Abstract
Gamma-ray bursts (GRBs) have been considered as potential very high energy photon emitters due to the large amount of energy released as well as the strong magnetic fields involved in their ...jets. However, the detection of teraelectronvolt photons is not expected from bursts beyond a redshift of
z
≳ 0.1, due to their attenuation with the extragalactic background light (EBL). For these reasons, the recent observation of photons with energies of 18 and 251 TeV from GRB 221009A (
z
= 0.151) last 2022 October 9 has challenged what we know about the teraelectronvolt-emission mechanisms and the extragalactic background. In order to explain the teraelectronvolt observations, recent works exploring candidates of dark matter have started to appear. In this paper, we discuss the required conditions and limitations within the most plausible scenario, synchrotron self-Compton radiation in the GRB afterglow, to interpret the one 18 TeV photon observation besides the EBL. To avoid the Klein–Nishina effect, we find an improbable value of the microphysical magnetic parameter below 10
−6
for a circumburst medium value >1 cm
−3
(expected in the collapsar scenario). Therefore, we explore possible scenarios in terms of axion-like particles (ALPs) and dark photon mechanisms to interpret this highly energetic photon and we discuss the implications in the GRB energetics. We find that the ALPs and dark photon scenarios can explain the 18 teraelectronvolt photon but not the 251 teraelectronvolt photon.
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.
SS 433 is a binary system containing a supergiant star that is overflowing its Roche lobe with matter accreting onto a compact object (either a black hole or neutron star)
. Two jets of ionized ...matter with a bulk velocity of approximately 0.26c (where c is the speed of light in vacuum) extend from the binary, perpendicular to the line of sight, and terminate inside W50, a supernova remnant that is being distorted by the jets
. SS 433 differs from other microquasars (small-scale versions of quasars that are present within our own Galaxy) in that the accretion is believed to be super-Eddington
, and the luminosity of the system is about 10
ergs per second
. The lobes of W50 in which the jets terminate, about 40 parsecs from the central source, are expected to accelerate charged particles, and indeed radio and X-ray emission consistent with electron synchrotron emission in a magnetic field have been observed
. At higher energies (greater than 100 gigaelectronvolts), the particle fluxes of γ-rays from X-ray hotspots around SS 433 have been reported as flux upper limits
. In this energy regime, it has been unclear whether the emission is dominated by electrons that are interacting with photons from the cosmic microwave background through inverse-Compton scattering or by protons that are interacting with the ambient gas. Here we report teraelectronvolt γ-ray observations of the SS 433/W50 system that spatially resolve the lobes. The teraelectronvolt emission is localized to structures in the lobes, far from the centre of the system where the jets are formed. We have measured photon energies of at least 25 teraelectronvolts, and these are certainly not Doppler-boosted, because of the viewing geometry. We conclude that the emission-from radio to teraelectronvolt energies-is consistent with a single population of electrons with energies extending to at least hundreds of teraelectronvolts in a magnetic field of about 16 microgauss.
Abstract
This paper reports on the
γ
-ray properties of the 2018 Galactic nova V392 Per, spanning photon energies ∼0.1 GeV–100 TeV by combining observations from the Fermi Gamma-ray Space Telescope ...and the HAWC Observatory. As one of the most rapidly evolving
γ
-ray signals yet observed for a nova, GeV
γ
-rays with a power-law spectrum with an index Γ = 2.0 ± 0.1 were detected over 8 days following V392 Per’s optical maximum. HAWC observations constrain the TeV
γ
-ray signal during this time and also before and after. We observe no statistically significant evidence of TeV
γ
-ray emission from V392 Per, but present flux limits. Tests disfavor the extension of the Fermi Large Area Telescope spectrum to energies above 5 TeV by 2 standard deviations (95%) or more. We fit V392 Per’s GeV
γ
-rays with hadronic acceleration models, incorporating optical observations, and compare the calculations with HAWC limits.
Abstract
The MGRO J2019+37 region is one of the brightest sources in the sky at TeV energies. It was detected in the second HAWC catalog as 2HWC J2019+367 and here we present a detailed study of this ...region using data from HAWC. This analysis resolves the region into two sources: HAWC J2019+368 and HAWC J2016+371. We associate HAWC J2016+371 with the evolved supernova remnant CTB 87, although its low significance in this analysis prevents a detailed study at this time. An investigation of the morphology (including possible energy-dependent morphology) and spectrum for HAWC J2019+368 is the focus of this work. We associate HAWC J2019+368 with PSR J2021+3651 and its X-ray pulsar wind nebula, the Dragonfly nebula. Modeling the spectrum measured by HAWC and Suzaku reveals a ∼7 kyr pulsar and nebula system producing the observed emission at X-ray and
γ
-ray energies.
Abstract
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.
Abstract 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.
Abstract
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.
We report the ground-level detection of a Galactic cosmic-ray (GCR) flux enhancement lasting ∼17 hr and associated with the passage of a magnetic flux rope (MFR) over the Earth. The MFR was ...associated with a slow coronal mass ejection (CME) caused by the eruption of a filament on 2016 October 9. Due to the quiet conditions during the eruption and the lack of interactions during the interplanetary CME transport to the Earth, the associated MFR preserved its configuration and reached the Earth with a strong magnetic field, low density, and a very low turbulence level compared to local background, thus generating the ideal conditions to redirect and guide GCRs (in the ∼8-60 GV rigidity range) along the magnetic field of the MFR. An important negative BZ component inside the MFR caused large disturbances in the geomagnetic field and a relatively strong geomagnetic storm. However, these disturbances are not the main factors behind the GCR enhancement. Instead, we found that the major factor was the alignment between the MFR axis and the asymptotic direction of the observer.
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