Compton Gamma Ray Observatory Research Articles

A Short History of the First 50 Years: From the GRB Prompt Emission and Afterglow Discoveries to the Multimessenger Era

More than fifty years have elapsed from the first discovery of gamma-ray bursts (GRBs) with American Vela satellites, and more than twenty-five years from the discovery with the BeppoSAX satellite of the first X-ray afterglow of a GRB. Thanks to the afterglow discovery and to the possibility given to the optical and radio astronomers to discover the GRB optical counterparts, the long-time mystery about the origin of these events has been solved. Now we know that GRBs are huge explosions, mainly ultra relativistic jets, in galaxies at cosmological distances. Starting from the first GRB detection with the Vela satellites, I will review the story of these discoveries, those obtained with BeppoSAX, the contribution to GRBs by other satellites and ground experiments, among them being Venera, Compton Gamma Ray Observatory, HETE-2, Swift, Fermi, AGILE, MAGIC, H.E.S.S., which were, and some of them are still, very important for the study of GRB properties. Then, I will review the main results obtained thus far and the still open problems and prospects of GRB astronomy.

Recent Outbursts of the High-mass X-Ray Binary CI Camelopardalis

Recent Outbursts of the High-mass X-Ray Binary CI Camelopardalis

A pilot search for MeV gamma-ray emission from five galaxy clusters using archival COMPTEL data

We search for MeV gamma-ray emission between 0.75–30 MeV from five galaxy clusters, viz. Coma, VIRGO, SPT-CL J2012-5649, Bullet, and El Gordo, using archival data from the COMPTEL telescope. For this purpose we use three search templates: point source, radial disk and radial Gaussian. We do not detect any signals from Coma, SPT-CL J2012-5649, Bullet and El Gordo clusters with the 95% c.l. photon energy flux limit ∼ 10-10erg/cm2/s.For VIRGO, we detect a non-zero signal between 0.75 to 1.50 MeV having marginal significance of about 2.5σ, with the observed energy flux equal to ∼ 10-9 ergs/cm2/s. However, we do not confirm the previously reported evidence in literature for a gamma-ray line from Coma and VIRGO clusters between 5–7 MeV.

Evaluation of the performance of a CdZnTe-based soft γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma $$\\end{document}-ray detector for CubeSat payloads

The low-energy γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varvec{\\gamma }$$\\end{document}-ray (0.1-30 MeV) sky has been relatively unexplored since the decommissioning of the COMPTEL instrument on the Compton Gamma-Ray Observatory (CGRO) satellite in 2000. However, the study of this part of the energy spectrum (the “MeV gap”) is crucial for addressing numerous unresolved questions in high-energy and multi-messenger astrophysics. Although several large MeV γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varvec{\\gamma }$$\\end{document}-ray missions like AMEGO and e-ASTROGAM are being proposed, they are predominantly in the developmental phase, with launches not anticipated until the next decade at the earliest. In recent times, there has been a surge in proposed CubeSat missions as cost-effective and rapidly implementable “pathfinder” alternatives. A MeV CubeSat dedicated to γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varvec{\\gamma }$$\\end{document}-ray astronomy has the potential to serve as a demonstrator for future, larger-scale MeV payloads. This paper presents a γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varvec{\\gamma }$$\\end{document}-ray payload design featuring a CdZnTe crystal calorimeter module developed by IDEAS. We report the detailed results of simulations to assess the performance of this proposed payload and compare it with those of previous γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varvec{\\gamma }$$\\end{document}-ray instruments.

The role of a standard family of Ic supernovae in BDHN I, BDHN II, and BDHN III GRBs

