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 when ejected material ...slams into the companion star's wind can accelerate particles. We report very-high-energy (VHE; Formula: see text) gamma rays from the recurrent nova RS Ophiuchi, up to 1 month after its 2021 outburst, observed using the High Energy Stereoscopic System (H.E.S.S.). The temporal profile of VHE emission is similar to that of lower-energy giga-electron volt emission, indicating a common origin, with a 2-day delay in peak flux. These observations constrain models of time-dependent particle energization, favoring a hadronic emission scenario over the leptonic alternative. Shocks in dense winds provide favorable environments for efficient acceleration of cosmic rays to very high energies.
Aims. 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. Methods. 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 likelihood analysis to model the source region and adjust non thermal radiative spectral models to the γ -ray data. We also analyzed archival Fermi Large Area Telescope data to constrain the source spectrum at γ -ray energies > 10 GeV. Results. We report the detection of γ -rays up to 100 TeV from a specific region of HESS J1702-420, which is well described by a new source component called HESS J1702-420A that was separated from the bulk of TeV emission at a 5.4 σ confidence level. The power law γ -ray spectrum of HESS J1702-420A extends with an index of Γ = 1.53 ± 0.19 stat ± 0.20 sys and without curvature up to the energy band 64−113 TeV, in which it was detected by H.E.S.S. at a 4.0 σ confidence level. This makes HESS J1702-420A a compelling candidate site for the presence of extremely high energy cosmic rays. With a flux above 2 TeV of (2.08 ± 0.49 stat ± 0.62 sys ) × 10 −13 cm −2 s −1 and a radius of (0.06 ± 0.02 stat ± 0.03 sys )°, HESS J1702-420A is outshone – below a few tens of TeV – by the companion HESS J1702-420B. The latter has a steep spectral index of Γ = 2.62 ± 0.10 stat ± 0.20 sys and an elongated shape, and it accounts for most of the low-energy HESS J1702-420 flux. Simple hadronic and leptonic emission models can be well adjusted to the spectra of both components. Remarkably, in a hadronic scenario, the cut-off energy of the particle distribution powering HESS J1702-420A is found to be higher than 0.5 PeV at a 95% confidence level. Conclusions. For the first time, H.E.S.S. resolved two components with significantly different morphologies and spectral indices, both detected at > 5 σ confidence level, whose combined emissions result in the source HESS J1702-420. We detected HESS J1702-420A at a 4.0 σ confidence level in the energy band 64−113 TeV, which brings evidence for the source emission up to 100 TeV. In a hadronic emission scenario, the hard γ -ray spectrum of HESS J1702-420A implies that the source likely harbors PeV protons, thus becoming one of the most solid PeVatron candidates detected so far in H.E.S.S. data. However, a leptonic origin of the observed TeV emission cannot be ruled out either.
ABSTRACT
We report on the detection of very high energy (VHE; E > 100 GeV) γ-ray emission from the BL Lac objects KUV 00311−1938 and PKS 1440−389 with the High Energy Stereoscopic System (H.E.S.S.). ...H.E.S.S. observations were accompanied or preceded by multiwavelength observations with Fermi/LAT, XRT and UVOT onboard the Swift satellite, and ATOM. Based on an extrapolation of the Fermi/LAT spectrum towards the VHE γ-ray regime, we deduce a 95 per cent confidence level upper limit on the unknown redshift of KUV 00311−1938 of $z$ < 0.98 and of PKS 1440−389 of $z$ < 0.53. When combined with previous spectroscopy results, the redshift of KUV 00311−1938 is constrained to 0.51 ≤ $z$ < 0.98 and of PKS 1440−389 to 0.14 ⪅ $z$ < 0.53.
Abstract
Cosmological
N
-body simulations show that Milky Way–sized galaxies harbor a population of unmerged dark matter (DM) subhalos. These subhalos could shine in gamma-rays and eventually be ...detected in gamma-ray surveys as unidentified sources. We performed a thorough selection among unidentified Fermi-Large Area Telescope Objects (UFOs) to identify them as possible tera-electron-volt-scale DM subhalo candidates. We search for very-high-energy (E ≳ 100 GeV) gamma-ray emissions using H.E.S.S. observations toward four selected UFOs. Since no significant very-high-energy gamma-ray emission is detected in any data set of the four observed UFOs or in the combined UFO data set, strong constraints are derived on the product of the velocity-weighted annihilation cross section 〈
σ
v
〉 by the
J
factor for the DM models. The 95% confidence level observed upper limits derived from combined H.E.S.S. observations reach 〈
σ
v
〉
J
values of 3.7 × 10
−5
and 8.1 × 10
−6
GeV
2
cm
−2
s
−1
in the
W
+
W
−
and
τ
+
τ
−
channels, respectively, for a 1 TeV DM mass. Focusing on thermal weakly interacting massive particles, the H.E.S.S. constraints restrict the
J
factors to lie in the range 6.1 × 10
19
–2.0 × 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 × 10
19
–7.1 × 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 DM models with masses >0.3 TeV for the UFO emissions can be ruled out at high confidence level.
Aims.
Colliding wind binary systems have long been suspected to be high-energy (HE; 100 MeV <
E
< 100 GeV)
γ
-ray emitters.
η
Car is the most prominent member of this object class and is confirmed to ...emit phase-locked HE
γ
rays from hundreds of MeV to ~100 GeV energies. This work aims to search for and characterise the very-high-energy (VHE;
E
>100 GeV)
γ
-ray emission from
η
Car around the last periastron passage in 2014 with the ground-based High Energy Stereoscopic System (H.E.S.S.).
