of this paper are: nucl-ex
10
The categories of this paper are: q-bio
16
The categories of this paper are: stat
37
The categories of this paper are: supr-con
8
The categories of this paper are: hep-ex
7
The categories of this paper are: hep-th
17
The categories of this paper are: q-fin