We report improved measurements of the all flavor astrophysical neutrino spectrum with IceCube by combining complementary neutrino samples in two independent analyses. Both analyses show evidence of a harder spectrum at energies below ∼30 TeV compared to higher energies where the spectrum is well characterized by a power law. The spectrum is better described by a log parabola or a broken power law, the latter being the preferred model. Both, however, reject a single power law over an energy range 5 TeV-10 PeV with a significance >4σ, providing new constraints on properties of cosmic neutrino sources.

Recently, IceCube reported neutrino emission from the Seyfert galaxy NGC 1068. Using 13.1 yr of IceCube data, we present a follow-up search for neutrino sources in the northern sky. NGC 1068 remains the most significant neutrino source among 110 preselected gamma-ray emitters while also being spatially compatible with the most significant location in the northern sky. Its energy spectrum is characterized by an unbroken power-law with spectral index γ = 3.4 ± 0.2. Consistent with previous results, the observed neutrino flux exceeds its gamma-ray counterpart by at least 2 orders of magnitude. Motivated by this disparity and the high X-ray luminosity of the source, we selected 47 X-ray-bright Seyfert galaxies from the Swift/BAT spectroscopic survey that were not included in the list of gamma-ray emitters. When testing this collection for neutrino emission, we observe a 3.3 σ excess from an ensemble of 11 sources, with NGC 1068 excluded from the sample. Our results strengthen the evidence that X-ray-bright cores of active galactic nuclei are neutrino emitters.

The observation of very-high-energy (VHE; > 10 GeV) γ-ray emission from γ-ray bursts (GRBs), especially in the prompt phase, will provide critical information for understanding many aspects of their nature including the physical environment, the relativistic bulk motion, the mechanisms of particle acceleration of GRBs, and for studying Lorentz invariance violation, etc. For the afterglow phase, the highest-energy photons detected to date by the imaging atmospheric Cherenkov telescopes extend to the TeV regime. However, for the prompt phase, years of efforts in searching for the VHE emission has yielded no statistically significant detections. A wide field of view and large effective area above tens of GeV are essential for detecting the VHE emissions from GRBs in the prompt phase. The High Altitude Detection of Astronomical Radiation (HADAR) experiment has such merits. In this paper, we report the estimates of its expected annual GRB detection rate, which are obtained by combining the performance of the HADAR instrument with the theoretical calculations based on a phenomenological model to generate the pseudo-GRB population. The expected detectable gamma-ray signal from GRBs above the background is then obtained to give the detection rate. In the spectral model, an extra component is assigned to every GRB event in addition to the Band function. The results indicate that if the energy of the cutoff due to internal absorption is higher than 50 GeV, the detection rate for GRBs for the HADAR experiment is approximately two or three GRBs per year, which varies slightly depending upon the characteristics of the extra component.

Cosmic ray (CR) spectra show a two-component structure for both primary and secondary particles. In our study, we think that this feature roots in a nearby source halo. This halo acts as a reservoir for CRs in the source region, leading to the high-energy component. Furthermore, it acts as a barrier, effectively halting the travel of CRs from other sources directly in the disk, this causes CRs to propagate from the outer disk and contribute to the low-energy component. As a result, all the spectra anomalies could be well reproduced. This scenario can be extended to the whole disk, we prospect high-energy diffuse $\gamma$-ray emissions exhibit highly spatial dependence, emanating from local sources. We urge HAWC/LHAASO to detect diffuse $\gamma$ ray on the spatial scale of a few square degrees.

High-precision measurement of the isotropic diffuse γ-ray background (IGRB) has been extrapolated to the TeV energy region using the Fermi-LAT experiment. Various kinds of astrophysical sources are candidates for its origin. However, a consensus on the dominant source has been difficult to reach. Recent observations of the γ-ray emission of γ-ray bursts (GRBs), denoted as the synchrotron self-Compton (SSC) component in the afterglow phase, in the sub-TeV energy region by MAGIC and HESS experiments shed new light on this topic. In this work, we revisit the contribution from the SSC component of GRBs to the IGRB. First, a sample set of GRB events is obtained and examined using observations from Fermi-LAT. Second, the SSC component, described by the energy ratio R _ext and spectral index β _ext, is assigned to every GRB event. We can obtain the total spectrum contribution based on this GRB sample. We find that when R _ext and β _ext reach ∼20% and −1.6, respectively, the contribution from GRB emission dominates in the energy region of hundreds of GeV. We hope that the LHAASO and CTA experiments under construction can observe a large number of GRBs to fix those parameters in coming years. A surviving tail is expected, which can serve to check our calculations based on future satellite experiments such as HERD and GAMMA400.