arXiv subjects

J. Bolmont

Publications and source records attributed to J. Bolmont.

At least 55 records · Page 3Linked to original sources

arXiv2022

Quantum gravity phenomenology at the dawn of the multi-messenger era -- A review

The exploration of the universe has recently entered a new era thanks to the multi-messenger paradigm, characterized by a continuous increase in the quantity and quality of experimental data that is obtained by the detection of the various cosmic messengers (photons, neutrinos, cosmic rays and gravitational waves) from numerous origins. They give us information about their sources in the universe and the properties of the intergalactic medium. Moreover, multi-messenger astronomy opens up the possibility to search for phenomenological signatures of quantum gravity. On the one hand, the most energetic events allow us to test our physical theories at energy regimes which are not directly accessible in accelerators; on the other hand, tiny effects in the propagation of very high energy particles could be amplified by cosmological distances. After decades of merely theoretical investigations, the possibility of obtaining phenomenological indications of Planck-scale effects is a revolutionary step in the quest for a quantum theory of gravity, but it requires cooperation between different communities of physicists (both theoretical and experimental). This review is aimed at promoting this cooperation by giving a state-of-the art account of the interdisciplinary expertise that is needed in the effective search of quantum gravity footprints in the production, propagation and detection of cosmic messengers.

hep-ph↗

arXiv2022

Time-resolved hadronic particle acceleration in the recurrent Nova RS Ophiuchi

Recurrent Novae are repeating thermonuclear explosions in the outer layers of white dwarfs, due to the accretion of fresh material from a binary companion. The shock generated by ejected material slamming into the companion star's wind, accelerates particles to very-high-energies. We report very-high-energy (VHE, $\gtrsim100$\,GeV) gamma rays from the recurrent nova RS\,Ophiuchi up to a month after its 2021 outburst, using the High Energy Stereoscopic System. The VHE emission has a similar temporal profile to lower-energy GeV emission, indicating a common origin, with a two-day delay in peak flux. These observations constrain models of time-dependent particle energization, favouring a hadronic emission scenario over the leptonic alternative. This confirms that shocks in dense winds provide favourable environments for efficient cosmic-ray acceleration to very-high-energies.

astro-ph.HE↗

arXiv2022

First Combined Study on LIV from Observations of Energy-dependent Time Delays from Multiple-type Gamma-ray Sources -- Part I. Motivation, Method Description and Validation through Simulations of H.E.S.S., MAGIC and VERITAS Datasets

Gamma-ray astronomy has become one of the main experimental ways to test the modified dispersion relations (MDRs) of photons in vacuum, obtained in some attempts to formulate a theory of Quantum Gravity. The MDRs in use imply time delays which depend on the energy, and which increase with distance following some function of redshift. The use of transient, or variable, distant and highly energetic sources, already allows us to set stringent limits on the energy scale related to this phenomenon, usually thought to be of the order of the Planck energy, but robust conclusions on the existence of MDR-related propagation effects still require the analysis of a large population of sources. In order to gather the biggest sample of sources possible for MDR searches at teraelectronvolt energies, the H.E.S.S., MAGIC and VERITAS collaborations enacted a joint task force to combine all their relevant data to constrain the Quantum Gravity energy scale. In the present article, the likelihood method used, to combine the data and provide a common limit, is described in detail and tested through simulations of recorded data sets for a gamma-ray burst, three flaring active galactic nuclei and two pulsars. Statistical and systematic errors are assessed and included in the likelihood as nuisance parameters. In addition, a comparison of two different formalisms for distance dependence of the time lags is performed for the first time. In a second article, to appear later, the method will be applied on all relevant data from the three experiments.

astro-ph.HE↗

arXiv2021

A MeerKAT, e-MERLIN, H.E.S.S. and Swift search for persistent and transient emission associated with three localised FRBs

