Abstract GRB 221009A has posed a significant challenge to our current understanding of the mechanisms that produce TeV photons in gamma-ray bursts (GRBs). On one hand, the Klein–Nishina (KN) effect ...of the inverse Compton scattering leads to less efficient energy losses of high-energy electrons. On the other hand, at a redshift of 0.151, the TeV spectrum of GRB 221009A undergoes significant absorption by the extragalactic background light (EBL). Therefore, the observation of a 13 TeV photon in this event implies the presence of enormous photon fluxes at the source, which the synchrotron self-Compton mechanism in external shocks cannot easily generate. As an alternative, some authors have suggested the possibility of converting the TeV photons into axion-like particles (ALPs) at the host galaxy, in order to avoid the effects of EBL absorption, and then reconverting them into photons within the Milky Way. While this solution relaxes the requirement of very high photon fluxes, the KN effect still poses a challenge. Previously, we have shown that the injections of ALPs could explain the observation of 13 TeV photons. Here, we include the energy dependence of the probability of survival and the amount of energy carried to determine the ALP candidates, which could potentially explain the TeV photons observed by the Large High Altitude Air Shower Observatory and their hard spectrum. We found that the allowed candidates are generally clustered around masses of 10 −7 eV. We also considered different EBL models, for the one predicting larger attenuation tends to reject ALP candidates with the lowest coupling factor. For some hypotheses of the EBL model, these candidates are found below a region of the parameter space in which, if detected, ALPs could account for all of the cold dark matter in the Universe.
The pandemic has caused fear, especially due to the daily disseminated news; however, there is not an instrument to measure this fear in multiple realities.
To validate a scale for Latin American ...perception of fear and concern transmitted by the media during the pandemic.
This is an instrumental study. The survey was based on an instrument which was pre-validated in Peru and submitted to 15 experts in almost 10 countries. Subsequently, thousands of people were surveyed in 13 Latin American countries, whose answers were used for descriptive statistics for validation.
Confirmatory Factor Analysis (CFA) generated two re-specifications, where four items were eliminated from the original scale. With these changes, the global goodness of fit (absolute and incremental) were satisfactory (CFI = 0.978; TLI = 0.964; GFI = 0.976; AGFI = 0.949; RMSEA = 0.075 and RMR = 0.029). The first factor measures the media exaggeration (three questions); the second, the fear transmitted by the media (three questions); and the third, the fear transmitted by others different from the media (two questions). The Cronbach’s alpha coefficient was higher than 0.70 for the scale and its factors.
The MED-LAT-COVID-19 scale reported a good adjustment. It has eight items in three factors, which could be measured in an isolated way, or along with other tests that assess mental health in the current pandemic context.
Communications media; Fear; Pandemics; COVID-19 (Source: MeSH NLM).
Abstract
The High Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory surveys the very high-energy sky in the 300 GeV to >100 TeV energy range. HAWC has detected two blazars above 11
σ
, Markarian ...421 (Mrk 421) and Markarian 501 (Mrk 501). The observations are comprised of data taken in the period between 2015 June and 2018 July, resulting in ∼1038 days of exposure. In this work, we report the time-averaged spectral analyses for both sources, above 0.5 TeV. Taking into account the flux attenuation due to the extragalactic background light, the intrinsic spectrum of Mrk 421 is described by a power law with an exponential energy cutoff with index
α
=
2.26
±
0.12
stat
−
0.2
+
0.17
sys
and energy cutoff
E
c
=
5.1
±
1.6
stat
−
2.5
+
1.4
sys
TeV, while the intrinsic spectrum of Mrk 501 is better described by a simple power law with index
α
=
2.61
±
0.11
stat
−
0.07
+
0.01
sys
. The maximum energies at which the Mrk 421 and Mrk 501 signals are detected are 9 and 12 TeV, respectively. This makes these some of the highest energy detections to date for spectra averaged over years-long timescales. Since the observation of gamma radiation from blazars provides information about the physical processes that take place in their relativistic jets, it is important to study the broadband spectral energy distributions (SEDs) of these objects. For this purpose, contemporaneous data in the gamma-ray band to the X-ray range, and literature data in the radio to UV range, were used to build time-averaged SEDs that were modeled within a synchrotron-self Compton leptonic scenario.
Context.
Ground-based γ-ray astronomy is still a rather young field of research, with strong historical connections to particle physics. This is why most observations are conducted by experiments ...with proprietary data and analysis software, as is usual in the particle physics field. However, in recent years, this paradigm has been slowly shifting toward the development and use of open-source data formats and tools, driven by upcoming observatories such as the Cherenkov Telescope Array (CTA). In this context, a community-driven, shared data format (the
gamma-astro-data-format
, or GADF) and analysis tools such as
Gammapy
and
ctools
have been developed. So far, these efforts have been led by the Imaging Atmospheric Cherenkov Telescope community, leaving out other types of ground-based
γ
-ray instruments.
Aims.
We aim to show that the data from ground particle arrays, such as the High-Altitude Water Cherenkov (HAWC) observatory, are also compatible with the GADF and can thus be fully analyzed using the related tools, in this case,
Gammapy.
Methods.
We reproduced several published HAWC results using
Gammapy
and data products compliant with GADF standard. We also illustrate the capabilities of the shared format and tools by producing a joint fit of the Crab spectrum including data from six different
γ
-ray experiments.
Results.
We find excellent agreement with the reference results, a powerful confirmation of both the published results and the tools involved.
Conclusions.
The data from particle detector arrays such as the HAWC observatory can be adapted to the GADF and thus analyzed with
Gammapy.
