scholarly journals Late Ordovician geographic patterns of extinction compared with simulations of astrophysical ionizing radiation damage

Paleobiology ◽  
2009 ◽  
Vol 35 (3) ◽  
pp. 311-320 ◽  
Author(s):  
Adrian L. Melott ◽  
Brian C. Thomas
Keyword(s):  
Solar Flares ◽  
Gamma Ray ◽  
High Energy ◽  
Gamma Ray Bursts ◽  
X Rays ◽  
Mass Extinctions ◽  
Observable Universe ◽  
Variable Intensity ◽  
High Rotational Speed ◽  
Wide Range

Terrestrial mass extinctions have been attributed to a wide range of causes. Some of them are external to Earth, such as bolide impacts (as widely discussed for the K/T boundary) and radiation events. Among radiation events, there are possible large solar flares, nearby supernovae, gamma-ray bursts (GRBs), and others. These have variable intensity, duration, and probability of occurrence, although some generalizations are possible in understanding their effects (Ejzak et al. 2007). Here we focus on gamma-ray bursts (Thorsett 1995; Scalo and Wheeler 2002), a proposed causal agent for the end-Ordovician extinction. These are the most remote and infrequent of events, but by virtue of their power, a threat approximately competitive with, for example, that of nearby supernovae. A GRB of the most powerful type (Woosley and Bloom 2006) is thought to result from a supernova at the end of stellar evolution for very massive stars with high rotational speed. Much of their energy is channeled into beams, or jets, which include very high energy electromagnetic energy, i.e., gamma-rays and X-rays. It is a testament to the power of these events, far across the observable universe, that they were first detected in the 1969–1970 results from monitoring satellites designed to detect nuclear explosions on Earth's surface. It was not until the 1990s, when the distance to the events became known, that their power became apparent. Several such events occur every day in the observable universe. Other kinds of events are also potentially damaging, such as so-called short bursts and solar flares, but rate information is only now beginning to clarify how much threat is likely from such sources.

scholarly journals e±-rich GRB Fireball and Infrared Flashes

2003 ◽  
Vol 214 ◽  
pp. 331-332
Author(s):  
Zhuo Li ◽  
Z. G. Dai ◽  
T. Lu
Keyword(s):  
Gamma Ray ◽  
Lorentz Factor ◽  
High Energy ◽  
Gamma Ray Bursts ◽  
Rapid Response ◽  
Model Parameters ◽  
Wide Range ◽  
Very High Energy ◽  
Very High

Gamma-ray bursts (GRBs) are believed to originate from ultra-relativistic fireballs, with initial Lorentz factor η ∼ 102 − 103. However very high energy photons may still suffer from γγ interaction. We show here that in a wide range of model parameters, the resulting pairs may dominate electrons associated with the fireball baryons. This may provide an explanation for the rarity of prompt optical detections. A rapid response to the GRB trigger at the IR band would detect such a strong flash.

scholarly journals Gamma-Ray Precursors of Solar Flares

1994 ◽  
Vol 142 ◽  
pp. 645-648
Author(s):  
E. Rieger
Keyword(s):  
Spatial Resolution ◽  
Gamma Rays ◽  
Solar Flares ◽  
Gamma Ray ◽  
High Energy ◽  
X Rays ◽  
High Energy Gamma ◽  
Gamma Ray Spectrometer ◽  
Energy Gamma ◽  
Negligible Contribution

AbstractBursts have been observed by the gamma-ray spectrometer on SMM at medium- and high-energy gamma-rays that precede the flare maximum. The negligible contribution of nuclear lines in the spectra of these events and their impulsive appearance suggests that they are hard-electron-dominated events superposed on the flares. Spatial resolution at gamma-ray energies will be necessary to decide whether this kind of bursts is cospatial with the flares or whether they occur in the flares’ vicinity.Subject headings: Sun: flares — Sun: X-rays, gamma rays

scholarly journals VERY HIGH-ENERGY NEUTRINOS FROM SLOWLY DECAYING, MASSIVE DARK MATTER AS A SOURCE OF EXPLOSIVE ENERGY FOR GAMMA-RAY BURSTS

