Exploring the Coronal Magnetic Field with Galactic Cosmic Rays: The Sun Shadow Observed by HAWC

Galactic cosmic rays (GCRs) are charged particles that reach the heliosphere almost isotropically in a wide energy range. In the inner heliosphere, the GCR flux is modulated by solar activity so that only energetic GCRs reach the lower layers of the solar atmosphere. In this work, we propose that high-energy GCRs can be used to explore the solar magnetic fields at low coronal altitudes. We used GCR data collected by the High-Altitude Water Cherenkov observatory to construct maps of GCR flux coming from the Sun’s sky direction and studied the observed GCR deficit, known as Sun shadow (SS), over a 6 yr period (2016-2021) with a time cadence of 27.3 days. We confirm that the SS is correlated with sunspot number, but we focus on the relationship between the photospheric solar magnetic field measured at different heliolatitudes and the relative GCR deficit at different energies. We found a linear relationship between the relative deficit of GCRs represented by the depth of the SS and the solar magnetic field. This relationship is evident in the observed energy range of 2.5-226 TeV, but is strongest in the range of 12.4 33.4 TeV, which implies that this is the best energy range to study the evolution of magnetic fields in the low solar atmosphere

Galactic Gamma-Ray Diffuse Emission at TeV Energies with HAWC Data

Galactic gamma-ray diffuse emission (GDE) is emitted by cosmic rays (CRs), ultra-relativistic protons, and electrons, interacting with gas and electromagnetic radiation fields in the interstellar medium. Here we present the analysis of teraelectronvolt diffuse emission from a region of the Galactic plane over the range in longitude of l ∈ [43°, 73°], using data collected with the High Altitude Water Cherenkov (HAWC) detector. Spectral, longitudinal, and latitudinal distributions of the teraelectronvolt diffuse emission are shown. The radiation spectrum is compatible with the spectrum of the emission arising from a CR population with an index similar to that of the observed CRs. When comparing with the DRAGON base model, the HAWC GDE flux is higher by about a factor of 2. Unresolved sources such as pulsar wind nebulae and teraelectronvolt halos could explain the excess emission. Finally, deviations of the Galactic CR flux from the locally measured CR flux may additionally explain the difference between the predicted and measured diffuse fluxes

Probing the Extragalactic Mid-infrared Background with HAWC

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: \u3e100 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 μm. 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 \u3e 10 μm also observed in previous measurements

Searching for TeV Dark Matter in Irregular Dwarf Galaxies with HAWC Observatory

We present the results of dark matter (DM) searches in a sample of 31 dwarf irregular (dIrr) galaxies within the field of view of the HAWC Observatory. dIrr galaxies are DM-dominated objects in which astrophysical gamma-ray emission is estimated to be negligible with respect to the secondary gamma-ray flux expected by annihilation or decay of weakly interacting massive particles (WIMPs). While we do not see any statistically significant DM signal in dIrr galaxies, we present the exclusion limits (95% C.L.) for annihilation cross section and decay lifetime for WIMP candidates with masses between 1 and 100 TeV. Exclusion limits from dIrr galaxies are relevant and complementary to benchmark dwarf Spheroidal (dSph) galaxies. In fact, dIrr galaxies are targets kinematically different from benchmark dSph, preserving the footprints of different evolution histories. We compare the limits from dIrr galaxies to those from ultrafaint and classical dSph galaxies previously observed with HAWC. We find that the constraints are comparable to the limits from classical dSph galaxies and ∼2 orders of magnitude weaker than the ultrafaint dSph limits

SATCON2: Community Engagement Working Group Report

The SATCON2 Community Engagement Working Group aimed to engage a broad and diverse swath of stakeholders in dark skies and near-Earth space who are impacted by large mega-constellations of tens of thousands of low-Earth orbit (LEO) satellites, beyond professional astronomy alone. The working group consisted of 22 members across 23 time zones including professional and amateur astronomers, members of sovereign Indigenous/First Nations communities, dark-sky advocates, planetarium professionals, and environmental/ecological non-governmental organizations. We set out to work together towards a new and effective conceptual, ethical, legal, and regulatory framework for the protection and sustainability of space and the night sky as a global cultural, natural and scientific commons. Community Engagement Working Group members invested thousands of volunteer hours in working group meetings, listening sessions with impacted constituencies, numerous conversations, developing, conducting and analyzing surveys, and finalizing our results and recommendations

Study of the Very High Energy Emission of M87 through its Broadband Spectral Energy Distribution