AbstractA profound difference has occurred in the analysis of Gamma Ray Bursts (GRBs) initially analyzed in the domain of gamma‐ray astronomy with the Compton Gamma Ray Observatory and the BATSE Detector with the extension to x‐ray astronomy and optical astronomy introduced by Beppo‐SAX and the KEK and VLT optical observatory, followed by the AGILE, Fermi mission, Niels Gehrels SWIFT mission as well as HEHSS and MAGIC observations An authentic “Copernican revolution” has occurred in the transition from the traditional model of GRBs originating in a single star progenitor (collapsar) to GRBs with a binary progenitor composed of a CO core and a companion NS. We have evidence from 24 SN observations related to GRBs that all of them, once analyzed with the general relativistic corrections can be identified with I Bc Sn with a common value of the Luminosity and common time of occurrence of the peak of the optical emission. This can be understood in terms of a precursor composed of a CO core and a binary NS companion. By contrast, the GRBs differ profoundly in their energetics which can be expressed in terms of 3 different classes of BDHNe: BDHN I, BDHN II, and BDHN III, also originating from Precursors composed of a CO core and a Binary companion. It is pointed out how the analysis of these systems has profoundly modified the concept of the BH and the associated fundamental physics necessary for their description since the “introducing of the Black Hole” by Ruffini and Wheeler in 1971. At first, it is illustrated how the most radical change has occurred in the introduction of the effective BH charge, with an electric field only function of the BH dimensionless spin and a background magnetic field Bo. This definitely indicates the abandonment of the Kerr‐Newman solution in favor of the Kerr metric, for energy extraction processes in BH physics. We then enter into the detailed description of the “seven Seals,” the seven Episodes characterizing GRB 190114c, and the associated SN 2019jrj.This is based on the article by Aimuratov et al. (in preparation).

On the nature of the ultrarelativistic prompt emission phase of GRB 190114C and GRB 180720B

A profound difference has occurred in the analysis of GRBs initially analyzed in the domain of gamma-ray astronomy with the Compton Gamma Ray Observatory and the BATSE Detector with the extension to X-ray astronomy and optical astronomy introduced by Beppo-SAX and the KEK and VLT optical observatory, followed by the AGILE, Fermi mission, Niels Gehrels SWIFT mission as well as HEHSS and MAGIC observations. An authentic ``Copernican revolution" has occurred in the transition from the traditional model of GRBs originating in a single star progenitor (collapsar) to GRBs with a binary progenitor composed of a CO core and a companion NS. We evidence from 24 SN observations related to GRBs that all of them, once analyzed with the general relativistic corrections, can be identified with I Bc Sn with a common value of the luminosity and common time of occurrence of the peak of the optical emission. This can be understood in terms of a precursor composed of a CO core and a binary NS companion. By contrast, the GRBs differ profoundly in their energetics which can be expressed in terms of 3 different classes of BDHNe: BDHN I, BDHN II, BDHN III, also originating from precursors composed of a CO core and a binary companion. It is pointed out how the analysis of these systems has profoundly modified the concept of the BH and the associated fundamental physics necessary for their description since the publication of ``Introducing the Black Hole" by Ruffini and Wheeler in 1971. At first, it is illustrated how the most radical change has occurred in the introduction of the effective BH charge, with an electric field only function of the BH dimensionless spin and a background magnetic field $B0$. This definitely indicates the abandonment of the Kerr--Newman solution in favour of the Kerr metric, for energy extraction processes in BH physics. We then enter in the detailed description of the ``seven Seals", the seven Episodes characterizing GRB 190114c and the associated SN 2019jrj. Based on the article by Aimuratov et al., in preparation.

COMPTEL data analysis using GammaLib and ctools

More than 20 yr after the end of NASA’s Compton Gamma-Ray Observatory mission, the data collected by its Imaging Compton Telescope (COMPTEL) still provide the most comprehensive and deepest view of our Universe in MeV gamma rays. While most of the COMPTEL data are archived at NASA’s High Energy Astrophysics Science Archive Research Center (HEASARC), the absence of any publicly available software for their analysis means the data cannot benefit from the scientific advances made in the field of gamma-ray astronomy at higher energies. To make this unique treasure again accessible for science, we developed open source software that enables a comprehensive and modern analysis of the archived COMPTEL telescope data. Our software is based on a dedicated plug-in to the GammaLib library, a community-developed toolbox for the analysis of astronomical gamma-ray data. We implemented high-level scripts for building science analysis workflows in ctools, a community-developed gamma-ray astronomy science analysis software framework. We describe the implementation of our software and provide the underlying algorithms. Using data from the HEASARC archive, we demonstrate that our software reproduces derived data products that were obtained in the past using the proprietary COMPTEL software. We furthermore demonstrate that our software reproduces COMPTEL science results published in the literature. This brings the COMPTEL telescope data back into life, allowing them to benefit from recent advances in gamma-ray astronomy, and gives the community a means to unveil its still hidden treasures.