We report on a search for persistent radio emission from the one-off Fast Radio Burst (FRB) 20190714A, as well as from two repeating FRBs, 20190711A and 20171019A, using the MeerKAT radio telescope. For FRB 20171019A we also conducted simultaneous observations with the High Energy Stereoscopic System (H.E.S.S.) in very high energy gamma rays and searched for signals in the ultraviolet, optical, and X-ray bands. For this FRB, we obtain a UV flux upper limit of 1.39x10^-16 erg/cm^-2/s/Amstrong, X-ray limit of ~ 6.6x10^-14 erg/cm^-2/s and a limit on the very-high-energy gamma-ray flux (Phi) (E > 120 GeV) < 1.7 x 10^-12 erg/cm^-2/s. We obtain a radio upper limit of ~15 microJy/beam for persistent emission at the locations of both FRBs 20190711A and 20171019A, but detect diffuse radio emission with a peak brightness of ~53 microJy/beam associated with FRB 20190714A at z = 0.2365. This represents the first detection of the radio continuum emission potentially associated with the host (galaxy) of FRB 20190714A, and is only the third known FRB to have such an association. Given the possible association of a faint persistent source, FRB 20190714A may potentially be a repeating FRB whose age lies between that of FRB 20121102A and FRB 20180916A. A parallel search for repeat bursts from these FRBs revealed no new detections down to a fluence of 0.08 Jy ms for a 1 ms duration burst.

astro-ph.HE↗

arXiv2021

H.E.S.S. follow-up observations of Binary Black Hole Coalescence events during the second and third Gravitational Waves observing runs of Advanced LIGO and Advanced Virgo

We report on the observations of four well-localized binary black hole (BBH) mergers by the High Energy Stereoscopic System (H.E.S.S.) during the second and third observing runs of Advanced LIGO and Advanced Virgo, O2 and O3. H.E.S.S. can observe $\mathrm{20\,deg^2}$ of the sky at a time and follows up gravitational-wave (GW) events by ``tiling'' localization regions to maximize the covered localization probability. During O2 and O3, H.E.S.S. observed large portions of the localization regions, between 35\% and 75\%, for four BBH mergers (GW170814, GW190512\_180714, GW190728\_064510, and S200224ca). For these four GW events, we find no significant signal from a pointlike source in any of the observations, and set upper limits on the very high energy ($>$100 GeV) $γ$-ray emission. The 1-10 TeV isotropic luminosity of these GW events is below $10^{45}$ erg s$^{-1}$ at the times of the H.E.S.S. observations, around the level of the low-luminosity GRB 190829A. Assuming no changes are made to how follow-up observations are conducted, H.E.S.S. can expect to observe over 60 GW events per year in the fourth GW observing run, O4, of which eight would be observable with minimal latency.

astro-ph.HE↗

arXiv2021

Measurement of performance of the NectarCAM photodetectors

NectarCAM is a camera for the medium-sized telescopes of the Cherenkov Telescope Array (CTA), which covers the energy range of 100 GeV to 30 TeV. The camera is equipped with 265 focal plane modules (FPMs). Each FPM comprises 7 pixels, each consisting of a photo-multiplier tube, a preamplifier, an independently controlled power supply, and a common control system. We developed a dedicated test bench to validate and qualify the industrial FPM production and to measure the performance of each FPM in a dark room before its integration in the camera. We report the measured performance of 61 FPM prototypes obtained with our experimental setup. We demonstrate that the gains of the photo multiplier tubes are stable and that pulse widths, transit time spreads, afterpulse rates and charge resolutions are within the specifications for NectarCAM.

astro-ph.IM↗

arXiv2021

Searching for TeV gamma-ray emission from SGR\,1935+2154 during its 2020 X-ray and radio bursting phase