A common data format and shared analysis tools allow multi-instrument joint analysis and effective data sharing. To emphasize this, a sample of Crab nebula event lists is made public with this paper. Because of the complementary nature of pointing and wide-field instruments, this synergy will be distinctly beneficial for the joint scientific exploitation of future observatories such as the Southern Wide-field Gamma-ray Observatory and CTA.
Abstract
The radio galaxy M87 is the central dominant galaxy of the Virgo Cluster. Very high-energy (VHE, ≳0.1 TeV) emission from M87 has been detected by imaging air Cherenkov telescopes. Recently, ...marginal evidence for VHE long-term emission has also been observed by the High Altitude Water Cherenkov Observatory, a gamma-ray and cosmic-ray detector array located in Puebla, Mexico. The mechanism that produces VHE emission in M87 remains unclear. This emission originates in its prominent jet, which has been spatially resolved from radio to X-rays. In this paper, we construct a spectral energy distribution from radio to gamma rays that is representative of the nonflaring activity of the source, and in order to explain the observed emission, we fit it with a lepto-hadronic emission model. We found that this model is able to explain nonflaring VHE emission of M87 as well as an orphan flare reported in 2005.
Gamma/hadron separation with the HAWC observatory Alfaro, R.; Alvarez, C.; Álvarez, J.D. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2022, Letnik:
1039
Journal Article
Recenzirano
Odprti dostop
The High Altitude Water Cherenkov (HAWC) gamma-ray observatory observes atmospheric showers produced by incident gamma rays and cosmic rays with energy from 300 GeV to more than 100 TeV. A crucial ...phase in analyzing gamma-ray sources using ground-based gamma-ray detectors like HAWC is to identify the showers produced by gamma rays or hadrons. The HAWC observatory records roughly 25,000 events per second, with hadrons representing the vast majority (>99.9%) of these events. The standard gamma/hadron separation technique in HAWC uses a simple rectangular cut involving only two parameters. This work describes the implementation of more sophisticated gamma/hadron separation techniques, via machine learning methods (boosted decision trees and neural networks), and summarizes the resulting improvements in gamma/hadron separation obtained in HAWC.
Abstract
The extragalactic background light (EBL) contains all the radiation emitted by nuclear and accretion processes in stars and compact objects since the epoch of recombination. Measuring the ...EBL density directly is challenging, especially in the near-to-far-infrared wave band, mainly due to the zodiacal light foreground. Instead, gamma-ray astronomy offers the possibility to indirectly set limits on the EBL by studying the effects of gamma-ray absorption in the very high energy (VHE: >100 GeV) spectra of distant blazars. The High Altitude Water Cherenkov Gamma Ray Observatory (HAWC) is one of the few instruments sensitive to gamma rays with energies above 10 TeV. This offers the opportunity to probe the EBL in the near/mid-IR region:
λ
= 1–100
μ
m. In this study, we fit physically motivated emission models to Fermi-LAT gigaelectronvolt data to extrapolate the intrinsic teraelectronvolt spectra of blazars. We then simulate a large number of absorbed spectra for different randomly generated EBL model shapes and calculate Bayesian credible bands in the EBL intensity space by comparing and testing the agreement between the absorbed spectra and HAWC extragalactic observations of two blazars. The resulting bands are in agreement with current EBL lower and upper limits, showing a downward trend toward higher wavelength values
λ
> 10
μ
m also observed in previous measurements.
Recent silicon photomultipliers (SiPMs) boast excellent production quality, eliminating the need for individual breakdown voltage calibration. We present measurements of cross-talk probability and ...relative gain for 122 SensL MicroFJ-60035-TSV SiPMs. These semiconductor photosensors have replaced photomultiplier tubes in many applications due to their single-photon resolution, insensitivity to magnetic fields, robustness, and cost-effective photon detection at lower voltages. Light guides expand SiPMs' small photosensitive area, and optical coupling reduces cross-talk probability compared to bare sensors at nominal bias voltage, as demonstrated in this study.
The close location of the HAWC observatory to the largest volcano in Mexico allows to perform a search for neutrino-induced horizontal muon and tau charged leptons. The section of the volcano located ...at the horizon reaches values of slant depth larger than 8 km of rock, making it an excellent shield for the cosmic ray horizontal background. We report the search method and background suppression technique developed for the detection of Earth-skimming neutrinos with HAWC, as well as a model that describes the remaining background produced by scattered muons. We show that by increasing the detection energy threshold we could use HAWC to search for neutrino-induced charged leptons.
El objetivo principal de la investigación fue tratar de ver la percepción de las clases virtuales y las posibles repercusiones académicas que tuviesen estudiantes universitarios en el Perú, y sus ...factores asociados a los mismos, durante la pandemia de la COVID-19. Estudio transversal analítico, en estudiantes universitarios del Perú durante la primera ola de la pandemia, la variable que media la percepción se obtuvo a través de una escala validada. En la estadística analítica, se encontró que las mujeres tuvieron una mayor frecuencia de percepción de repercusiones académicas (RPa: 1,37; IC95%: 1,18-1,59; valor p<0,001), esto ajustado por la edad, la carrera de estudios y la universidad. Las mujeres fueron las que percibían más repercusiones. Si bien solo se encontró asociación con el sexo de los encuestados, se deberían realizar estudios más grandes y en etapas más avanzadas de la pandemia, ya que, nuestros resultados se pueden tomar como basales, pero debería hacerse el seguimiento y determinar la influencia de otras variables.
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