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DOE OSTI2024

Probing Heavy Axion-like Particles from Massive Stars with X-rays and Gamma Rays

The hot interiors of massive stars in the later stages of their evolution provide an ideal place for the production of heavy axion-like particles (ALPs) with mass up to O(100 keV) range. We show that a fraction of these ALPs could stream out of the stellar photosphere and subsequently decay into two photons that can be potentially detected on or near the Earth. In particular, we estimate the photon flux originating from the spontaneous decay of heavy ALPs produced inside Horizontal Branch and Wolf-Rayet stars, and assess its detectability by current and future $X$-ray and gamma-ray telescopes. Our results indicate that current and future telescopes can probe axion-photon couplings down to $g_{a\gamma} \sim 4\times 10^{-11}$ GeV${}^{-1}$ for $m_a\sim 10-100$ keV, which covers new ground in the ALP parameter space.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2025

Fermi-LAT Captures a Late-2024 Gamma-Ray Outburst near Two Newly Identified Gamma-Ray-emitting Galactic Supernova Remnants, without Evidence of Physical Association

We report the gamma-ray study of two neighboring in the sky Galactic supernova remnants (SNRs), namely, 3C 434.1 (or G094.0+01.0) and G093.7–00.2. In the vicinity of the two SNRs, a late-2024 gamma-ray outburst—not physically connected to the SNRs—was detected with the Fermi Large Area Telescope (LAT). Employing 16.5 yr of Fermi-LAT data, we report the first firm detection of the gamma-ray counterpart of 3C 434.1 at a 7.2σ significance and a likely detection of an enhanced gamma-ray emission signal at a 4.5σ level from G093.7–00.2. The late-2024 gamma-ray outburst is detected at a ∼12σ significance level over a duration of 3 days. For all three objects, a comprehensive morphological and spectral analysis of the corresponding gamma-ray data was conducted. The prevalent scenario for the nature of the gamma-ray emission of both SNRs is attributed to their surrounding environment. Both are likely interacting with nearby dense material, resulting in hadronically induced gamma-ray emission. We deduce that the outburst source is most likely a blazar in flare, linked to the compact, flat-spectrum radio source TXS 2138+527 (also known as NVSS J213953+530016). Further, the spectral analysis of the gamma-ray source conducted within the 100 MeV–800 GeV energy range using the complete LAT data sets, which yielded a soft averaged spectral shape, supports the hypothesis of a flat spectrum radio quasar (FSRQ) origin for the source; with a most likely leptonically induced scenario for the observed gamma-ray outburst as inferred from the obtained hard spectral shape when utilizing short time intervals focusing on the outburst.

Michailidis, Miltiadis [Stanford Univ., CA (United↗

DOE OSTI2023

A Multiwavelength Investigation of PSR J2229+6114 and its Pulsar Wind Nebula in the Radio, X-Ray, and Gamma-Ray Bands

Abstract G106.3+2.7, commonly considered to be a composite supernova remnant (SNR), is characterized by a boomerang-shaped pulsar wind nebula (PWN) and two distinct (“head” and “tail”) regions in the radio band. A discovery of very-high-energy gamma-ray emission (E γ > 100 GeV) followed by the recent detection of ultrahigh-energy gamma-ray emission (E γ > 100 TeV) from the tail region suggests that G106.3+2.7 is a PeVatron candidate. We present a comprehensive multiwavelength study of the Boomerang PWN (100″ around PSR J2229+6114) using archival radio and Chandra data obtained two decades ago, a new NuSTAR X-ray observation from 2020, and upper limits on gamma-ray fluxes obtained by Fermi-LAT and VERITAS observatories. The NuSTAR observation allowed us to detect a 51.67 ms spin period from the pulsar PSR J2229+6114 and the PWN emission characterized by a power-law model with Γ = 1.52 ± 0.06 up to 20 keV. Contrary to the previous radio study by Kothes et al., we prefer a much lower PWNB-field (B∼ 3μG) and larger distance (d∼ 8 kpc) based on (1) the nonvarying X-ray flux over the last two decades, (2) the energy-dependent X-ray size of the PWN resulting from synchrotron burn-off, and (3) the multiwavelength spectral energy distribution (SED) data. Our SED model suggests that the PWN is currently re-expanding after being compressed by the SNR reverse shock ∼1000 yr ago. In this case, the head region should be formed by GeV–TeV electrons injected earlier by the pulsar propagating into the low-density environment.