What are the Composition and Power of the Jet in Cyg X-1?

We calculate the electron–positron pair production rate at the base of the jet of Cyg X-1 by collisions of photons from its hot accretion flow using the measurement of its average soft gamma-ray spectra by the Compton Gamma Ray Observatory and INTEGRAL satellites. We have found that this rate approximately equals the flow rate of the leptons emitting the observed synchrotron radio-to-IR spectrum of the jet, calculated using an extended jet model following that of Blandford & Königl. This coincidence shows the jet composition is likely to be pair dominated. The same coincidences were found before in the microquasar MAXI J1820+070 and in the radio galaxy 3C 120, which shows that the considered mechanism can be universal for at least some classes of relativistic jets. Furthermore, we recalculate the jet power of Cyg X-1. The presence of pairs can strongly reduce the power in the bulk motion of ions, which then limits the parameter space at which the jet can power the ∼5 pc nebular structure present in its vicinity.

Introducing the MeVCube concept: a CubeSat for MeV observations

Despite the impressive progress achieved both by X-ray and gamma-ray observatories in the last few decades, the energy range between ∼ 200 keV and ∼ 50 MeV remains poorly explored. COMPTEL, on-board the Compton Gamma-Ray Observatory (CGRO, 1991-2000), opened the MeV gamma-ray band as a new window to astronomy, performing the first all-sky survey in the energy range from 0.75 to 30 MeV. More than 20 years after the de-orbit of CGRO, no successor mission is yet operating. Over the past years many concepts have been proposed, for new observatories exploring different configurations and imaging techniques; a selection of the most recent ones includes AMEGO, ETCC, GECCO and COSI.We propose here a novel concept for a Compton telescope based on the CubeSat standard, named MeVCube, with the advantages of small cost and relatively short development time. The scientific payload is based on two layers of pixelated Cadmium-Zinc-Telluride (CdZnTe) detectors, coupled with low-power read-out electronics (ASIC, VATA450.3). The performance of the read-out electronics and CdZnTe custom designed detectors have been measured extensively at DESY [1]. The performance of the telescope is accessed through simulations: despite a small effective area limited to a few cm2, MeVCube can reach an angular resolution of 1.5° and a sensitivity comparable to the one achieved by the last generation of large-scale satellites like COMPTEL and INTEGRAL. Combined with a large field-of-view and a moderate cost, MeVCube can be a powerful instrument for transient observations and searches of electromagnetic counterparts of gravitational wave events.

The Cosmic History of Long Gamma-Ray Bursts

The cosmic formation rate of long gamma-ray bursts (LGRBs) encodes the evolution, across cosmic times, of the properties of their progenitors and of their environment. The LGRB formation rate and the luminosity function, with its redshift evolution, are derived by reproducing the largest sets of observations collected over the last four decades, namely the observer-frame prompt emission properties of the GRB samples detected by the Fermi and Compton Gamma Ray Observatory satellites and the redshift, luminosity, and energy distributions of the flux-limited, redshift-complete samples of GRBs detected by Swift. The model that best reproduces all these constraints consists of a GRB formation rate increasing with redshift ∝(1 + z)3.2, i.e., steeper than the star formation rate, up to z ∼ 3, followed by a decrease ∝(1 + z)−3. On top of this, our model also predicts a moderate evolution of the characteristic luminosity function break ∝(1 + z)0.6. Models with only luminosity or rate evolution are excluded at >5σ significance. The cosmic rate evolution of LGRBs is interpreted as their preference for occurring in environments with metallicity , consistent with theoretical models and host galaxy observations. The LGRB rate at z = 0, accounting for their collimation, is Gpc−3 yr−1 (68% confidence interval). This corresponds to ∼1% of broad-line Type Ibc supernovae producing a successful jet in the local universe. This fraction increases up to ∼7% at z ≥ 3. Finally, we estimate that at least ≈0.2−0.7 yr−1 of the Swift- and Fermi-detected bursts at z < 0.5 are jets observed slightly off-axis.

