Observation of the Gamma-Ray Binary HESS J0632+057 with the H.E.S.S., MAGIC, and VERITAS Telescopes

The results of gamma-ray observations of the binary system HESS J0632 + 057 collected during 450 hr over 15 yr, between 2004 and 2019, are presented. Data taken with the atmospheric Cherenkov telescopes H.E.S.S., MAGIC, and VERITAS at energies above 350 GeV were used together with observations at X-ray energies obtained with Swift-XRT, Chandra, XMM-Newton, NuSTAR, and Suzaku. Some of these observations were accompanied by measurements of the Hα emission line. A significant detection of the modulation of the very high-energy gamma-ray fluxes with a period of 316.7 ± 4.4 days is reported, consistent with the period of 317.3 ± 0.7 days obtained with a refined analysis of X-ray data. The analysis of data from four orbital cycles with dense observational coverage reveals short-timescale variability, with flux-decay timescales of less than 20 days at very high energies. Flux variations observed over a timescale of several years indicate orbit-to-orbit variability. The analysis confirms the previously reported correlation of X-ray and gamma-ray emission from the system at very high significance, but cannot find any correlation of optical Hα parameters with fluxes at X-ray or gamma-ray energies in simultaneous observations. The key finding is that the emission of HESS J0632 + 057 in the X-ray and gamma-ray energy bands is highly variable on different timescales. The ratio of gamma-ray to X-ray flux shows the equality or even dominance of the gamma-ray energy range. This wealth of new data is interpreted taking into account the insufficient knowledge of the ephemeris of the system, and discussed in the context of results reported on other gamma-ray binary systems.

Duration of the Carbon Isotope Excursion in the Zhuya Group (Patom Basin, South Siberia)

<p>Probably the largest negative δ13С anomaly in Earth history called the “Shuram” excursion (SE) had taken place in the Ediacaran period. Determining the duration of SE is needed to resolve its nature and for the stratigraphic correlation of Ediacaran rocks. The cyclostartigraphic method allows to precisely determine the accumulation rates of ancient deposits (the theoretical error is up to 10,000 years), but the testing of the accuracy of the cyclostratigraphic method usually based on biostratigraphy and geochronology meets difficulties for the Precambrian deposits. The reliability of cyclostartigarphic estimates of the SE duration can be determined by the convergence of cyclostratigraphic results obtained from distant sections on different continents and in sections representing different depositional environments. Recently limitations on the SE duration have been obtained in Australia, California, Oman, and China. Recently limitations on the SE duration have been obtained in Australia, California, Oman, and China. Here we present the first cyclostratigraphic estimates of the SE duration from the Zhuya Group of the Patom basin in South Siberia.</p><p>Two sections of the Zhuya Group were studied, both recording the decrease of the δ13С values up to -12 ‰  in the nadir point and then increase till -9 ‰. In both sections, the cyclicity of variations in magnetic susceptibility (MS) was studied. The first section (57 m, Nikolskoe Fm.) represents sediments deposited on the slope of the carbonate platform. Spectral analysis of the MS variations revealed peaks above 95% significance level on the period lengths of 11.5, 1.73, 1.04, 0.67, 0.51 m with ratios 1/6.6 /11/17/22.3 respectively. This cyclicity is interpreted as a reflection of orbitally forced climate changes, where the longest-period variations correspond to short eccentricity cycles (100 ky). Then, the studied interval lasted approximately 500 ky, and the duration of the entire Nikolskaya Fm., corresponding to the lower third of the SE, is about 2.5 My.</p><p>The second section belongs to the Torgo Fm. in the Berezovskaya depression, which is the epicontinental part of the Patom Basin. MS variations in the studied 14.2 m interval shows significant peaks at period lengths of 2.3, 0.74, 0.51, 0.38, 0.28, 0.27, 0.25, 0.20 m with ratios 1.00/3.13/4.52/6.10/8.03/8.48/9.19/11.52. In this section, we also interpret the longest-period of the MS variations as a reflection of cycles of short eccentricity (100 ka). Then, the duration of the studied interval is 613 ky.  and the SE duration in the whole 200 meters of the Torgo Fm. is estimated as 8.6 My.</p><p> </p><p>The obtained preliminary results are in good agreement with those from Australia (ca. 8 My), Oman (7.7 +/- 0.2 My), North America (8.2 +/- 1.2 My), and China (9.1 +/- 1 My). Thus, the influence of Milankovitch's orbital cycles on the formation of carbonate deposits of the Late Precambrian seems to be quite convincing, and the cyclostratigraphic estimate of the duration of the SE about 10 Ma is more and more reliable.</p><p>Research supported by the Russian Science Foundation (project № 20-77-10066)</p>

Role of Longitudinal Lithological Contrast On the Channel Evolution of Piedmont Rivers

