Abstract
Magnetic fields in galaxies and galaxy clusters are believed to be the result of the amplification of intergalactic seed fields during the formation of large-scale structures in the ...universe. However, the origin, strength, and morphology of this intergalactic magnetic field (IGMF) remain unknown. Lower limits on (or indirect detection of) the IGMF can be obtained from observations of high-energy gamma rays from distant blazars. Gamma rays interact with the extragalactic background light to produce electron−positron pairs, which can subsequently initiate electromagnetic cascades. The gamma-ray signature of the cascade depends on the IGMF since it deflects the pairs. Here we report on a new search for this cascade emission using a combined data set from the Fermi Large Area Telescope and the High Energy Stereoscopic System. Using state-of-the-art Monte Carlo predictions for the cascade signal, our results place a lower limit on the IGMF of
B
> 7.1 × 10
−16
G for a coherence length of 1 Mpc even when blazar duty cycles as short as 10 yr are assumed. This improves on previous lower limits by a factor of 2. For longer duty cycles of 10
4
(10
7
) yr, IGMF strengths below 1.8 × 10
−14
G (3.9 × 10
−14
G) are excluded, which rules out specific models for IGMF generation in the early universe.
Abstract
We report on multiwavelength target-of-opportunity observations of the blazar PKS 0735+178, located 2.°2 away from the best-fit position of the IceCube neutrino event IceCube-211208A ...detected on 2021 December 8. The source was in a high-flux state in the optical, ultraviolet, X-ray, and GeV
γ
-ray bands around the time of the neutrino event, exhibiting daily variability in the soft X-ray flux. The X-ray data from Swift-XRT and NuSTAR characterize the transition between the low-energy and high-energy components of the broadband spectral energy distribution (SED), and the
γ
-ray data from Fermi-LAT, VERITAS, and H.E.S.S. require a spectral cutoff near 100 GeV. Both the X-ray and
γ
-ray measurements provide strong constraints on the leptonic and hadronic models. We analytically explore a synchrotron self-Compton model, an external Compton model, and a lepto-hadronic model. Models that are entirely based on internal photon fields face serious difficulties in matching the observed SED. The existence of an external photon field in the source would instead explain the observed
γ
-ray spectral cutoff in both the leptonic and lepto-hadronic models and allow a proton jet power that marginally agrees with the Eddington limit in the lepto-hadronic model. We show a numerical lepto-hadronic model with external target photons that reproduces the observed SED and is reasonably consistent with the neutrino event despite requiring a high jet power.
Abstract
In 2021 July,
PKS 1510−089
exhibited a significant flux drop in the high-energy
γ
-ray (by a factor 10) and optical (by a factor 5) bands and remained in this low state throughout 2022. ...Similarly, the optical polarization in the source vanished, resulting in the optical spectrum being fully explained through the steady flux of the accretion disk and the broad-line region. Unlike the aforementioned bands, the very-high-energy
γ
-ray and X-ray fluxes did not exhibit a significant flux drop from year to year. This suggests that the steady-state very-high-energy
γ
-ray and X-ray fluxes originate from a different emission region than the vanished parts of the high-energy
γ
-ray and optical jet fluxes. The latter component has disappeared through either a swing of the jet away from the line of sight or a significant drop in the photon production efficiency of the jet close to the black hole. Either change could become visible in high-resolution radio images.
Le but était de définir les déterminants du choix des parents concernant le suivi médical de leur enfant et comparer leurs attentes au suivi effectif de l’enfant.
Etude de cohorte prospective ...multicentrique. Un questionnaire (phase 1) a évalué le souhait de 330 parturientes pour le suivi médical de leur nouveau-né. 6 à 12 mois après la naissance, nous les avons interrogées (phase2) sur le suivi effectif dont avait bénéficié leur enfant.
En phase 1, 38% s’orientaient vers le pédiatre, 35% vers le médecin généraliste (MG) et 13% vers la PMI. La connaissance était le critère retenu pour le choix du MG, celui du pédiatre ou de la PMI était le choix d’un spécialiste. En phase 2, les MG suivaient 51% des enfants. 48% des enfants avaient un suivi mixte. Les déterminants significatifs étaient le type de foyer, l’âge maternel, le lieu de vie, le délai d’accès estimé aux différents cabinets médicaux et le niveau d’étude.