Magnetar hyperflares are the most plausible explanation for fast radio bursts (FRB) -- enigmatic powerful radio pulses with durations of several milliseconds and high brightness temperatures. The first observational evidence for this scenario was obtained in 2020 April when a FRB was detected from the direction of the Galactic magnetar and soft gamma-ray repeater SGR\,1935+2154. The FRB was preceded by two gamma-ray outburst alerts by the BAT instrument aboard the Swift satellite, which triggered follow-up observations by the High Energy Stereoscopic System (H.E.S.S.). H.E.S.S. has observed SGR\,1935+2154 for 2 hr on 2020 April 28. The observations are coincident with X-ray bursts from the magnetar detected by INTEGRAL and Fermi-GBM, thus providing the first very high energy (VHE) gamma-ray observations of a magnetar in a flaring state. High-quality data acquired during these follow-up observations allow us to perform a search for short-time transients. No significant signal at energies $E>0.6$~TeV is found and upper limits on the persistent and transient emission are derived. We here present the analysis of these observations and discuss the obtained results and prospects of the H.E.S.S. follow-up program for soft gamma-ray repeaters.

astro-ph.HE↗

arXiv2021

TeV emission of Galactic plane sources with HAWC and H.E.S.S

The High Altitude Water Cherenkov (HAWC) observatory and the High Energy Stereoscopic System (H.E.S.S.) are two leading instruments in the ground-based very-high-energy gamma-ray domain. HAWC employs the water Cherenkov detection (WCD) technique, while H.E.S.S. is an array of Imaging Atmospheric Cherenkov Telescopes (IACTs). The two facilities therefore differ in multiple aspects, including their observation strategy, the size of their field of view and their angular resolution, leading to different analysis approaches. Until now, it has been unclear if the results of observations by both types of instruments are consistent: several of the recently discovered HAWC sources have been followed up by IACTs, resulting in a confirmed detection only in a minority of cases. With this paper, we go further and try to resolve the tensions between previous results by performing a new analysis of the H.E.S.S. Galactic plane survey data, applying an analysis technique comparable between H.E.S.S. and HAWC. Events above 1 TeV are selected for both datasets, the point spread function of H.E.S.S. is broadened to approach that of HAWC, and a similar background estimation method is used. This is the first detailed comparison of the Galactic plane observed by both instruments. H.E.S.S. can confirm the gamma-ray emission of four HAWC sources among seven previously undetected by IACTs, while the three others have measured fluxes below the sensitivity of the H.E.S.S. dataset. Remaining differences in the overall gamma-ray flux can be explained by the systematic uncertainties. Therefore, we confirm a consistent view of the gamma-ray sky between WCD and IACT techniques.

astro-ph.IM↗

arXiv2021

LMC N132D: A mature supernova remnant with a power-law gamma-ray spectrum extending beyond 8 TeV

We analyzed 252 hours of High Energy Stereoscopic System (H.E.S.S.) observations towards the supernova remnant (SNR) LMC N132D that were accumulated between December 2004 and March 2016 during a deep survey of the Large Magellanic Cloud, adding 104 hours of observations to the previously published data set to ensure a > 5 sigma detection. To broaden the gamma-ray spectral coverage required for modeling the spectral energy distribution, an analysis of Fermi-LAT Pass 8 data was also included. We unambiguously detect N132D at very high energies (VHE) with a significance of 5.7 sigma. We report the results of a detailed analysis of its spectrum and localization based on the extended H.E.S.S. data set. The joint analysis of the extended H.E.S.S and Fermi-LAT data results in a spectral energy distribution in the energy range from 1.7 GeV to 14.8 TeV, which suggests a high luminosity of N132D at GeV and TeV energies. We set a lower limit on a gamma-ray cutoff energy of 8 TeV with a confidence level of 95%. The new gamma-ray spectrum as well as multiwavelength observations of N132D when compared to physical models suggests a hadronic origin of the VHE gamma-ray emission. SNR N132D is a VHE gamma-ray source that shows a spectrum extending to the VHE domain without a spectral cutoff at a few TeV, unlike the younger oxygen-rich SNR Cassiopeia A. The gamma-ray properties of N132D may be affected by an interaction with a nearby molecular cloud that partially lies inside the 95% confidence region of the source position. [Abridged]

astro-ph.HE↗

arXiv2021

Origin and role of relativistic cosmic particles

This white paper briefly summarizes the importance of the study of relativistic cosmic rays, both as a constituent of our Universe, and through their impact on stellar and galactic evolution. The focus is on what can be learned over the coming decade through ground-based gamma-ray observations over the 20 GeV to 300 TeV range. The majority of the material is drawn directly from "Science with the Cherenkov Telescope Array", which describes the overall science case for CTA. We request that authors wishing to cite results contained in this white paper cite the original work.