First Observation of the MeV Gamma-Ray Universe with Bijective Imaging Spectroscopy Using the Electron-tracking Compton Telescope on Board SMILE-2+

MeV gamma-rays provide a unique window for the direct measurement of line emissions from radioisotopes, but observations have made little significant progress since COMPTEL on board the Compton Gamma-ray Observatory (CGRO). To observe celestial objects in this band, we are developing an electron-tracking Compton camera (ETCC) that realizes both bijective imaging spectroscopy and efficient background reduction gleaned from the recoil-electron track information. The energy spectrum of the observation target can then be obtained by a simple ON–OFF method using a correctly defined point-spread function on the celestial sphere. The performance of celestial object observations was validated on the second balloon SMILE-2+ , on which an ETCC with a gaseous electron tracker was installed that had a volume of 30 × 30 × 30 cm3. Gamma-rays from the Crab Nebula were detected with a significance of 4.0σ in the energy range 0.15–2.1 MeV with a live time of 5.1 hr, as expected before launch. Additionally, the light curve clarified an enhancement of gamma-ray events generated in the Galactic center region, indicating that a significant proportion of the final remaining events are cosmic gamma-rays. Independently, the observed intensity and time variation were consistent with the prelaunch estimates except in the Galactic center region. The estimates were based on the total background of extragalactic diffuse, atmospheric, and instrumental gamma-rays after accounting for the variations in the atmospheric depth and rigidity during the level flight. The Crab results and light curve strongly support our understanding of both the detection sensitivity and the background in real observations. This work promises significant advances in MeV gamma-ray astronomy.

Measurement of Galactic 26Al with the Compton Spectrometer and Imager

Abstract The Compton Spectrometer and Imager (COSI) is a balloon-borne compact Compton telescope designed to survey the 0.2–5 MeV sky. COSI’s energy resolution of ∼0.2% at 1.8 MeV, single-photon reconstruction, and wide field of view make it capable of studying astrophysical nuclear lines, particularly the 1809 keV γ-ray line from decaying Galactic 26Al. Most 26Al originates in massive stars and core-collapse supernova nucleosynthesis, but the path from stellar evolution models to Galaxy-wide emission remains unconstrained. In 2016, COSI had a successful 46 day flight on a NASA superpressure balloon. Here, we detail the first search for the 1809 keV 26Al line in the COSI 2016 balloon flight using a maximum-likelihood analysis. We find a Galactic 26Al flux of (8.6 ± 2.5) × 10−4 ph cm−2 s−1 within the Inner Galaxy (∣ℓ∣ ≤ 30°, ∣b∣ ≤ 10°) with 3.7σ significance above background. Within uncertainties, this flux is consistent with expectations from previous measurements by SPectrometer on INTEGRAL (SPI) and the Compton Telescope on the Compton Gamma-Ray Observatory (COMPTEL). This analysis demonstrates COSI’s powerful capabilities for studies of γ-ray lines and underscores the scientific potential of future compact Compton telescopes. In particular, the next iteration of COSI as a NASA Small Explorer satellite has recently been approved for launch in 2025.

The Composition and Power of the Jet of the Broad-line Radio Galaxy 3C 120

Abstract We calculated the electron–positron pair-production rate at the base of the jet of 3C 120 due to collisions of photons from the hot accretion flow using the measurement of its average soft gamma-ray spectrum by the Compton Gamma Ray Observatory. We found that this rate approximately equals the flow rate of leptons emitting the observed synchrotron radio-to-IR spectrum of the jet core, calculated using the extended jet model following Blandford &amp; Königl. This coincidence shows the jet composition is likely to be pair dominated. We then calculated the jet power in the bulk motion of ions and found it greatly exceeds that achievable by the magnetically arrested disk scenario for the maximum black hole spin unless the jet contains mostly pairs. Next, we found that the magnetic flux through the synchrotron-emitting jet equals the maximum poloidal flux that can thread the black hole. Finally, we compared two estimates of the magnetization parameter at the onset of the synchrotron emission and found they are in agreement only if pairs dominate the jet content.

Unveiling the Origin of the Fermi Bubbles with MeV Photon Telescopes

Abstract The Fermi Bubbles (FBs) are a pair of large-scale ellipsoidal structures extending above and below the Galactic plane almost symmetrically aligned with the Galactic center. After more than 10 yr since their discovery, their nature and origin remain unclear. Unveiling the primary emission mechanisms, whether hadronic or leptonic, is considered to be the main tool to shed light on the topic. We explore the potential key role of MeV observations of the FB, and we provide a recipe to determine the sensitivity of Compton and Compton-pair telescopes to the extended emission of the FB. We illustrate the capabilities of the Imaging Compton Telescope COMPTEL, the newly selected NASA MeV mission Compton Spectrometer and Imager, as well as the expectations for a potential future Compton-pair telescope such as the All-sky Medium Energy Gamma-ray Observatory eXplorer.