Astronomy & Astrophysics↗

DOE OSTI2024

Identification and Suppression of Point Defects in Bromide Perovskite Single Crystals Enabling Gamma‐Ray Spectroscopy

Abstract Methylammonium lead tribromide (MAPbBr 3 ) stands out as the most easily grown wide‐band‐gap metal halide perovskite. It is a promising semiconductor for room‐temperature gamma‐ray ( γ ‐ray) spectroscopic detectors, but no operational devices are realized. This can be largely attributed to a lack of understanding of point defects and their influence on detector performance. Here, through a combination of crystal growth design and defect characterization, including positron annihilation and impedance spectroscopy, the presence of specific point defects are identified and correlated to detector performance. Methylammonium (MA) vacancies, MA interstitials, and Pb vacancies are identified as the dominant charge‐trapping defects in MAPbBr 3 crystals, while Br vacancies caused doping. The addition of excess MABr reduces the MA and Br defects and so enables the detection of energy‐resolved γ ‐ray spectra using a MAPbBr 3 single‐crystal device. Interestingly, the addition of formamidinium (FA) cations, which converted to methylformamidinium (MFA) cations by reaction with MA + during crystal growth further reduced MA defects. This enabled an energy resolution of 3.9% for the 662 keV 137 Cs line using a low bias of 100 V. The work provides direction toward enabling further improvements in wide‐bandgap perovskite‐based device performance by reducing detrimental defects.

Ni, Zhenyi↗

DOE OSTI2021

Cosmic-ray transport and gamma-ray emission in M31

Here we study the possibility that an extended cosmic-ray leptonic and/or hadronic halo is at the origin of the large-scale gamma-ray emission detected from the Andromeda galaxy (M31). We consider a broad ensemble of nonhomogeneous diffusion scenarios and of cosmic-ray injection sources. We find that cosmic-ray electrons and protons could be, and very likely are, responsible for part, or all, of the gamma-ray emission from M31, including out to more than 100 kpc from the center of the galaxy. We also simulate possible emission from pulsars in M31 and consider the effect of regions of highly inefficient diffusion around cosmic-ray acceleration sites, as suggested by recent TeV halo observations with Cherenkov telescopes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2022

Standardizing Platinum Dainotti-correlated gamma-ray bursts, and using them with standardized Amati-correlated gamma-ray bursts to constrain cosmological model parameters

ABSTRACT We show that the Platinum gamma-ray burst (GRB) data compilation, probing the redshift range 0.553 ≤ z ≤ 5.0, obeys a cosmological-model-independent three-parameter Fundamental Plane (Dainotti) correlation and so is standardizable. While they probe the largely unexplored z ∼ 2.3–5 part of cosmological redshift space, the GRB cosmological parameter constraints are consistent with, but less precise than, those from a combination of baryon acoustic oscillation (BAO) and Hubble parameter [H(z)] data. In order to increase the precision of GRB-only cosmological constraints, we exclude common GRBs from the larger Amati-correlated A118 data set composed of 118 GRBs and jointly analyse the remaining 101 Amati-correlated GRBs with the 50 Platinum GRBs. This joint 151 GRB data set probes the largely unexplored z ∼ 2.3–8.2 region; the resulting GRB-only cosmological constraints are more restrictive, and consistent with, but less precise than, those from H(z) + BAO data.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2025

New determination of the millisecond pulsar gamma-ray luminosity function and implications for the Galactic Center gamma-ray excess

It has been suggested that the Galactic Center gamma-ray excess (GCE) could be produced by a large number of centrally located millisecond pulsars. The fact that no such pulsar population has been detected implies that these sources must be very faint and very numerous. Here, in this study, we use the contents of Fermi’s recently released Third Pulsar Catalog (3PC) to measure the luminosity function of the millisecond pulsars in the Milky Way’s disk. We find that this source population exhibits a luminosity function with a mean γ -ray luminosity of ⟨ L γ ⟩ ∼ 6 × 10 32 erg / s (integrated above 0.1 GeV). If the GCE were generated by millisecond pulsars with the same luminosity function, we find that ∼ 20 such sources from the inner Galaxy population should have already been detected by Fermi and included in the 3PC. Given the lack of such observed sources, we exclude the hypothesis that the GCE is generated by pulsars with the same luminosity function as those in the Galactic disk with a significance of 3.4 σ . We conclude that either less than 39% of the GCE is generated by pulsars, or that the millisecond pulsars in the inner Galaxy are at least 5 times less luminous on average than those found in the Galactic disk.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