astro-ph.HE↗

arXiv2021

Search for dark matter annihilation signals from unidentified Fermi-LAT objects with H.E.S.S

Cosmological $N$-body simulations show that Milky Way-sized galaxies harbor a population of unmerged dark matter subhalos. These subhalos could shine in gamma-rays and be eventually detected in gamma-ray surveys as unidentified sources. We performed a thorough selection among unidentified Fermi-LAT Objects (UFOs) to identify them as possible TeV-scale dark matter subhalo candidates. We search for very-high-energy (E $\gtrsim$ 100 GeV) gamma-ray emissions using H.E.S.S. observations towards four selected UFOs. Since no significant very-high-energy gamma-ray emission is detected in any dataset of the four observed UFOs nor in the combined UFO dataset, strong constraints are derived on the product of the velocity-weighted annihilation cross section $\langle σv \rangle$ by the $J$-factor for the dark matter models. The 95% C.L. observed upper limits derived from combined H.E.S.S. observations reach $\langle σv \rangle J$ values of 3.7$\times$10$^{-5}$ and 8.1$\times$10$^{-6}$ GeV$^2$cm$^{-2}$s$^{-1}$ in the $W^+W^-$ and $τ^+τ^-$ channels, respectively, for a 1 TeV dark matter mass. Focusing on thermal WIMPs, the H.E.S.S. constraints restrict the $J$-factors to lie in the range 6.1$\times$10$^{19}$ - 2.0$\times$10$^{21}$ GeV$^2$cm$^{-5}$, and the masses to lie between 0.2 and 6 TeV in the $W^+W^-$ channel. For the $τ^+τ^-$ channel, the $J$-factors lie in the range 7.0$\times$10$^{19}$ - 7.1$\times$10$^{20}$ GeV$^2$cm$^{-5}$ and the masses lie between 0.2 and 0.5 TeV. Assuming model-dependent predictions from cosmological N-body simulations on the $J$-factor distribution for Milky Way-sized galaxies, the dark matter models with masses greater than 0.3 TeV for the UFO emissions can be ruled out at high confidence level.

astro-ph.HE↗

arXiv2021

Evidence of 100 TeV $γ$-ray emission from HESS J1702-420: A new PeVatron candidate

The identification of PeVatrons, hadronic particle accelerators reaching the knee of the cosmic ray spectrum (few $10^{15}$ eV), is crucial to understand the origin of cosmic rays in the Galaxy. We provide an update on the unidentified source HESS J1702-420, a promising PeVatron candidate. We present new observations of HESS J1702-420 made with the High Energy Stereoscopic System (H.E.S.S.), and processed using improved analysis techniques. The analysis configuration was optimized to enhance the collection area at the highest energies. We applied a three-dimensional (3D) likelihood analysis to model the source region and adjust non thermal radiative spectral models to the $γ$-ray data. We also analyzed archival data from the Fermi Large Area Telescope (LAT) to constrain the source spectrum at $γ$-ray energies >10 GeV. We report the detection of a new source component called HESS J1702-420A, that was separated from the bulk of TeV emission at a $5.4σ$ confidence level. The power law $γ$-ray spectrum of HESS J1702-420A extends with an index of $Γ=1.53\pm0.19_\text{stat}\pm0.20_\text{sys}$ and without curvature up to the energy band 64-113 TeV, in which it was detected by H.E.S.S. at a $4.0σ$ confidence level. This brings evidence for the source emission up to $100\,\text{TeV}$, which makes HESS J1702-420A a compelling candidate site for the presence of extremely high energy cosmic rays. Remarkably, in a hadronic scenario, the cut-off energy of the proton distribution powering HESS J1702-420A is found to be higher than 0.5 PeV at a 95% confidence level. HESS J1702-420A becomes therefore one of the most solid PeVatron candidates detected so far in H.E.S.S. data, altough a leptonic origin of its emission could not be ruled out either.

