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An automatic procedure for identification of VLF detected lightning discharges in Extremely Low Frequency (ELF) measurements is presented to enable large scale analysis of global lightning and ELF propagation properties which are determined by the lower ionosphere. Using a single ELF sensor in Poland we are able to identify the majority (∼80% or more) of lightning events detected by the WWLLN VLF network. Measured in ELF magnetic impulse components, EW and NS, enable the polarity (positive or negative) determination of the WWLLN‐detected strokes, thereby complementing the WWLLN data set with polarity information. We separately analyzed the data from Africa and from the whole globe, identifying positive discharges among all identified impulses. We find that the lightning energy evaluations based on VLF measurements are only weakly correlated with lightning charge moments, which manifest themselves in the measured signal amplitudes in the ELF band. The ratio of positive discharges shows an expected significant increase for the highest amplitude impulses. We also reveal a low amplitude component dominated by positive discharges that we attribute to artifacts of the recording hardware and filtering processes. 

The Extremely Low Frequency band (ELF: 0.03–1,000 Hz) electromagnetic signals from thunderstorm lightning discharges can propagate around the globe in the Earth‐ionosphere resonance cavity and thus be used for ionosphere monitoring. We use ELF observations of impulses detected by the World Wide Lightning Location Network (WWLLN) to investigate ELF propagation velocity and arrival azimuth under diurnal changes over 2 days in September 2023. Also, temporary effects of solar flares' ionizing fluxes are monitored, leading to increase of the ELF signal propagation speed in proportion to the X‐ray flux intensity. We present a simple method for automatic and large‐scale analysis, utilizing data from two registration systems (our ELF reciever and WWLLN) and enabling easy evaluation of changes in wave propagation speed. Comparative analysis of WWLLN identified impulses generated in Africa and America reveals varying effects of signal refraction, with increased azimuth changes for signals propagating across the ionospheric ionization gradients associated with the day/night terminator. The method has a potential to become a standard tool for the analysis and monitoring of the lower layers of the ionosphere. 

Solar flares have profound impacts on the lower ionosphere and long‐distance radio propagation. Extremely low frequency (ELF: 3–3,000 Hz) waves are challenging to observe and experience unique interactions with the lower ionosphere. The primary natural sources of ELF waves are thunderstorm lightnings across the globe. Using a newly developed azimuth determination technique and improved observation hardware we show that ELF attenuation in the Earth‐Ionosphere spherical cavity decreases and propagation velocity increases under the influence of an M‐class solar flare. Using a two‐parameter model of the lower ionosphere, the observations are shown to be consistent with increased electron density and sharper gradients in the D‐region resulting from X‐ray radiation. The sharper electron density gradient is primarily responsible for the propagation velocity increase, suggesting a unique capability that ELF observations can bring to global remote sensing of the lower ionosphere under space weather perturbations. 

A new method is proposed for deriving extremely low frequency (ELF) wave arrival azimuths using the wide range of signal amplitudes, contrary to previously applied high amplitude impulses only. The method is applied to observations from our new magnetic sensor in the Hylaty station with an 18 bit dynamic range and a 3 kHz sampling frequency. We analyzed a day of 15 January 2022, to test the procedure against the ability to extract ELF signals generated during the Hunga Tonga volcano eruption. With complementary filtering of power line 50 Hz signatures, precise azimuth information can be extracted for waves from a multitude of thunderstorms on Earth varying during the day at different azimuths. A phenomenon of successive regular variation—decay or activation—of thunderstorms activity with varying azimuth is observed, possibly due to passing over the solar (day/night) terminator, and signatures of azimuth direction change during this passage can be noted. We also show that the erupting Hunga Tonga volcano associated impulses dispersed due to a long propagation path are clearly revealed in the azimuth distribution with analysis using parameters fitted to measure slowly varying signals, but not for fast varying impulses. We show that the Hunga Tonga related signals arrive from the azimuth ≈10° smaller than the geographic great circle path. The discrepancy is believed to be due to propagation through the polar region and in the vicinity of the solar terminator. 