Standardizing Dainotti-correlated gamma-ray bursts, and using them with standardized Amati-correlated gamma-ray bursts to constrain cosmological model parameters

ABSTRACT We show that each of the three Dainotti-correlated gamma-ray burst (GRB) data sets recently compiled by Wang et al. and Hu et al., that together probe the redshift range 0.35 ≤ z ≤ 5.91, obey cosmological-model-independent Dainotti correlations and so are standardizable. We use these GRB data in conjunction with the best currently available Amati-correlated GRB data, that probe 0.3399 ≤ z ≤ 8.2, to constrain cosmological model parameters. The resulting cosmological constraints are weak, providing lower limits on the non-relativistic matter density parameter, mildly favouring non-zero spatial curvature, and largely consistent with currently accelerated cosmological expansion as well as with constraints determined from better-established data.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2022

Gamma-ray observations of MAXI J1820+070 during the 2018 outburst

ABSTRACT MAXI J1820+070 is a low-mass X-ray binary with a black hole (BH) as a compact object. This binary underwent an exceptionally bright X-ray outburst from 2018 March to October, showing evidence of a non-thermal particle population through its radio emission during this whole period. The combined results of 59.5 h of observations of the MAXI J1820+070 outburst with the H.E.S.S., MAGIC and VERITAS experiments at energies above 200 GeV are presented, together with Fermi-LAT data between 0.1 and 500 GeV, and multiwavelength observations from radio to X-rays. Gamma-ray emission is not detected from MAXI J1820+070, but the obtained upper limits and the multiwavelength data allow us to put meaningful constraints on the source properties under reasonable assumptions regarding the non-thermal particle population and the jet synchrotron spectrum. In particular, it is possible to show that, if a high-energy (HE) gamma-ray emitting region is present during the hard state of the source, its predicted flux should be at most a factor of 20 below the obtained Fermi-LAT upper limits, and closer to them for magnetic fields significantly below equipartition. During the state transitions, under the plausible assumption that electrons are accelerated up to ∼500 GeV, the multiwavelength data and the gamma-ray upper limits lead consistently to the conclusion that a potential HE and very-HE gamma-ray emitting region should be located at a distance from the BH ranging between 1011 and 1013 cm. Similar outbursts from low-mass X-ray binaries might be detectable in the near future with upcoming instruments such as CTA.

Astronomy & Astrophysics↗

DOE OSTI2022

CubeSats for Gamma-Ray Astronomy [Book Chapter]

After many years of flying in space primarily for educational purposes, CubeSats – tiny satellites with form factors corresponding to arrangements of “1U” units, or cubes, each 10 cm on a side – have come into their own as valuable platforms for technology advancement and scientific investigations. CubeSats offer comparatively rapid, low-cost access to space for payloads that can be built, tested, and operated by relatively small teams, with substantial contributions from students and early career researchers. Continuing advances in compact, low-power detectors, readout electronics, and flight computers have now enabled X-ray and gamma-ray sensing payloads that can fit within the constraints of CubeSat missions, permitting in-orbit demonstrations of new techniques and innovative high-energy astronomy observations. Gamma-ray-sensing CubeSats are certain to make an important contribution in the new era of multi-messenger, time-domain astronomy by detecting and localizing bright transients such as gamma-ray bursts, solar flares, and terrestrial gamma-ray flashes; however, other astrophysical science areas requiring long observations in a low-background environment, including gamma-ray polarimetry, studies of nuclear lines, and measurement of diffuse backgrounds, will likely benefit as well. Here we present the primary benefits of CubeSats for high-energy astronomy, highlight the scientific areas currently or soon to be studied, and review the missions that are currently operating, under development, or proposed. A rich portfolio of CubeSats for gamma-ray astronomy already exists, and the potential for a broad range of creative and scientifically productive missions in the near future is very high.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2023

Xtreme progenitors of Gamma-ray bursts [Slides]

Gamma-ray burst are typically classified as “short” or “long." They are categorized by their gamma ray emission, Short GRBs have gamma-ray emission less than 2 seconds and long GRBs are greater 2 seconds. Within long GRBs, further categorized as radio-loud or quiet. Radio loud are more energetic and have longer gamma-ray emission. We’re studying a binary system with a massive star and black hole.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2026

