Hard Γ-rays Research Articles

Constraining leptonic emission scenarios for the PeVatron candidate HESS J1702−420 with deep XMM-Newton observations

Aims. We aim to search for a hidden leptonic accelerator, such as a high-Ė pulsar, associated with the unidentified TeV object HESS J1702−420A. Methods. We carried out a 72 ks X-ray observation with the XMM-Newton satellite and analyzed the resulting data jointly with the publicly available HESS spectral energy distribution (SED) results to derive constraints on the leptonic contribution to the TeV emission of HESS J1702−420A. A set of scripts dedicated to the multi-wavelength modeling of X-ray and γ-ray data, based on Gammapy, Naima, and Xspec, has been developed in the context of this work and made publicly available along with this paper. Results. No object clearly associated with HESS J1702−420A was found in the XMM-Newton data. After excluding the unidentified object Suzaku src B as a possible X-ray counterpart and classifying it as a new cataclysmic variable source candidate, we derived strict upper limits on the level of diffuse X-ray emission in the HESS J1702−420A region: F(2 − 10 keV)≲5.4 × 10−5 keV cm−2 s−1 at 2σ (≈95.5%) confidence level. A tight constraint on the magnetic field was derived, under a one-zone leptonic scenario, by jointly fitting the XMM-Newton spectra and the HESS SED: B ≲ 1.45 μG at 2σ level. We additionally report the serendipitous discovery of a new extended X-ray source with a hard spectral index of 1.99 ± 0.45, named XMMU J170147.3−421407 which is likely Galactic. Its classification as a high-speed runaway pulsar wind nebula (PWN), possibly associated with HESS J1702−420A, is not obvious but cannot be ruled out either. Conclusions. The hard γ-ray object HESS J1702−420A remains unidentified, but the absence of a clear X-ray counterpart strongly challenges simple leptonic scenarios. The only remaining possible leptonic counterpart for HESS J1702−420A appears to be a newly discovered X-ray source with extended morphology and hard spectral index, which may be a PWN powered by a high-speed runaway pulsar.

Impact of γ-rays Irradiation on Hybrid TiO2-SiO2 Sol-Gel Films Doped with RHODAMINE 6G.

In the present paper, we investigate how the optical and structural properties, in particular the observed photoluminescence (PL) of photocurable and organic-inorganic TiO2-SiO2 sol-gel films doped with Rhodamine 6G (R6G) are affected by γ-rays. For this, four luminescent films, firstly polymerized with UV photons (365 nm), were submitted to different accumulated doses of 50 kGy, 200 kGy, 500 kGy and 1 MGy while one sample was kept as a reference and unirradiated. The PL, recorded under excitations at 365 nm, 442 nm and 488 nm clearly evidences that a strong signal peaking at 564 nm is still largely present in the γ-irradiated samples. In addition, M-lines and Fourier-transform infrared (FTIR) spectroscopies are used to quantify the radiation induced refractive index variation and the chemical changes, respectively. Results show that a refractive index decrease of 7 × 10−3 at 633 nm is achieved at a 1 MGy accumulated dose while a photo-induced polymerization occurs, related to the consumption of CH=C, Si-OH and Si-O-CH3 groups to form Ti-O and Si-O bonds. All these results confirm that the host matrix (TiO2-SiO2) and R6G fluorophores successfully withstand the hard γ-ray exposure, opening the way to the use of this material for sensing applications in radiation-rich environments.

Gamma-Ray Line Observations of the 2000 July 14 Flare and SEP Impact on the Earth

The HXS and GRS detectors on Yohkoh observed the 14 July 2000, X5.7 flare, beginning at ∼ 10:20 UT, ∼ 4 min before the peak in soft X-rays. The hard X-rays and γ-rays peaked ∼ 3 min later at ∼ 10:27 UT. Solar γ-ray emission lasted until ∼ 10:40 UT. Impact of high-energy ions at the Sun is revealed by the γ-ray lines from neutron capture, annihilation radiation and de-excitation that are visible above the bremsstrahlung continuum. From measurement of these lines we find that the flare-averaged spectrum of accelerated protons is consistent with a power law ge10 MeV with index 3.14±0.15 and flux 1.1×1032 protons MeV−1 at 10 MeV. We estimate that there were ∼1.5×1030 erg in accelerated ions if the power law extended without a break down to 1 MeV; this is about 1% of the energy in electrons > 20 keV from measurements of the hard X-rays. We find no evidence for spectral hardening in the hard X-rays that has been suggested as a predictor for the occurrence of solar energetic particle (SEP) events. This was the third largest proton event above 10 MeV since 1976. The GRS and HXS also observed γ-ray lines and continuum produced by the impact of SEP on the Earth's atmosphere beginning about 13 UT on 14 July. These measurements show that the SEP spectrum softened considerably over the next 24 hours. We compare these measurements with proton measurements in space.