Methods.
The region around
η
Car was observed with H.E.S.S. between orbital phase
p
= 0.78−1.10, with a closer sampling at
p
≈ 0.95 and
p
≈ 1.10 (assuming a period of 2023 days). Optimised hardware settings as well as adjustments to the data reduction, reconstruction, and signal selection were needed to suppress and take into account the strong, extended, and inhomogeneous night sky background (NSB) in the
η
Car field of view. Tailored run-wise Monte-Carlo simulations (RWS) were required to accurately treat the additional noise from NSB photons in the instrument response functions.
Results.
H.E.S.S. detected VHE
γ
-ray emission from the direction of
η
Car shortly before and after the minimum in the X-ray light-curve close to periastron. Using the point spread function provided by RWS, the reconstructed signal is point-like and the spectrum is best described by a power law. The overall flux and spectral index in VHE
γ
rays agree within statistical and systematic errors before and after periastron. The
γ
-ray spectrum extends up to at least ~400 GeV. This implies a maximum magnetic field in a leptonic scenario in the emission region of 0.5 Gauss. No indication for phase-locked flux variations is detected in the H.E.S.S. data.
Abstract
Magnetar hyperflares are the most plausible explanation for fast radio bursts (FRBs)—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 an 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. 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 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.
The detection of the first electromagnetic counterpart to the binary neutron star (BNS) merger remnant GW170817 established the connection between short γ-ray bursts and BNS mergers. It also ...confirmed the forging of heavy elements in the ejecta (a so-called kilonova) via the r-process nucleosynthesis. The appearance of nonthermal radio and X-ray emission, as well as the brightening, which lasted more than 100 days, were somewhat unexpected. Current theoretical models attempt to explain this temporal behavior as either originating from a relativistic off-axis jet or a kilonova-like outflow. In either scenario, there is some ambiguity regarding how much energy is transported in the nonthermal electrons versus the magnetic field of the emission region. Combining the Very Large Array (radio) and Chandra (X-ray) measurements with observations in the GeV-TeV domain can help break this ambiguity, almost independently of the assumed origin of the emission. Here we report for the first time on deep H.E.S.S. observations of GW170817/GRB 170817A between 124 and 272 days after the BNS merger with the full H.E.S.S. array of telescopes, as well as on an updated analysis of the prompt (<5 days) observations with the upgraded H.E.S.S. phase-I telescopes. We discuss implications of the H.E.S.S. measurement for the magnetic field in the context of different source scenarios.
The sediments from the Coari lake, a "terra firme" lake sculpted into Plio-Pleistocene deposits, and the Acará lake, a flooding-type lake developed on Quaternary sediments in the floodplain of the ...mid-Solimões river, in the western Amazônia, Brazil, were studied to investigate the environmental condition of their developing. This study includes mineral composition, geochemistry, Pb isotope, palinology, radiocarbon-age and morphological framework of the lakes obtained from SRTM satellite images. The geological and the environmental conditions in the two lakes are highly variable and suggest that their evolution reflect autogenic processes under humid rainforest condition. Although kaolinite, quartz, muscovite, illite, and smectite are the main minerals in both lakes, the geochemistry indicates distinct source, the Acará lake sediments have higher concentrations of Al(2)O(3), Fe(2)O(3), FeO, CaO, K(2)O, MgO, Na(2)O, P(2)O(5), Ba, V, Cu, Ni, Zn, Pb, Sr, Li, Y and La and have more radiogenic Pb than the Coari lake sediments. The radiocarbon ages suggest that at 10160 yr BP the Coari lake started to be developed due to avulsion of the Solimões river, and the Acará lake was formed by the meander abandonment of Solimões river retaining its grass dominated shore at ca. 3710 yr BP.
Stable isotopes in gibbsite and kaolinite were analyzed to reconstruct the Amazonia palaeoclimate during the Cenozoic and to investigate the environmental conditions of the weathering process and the ...origin of the Oxisol that cover the lateritic/bauxite crust. At least two types of kaolinite were identified in the Oxisol; near the surface, the kaolinite is less fractionated and was developed at a higher temperature (35
°C). This is probably due to the effect of vegetation and/or evapotranspiration or is a consequence of surface microenvironmental conditions or allochthonous inputs. The other kaolinite samples ranged in formation temperatures from 21
°C to 26
°C and developed under conditions similar to the Pleistocene and the modern climate of Amazonia. At least two types of gibbsite were found. One type developed in the modern Amazonia climate, in a way similar to most kaolinite samples, whereas the samples of the other type are more fractionated. This is because they may have been formed in low recycling rainwater and/or under a low amount of precipitation. These two conditions indicate a seasonal climate for bauxite development that can be linked to the low exhumation of the Andes cordillera and its geographical position relative to the Trombetas region during the period ranging from the Late Oligocene to the Early Miocene. At the end of the Cenozoic, the climate was less seasonal and wetter and the temperature was lower In addition, there was the probable inland position of the Trombetas region, which allowed Oxisol development. The gibbsite developed earlier than the kaolinite of the Oxisol, but there is a partial inheritance, or temporal equivalence, among the bauxite horizon and the Oxisol, as well as multiple generations of gibbsite and kaolinite, which is to be expected for materials developing over long periods in hard leaching conditions.
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