<p>The cut-and-fill terrace sequence, resulted from aggradation and incision cycles of alluvial rivers on the piedmont of active orogens, is a common tectonic geomorphological feature observed across different continents under different climatic regimes. Such aggradation and incision cycles are identified on both the orbital and sub-orbital cycles, which poses a question about their origins. Efforts have been put into disentangling the contributions from tectonics, climate and other autogenic sources. In this study, we investigated it by exploring the cut-and-fill terrace sequences along the Jingou River on the northern piedmont of Chinese Tianshan, where numerous terraces are seen along tens of alluvial rivers flowing through the fold-and-thrust belt. More than ten terrace flights, are observed where Jingou River flows across the active Huoerguosi anticline. We collected sediment samples for OSL dating to decipher the building and abandonment processes of these terraces and made topographic measurements to evaluate the paleo-slope of this section of Jingou River. Detailed field survey of sedimentary structure and luminescence dates unambiguously unveil the aggradation and incision cycles on sub-orbital cycles since the last interglacial. Down-cutting of no less than 80 meters is identified during the last ten thousands of years. We tentatively evaluated the possible roles of regional climatic variation, anticline deformation and the autogenic processes. Of all these factors, we detailedly investigated the role of longitudinal contrast of lithologies along the river due to the deformation of the Huoerguosi anticline, which always promotes the channel incision.</p>

Transient Climate Simulations of Orbital Effects on Mesozoic Climates

<p>The Mesozoic era (~252—66 Ma) is traditionally considered as a prolonged greenhouse period, witnessing the breakup of the Pangaean supercontinent. Orbital cycles have, for example, been invoked as drivers of e.g. Pangaean „Megamonsoon“ variability and eustatic sea level cycles in the Mesozoic.</p><p>We aim to contribute to a more comprehensive understanding of orbital effects on Mesozoic climates by employing the newly developed CLIMBER-X Earth System Model. Here, we primarily use its coupled atmosphere, ocean, sea ice and vegetation modules, but also include preliminary tests with dynamic carbon cycle and ice-sheets. We present first results from a set of transient climate simulations of four Mesozoic timeslices representative for Triassic, Jurassic, Early Cretaceous and Late Cretaceous boundary conditions (e.g. paleogeography and solar luminosity). The simulations each cover ~100,000 years and are driven by changing precession, obliquity, and eccentricity.</p><p>We would like to use the opportunity to discuss this approach and associated questions with the community. For example: Would changing paleogeography and climate background state have modified the response to orbital forcings? Could eustatic sea level cycles have been caused by orbitally-driven redistribution of water between the ocean and land water storages or should orbitally-forced ice sheets also have played a role in the alleged Mesozoic greenhouse? Which connections can be established to proxy records?</p>

Gulf of Nuna: Astrochronologic correlation of a Mesoproterozoic oceanic euxinic event

The ca. 1.4 Ga Velkerri and Xiamaling Formations, in Australia and the north China craton, respectively, are both carbonaceous shale deposits that record a prominent euxinic interval and were intruded by ca. 1.3 Ga dolerite sills. These similarities raise the possibility that these two units correlate, which would suggest the occurrence of widespread euxinia, organic carbon burial, and source rock deposition. Paleomagnetic data are consistent with Australia and the north China craton being neighbors in the supercontinent Nuna and thus permit deposition in a single large basin, and the putative stratigraphic correlation. However, lack of geochronological data has precluded definitive testing. The Xiamaling Formation has been shown to exhibit depositional control by orbital cycles. Here, we tested the putative correlation with the Velkerri Formation by cyclostratigraphic analysis. The Velkerri Formation exhibits sedimentological cycles that can be interpreted to represent the entire hierarchy of orbital cycles, according to a sedimentation rate that is consistent with Re-Os ages. Comparison of the inferred durations of the euxinic intervals preserved in both the Xiamaling and Velkerri Formations reveals a nearly identical ∼10-m.y.-long oceanic euxinic event. This permits the interpretation that the two hydrocarbon-rich units were deposited and matured in the same basin of Nuna, similar to the Gulf of Mexico during the breakup of Pangea.

Orbital pacing and secular evolution of the Early Jurassic carbon cycle

Global perturbations to the Early Jurassic environment (∼201 to ∼174 Ma), notably during the Triassic–Jurassic transition and Toarcian Oceanic Anoxic Event, are well studied and largely associated with volcanogenic greenhouse gas emissions released by large igneous provinces. The long-term secular evolution, timing, and pacing of changes in the Early Jurassic carbon cycle that provide context for these events are thus far poorly understood due to a lack of continuous high-resolution δ13C data. Here we present a δ13CTOC record for the uppermost Rhaetian (Triassic) to Pliensbachian (Lower Jurassic), derived from a calcareous mudstone succession of the exceptionally expanded Llanbedr (Mochras Farm) borehole, Cardigan Bay Basin, Wales, United Kingdom. Combined with existing δ13CTOC data from the Toarcian, the compilation covers the entire Lower Jurassic. The dataset reproduces large-amplitude δ13CTOC excursions (>3‰) recognized elsewhere, at the Sinemurian–Pliensbachian transition and in the lower Toarcian serpentinum zone, as well as several previously identified medium-amplitude (∼0.5 to 2‰) shifts in the Hettangian to Pliensbachian interval. In addition, multiple hitherto undiscovered isotope shifts of comparable amplitude and stratigraphic extent are recorded, demonstrating that those similar features described earlier from stratigraphically more limited sections are nonunique in a long-term context. These shifts are identified as long-eccentricity (∼405-ky) orbital cycles. Orbital tuning of the δ13CTOC record provides the basis for an astrochronological duration estimate for the Pliensbachian and Sinemurian, giving implications for the duration of the Hettangian Stage. Overall the chemostratigraphy illustrates particular sensitivity of the marine carbon cycle to long-eccentricity orbital forcing.