X-ray observations of TeV blazars and multi-frequency analysis

The nonthermal spectra of blazars, observed from radio to GeV/TeV γ-rays, reveal two pronounced components, both produced by radiation by energetic particles. One peaks in the IR-to-soft X-ray band, radiating via the synchrotron process; the other, peaking in the high-energy γ-rays, is produced by the Compton process. These spectra - and, in particular, the ASCA data - suggest that the origin of the seed photons for Comptonization is diverse. In the High-energy peaked BL Lac objects (HBLs), the dominant seed photons for Comptonization appear to be the synchrotron photons internal to the jet (SSC process). In the quasar-hosted blazars (QHBs), on the other hand, the X-ray band emission is still dominated by the SSC process, while the MeV to GeV range is produced by Comptonization of external photons such as the emission line light. In the context of this three-component model, we derive the magnetic field of 0.1–1 Gauss for all classes of blazars. Lorentz factors γ peak of electrons radiating at each peak of the vF( v) spectra are estimated to be ∼ 10 5 for HBLs; this is much higher than ∼ 10 3 for QHBs. This difference is consistent with the fact that the four sources that are known to emit TeV γ-rays (TeV blazars) are all classified as HBLs. Among the TeV blazars, Mkn 421 is one of the brightest and most variable emitters from ultraviolet (eV) to hard γ-ray (TeV) energies, and its correlated inter-band variability suggests that both keV and TeV spectral regimes are produced by the same, most energetic end of the electron population radiating via the synchrotron process in the keV, and the SSC process in TeV band. The multi-frequency observations including TeV energy band provide the best opportunity to understand high-energy emission from blazar jets. In this paper, we discuss results of multi-frequency analysis and review the results of intensive campaigns for Mkn 421 from 1994 to 1998.

Inverse Compton emission of TeV gamma rays from PSR B1259-63

We derive light curves for the hard γ-ray emission, at energies up to several TeV, expected from the unique pulsar/Be-star binary system PSR B1259-63. This is the only known system in our galaxy in which a radio pulsar is orbiting a main sequence star. We show that inverse Compton emission from the electrons and positrons in the shocked pulsar wind, scattering target photons from the Be star, produces a flux of hard γ-rays that should be above the sensitivity threshold of present day atmospheric Cerenkov detectors. Furthermore, we predict that the flux of hard γ-rays produced via this mechanism has a characteristic variation with orbital phase that should be observable, and which is not expected from any other mechanism

High‐Energy Gamma‐Ray Emission from Galactic Kerr‐Newman Black Holes. II. The Radiative Jets

A model of the unidentified high-latitude Galactic hard γ-ray (EGRET) sources based on black hole electrodynamics is presented in this paper and its companion. The γ-ray emission is produced in a bipolar outflow from a charged, rotating black hole (Kerr-Newman black hole) in a low-density region of the Galaxy. The model is a synthesis of pair creation scenarios for pulsars, the theory of black hole magnetospheres and synchrotron self-Compton (SSC) large-scale jets. In this article it is shown that the resulting emission from the SSC jet is consistent with the constraints imposed on the broadband spectral energy distribution implied by the lack of identification of the γ-ray sources in other frequency bands.

High‐Energy Gamma‐Ray Emission from Galactic Kerr‐Newman Black Holes. I. The Central Engine

A model of the central engine of the unidentified high-latitude galactic hard γ-ray (EGRET) sources based on black hole electrodynamics is presented. The γ-ray emission is produced in a bipolar outflow from a charged, rotating black hole (a Kerr-Newman black hole) in a low-density region of the Galaxy, the details of which are provided in a companion paper. The model proposed in this article and its companion is a synthesis of pair creation scenarios for pulsars, the theory of black hole magnetospheres and synchrotron self-Compton large-scale jets. This article describes the physics of the putative central engine. Kerr-Newman black holes are plausible endpoints of the catastrophic gravitational collapse of the most massive magnetized rotating stars. In the following, the ability of a Kerr-Newman black hole to drive a magnetically dominated plasma wind in the charge-starved limit is explored for the first time. Although there are important analogies to magnetohydrodynamic (MHD) wind theory of Kerr (uncharged rotating) black holes, there are also enormous distinctions. However, previous experience with the MHD Kerr case is exploited to render this more complicated problem tractable. The most important parameter for quantifying the wind energy is the magnetic field line angular velocity, ΩF (and unfortunately the most difficult to calculate). The determination of ΩF is tied directly to the process by which a pair plasma is created on large-scale magnetic field lines through high-energy quantum electrodynamic processes typical of pulsar magnetospheres. It is argued in principle how ΩF is determined by the plasma injection mechanism. Furthermore, the most significant result of this effort is the calculation of ΩF for a model that is determined by a plausible set of astronomical parameters. It is essential to realize a distinction from some charge-starved pulsar models: the energy source for the wind is quantified by the field line rotation rate (the cross-field potential), ultimately powered by the rotation of the hole through dissipative gravitomagnetic processes and not the volage drop across the vacuum pair creation gap.

