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Register a new userThermal neutron flux produced by EAS at various altitudes
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The results of Monte-Carlo simulations of Extensive Air Shower are presented to show the difference of hadronic component content at various altitudes with the aim to choose an optimal altitude for the PRISMA-like experiment. CORSIKA program for EAS simulations with QGSJET and GHEISHA models was used to calculate the number of hadrons reaching the observational level inside a ring of 50 m radius around the EAS axis. Then the number of neutrons produced by the hadronic component was calculated using an empirical relationship between the two components. We have tested the results with the ProtoPRISMA array at sea level, and recorded neutrons are close to the simulation results.
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A novel type of EAS array (PRISMA-32) has been constructed on the base of NEVOD-DECOR experiment (MEPhI,Moscow) and is now taking data. It consists of 32 specially designed scintillator en-detectors able to measure two main EAS components: hadrons (n) and electrons (e). First results on thermal neutron lateral as well as temporal distributions are presented. Obtained exponential neutron lateral distributions are consistent with that expected for normal hadron production with exponential transverse momentum distribution. As there are no other experimental data on thermal neutron distributions and so, to compare results with other measurements, we additionally obtained electron lateral distribution function (using the same detectors) and compared it with NKG - function. Recorded neutron temporal distributions are very close to that obtained with data of our previous prototypes.
The observation of a radioactively powered kilonova AT~2017gfo associated with the gravitational wave-event GW170817 from binary neutron star merger proves that these events are ideal sites for the production of heavy $r$-process elements. The gamma-ray photons produced by the radioactive decay of heavy elements are unique probes for the detailed nuclide compositions. Basing on the detailed $r$-process nucleosynthesis calculations and considering radiative transport calculations for the gamma-rays in different shells, we study the gamma-ray emission in a merger ejecta on a timescale of a few days. It is found that the total gamma-ray energy generation rate evolution is roughly depicted as $dot{E}propto t^{-1.3}$. For the dynamical ejecta with a low electron fraction ($Y_{rm e}lesssim0.20$), the dominant contributors of gamma-ray energy are the nuclides around the second $r$-process peak ($Asim130$), and the decay chain of $^{132}$Te ($t_{1/2}=3.21$~days) $rightarrow$ $^{132}$I ($t_{1/2}=0.10$~days) $rightarrow$ $^{132}$Xe produces gamma-ray lines at $228$ keV, $668$ keV, and $773$ keV. For the case of a wind ejecta with $Y_{rm e}gtrsim0.30$, the dominant contributors of gamma-ray energy are the nuclides around the first $r$-process peak ($Asim80$), and the decay chain of $^{72}$Zn ($t_{1/2}=1.93$~days) $rightarrow$ $^{72}$Ga ($t_{1/2}=0.59$~days) $rightarrow$ $^{72}$Ge produces gamma-ray lines at $145$ keV, $834$ keV, $2202$ keV, and $2508$ keV. The peak fluxes of these lines are $10^{-9}sim 10^{-7}$~ph~cm$^{-2}$ s$^{-1}$, which are marginally detectable with the next-generation MeV gamma-ray detector emph{ETCC} if the source is at a distance of $40$~Mpc.
The binary neutron star merger event GW170817 was detected through both electromagnetic radiation and gravitational waves. Its afterglow emission may have been produced by either a narrow relativistic jet or an isotropic outflow. High spatial resolution measurements of the source size and displacement can discriminate between these scenarios. We present Very Long Baseline Interferometry observations, performed 207.4 days after the merger, using a global network of 32 radio telescopes. The apparent source size is constrained to be smaller than 2.5 milliarcseconds at the 90% confidence level. This excludes the isotropic outflow scenario, which would have produced a larger apparent size, indicating that GW170817 produced a structured relativistic jet. Our rate calculations show that at least 10% of neutron star mergers produce such a jet.
The events of multiple neutron production under 2000g/cm$^2$ thick rock absorber were studied at the Tien~Shan mountain cosmic ray station, at the altitude of 3340m above the sea level. From comparison of the experimental and Geant4 simulated neutron multiplicity spectra it follows that the great bulk of these events can be explained by interaction of cosmic ray muons with internal material of the neutron detector. In synchronous operation of the underground neutron monitor with the Tien~Shan shower detector system it was found that the characteristics of the muonic component of extensive air showers which is seemingly responsible for generation of the neutron events underground do change noticeably within the energy range of the knee of primary cosmic ray spectrum. Some peculiar shower events were detected when the neutron signal reveals itself only $sim$(100--1000),$mu$s after the passage of the shower particles front which probably means an existence of corresponding delay of the muon flux in such events.
Obtaining high-sensitivity measurements of degree-scale cosmic microwave background (CMB) polarization is the most direct path to detecting primordial gravitational waves. Robustly recovering any primordial signal from the dominant foreground emission will require high-fidelity observations at multiple frequencies, with excellent control of systematics. We explore the potential for a new platform for CMB observations, the Airlander 10 hybrid air vehicle, to perform this task. We show that the Airlander 10 platform, operating at commercial airline altitudes, is well-suited to mapping frequencies above 220 GHz, which are critical for cleaning CMB maps of dust emission. Optimizing the distribution of detectors across frequencies, we forecast the ability of Airlander 10 to clean foregrounds of varying complexity as a function of altitude, demonstrating its complementarity with both existing (Planck) and ongoing (C-BASS) foreground observations. This novel platform could play a key role in defining our ultimate view of the polarized microwave sky.
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