Half-a-century of gamma-ray astrophysics at the Max-Planck Institute for Extraterrestrial Physics

Gamma-ray astronomy has been one of the prime scientific research fields of the Max-Planck Institute for Extraterrestrial Physics (MPE) from its beginning. Over the years, the entire gamma-ray energy range accessible from space was explored. The purpose of this review article is to summarise the achievements of the gamma-ray group at MPE during the last 50+ years. This covers a substantial part of the general history of space-based gamma-ray astronomy, for which both, general review articles (e.g. Pinkau in Exp Astron 5: 157, 2009; Schönfelder in AN 323: 524, 2002; Trimble in AIP Conf Proc 304: 40, 1994) and a detailed tabular list of events and missions (Leonard and Gehrels in https://heasarc.gsfc.nasa.gov/docs/history, version 1.0.8, 2009), have been compiled. Here, we describe the gamma-ray activities at MPE from the beginning till the present, reviewing the tight interplay between new technological developments towards new instruments and scientific progress in understanding gamma-ray sources in the sky. This covers (i) the early development of instruments and their tests on half a dozen balloon flights, (ii) the involvement in the most important space missions at the time, i.e. ESA’s COS-B satellite, NASA’s Compton Gamma-ray Observatory and Fermi Space Telescope, as well as ESA’s INTEGRAL observatory, (iii) the participation in several other missions such as TD-1, Solar Maximum Mission, or Ulysses, and (iv) the complementary ground-based optical instruments OPTIMA and GROND to enhance selected science topics (pulsars, gamma-ray bursts). With the gradual running-out of institutional support since 2010, gamma-ray astrophysics as a main research field has now come to an end at MPE.

Temporal Properties of Precursors, Main Peaks, and Extended Emissions of Short GRBs in the Third Swift/BAT GRB Catalog

Abstract A comprehensive study is given to short gamma-ray bursts (sGRBs) in the third Swift Burst Alert Telescope (BAT) GRB Catalog from 2004 December to 2019 July. We examine in detail the temporal properties of the three components in the prompt gamma-ray emission phase, including precursors, main peaks, and extended emissions (EEs). We investigate the similarity of the main peaks between one-component and two-component sGRBs. It is found that there is no substantial difference among their main peaks. Importantly, comparisons are made between in the single-peaked sGRBs and the double-peaked sGRBs. It is found that our results for main peaks in Swift/BAT sGRBs are essentially consistent with those in the Compton Gamma Ray Observatory Burst And Transient Source Experiment (BATSE) ones recently found in our Paper I. Interestingly, we suspect, besides the newly found MODE I/II evolution forms of pulses in BATSE sGRBs in Paper I, that there would have been more evolution modes of pulses across differently adjacent energy channels in view of the Swift/BAT observations. We further inspect the correlation of the main peaks with either the precursors or the EEs. We find that the main peaks tend to last longer than the precursors but shorter than the EEs. Moreover, we verify the power-law correlations related with peak fluxes of the three components, strongly suggesting that they are produced from the similar central-engine activities. In particular, we compare the temporal properties of GRB 170817A with other sGRBs with EE and find no obvious differences between them.

Very Long Baseline Interferometry Observations of the Proposed Radio Counterpart of an EGRET Source

We present high-resolution radio interferometric imaging observations of the radio source NVSS J182659+343113 (hereafter J1826+3431), the proposed radio counterpart of the γ-ray source, 3EG J1824+3441 detected by the Energetic Gamma Ray Experiment Telescope (EGRET) on board the Compton Gamma Ray Observatory satellite. We analyzed eight epochs of archival multi-frequency very long baseline interferometry data. We imaged the asymmetric core–jet structure of the source, and detected apparent superluminal motion in the jet. At the highest observing frequency, 15.3 GHz, the core shows high brightness temperature indicating Doppler boosting. Additionally, the radio features undergo substantial flux density variability. These findings strengthen the previous claim of the association of the blazar J1826+3431 with the possible γ-ray source, 3EG J1824+3441.