astro-ph.HE↗

arXiv2021

Probing Dark Matter and Fundamental Physics with the Cherenkov Telescope Array

Astrophysical observations provide strong evidence that more than 80% of all matter in the Universe is in the form of dark matter (DM). Two leading candidates of particles beyond the Standard Model that could constitute all or a fraction of the DM content are the so-called Weakly Interacting Massive Particles (WIMPs) and Axion-Like Particles (ALPs). The upcoming Cherenkov Telescope Array, which will observe gamma rays between 20 GeV and 300 TeV with unprecedented sensitivity, will have unique capabilities to search for these DM candidates. A particularly promising target for WIMP searches is the Galactic Center. WIMPs with annihilation cross sections correctly producing the DM relic density will be detectable with CTA, assuming an Einasto-like density profile and WIMP masses between 200 GeV and 10 TeV. Regarding new physics beyond DM, CTA observations will also enable tests of fundamental symmetries of nature such as Lorentz invariance.

astro-ph.HE↗

arXiv2021

Multi-messenger and transient astrophysics with the Cherenkov Telescope Array

The discovery of gravitational waves, high-energy neutrinos or the very-high-energy counterpart of gamma-ray bursts has revolutionized the high-energy and transient astrophysics community. The development of new instruments and analysis techniques will allow the discovery and/or follow-up of new transient sources. We describe the prospects for the Cherenkov Telescope Array (CTA), the next-generation ground-based gamma-ray observatory, for multi-messenger and transient astrophysics in the decade ahead. CTA will explore the most extreme environments via very-high-energy observations of compact objects, stellar collapse events, mergers and cosmic-ray accelerators.

astro-ph.HE↗

arXiv2021

Probing extreme environments with the Cherenkov Telescope Array

The physics of the non-thermal Universe provides information on the acceleration mechanisms in extreme environments, such as black holes and relativistic jets, neutron stars, supernovae or clusters of galaxies. In the presence of magnetic fields, particles can be accelerated towards relativistic energies. As a consequence, radiation along the entire electromagnetic spectrum can be observed, and extreme environments are also the most likely sources of multi-messenger emission. The most energetic part of the electromagnetic spectrum corresponds to the very-high-energy (VHE, E>100 GeV) gamma-ray regime, which can be extensively studied with ground based Imaging Atmospheric Cherenkov Telescopes (IACTs). The results obtained by the current generation of IACTs, such as H.E.S.S., MAGIC, and VERITAS, demonstrate the crucial importance of the VHE band in understanding the non-thermal emission of extreme environments in our Universe. In some objects, the energy output in gamma rays can even outshine the rest of the broadband spectrum. The Cherenkov Telescope Array (CTA) is the next generation of IACTs, which, with cutting edge technology and a strategic configuration of ~100 telescopes distributed in two observing sites, in the northern and southern hemispheres, will reach better sensitivity, angular and energy resolution, and broader energy coverage than currently operational IACTs. With CTA we can probe the most extreme environments and considerably boost our knowledge of the non-thermal Universe.

astro-ph.IM↗

arXiv2021

Search for dark matter annihilation in the dwarf irregular galaxy WLM with H.E.S.S

