arXiv subjects

Remi Adam

Publications and source records attributed to Remi Adam.

4 recordsLinked to original sources

arXiv2025

Multi-messenger constraints on transient accelerators of ultra-high energy cosmic rays

The origin of ultra-high-energy cosmic rays (UHECRs) remains an open questions in astrophysics. We explore two primary scenarios for the distribution of UHECR sources, assuming that their production rate follows either the cosmic star-formation-rate or stellar-mass density. By jointly fitting the UHECR energy spectrum and mass composition measured by the Pierre Auger Observatory above the ankle (10^{18.7} eV), we derive constraints on the acceleration mechanisms, source energetics, and elemental abundances at escape. Using these constraints, we generate sky maps above 40 EeV based on a catalog of over 400,000 galaxies out to 350 Mpc, providing a near-infrared flux-limited sample that maps the two stellar-activity tracers across the full sky. A crucial factor in understanding UHECR propagation is the influence of large-scale cosmic structures, particularly galaxy clusters, the largest gravitationally bound systems in the Universe, which are filled with magnetized diffuse plasma. Intermittent sources hosted in galaxies within such structures, coupled with cosmic magnetic fields, shape the observed UHECR arrival directions and provide insights into the burst rate of the sources. We show that these environments can significantly impact UHECR transport, making them particularly opaque to heavy nuclei. Additionally, we compute the expected secondary neutrino and photon fluxes from UHECR interactions in these environments and compare them with current experimental limits, constraining the maximum energy that particles can achieve. Finally, we assess the compatibility of these constraints with astrophysical candidates, identifying long gamma-ray bursts as the most promising sources.

astro-ph.HE↗

arXiv2023

Chasing Gravitational Waves with the Cherenkov Telescope Array

The detection of gravitational waves from a binary neutron star merger by Advanced LIGO and Advanced Virgo (GW170817), along with the discovery of the electromagnetic counterparts of this gravitational wave event, ushered in a new era of multimessenger astronomy, providing the first direct evidence that BNS mergers are progenitors of short gamma-ray bursts (GRBs). Such events may also produce very-high-energy (VHE, > 100GeV) photons which have yet to be detected in coincidence with a gravitational wave signal. The Cherenkov Telescope Array (CTA) is a next-generation VHE observatory which aims to be indispensable in this search, with an unparalleled sensitivity and ability to slew anywhere on the sky within a few tens of seconds. New observing modes and follow-up strategies are being developed for CTA to rapidly cover localization areas of gravitational wave events that are typically larger than the CTA field of view. This work will evaluate and provide estimations on the expected number of of gravitational wave events that will be observable with CTA, considering both on- and off-axis emission. In addition, we will present and discuss the prospects of potential follow-up strategies with CTA.

astro-ph.HE↗

arXiv2023

Impact of Galaxy Clusters on UHECR propagation

Galaxy clusters are the universe's largest objects in the universe kept together by gravity. Most of their baryonic content is made of a magnetized diffuse plasma. We investigate the impact of such magnetized environment on ultra-high-energy-cosmic-ray (UHECR) propagation. The intracluster medium is described according to the self-similar assumption, in which the gas density and pressure profiles are fully determined by the cluster mass and redshift. The magnetic field is scaled to the thermal components of the intracluster medium under different assumptions. We model the propagation of UHECRs in the intracluster medium using a modified version of the Monte Carlo code {\it SimProp}, where hadronic processes and diffusion in the turbulent magnetic field are implemented. We provide a universal parametrization that approximates the UHECR fluxes escaping from the environment as a function of the most relevant quantities, such as the mass of the cluster, the position of the source with respect to the center of the cluster and the nature of the accelerated particles. We show that galaxy clusters are an opaque environment especially for UHECR nuclei. The role of the most massive nearby clusters in the context of the emerging UHECR astronomy is finally discussed.

astro-ph.HE↗

arXiv2017

The NIKA2 large field-of-view millimeter continuum camera for the 30-m IRAM telescope

Millimeter-wave continuum astronomy is today an indispensable tool for both general Astrophysics studies and Cosmology. General purpose, large field-of-view instruments are needed to map the sky at intermediate angular scales not accessible by the high-resolution interferometers and by the coarse angular resolution space-borne or ground-based surveys. These instruments have to be installed at the focal plane of the largest single-dish telescopes. In this context, we have constructed and deployed a multi-thousands pixels dual-band (150 and 260 GHz, respectively 2mm and 1.15mm wavelengths) camera to image an instantaneous field-of-view of 6.5arc-min and configurable to map the linear polarization at 260GHz. We are providing a detailed description of this instrument, named NIKA2 (New IRAM KID Arrays 2), in particular focusing on the cryogenics, the optics, the focal plane arrays based on Kinetic Inductance Detectors (KID) and the readout electronics. We are presenting the performance measured on the sky during the commissioning runs that took place between October 2015 and April 2017 at the 30-meter IRAM (Institut of Millimetric Radio Astronomy) telescope at Pico Veleta. NIKA2 has been successfully deployed and commissioned, performing in-line with the ambitious expectations. In particular, NIKA2 exhibits FWHM angular resolutions of around 11 and 17.5 arc-seconds at respectively 260 and 150GHz. The NEFD (Noise Equivalent Flux Densities) demonstrated on the maps are, at these two respective frequencies, 33 and 8 mJy*sqrt(s). A first successful science verification run has been achieved in April 2017. The instrument is currently offered to the astronomical community during the coming winter and will remain available for at least the next ten years.

astro-ph.IM↗