14 research outputs found
Propagation of ultra-high energy protons in regular extragalactic magnetic fields
We study the proton flux expected from sources of ultra high energy cosmic
rays (UHECR) in the presence of regular extragalactic magnetic fields. It is
assumed that a local source of ultra-high energy protons and the magnetic field
are all in a wall of matter concentration with dimensions characteristic of the
supergalactic plane. For a single source, the observed proton flux and the
local cosmic ray energy spectrum depend strongly on the strength of the field,
the position of the observer, and the orientation of the field relative to the
observer's line of sight. Regular fields also affect protons emitted by sources
outside the local magnetic fields structure. We discuss the possibility that
such effects could contribute to an explanation of the excess of UHECR above
eV, and the possibility that sources of such particles may be
missed if such magnetic fields are not taken into account.Comment: 6 pages, 4 figures Comments for revised version: 12 pages, 12
figures. Enlarged discussion of effects on cosmic ray spectrum. Additional
discussion focussing on spatial and temporal boundary condition
Searching for a Correlation Between Cosmic-Ray Sources Above 10^{19} eV and Large-Scale Structure
We study the anisotropy signature which is expected if the sources of ultra
high energy, >10^{19} eV, cosmic-rays (UHECRs) are extragalactic and trace the
large scale distribution of luminous matter. Using the PSCz galaxy catalog as a
tracer of the large scale structure (LSS), we derive the expected all sky
angular distribution of the UHECR intensity. We define a statistic, that
measures the correlation between the predicted and observed UHECR arrival
direction distributions, and show that it is more sensitive to the expected
anisotropy signature than the power spectrum and the two point correlation
function. The distribution of the correlation statistic is not sensitive to the
unknown redshift evolution of UHECR source density and to the unknown strength
and structure of inter-galactic magnetic fields. We show, using this statistic,
that recently published >5.7x10^{19} eV Auger data are inconsistent with
isotropy at ~98% CL, and consistent with a source distribution that traces LSS,
with some preference to a source distribution that is biased with respect to
the galaxy distribution. The anisotropy signature should be detectable also at
lower energy, >4x10^{19} eV. A few fold increase of the Auger exposure is
likely to increase the significance to >99% CL, but not to >99.9% CL (unless
the UHECR source density is comparable or larger than that of galaxies). In
order to distinguish between different bias models, the systematic uncertainty
in the absolute energy calibration of the experiments should be reduced to well
below the current ~25%.Comment: 17 pages, 8 figures. v2: reference added, typos corrected, accepted
to JCA
Astrophysical Origins of Ultrahigh Energy Cosmic Rays
In the first part of this review we discuss the basic observational features
at the end of the cosmic ray energy spectrum. We also present there the main
characteristics of each of the experiments involved in the detection of these
particles. We then briefly discuss the status of the chemical composition and
the distribution of arrival directions of cosmic rays. After that, we examine
the energy losses during propagation, introducing the Greisen-Zaptsepin-Kuzmin
(GZK) cutoff, and discuss the level of confidence with which each experiment
have detected particles beyond the GZK energy limit. In the second part of the
review, we discuss astrophysical environments able to accelerate particles up
to such high energies, including active galactic nuclei, large scale galactic
wind termination shocks, relativistic jets and hot-spots of Fanaroff-Riley
radiogalaxies, pulsars, magnetars, quasar remnants, starbursts, colliding
galaxies, and gamma ray burst fireballs. In the third part of the review we
provide a brief summary of scenarios which try to explain the super-GZK events
with the help of new physics beyond the standard model. In the last section, we
give an overview on neutrino telescopes and existing limits on the energy
spectrum and discuss some of the prospects for a new (multi-particle)
astronomy. Finally, we outline how extraterrestrial neutrino fluxes can be used
to probe new physics beyond the electroweak scale.Comment: Higher resolution version of Fig. 7 is available at
http://www.angelfire.com/id/dtorres/down3.html. Solicited review article
prepared for Reports on Progress in Physics, final versio
The Magnetized Universe
Cosmology, high-energy physics and astrophysics are converging on the study
of large-scale magnetic fields. While the experimental evidence for the
existence of large-scale magnetization in galaxies, clusters and superclusters
is rather compelling, the origin of the phenomenon remains puzzling especially
in light of the most recent observations. The purpose of the present review is
to describe the physical motivations and some of the open theoretical problems
related to the existence of large-scale magnetic fields.Comment: 147 pages, 10 included figures. Few corrected typos and added
reference
Multi-messenger observations of a binary neutron star merger
On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta