The LIGO/Virgo Collaboration (LVC) detected on 2017 January 4 a significant gravitational-wave (GW) event (now named GW170104). We report in this Letter the main results obtained from the analysis of ...hard X-ray and gamma-ray data of the AGILE mission that repeatedly observed the GW170104 localization region (LR). At the LVC detection time T0 AGILE observed about 36% of the LR. The gamma-ray imaging detector did not reveal any significant emission in the energy range 50 MeV-30 GeV. Furthermore, no significant gamma-ray transients were detected in the LR that was repeatedly exposed over timescales of minutes, hours, and days. We also searched for transient emission using data near T0 of the omnidirectional detector MCAL operating in the energy band 0.4-100 MeV. A refined analysis of MCAL data shows the existence of a weak event (that we call "E2") with a signal-to-noise ratio of 4.4 lasting about 32 ms and occurring 0.46 0.05 s before T0. A study of the MCAL background and of the false-alarm rate of E2 leads to the determination of a post-trial significance between 2.4 and 2.7 for a temporal coincidence with GW170104. We note that E2 has characteristics similar to those detected from the weak precursor of GRB 090510. The candidate event E2 is worth consideration for simultaneous detection by other satellites. If associated with GW170104, it shows emission in the MeV band of a short burst preceding the final coalescence by 0.46 s and involving ∼10−7 of the total rest mass energy of the system.
FRB 180916 is a most intriguing source capable of producing repeating fast radio bursts with a periodic 16.3 day temporal pattern. The source is well positioned in a star-forming region in the ...outskirts of a nearby galaxy at 150 Mpc distance. In this Letter we report on the X-ray and γ-ray observations of FRB 180916 obtained by AGILE and Swift. We focused especially on the recurrent 5 day time intervals of enhanced radio bursting. In particular, we report on the results obtained in the time intervals 2020 February 3-8, 2020 February 25, 2020 March 5-10, and 2020 March 22-28 during a multiwavelength campaign involving high-energy and radio observations of FRB 180916. We also searched for temporal coincidences at millisecond timescales between the 32 known radio bursts of FRB 180916 and X-ray and MeV events detectable by AGILE. We do not detect any simultaneous event or any extended X-ray and γ-ray emission on timescales of hours/days/weeks. Our cumulative X-ray (0.3-10 keV) flux upper limit of 5 × 10−14 erg cm−2 s−1 (obtained during 5 day active intervals from several 1-2 ks integrations) translates into an isotropic luminosity upper limit of LX,UL ∼ 1.5 × 1041 erg s−1. Deep γ-ray observations above 100 MeV over a many-year timescale provide an average luminosity upper limit one order of magnitude larger. These results provide the so-far most stringent upper limits on high-energy emission from the FRB 180916 source. Our results constrain the dissipation of magnetic energy from a magnetar-like source of radius Rm, internal magnetic field Bm, and dissipation timescale τd to satisfy the relation , where Rm,6 is Rm in units of 106 cm, Bm,16 is Bm in units of 1016 G, and τd,8 in units of 108 s.
Abstract
We report the AGILE observations of GRB 220101A, which took place at the beginning of 2022 January 1 and was recognized as one of the most energetic gamma-ray bursts (GRBs) ever detected ...since their discovery. The AGILE satellite acquired interesting data concerning the prompt phase of this burst, providing an overall temporal and spectral description of the event in a wide energy range, from tens of kiloelectronvolts to tens of megaelectronvolts. Dividing the prompt emission into three main intervals, we notice an interesting spectral evolution, featuring a notable hardening of the spectrum in the central part of the burst. The average fluxes encountered in the different time intervals are relatively moderate, with respect to those of other remarkable bursts, and the overall fluence exhibits a quite ordinary value among the GRBs detected by MCAL. However, GRB 220101A is the second farthest event detected by AGILE, and the burst with the highest isotropic equivalent energy of the entire MCAL GRB sample, releasing
E
iso
= 2.54 × 10
54
erg and exhibiting an isotropic luminosity of
L
iso
= 2.34 × 10
52
erg s
−1
(both in the 400 keV–10 MeV energy range). We also analyzed the first 10
6
s of the afterglow phase, using the publicly available Swift-XRT data, carrying out a theoretical analysis of the afterglow, based on the forward shock model. We notice that GRB 220101A is with high probability surrounded by a wind-like density medium, and that the energy carried by the initial shock shall be a fraction of the total
E
iso
, presumably near ∼50%.
ABSTRACT
PKS 1830 -211 is a γ-ray emitting, high-redshift (z =2.507 ± 0.002), lensed flat-spectrum radio quasar. During the period 2019 mid-February to mid-April, this source underwent a series of ...strong γ-ray flares that were detected by both AGILE-GRID (Gamma-Ray Imaging Detector) and Fermi Large Area Telescope (Fermi-LAT), reaching a maximum γ-ray flux of $F_{\rm E\gt 100\, MeV}\approx 2.3\times 10^{-5}$ photons cm−2 s−1. Here, we report on a coordinated campaign from both on-ground Medicina, Owens Valley Radio Observatory (OVRO), Rapid Eye Mount (REM), and Sardinia Radio Telescope (SRT) and orbiting facilities (AGILE, Fermi, INTEGRAL, NuSTAR, Swift, and Chandra), with the aim of investigating the multiwavelength properties of PKS 1830-211 through nearly simultaneous observations presented here for the first time. We find a possible break in the radio spectra in different epochs above 15 GHz, and a clear maximum of the 15 GHz data approximately 110 d after the γ-ray main activity periods. The spectral energy distribution shows a very pronounced Compton dominance (> 200) which challenges the canonical one-component emission model. Therefore, we propose that the cooled electrons of the first component are re-accelerated to a second component by, for example, kink or tearing instability during the γ-ray flaring periods. We also note that PKS 1830-211 could be a promising candidate for future observations with both Compton satellites e.g. enhanced ASTROGAM (e-ASTROGAM) and Cherenkov arrays Cherenkov Telescope Array Observatory (CTAO) which will help, thanks to their improved sensitivity, in extending the data availability in energy bands currently uncovered.
The LIGO-Virgo Collaboration (LVC) detected, on 2017 August 17, an exceptional gravitational-wave (GW) event temporally consistent within with the GRB 1708117A observed by Fermi-GBM and INTEGRAL. The ...event turns out to be compatible with a neutron star-neutron star (NS-NS) coalescence that subsequently produced a radio/optical/X-ray transient detected at later times. We report the main results of the observations by the AGILE satellite of the GW170817 localization region (LR) and its electromagnetic (EM) counterpart. At the LVC detection time T0, the GW170817 LR was occulted by the Earth. The AGILE instrument collected useful data before and after the GW/GRB event because in its spinning observation mode it can scan a given source many times per hour. The earliest exposure of the GW170817 LR by the gamma-ray imaging detector started about 935 s after T0. No significant X-ray or gamma-ray emission was detected from the LR that was repeatedly exposed over timescales of minutes, hours, and days before and after GW170817, also considering Mini-calorimeter and Super-AGILE data. Our measurements are among the earliest ones obtained by space satellites on GW170817 and provide useful constraints on the precursor and delayed emission properties of the NS-NS coalescence event. We can exclude with high confidence the existence of an X-ray/gamma-ray emitting magnetar-like object with a large magnetic field of . Our data are particularly significant during the early stage of evolution of the EM remnant.
The origin of cosmic neutrinos is still largely unknown. Using data obtained by the gamma-ray imager on board the Astro-rivelatore Gamma a Immagini Leggero (AGILE) satellite, we systematically ...searched for transient gamma-ray sources above 100 MeV that are temporally and spatially coincident with 10 recent high-energy neutrino IceCube events. We found three AGILE candidate sources that can be considered possible counterparts to neutrino events. Detecting three gamma-ray/neutrino associations out of 10 IceCube events is shown to be unlikely due to a chance coincidence. One of the sources is related to the BL Lac source TXS 0506+056. For the other two AGILE gamma-ray sources there are no obvious known counterparts, and both Galactic and extragalactic origin should be considered.
GRB 190114C represents a breakthrough for the physics of gamma-ray bursts (GRBs), being the first GRB with delayed emission above 300 GeV, as reported by MAGIC. We present in this paper the ...sub-MeV/MeV data of the prompt and early afterglow emissions of GRB 190114C, as detected by AGILE and Konus-Wind, in the 20 keV-100 MeV energy range. The first stages of the burst exhibit multiple emission components, associated with an interesting spectral evolution. The first 2 s of the prompt emission can be described by a single "Band-like" spectral component. The successive 4 s show the presence of an additional high-energy spectral component, which quickly evolves into a "hard-flat" component of the F spectrum, extending up to 10-100 MeV and likely produced by inverse Compton radiation, whose onset and evolution are clearly shown in our data. After this phase, the F spectrum evolves into a "V shape," showing the persistence and spectral hardening of the additional high-energy component in substantial agreement with Fermi and Swift results. We also analyze the first ∼200 s of the early afterglow that show a reflaring episode near T0 + 15 s. We identify a new, so-far-unnoticed flux temporal break near T0 + 100 s, which is detected in hard X-rays by both Konus-Wind and INTEGRAL/SPI-ACS. We find this break incompatible with the commonly assumed adiabatic evolution of a fireball in a constant-density medium. We interpret this break as a consequence of radiative evolution of the early afterglow from a fireball expanding in a wind-like circumburst medium.
Super-massive black holes in active galaxies can accelerate particles to relativistic energies, producing jets with associated -ray emission. Galactic 'microquasars', which are binary systems ...consisting of a neutron star or stellar-mass black hole accreting gas from a companion star, also produce relativistic jets, generally together with radio flares. Apart from an isolated event detected in Cygnus X-1, there has hitherto been no systematic evidence for the acceleration of particles to gigaelectronvolt or higher energies in a microquasar, with the consequence that we are as yet unsure about the mechanism of jet energization. Here we report four -ray flares with energies above 100 MeV from the microquasar Cygnus X-3 (an exceptional X-ray binary that sporadically produces radio jets). There is a clear pattern of temporal correlations between the -ray flares and transitional spectral states of the radio-frequency and X-ray emission. Particle acceleration occurred a few days before radio-jet ejections for two of the four flares, meaning that the process of jet formation implies the production of very energetic particles. In Cygnus X-3, particle energies during the flares can be thousands of times higher than during quiescent states.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
BACKGROUND AND PURPOSE: Nonalcoholic fatty liver disease is frequently associated with type 2 diabetes mellitus, obesity, and dyslipidemia, but some patients have normal glucose tolerance or normal ...weight. We tested the hypothesis that there is an association between nonalcoholic fatty liver disease and insulin resistance that is independent of diabetes and obesity.
SUBJECTS AND METHODS: We measured anthropometric and metabolic variables in 46 patients with chronically elevated serum aminotransferase levels, “bright liver” on ultrasound scan, and normal glucose tolerance. Indexes of insulin resistance and secretion were determined using the homeostasis model assessment method. They were compared with 92 normal subjects who were matched for age and sex.
RESULTS: Patients with nonalcoholic fatty liver disease were characterized by fasting and glucose-induced hyperinsulinemia, insulin resistance, postload hypoglycemia, and hypertriglyceridemia. Insulin resistance odds ratio (OR) = 15 per percent increase, 95% confidence interval (CI): 3.0 to 70, fasting triglyceride level (OR = 3.1 per mmol/liter increase, 95% CI: 1.1 to 8.9), 180-minute blood glucose level (OR = 4.3 per mmol/liter decrease, 95% CI: 1.6 to 12), and average insulin concentration in response to oral glucose (OR = 3.0 per 100 pmol/liter increase, 95% CI: 1.5 to 6.2) were independently associated with nonalcoholic fatty liver disease. The exclusion of overweight and obese subjects did not change the results.
CONCLUSION: Nonalcoholic fatty liver disease is associated with insulin resistance and hyperinsulinemia even in lean subjects with normal glucose tolerance. Genetic factors that reduce insulin sensitivity and increase serum triglyceride levels may be responsible for its development.
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