Initialement le choix du pédiatre devance celui du MG, mais ce dernier est favorisé pour le suivi effectif. Près de 1 enfant sur 2 a un suivi mixte. Ceci souligne la complémentarité des acteurs et pose la question de la formation de chacun, et d’un usage des soignants basé sur l’offre et la demande ou orienté par la Santé Publique.
Abstract
GRB 221009A is the brightest gamma-ray burst (GRB) ever detected. To probe the very-high-energy (VHE; >100 GeV) emission, the High Energy Stereoscopic System (H.E.S.S.) began observations 53 ...hr after the triggering event, when the brightness of the moonlight no longer precluded observations. We derive differential and integral upper limits using H.E.S.S. data from the third, fourth, and ninth nights after the initial GRB detection, after applying atmospheric corrections. The combined observations yield an integral energy flux upper limit of
Φ
UL
95
%
=
9.7
×
10
−
12
erg
cm
−
2
s
−
1
above
E
thr
= 650 GeV. The constraints derived from the H.E.S.S. observations complement the available multiwavelength data. The radio to X-ray data are consistent with synchrotron emission from a single electron population, with the peak in the spectral energy distribution occurring above the X-ray band. Compared to the VHE-bright GRB 190829A, the upper limits for GRB 221009A imply a smaller gamma-ray to X-ray flux ratio in the afterglow. Even in the absence of a detection, the H.E.S.S. upper limits thus contribute to the multiwavelength picture of GRB 221009A, effectively ruling out an IC-dominated scenario.
Observations of transient phenomena, such as GRBs, FRBs, novae/supernovae explosions, coupled with the detection of cosmic messengers like high-energy neutrinos and gravitational waves, have ...transformed astrophysics. Maximizing the discovery potential necessitates tools for swiftly acquiring an overview of the most relevant information for each new detection. Introducing Astro-COLIBRI, a comprehensive platform designed to meet this challenge. Astro-COLIBRI features a public API, real-time databases and alert systems, a discussion forum, and a website and iOS/Android apps as user clients. In real time, it evaluates incoming astronomical observation messages from all available alert streams, filters them based on user-defined criteria, and contextualizes them in the multi-wavelength (MWL) and multi-messenger (MM) context. User clients offer a graphical representation, providing a succinct summary for quick identification of interesting phenomena and assessing observing conditions globally.
An intrinsic gamma-ray burst afterglow
Long gamma-ray bursts (GRBs) are emitted by relativistic jets generated during the collapse of a massive star in a distant galaxy. The GRB itself lasts only a ...few seconds but is followed by an afterglow that can persist for hours or days. The H.E.S.S. Collaboration observed the afterglow of GRB 190829A, a nearby long GRB. The proximity of this burst allowed it to be detected at tera–electron volt energies that would otherwise be absorbed in the intergalactic medium. By analyzing the spectrum and light curve at x-ray and gamma-ray wavelengths, the authors show that the afterglow cannot be explained by standard models.
Science
, abe8560, this issue p.
1081
Observations of a nearby gamma-ray burst at tera–electron volt energies cannot be explained by standard models.
Gamma-ray bursts (GRBs), which are bright flashes of gamma rays from extragalactic sources followed by fading afterglow emission, are associated with stellar core collapse events. We report the detection of very-high-energy (VHE) gamma rays from the afterglow of GRB 190829A, between 4 and 56 hours after the trigger, using the High Energy Stereoscopic System (H.E.S.S.). The low luminosity and redshift of GRB 190829A reduce both internal and external absorption, allowing determination of its intrinsic energy spectrum. Between energies of 0.18 and 3.3 tera–electron volts, this spectrum is described by a power law with photon index of 2.07 ± 0.09, similar to the x-ray spectrum. The x-ray and VHE gamma-ray light curves also show similar decay profiles. These similar characteristics in the x-ray and gamma-ray bands challenge GRB afterglow emission scenarios.
PDF