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

HAWC Study of the Very-high-energy γ-Ray Spectrum of HAWC J1844−034

Recently, the region surrounding eHWC J1842−035 has been studied extensively by γ-ray observatories due to its extended emission reaching up to a few hundred TeV and potential as a hadronic accelerator. In this work, we use 1910 days of cumulative data from the High Altitude Water Cherenkov (HAWC) observatory to carry out a dedicated systematic source search of the eHWC J1842−035 region. During the search, we found three sources in the region, namely, HAWC J1844−034, HAWC J1843−032, and HAWC J1846−025. We have identified HAWC J1844−034 as the extended source that emits photons with energies up to 175 TeV. We compute the spectrum for HAWC J1844−034, and by comparing with the observational results from other experiments, we have identified HESS J1843−033, LHAASO J1843−0338, and TASG J1844−038 as very-high-energy γ-ray sources with a matching origin. Also, we present and use the multiwavelength data to fit the hadronic and leptonic particle spectra. We have identified four pulsar candidates in the nearby region in which PSR J1844−0346 is found to be the most likely candidate due to its proximity to HAWC J1844−034 and the computed energy budget. We have also found SNR G28.6−0.1 as a potential counterpart source of HAWC J1844−034 for which both leptonic and hadronic scenarios are feasible

Detailed Analysis of the TeV γ-Ray Sources 3HWC J1928+178, 3HWC J1930+188, and the New Source HAWC J1932+192

The latest High Altitude Water Cherenkov (HAWC) point-like source catalog up to 56 TeV reported the detection of two sources in the region of the Galactic plane at galactic longitude 52° \u3c ℓ \u3c 55°, 3HWC J1930+188 and 3HWC J1928+178. The first one is associated with a known TeV source, the supernova remnant SNR G054.1+00.3. It was discovered by one of the currently operating Imaging Atmospheric Cherenkov Telescope (IACT), the Very Energetic Radiation Imaging Telescope Array System (VERITAS), detected by the High Energy Stereoscopic System (H.E.S.S), and identified as a composite SNR. However, the source 3HWC J1928+178, discovered by HAWC and coincident with the pulsar PSR J1928+1746, was not detected by any IACT despite their long exposure on the region, until a recent new analysis of H.E.S.S. data was able to confirm it. Moreover, no X-ray counterpart has been detected from this pulsar. We present a multicomponent fit of this region using the latest HAWC data. This reveals an additional new source, HAWC J1932+192, which is potentially associated with the pulsar PSR J1932+1916, whose γ-ray emission could come from the acceleration of particles in its pulsar wind nebula. In the case of 3HWC J1928+178, several possible explanations are explored, in an attempt to unveil the origins of the very-high-energy γ-ray emission

Sustainability and procurement practices in higher education institutions: Barriers and drivers

© 2019 A review of the literature reveals the scant research on sustainable procurement in the public sector, and in particular higher education institutions (HEIs). In this context, this paper aims to contribute to an emerging stream of research on drivers and challenges which higher education institutions and the extent to which they are endorsing sustainable procurement practices. The study is based on a survey of HEIs around the world, drawn from a network of sustainability practitioners and researchers at these institutions. Design of the survey drew on existing studies of barriers and enablers, the use of vignettes to provoke ideas among the research team, and a pilot study. Crucially, the study seeks to shed light on both drivers and critical barriers affecting the implementation of sustainable procurement at universities. The results and discussion identify previously unidentified barriers and enablers, and further suggest that smaller HEI have some catching up to do. Policy recommendations are presented and approaches on how to overcome barriers to sustainable procurement are set forth. These centre on the proposal that HEIs should consider developing a reflexive strategy to procurement purchasing policy, and to ensure there are suitable means for its implementation

Endocrine remodelling of the adult intestine sustains reproduction in Drosophila.

The production of offspring is energetically costly and relies on incompletely understood mechanisms that generate a positive energy balance. In mothers of many species, changes in key energy-associated internal organs are common yet poorly characterised functionally and mechanistically. In this study, we show that, in adult Drosophila females, the midgut is dramatically remodelled to enhance reproductive output. In contrast to extant models, organ remodelling does not occur in response to increased nutrient intake and/or offspring demands, but rather precedes them. With spatially and temporally directed manipulations, we identify juvenile hormone (JH) as an anticipatory endocrine signal released after mating. Acting through intestinal bHLH-PAS domain proteins Methoprene-tolerant (Met) and Germ cell-expressed (Gce), JH signals directly to intestinal progenitors to yield a larger organ, and adjusts gene expression and sterol regulatory element-binding protein (SREBP) activity in enterocytes to support increased lipid metabolism. Our findings identify a metabolically significant paradigm of adult somatic organ remodelling linking hormonal signals, epithelial plasticity, and reproductive output. DOI: http://dx.doi.org/10.7554/eLife.06930.00