Solar Microwave Bursts from Electron Populations with a 'Broken’ Energy Spectrum

Usually the gyrosynchrotron emission of microwave bursts from electron populations with a power-law (PL) energy distribution has been considered under the assumption that the spectral index of the distribution is constant over a wide range of energies. Meanwhile, there is strong evidence, in particular from hard X-ray and γ-ray, but also from cm/mm wavelength radio observations, that in many solar flare events the spectrum of the emitting electrons is characterized by a significant hardening at energies above 100–500 keV. We present some examples of calculated microwave burst spectra at cm/mm wavelengths taking into account the above evidence. It is shown that a break in the energy spectrum of the PL electrons can indeed result in a spectral hardening sometimes observed in microwave bursts at frequencies above 10–30 GHz.

Effects of Particle Beams in the Solar Atmosphere

This work addresses the observational and physical effects of particle beams in the solar atmosphere. Mainly electron beams are considered, but also some effects of proton and neutral beams are mentioned. Briefly describing acceleration mechanisms of superthermal particles, the main attention is devoted to effects influencing the particle beam propagation. The collisional energy losses and pitch-angle scattering, return current effects, mirroring in the converging magnetic field, and the scattering in the Alfven and whistler wave turbulence in specific situations are considered. The role of quasi-linear relaxation is discussed. Examples of observations showing effects of particle beams in the solar atmosphere are presented throughout the paper. Separate chapters are devoted to processes connected with particle beam bombardment of dense layers of the solar atmosphere: hard X-ray and γ-ray flare emissions, evaporation process, asymmetry of optical chromospheric lines, and impact linear Hα line polarization. The beam induced energy release processes are also included. The presented effects of particle beams are summarized in the conclusions and future prospects are suggested.

The Attenuation of Hard γ-rays in Strongly-Magnetized Pulsars

AbstractWe investigate the spectral attenuation due to one-photon pair production and photon splitting in neutron star magnetospheres. The calculations are performed in a Schwarzschild metric, thereby including redshift and field enhancement effects associated with curved spacetime. We find that pair production and splitting totally inhibit emission above around 10-30 MeV in PSR1509-58, whose surface field is inferred to be as high as 3 × 1013Gauss. Model pulsar spectra of splitting cascades for high field cases, where splitting is important, are consistent with the very low cutoff energy in PSR1509-58 for a wide range of polar cap sizes.

Nuclear tracks and analogue Fermi surfaces

Ranges of 1.65 GeV Xenon ions in muscovite mica vary strongly with incident angle. This anomalous effect is due to a new kind of ‘governed’ particle motion - ridging — which is caused by, and exploits the stark anisotropy of the basic crystal lattice. Substantial angular differences in ridging orbits (refractive pathways) at molecular layers are the cause of a corresponding angular dependence in the effective ‘non-linear’ electronic stopping power S e , and hence in the vector range R (θ,φ,E). In a 4π solid angle the surface described by range vectors R of common origin and energy - spherical for amorphous condensed matter - is characteristically topographic for a crystal, due to orbital ridging, bridging, channelling, quasichannelling, blocking, and other consequences of atomic order. It is shown that this classical mechanical surface in real space, not considered previously, is the direct analogue of the quantum mechanical Fermi surface in reciprocal space for conduction electrons. Transformation of the Fermi into this classical C-surface with increasingly relativistic electronic mass is described geometrically. Two-beam (Bloch wave) dispersive surfaces (Fermi) become a single quasi-classical surface in the many-beam (wave) limit. Kikuchi patterns become classical star patterns. The Maxwell-Boltzmann statistics overwhelm the Fermi-Dirac. The stable ‘fundamental’ particles - leptons, mesons, baryons etc. - exhibit equi-energy surfaces of one kind or the other, sometimes both, depending on mass, energy, spin, charge, and strength of interaction with crystalline condensed matter. For photons (massless Bosons) and Bose-Einstein statistics a duality in scattering is also evident - from the visible to hard γ-rays. For diffractive photon scattering in a crystal field a wave equation for the classic electric and magnetic field vectors now describes a corresponding structure in reciprocal space. We describe this as a Maxwell surface. The ‘old’ Fermi surface, and the new classical C- and Maxwell surfaces, round off our basic understanding of the scattering of radiation generally by crystals, and symmetry is restored to the physics. There are also ramifications for solid state nuclear tracks.