Interpolation of computed gamma-ray detector response functions

Gamma-ray spectra measured by traditional detectors contain features that result from a combination of the effects of detector materials/geometry, the incident gamma-ray energy, and the angle of entry. The features, such as the full-energy photopeak, Compton continuum, annihilation peak, and escape peaks, are governed by simple relationships depending on incident energy and have been known for a long time. Monte Carlo computer simulations of gamma rays interacting with a detector will show these features, and with a resolution function applied, the results should look similar to real measurements. The traditional approach to creating a detector response function requires many separate simulations of monoenergetic gamma rays striking the detector. This paper presents a new approach to developing computed detector response functions. The new approach involves a much smaller number of monoenergetic gamma-ray simulations and uses interpolation to quickly generate the responses of gamma rays that were not simulated. During the interpolation process, the underlying physics equations are used to accurately compute the response of a given energy gamma ray from the small set of simulations. Such work enables accelerated generation of synthetic radiation detector data.

Detector response↗

DOE OSTI2024

Investigation of the $\gamma $-ray Properties of the $2^+$ States in $^{14}$C

The properties of the 2$^+_1$ and 2$^+_2$ excited states in 14 C were studied in an experiment conducted at Argonne National Laboratory. A 9 Be( 6 Li,pγ) fusion-evaporation reaction and the GRETINA-ORRUBA setup were employed to populate states of 14 C and detect γ-particle coincidence events. Finally, the precise determination of the 2$^+_1$ level energy, complemented by the estimation of the γ-ray branch of the 2$^+_2$ near-threshold state, will serve as a benchmark to test the Shell Model Embedded in the Continuum calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2025

Geant4 Simulation of Cherenkov Photons in Perovskite CsPbBr 3 Gamma-Ray Detectors

Perovskite materials have recently attracted significant attention for hard X-ray and gamma-ray detection. Cherenkov light generated by fast electrons due to gamma-ray interaction with the material can be used to provide fast timing information. Here, in this study, we report Geant4 simulation results of Cherenkov photon generation, transport, and detection within perovskite CsPbBr3. The Cherenkov photon yield, energy spectrum and temporal distribution are investigated under different gamma-ray energy deposition within CsPbBr3. CsPbBr 3 has a similar Cherenkov photon yield as of TlBr that has demonstrated fast-timing capability based on Cherenkov light. The effect of crystal volume, surface finish and SiPM photon detection efficiency on the Cherenkov detection is also discussed. This work provides insights into Cherenkov processes of CsPbBr3.

Cherenkov photon↗

DOE OSTI2024

The cosmic-ray positron excess and its imprint in the Galactic gamma-ray sky

Abstract We study the origin of the positron excess observed in the local cosmic-ray spectrum at high energies, and relate it to the cosmic rays and gamma-ray emission across the entire Galaxy. In particular, we explore the hypothesis of a single, dominant source accountable for primary electron-positron pairs. Since we are agnostic about the physical nature of the underlying source population, we consider four models that are representative of young pulsars, old stars (as a tracer of millisecond pulsars), and annihilating dark matter particles. In the dark matter hypothesis, we consider both a cored and a cuspy model for the halo in the Milky Way. Then, we compare the associated gamma-ray sky maps withFermi-LAT data. We find that the emission arising from pulsar wind nebulae is fairly concentrated near the mid plane, and therefore additional cosmic-ray sources must be invoked to explain the emission at the center of the Galaxy. If the local positron excess were mainly due to millisecond pulsars, inverse Compton scattering by the particles injected would naturally account for a non-negligible fraction of the central gamma-ray emission. The same process would lead to a tension for a standard NFW dark matter profile, exceeding the gamma-ray data by almost a factor of 2 in some regions of the Galaxy. Although the results for an isothermal, cored profile are in agreement with these data, the cross section needed in both cases is around 2 orders of magnitude above the thermal cross-section, disfavouring the dark matter interpretation.