We search for an indirect signal of dark matter through very high-energy gamma rays from the Wolf-Lundmark-Melotte (WLM) dwarf irregular galaxy. The pair annihilation of dark matter particles would produce Standard Model particles in the final state such as gamma rays, which might be detected by ground-based Cherenkov telescopes. Dwarf irregular galaxies represent promising targets as they are dark matter dominated objects with well measured kinematics and small uncertainties on their dark matter distribution profiles. In 2018, the H.E.S.S. five-telescope array observed the dwarf irregular galaxy WLM for 18 hours. We present the first analysis based on data obtained from an imaging atmospheric Cherenkov telescope for this subclass of dwarf galaxy. As we do not observe any significant excess in the direction of WLM, we interpret the result in terms of constraints on the velocity-weighted cross section for dark matter pair annihilation as a function of the dark matter particle mass for various continuum channels as well as the prompt gamma-gamma emission. For the $τ^+τ^-$ channel the limits reach a $\langle σv \rangle$ value of about $4\times 10^{-22}$ cm3s-1 for a dark matter particle mass of 1 TeV. For the prompt gamma-gamma channel, the upper limit reaches a $\langle σv \rangle$ value of about $5 \times10^{-24}$ cm3s-1 for a mass of 370 GeV. These limits represent an improvement of up to a factor 200 with respect to previous results for the dwarf irregular galaxies for TeV dark matter search.

astro-ph.HE↗

arXiv2021

Sensitivity of the Cherenkov Telescope Array for probing cosmology and fundamental physics with gamma-ray propagation

The Cherenkov Telescope Array (CTA), the new-generation ground-based observatory for $γ$-ray astronomy, provides unique capabilities to address significant open questions in astrophysics, cosmology, and fundamental physics. We study some of the salient areas of $γ$-ray cosmology that can be explored as part of the Key Science Projects of CTA, through simulated observations of active galactic nuclei (AGN) and of their relativistic jets. Observations of AGN with CTA will enable a measurement of $γ$-ray absorption on the extragalactic background light with a statistical uncertainty below 15% up to a redshift $z=2$ and to constrain or detect $γ$-ray halos up to intergalactic-magnetic-field strengths of at least 0.3pG. Extragalactic observations with CTA also show promising potential to probe physics beyond the Standard Model. The best limits on Lorentz invariance violation from $γ$-ray astronomy will be improved by a factor of at least two to three. CTA will also probe the parameter space in which axion-like particles could constitute a significant fraction, if not all, of dark matter. We conclude on the synergies between CTA and other upcoming facilities that will foster the growth of $γ$-ray cosmology.

astro-ph.HE↗

arXiv2020

Observation of a sudden cessation of a very-high-energy gamma-ray flare in PKS 1510-089 with H.E.S.S. and MAGIC in May 2016

The flat spectrum radio quasar (FSRQ) PKS 1510-089 is known for its complex multiwavelength behavior, and is one of only a few FSRQs detected at very high energy (VHE, $E>100\,$GeV) $γ$-rays. VHE $γ$-ray observations with H.E.S.S. and MAGIC during late May and early June 2016 resulted in the detection of an unprecedented flare, which reveals for the first time VHE $γ$-ray intranight variability in this source. While a common variability timescale of $1.5\,$hr is found, there is a significant deviation near the end of the flare with a timescale of $\sim 20\,$min marking the cessation of the event. The peak flux is nearly two orders of magnitude above the low-level emission. For the first time, curvature is detected in the VHE $γ$-ray spectrum of PKS 1510-089, which is fully explained through absorption by the extragalactic background light. Optical R-band observations with ATOM reveal a counterpart of the $γ$-ray flare, even though the detailed flux evolution differs from the VHE ightcurve. Interestingly, a steep flux decrease is observed at the same time as the cessation of the VHE flare. In the high energy (HE, $E>100\,$MeV) $γ$-ray band only a moderate flux increase is observed with Fermi-LAT, while the HE $γ$-ray spectrum significantly hardens up to a photon index of 1.6. A search for broad-line region (BLR) absorption features in the $γ$-ray spectrum indicates that the emission region is located outside of the BLR. Radio VLBI observations reveal a fast moving knot interacting with a standing jet feature around the time of the flare. As the standing feature is located $\sim 50\,$pc from the black hole, the emission region of the flare may have been located at a significant distance from the black hole. If this correlation is indeed true, VHE $γ$ rays have been produced far down the jet where turbulent plasma crosses a standing shock.

astro-ph.HE↗