Pair Production in AGN

The X-ray luminosity and variability of many AGN are sufficiently extreme that any hard γ-rays produced in the source will collide with the X-rays and create electron-positron pairs, rather than escape. A small region where vast amounts of energy are produced, such as an AGN, is an ideal place to accelerate particles to relativistic energies and so produce γ-rays by Compton scattering. The observed X-ray spectra of AGN are hard and indicate that most of the luminosity is at the highest energies so that absorption of the γ-rays represents a large fraction of the energy flux, which can then be re-radiated at lower energies. Pairs can thus effectively reprocess much of the radiant power in an AGN.

Relationships among flare images at different wavelengths

The talk reviews briefly historical development of the imaging of the Sun, and flare imaging in particular, at different wavelengths. The present state is then critically analyzed, emphasizing and demonstrating problems related to simultaneity of observed data, differences in time resolution, limitations of the imaged field of view, unequal spatial resolution, and alignment of the images. Prospects for the future are briefly sketched, including imaging in very hard X-rays and γ-rays.

Chromospheric heating by electron and proton bombardment in the solar flare of June 7, 1980

Using observations of both hard X-rays and γ-rays in the large solar flare on June 7, 1980, we infer the amount of chromospheric heating due to bombardment both by non-thermal electrons and by protons, respectively. If a thick-target model for the X-ray bremsstrahlung is adopted, then proton heating is shown to be important only in the lower chromosphere; however, if the hard X-rays are substantially thermal in origin, then proton heating may play an important or indeed dominant role in determining the structure of the entire flaring chromosphere.

A New Nuclear but Non Radioactive Method for Rapid Elemental Analysis of Clays

AbstractA method using the bombardment of samples with protons and other positive ions of energy in the MeV range is described: the prompt atomic (γ-rays) and nuclear (γ-rays and charged particles) events generated during the bombardment, are detected with energy sensitive solid state detectors: cooled Ge(Li) for γ-rays and hard γ-rays, cooled Si(Li) detectors for soft γ-rays (3–20 keV) and Si-barrier detectors for charged particles. These 3 types of detectors can be simultaneously used for multipurpose experiments. These techniques are particularly useful for simultaneous detection of all the elements of interest in the sample. Comparisons are made with other microtechniques. Analyses of Li, Na, K, Ca, Rb, Cs and Cl exchanged in appropriate chloride solutions have been achieved for several clays (Geisenheim, Isola di Ponza, Layton). A new phenomenon relative to the anion contribution in cation exchangers is observed. A method of profile analysis of Na by resonant nuclear reactions is discussed.

Effect of Photo-Reactions on the Effective Yield of Delayed Neutrons in the Pressure Tube Type Heavy Water Reactor

A theoretical study with use made of the collision probability method has been undertaken on the effect of photo-reactions brought upon the effective yield β of delayed neutrons in a pressure tube type heavy water reactor loaded with 235U. It is concluded that the shielding effect of the reactor structural materials for the hard γ-rays emitted from fission products reduces the contribution of the photo-neutrons to β from the currently used value of 1.00×10−3 to 2.2×10−4.

Effect of Photo-Reactions on the Effective Yield of Delayed Neutrons in the Pressure Tube Type Heavy Water Reactor

A theoretical study with use made of the collision probability method has been undertaken on the effect of photo-reactions brought upon the effective yield β of delayed neutrons in a pressure tube type heavy water reactor loaded with 235U. It is concluded that the shielding effect of the reactor structural materials for the hard γ-rays emitted from fission products reduces the contribution of the photo-neutrons to β from the currently used value of 1.00×10−3 to 2.2×10−4.

OSO-III: Preliminary scientific results

OSO-III was placed into orbit on March 8, 1967; observations were made of the solar extreme ultraviolet, soft and hard solar X-rays, cosmic X-rays and γ-rays, cosmic ray particles, and the near-earth optical wavelength radiation environment.

High energy gamma rays in the decay of La 140

A three-crystal pair-spectrometer has been used for a reinvestigation of the hard γ-rays emitted in the decay of 40 h La 140. The following energies and relative intensities were observed: 1598(100), 2373(0.86), 2535(3.0), 2890(0.082) and 3100 (0.035). The results agree well with data obtained by Russian workers by means of a “ritron” and a “γ-hodoscope”. From γ-γ coincidence measurements limits of respectively 0.18% and 0.07% can be put on the hypothetical 1290 keV and 1500 keV γ-rays depopulating the 2890 and 3100 keV levels. From the decay scheme an absolute intensity of 96.1±0.8% is inferred for the 1598 keV γ-ray.

Internal Pair Creation in Magnesium-24

THE theory of quantum electrodynamics predicts the occasional emission of an electron-positron pair from an excited nucleus in place of a hard γ-ray. The probability of this event, or the ‘pair conversion coefficient’, has been calculated by Rose1. It is dependent on the quantum energy and on the multipole character of the nuclear transition.