Astronomy & Astrophysics↗

DOE OSTI2023

Gamma-Ray Emission from Galaxies Hosting Molecular Outflows

Many star-forming galaxies and those hosting active galactic nuclei show evidence of massive outflows of material in a variety of phases including ionized, neutral atomic, and molecular. Molecular outflows in particular have been the focus of recent interest as they may be responsible for removing gas from the galaxy, thereby suppressing star formation. As material is ejected from the cores of galaxies, interactions of the outflowing material with the interstellar medium can accelerate cosmic rays and produce high-energy gamma rays. In this work, we search for gamma-ray emission from a sample of local galaxies known to host molecular outflows using data collected by the Fermi Large Area Telescope. We employ a stacking technique in order to search for and characterize the average gamma-ray emission properties of the sample. Gamma-ray emission is detected from the galaxies in our sample at the 4.4σ level with a power-law photon index of Γ ≈ 2 in the 1–800 GeV energy range. The emission is found to correlate with tracers of star formation activity, namely the 8–1000 μm infrared luminosity. We also find that the observed signal can be predominantly attributed to H II galaxies hosting energy-driven outflows. While we do not find evidence suggesting that the outflows are accelerating charged particles directly, galaxies with molecular outflows may produce more gamma rays than galaxies without outflows. In particular, the set consisting of gamma-ray-detected galaxies with molecular outflows are nearly perfect calorimeters and may be future targets for searches of high-energy neutrinos.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2022

The Closure Relations in Optical Afterglow of Gamma-Ray Bursts

Gamma-ray bursts (GRBs) are extremely high-energy events that can be observed at very high redshift. In addition to γ rays, they can emit in X-ray, optical, and sometimes radio wavelengths. Here, following the approach in Srinivasaragavan et al.; Dainotti et al.; and Dainotti et al., we consider 82 GRBs from Dainotti et al. that have been observed in optical wavelengths and fitted with a broken power law. We consider the relations between the spectral and temporal indices (closure relations; CRs) according to the synchrotron forward-shock model evolving in the constant-density interstellar medium (ISM; k = 0) and the stellar wind environment (k = 2) in both slow- and fast-cooling regimes, where the density profile is defined as n ∝ r -k . We find the $ν$ > $max${$ν$ c , $ν$ m } regime is most favored, where ν c and ν m are the cooling and characteristic frequencies, respectively. Finally, we test the 2D Dainotti correlation between the rest-frame end time of the plateau and the luminosity at that time on GRBs that fulfill the most-favored CRs. When we compare the intrinsic scatter σ int of those 2D correlations to the scatter presented in Dainotti et al., we see the scatters of our correlations generally agree with the previous values within 1σ, both before and after correction for selection bias. This new information has helped us to pinpoint subsamples of GRBs with features that could drive the GRB emission mechanism, and eventually allow for GRBs to be used as standard candles.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2025

The Psyche Gamma-Ray and Neutron Spectrometer

A Gamma-Ray and Neutron Spectrometer (GRNS) instrument has been developed as part of the science payload for NASA’s Discovery Program Psyche mission to the M-class asteroid (16) Psyche. The GRNS instrument is designed to measure the elemental composition of Psyche with the goal to understand the origin of this mysterious, potentially metal-rich planetary body. The GRNS will measure the near-surface abundances for the elements Ni, Fe, Si, K, S, Al, and Ca, as well as the spatial distribution of Psyche’s metal-to-silicate fraction (or metal fraction). These measurements address three of the five Psyche mission science objectives: determine if Psyche is a core; determine whether small metal bodies incorporate light elements into the metal phase; and determine whether Psyche was formed under reducing conditions. The Gamma-Ray Spectrometer (GRS) uses a cryocooled, high-purity Ge (HPGe) sensor to detect cosmic-ray generated gamma rays in the 60 to 9000-keV energy range. The HPGe sensor is surrounded by a borated plastic anticoincidence shield that provides three functions: active background rejection from charged particle interactions in the HPGe sensor; fast neutron measurements; and direct measurements of the incident galactic cosmic ray flux. The Neutron Spectrometer (NS) uses three 3 He gas proportional sensors, each with different material wraps to measure thermal (<0.4 eV), low-energy epithermal (0.4 eV to 1 keV), and high-energy epithermal (up to 100 keV) neutrons. This paper provides an overview of the Psyche GRNS, including: its science and measurement objectives; the design of the instrument hardware, software, and operation; pre-launch performance measurements and its initial performance in space; and an overview of its data products and expected operation for different Psyche mission phases.

Engineering - Instrumentation related to nuclear s↗