10 research outputs found
Upper limits on the isotropic diffuse flux of cosmic PeV photons from Carpet-2 observations
Isotropic diffuse gamma-ray flux in the PeV energy band is an important tool
for multimessenger tests of models of the origin of high-energy astrophysical
neutrinos and for new-physics searches. So far, this flux has not yet been
observed. Carpet-2 is an air-shower experiment capable of detecting
astrophysical gamma rays with energies above 0.1 PeV. Here we report the upper
limits on the isotropic gamma-ray flux from Carpet-2 data obtained in 1999-2011
and 2018-2022. These results, obtained with the new statistical method based on
the shape of the muon-number distribution, summarize Carpet-2 observations as
the upgraded installation, Carpet-3, starts its operation.Comment: 5 pages, 3 figures, JETPL.cls; V2: references added, version accepted
by JETP Letter
STRUCTURAL SLOTTING WITH UNIFORM REDISTRIBUTION FOR ENHANCING TRUSTWORTHINESS OF INFORMATION STREAMS
Constraints on the extragalactic magnetic field strength from blazar spectra based on 145 months of Fermi-LAT observations
Properties of the extragalactic magnetic field (EGMF) outside of clusters and
filaments of the large-scale structure are essentially unknown. The EGMF could
be probed with -ray observations of distant (redshift )
blazars. TeV rays from these sources are strongly absorbed on
extragalactic background light photons; secondary electrons and positrons
produce cascade rays with the observable flux dependent on EGMF
parameters. We put constraints on the EGMF strength using 145 months of
Fermi-LAT observations of the blazars 1ES 1218+304, 1ES 1101-232, and 1ES
0347-121, and imaging atmospheric Cherenkov telescope observations of the same
sources. We perform a series of full direct Monte Carlo simulations of
intergalactic electromagnetic cascades with the ELMAG 3.01 code and construct a
model of the observable spectra inside the point spread functions of the
observing instruments for a range of EGMF strengths. We compare the observed
spectra with the models for various values of the EGMF strength and
calculate the exclusion statistical significance for every value of . We
find that the values of the EGMF strength G are excluded at a
high level of the statistical significance for all the four
options of the intrinsic spectral shape considered (power-law, power-law with
exponential cutoff, log-parabola, log-parabola with exponential cutoff). The
value of G is not excluded; it is still a viable option of the
EGMF strength. These results were obtained for the case of steady sources.Comment: 8 pages, 3 figures, 2 tables. Moderate text changes w.r.t. v1.
Supplementary material is available at
http://dx.doi.org/10.5281/zenodo.648335
The 6 September 2017 X-Class Solar Flares and Their Impacts on the Ionosphere, GNSS, and HF Radio Wave Propagation
International audienceOn 6 September 2017, the Sun emitted two significant solar flares (SFs). The first SF, classified X2.2, peaked at 09:10 UT. The second one, X9.3, which is the most intensive SF in the current solar cycle, peaked at 12:02 UT and was accompanied by solar radio emission. In this work, we study ionospheric response to the two X-class SFs and their impact on the Global Navigation Satellite Systems and high-frequency (HF) propagation. In the ionospheric absolute vertical total electron content (TEC), the X2.2 SF caused an overall increase of 2-4 TECU on the dayside. The X9.3 SF produced a sudden increase of~8-10 TECU at midlatitudes and of~15-16 TECU enhancement at low latitudes. These vertical TEC enhancements lasted longer than the duration of the EUV emission. In TEC variations within 2-20 min range, the two SFs provoked sudden increases of~0.2 TECU and 1.3 TECU. Variations in TEC from geostationary and GPS/GLONASS satellites show similar results with TEC derivative of~1.3-1.7 TECU/min for X9.3 and 0.18-0.24 TECU/min for X2.2 in the subsolar region. Further, analysis of the impact of the two SFs on the Global Navigation Satellite Systems-based navigation showed that the SF did not cause losses-of-lock in the GPS, GLONASS, or Galileo systems, while the positioning error increased by~3 times in GPS precise point positioning solution. The two X-class SFs had an impact on HF radio wave propagation causing blackouts at <30 MHz in the subsolar region and <15 MHz in the postmidday sector