Abstract On 9 October 2022, a powerful gamma ray burst (GRB), GRB221009A, caused significant changes in the electron density of the lower ionosphere, as evidenced by VLF (3–30 kHz) radio wave observations. However, GRB221009A did not yield any observable signatures at the Schumann resonances (∼8, ∼14 Hz), which are also sensitive to the lower ionosphere. We show that the effects of GRB221009A are observable in a decrease in propagation velocity of ELF (3–1,000 Hz) lightning impulses. Analytical and numerical analysis points to an ionospheric perturbation in which the GRB increased the daytime electron density uniformly over a wide altitude range from 50 to 90 km. The GRB perturbation is markedly different from perturbations from solar flares, which significantly increase the vertical gradient of the electron density. ELF propagation velocity is shown to be a technique that can identify the altitude range of ionospheric perturbations. 

Abstract Cercarial dermatitis (‘swimmer's itch’; SI), characterized by small itchy bumps caused by schistosome parasites of birds and mammals, is a common problem in Michigan. Research on avian schistosomes began nearly 100 years ago in Michigan inland lakes, yet scientists are still uncovering basic biological information including the identification of local snail and parasite species that cause SI. Previous research primarily focused on lakes in the northern half of Michigan's lower peninsula, although SI occurs throughout the state. We surveyed snails and snail-borne trematodes in lakes across Michigan's lower peninsula and used quantitative polymerase chain reaction analysis of filtered water samples to identify parasites to the species level, including a recently discovered parasite species that uses the snail Planorbella (Helisoma) trivolvis as its intermediate host. Most SI mitigation efforts have focused on a parasite species hosted by the snail Lymnaea catescopium ( = Stagnicola emarginata ); however, lymnaeid snails and their associated schistosome species were largely restricted to northern lakes. In contrast, P. trivolvis and its associated parasite species were common in both northern and southern Michigan lakes. A third schistosome species associated with physid snails was also present at low levels in both northern and southern lakes. These results indicate that the recently discovered parasite species and its planorbid snail intermediate host may be more important drivers of Michigan SI than previously thought, possibly due to increased definitive host abundance in recent decades. These results have potentially important implications for SI mitigation and control efforts. 

ABSTRACT OT 081 is a well-known, luminous blazar that is remarkably variable in many energy bands. We present the first broadband study of the source, which includes very high energy (VHE, $$E\gt $$ 100 GeV) $$\gamma$$-ray data taken by the MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov telescopes) and H.E.S.S. (High Energy Stereoscopic System) imaging Cherenkov telescopes. The discovery of VHE $$\gamma$$-ray emission happened during a high state of $$\gamma$$-ray activity in July 2016, observed by many instruments from radio to VHE $$\gamma$$-rays. We identify four states of activity of the source, one of which includes VHE $$\gamma$$-ray emission. Variability in the VHE domain is found on daily time-scales. The intrinsic VHE spectrum can be described by a power law with index $$3.27\pm 0.44_{\rm stat}\pm 0.15_{\rm sys}$$ (MAGIC) and $$3.39\pm 0.58_{\rm stat}\pm 0.64_{\rm sys}$$ (H.E.S.S.) in the energy range of 55–300 and 120–500 GeV, respectively. The broadband emission cannot be successfully reproduced by a simple one-zone synchrotron self-Compton model. Instead, an additional external Compton component is required. We test a lepto-hadronic model that reproduces the data set well and a proton-synchrotron-dominated model that requires an extreme proton luminosity. Emission models that are able to successfully represent the data place the emitting region well outside of the broad-line region to a location at which the radiative environment is dominated by the infrared thermal radiation field of the dusty torus. In the scenario described by this flaring activity, the source appears to be a flat spectrum radio quasar (FSRQ), in contrast with past categorizations. This suggests that the source can be considered to be a transitional blazar, intermediate between BL Lac and FSRQ objects. 