Development and performance verification of a 3-D position-sensitive Compton camera for imaging MeV gamma rays

In gamma-ray astronomy, the 1–10 MeV range is one of the most challenging energy bands to observe owing to low photon signals and a considerable amount of background contamination. This energy band, however, comprises a substantial number of nuclear gamma-ray lines that may hold the key to understanding the nucleosynthesis at the core of stars, spatial distribution of cosmic rays, and interstellar medium. Although several studies have attempted to improve observation of this energy window, development of a detector for astronomy has not progressed since NASA launched the Compton Gamma Ray Observatory (CGRO) in 1991. In this work, we first developed a prototype 3-D position-sensitive Compton camera (3D-PSCC), and then conducted a performance verification at NewSUBARU, Hyogo in Japan. To mimic the situation of astronomical observation, we used a MeV gamma-ray beam produced by laser inverse Compton scattering. As a result, we obtained sharp peak images of incident gamma rays irradiating from incident angles of 0° and 20°. The angular resolution of the prototype 3D-PSCC was measured by the Angular Resolution Measure and estimated to be 3.4° ± 0.1° (full width at half maximum (FWHM)) at 1.7 MeV and 4.0° ± 0.5° (FWHM) at 3.9 MeV. Subsequently, we conceived a new geometry of the 3D-PSCC optimized for future astronomical observations, assuming a 50-kg class small satellite mission. The SΩ of the 3D-PSCC is 11 cm2sr, anticipated at 1 MeV, which is small but provides an interesting possibility to observe bright gamma-ray sources owing to the high intrinsic efficiency and large field of view (FoV).

Comparing Long-duration Gamma-Ray Flares and High-energy Solar Energetic Particles

Little is known about the origin of the high-energy and sustained emission from solar Long-Duration Gamma-Ray Flares (LDGRFs), identified with the Compton Gamma Ray Observatory (CGRO), the Solar Maximum Mission (SMM), and now Fermi. Though Fermi/Large Area Space Telescope (LAT) has identified dozens of flares with LDGRF signature, the nature of this phenomenon has been a challenge to explain both due to the extreme energies and long durations. The highest-energy emission has generally been attributed to pion production from the interaction of >300 MeV protons with the ambient matter. The extended duration suggests that particle acceleration occurs over large volumes extending high in the corona, either from stochastic acceleration within large coronal loops or from back precipitation from coronal mass ejection driven shocks. It is possible to test these models by making direct comparison between the properties of the accelerated ion population producing the gamma-ray emission derived from the Fermi/LAT observations, and the characteristics of solar energetic particles (SEPs) measured by the Payload for Matter-Antimatter Exploration and Light Nuclei Astrophysics (PAMELA) spacecraft in the energy range corresponding to the pion-related emission detected with Fermi. For fourteen of these events we compare the two populations -- SEPs in space and the interacting particles at the Sun -- and discuss the implications in terms of potential sources. Our analysis shows that the two proton numbers are poorly correlated, with their ratio spanning more than five orders of magnitude, suggesting that the back precipitation of shock-acceleration particles is unlikely the source of the LDGRF emission.

Update on testing the isotropy of the properties of gamma-ray bursts

Abstract Previously, we proposed a novel method to inspect the isotropy of the properties of gamma-ray bursts (GRBs), such as their duration, fluences and peak fluxes at various energy bands and different time-scales, complementary to existing studies of the spatial distribution of GRBs by other authors. The method was then applied to the Fermi Gamma-ray Burst Monitor (GBM) Burst Catalog containing 1591 GRBs. Except for one particular direction where we noticed some hints of violation from statistical isotropy, the rest of the data showed consistency with isotropy. In this work, we apply our method, with some minor modifications, to the updated Fermi GBM data sample containing 2266 GRBs, which is thus ∼40 per cent larger. We also test two other major GRB catalogues: the Burst And Transient Source Experiment (BATSE) Current GRB Catalog of the Compton Gamma Ray Observatory (CGRO), containing ∼2000 bursts, and the Swift Burst Alert Telescope (BAT) GRB Catalog, containing ∼1200 bursts. The new results using the updated data are consistent with our previous findings and we find no statistically significant anisotropic feature in the observed properties of these samples of all GRBs.