Abstract Dwarf spheroidal galaxies (dSphs) are excellent targets for indirect dark matter (DM) searches using gamma-ray telescopes because they are thought to have high DM content and a low astrophysical background. The sensitivity of these searches is improved by combining the observations of dSphs made by different gamma-ray telescopes. We present the results of a combined search by the most sensitive currently operating gamma-ray telescopes, namely: the satellite-borneFermi-LAT telescope; the ground-based imaging atmospheric Cherenkov telescope arrays H.E.S.S., MAGIC, and VERITAS; and the HAWC water Cherenkov detector. Individual datasets were analyzed using a common statistical approach. Results were subsequently combined via a global joint likelihood analysis. We obtain constraints on the velocity-weighted cross section 〈σv〉 for DM self-annihilation as a function of the DM particle mass. This five-instrument combination allows the derivation of up to 2-3 times more constraining upper limits on 〈σv〉 than the individual results over a wide mass range spanning from 5 GeV to 100 TeV. Depending on the DM content modeling, the 95% confidence level observed limits reach 1.5×10^-24 cm³s^-1and 3.2×10^-25 cm³s^-1, respectively, in theτ⁺τ^-annihilation channel for a DM mass of 2 TeV. 

Abstract This paper presents the expected sensitivity to the neutrino oscillation parameters of the Hyper-Kamiokande long-baseline program. The Hyper-Kamiokande experiment, currently under construction in Japan, will measure the oscillations of accelerator-produced neutrinos with thousands of selected events per sample: this corresponds to an increase of statistics of a factor 25–100 with respect to recent results from the currently-running long-baseline neutrino oscillation experiment in Japan, T2K. In the most favorable scenario we will achieve the discovery of Charge-Parity (CP) violation in neutrino oscillation at$$5\sigma $$ $5\sigma$ C.L. in less than 3 years. With 10 years of data-taking, and assuming a neutrino : antineutrino beam running ratio of 1:3, a CP violation discovery at$$5\sigma $$ $5\sigma$ C.L. is possible for more than 60% of the actual values of the CP-violating phase,$$\delta _{CP}.$$ ${\delta }_{\mathrm{CP}}.$ Moreover, we will measure$$\delta _{CP}$$ ${\delta }_{\mathrm{CP}}$ with a precision ranging from 20$$^{\circ },$$ $_{}^{\circ },$ in the case of maximal CP violation, to 6$$^{\circ },$$ $_{}^{\circ },$ in the case of CP conservation. We aim to achieve a 0.5% resolution on the$$\Delta m^2_{32}$$ $\Delta m_{32}^2$ parameter, and a resolution between 3% and 0.5% on the$$\sin ^2\theta _{23}$$ ${sin}^2{\theta }_{23}$ parameter, depending on its true value. These results are obtained by extending the analysis methods of T2K with dedicated tuning to take into account the Hyper-Kamiokande design: the larger far detector, the more powerful beam, the upgraded near detector ND280, and the planned additional Intermediate Water Cherenkov Detector. 

ABSTRACT A wide variety of Galactic sources show transient emission at soft and hard X-ray energies: low- and high-mass X-ray binaries containing compact objects, isolated neutron stars exhibiting extreme variability as magnetars as well as pulsar-wind nebulae. Although most of them can show emission up to MeV and/or GeV energies, many have not yet been detected in the TeV domain by Imaging Atmospheric Cherenkov Telescopes. In this paper, we explore the feasibility of detecting new Galactic transients with the Cherenkov Telescope Array Observatory (CTAO) and the prospects for studying them with Target of Opportunity observations. We show that CTAO will likely detect new sources in the TeV regime, such as the massive microquasars in the Cygnus region, low-mass X-ray binaries with low-viewing angle, flaring emission from the Crab pulsar-wind nebula or other novae explosions, among others. Since some of these sources could also exhibit emission at larger time-scales, we additionally test their detectability at longer exposures. We finally discuss the multiwavelength synergies with other instruments and large astronomical facilities.