2003 ◽  
Vol 18 (07) ◽  
pp. 477-489
Author(s):  
SAUL BARSHAY ◽  
GEORG KREYERHOFF
Keyword(s):  
Gamma Rays ◽  
Gamma Ray ◽  
Dense Matter ◽  
High Energy ◽  
Wide Distribution ◽  
Gamma Ray Bursts ◽  
Moderate Degree ◽  
X Rays ◽  
Very High Energy ◽  
Total Energies

We consider a speculative model for gamma-ray bursts (GRB), which predicts that the total kinetic energy in the ejected matter is less than the total energy in the gamma rays. There is also secondary energy in X-rays, which are emitted contemporaneously with the gamma rays. The model suggests that bremsstrahlung and Compton up-scattering by very energetic electrons, are important processes for producing the observed burst radiation. The dynamics naturally allows for the possibility of a moderate degree of beaming of matter and radiation in some gamma-ray bursts. GRB are predicted to have an intrinsically wide distribution in total energies, in particular, on the low side. They are predicted to occur at large redshifts, z ~ 8, in local regions of dense matter.

High Energy Transient Ionospheric Monitoring Network

1990 ◽  
Vol 8 (3) ◽  
pp. 263-265
Author(s):  
Paul J. Edwards
Keyword(s):  
Gravity Waves ◽  
Solar Flares ◽  
Gamma Ray ◽  
Monitoring Network ◽  
High Energy ◽  
Gamma Ray Bursts ◽  
Ionospheric Perturbations ◽  
X Ray ◽  
Radio Receivers ◽  
Computer Based

AbstractContinuous, wide sky coverage is essential for the detection and monitoring of infrequent, short-lived events of astrophysical interest such as supernova and nova explosions, variable X-ray sources, gamma ray bursts, gravity waves and stellar and solar flares. We propose to (1) examine past radio propagation records and (2) develop new computer based radio receivers to monitor and log ionospheric perturbations associated with these events.

KLEIN–NISHINA EFFECTS IN THE PROMPT AND EXTENDED HIGH-ENERGY GAMMA-RAY EMISSION OF GAMMA-RAY BURSTS

2011 ◽  
Vol 20 (10) ◽  
pp. 2023-2027 ◽  
Author(s):  
XIANG-YU WANG ◽  
HAO-NING HE ◽  
ZHUO LI
Keyword(s):  
Gamma Ray ◽  
Early Time ◽  
High Energy ◽  
Gamma Ray Bursts ◽  
Low Energy ◽  
Large Area ◽  
Wide Range ◽  
Inverse Compton ◽  
Energy Gamma ◽  
Gamma Ray Emission

Prompt and extended high-energy (> 100 MeV) gamma-ray emission has been observed from more than ten gamma-ray bursts by Fermi Large Area Telescope (LAT). Such emission is likely to be produced by synchrotron radiation of electrons accelerated in internal or external shocks. We show that IC scattering of these electrons with synchrotron photons are typically in the Klein–Nishina (KN) regime. For the prompt emission, the KN effect can suppress the IC component and as a result, one single component is seen in some strong bursts. The KN inverse-Compton cooling may also affect the low-energy electron number distribution and hence result in a hard low-energy synchrotron photon spectrum. During the afterglow, KN effect makes the Compton-Y parameter generally less than 1 in the first seconds for a wide range of parameter space. Furthermore, we suggest that the KN effect can explain the somewhat faster-than-expected decay of the early-time high-energy emission observed in GRB090510 and GRB090902B.

scholarly journals Solar Hard X-Ray and Gamma-Ray Observations from GRANAT

1994 ◽  
Vol 142 ◽  
pp. 611-621
Author(s):  
N. Vilmer
Keyword(s):  
Gamma Rays ◽  
Solar Flares ◽  
Gamma Ray ◽  
Ground Level ◽  
High Energy ◽  
Angle Distribution ◽  
X Rays ◽  
X Ray ◽  
Electrons And Ions ◽  
Solar Bursts

AbstractHard X-rays and gamma-rays are the most direct signature of the energetic electrons and ions which are accelerated during solar flares. Since the beginning of 1990 the PHEBUS instrument and the SIGMA anticoincidence shield aboard GRANAT have provided hard X-ray and gamma-ray observations of solar bursts in the energy range 0.075-124 and 0.200-15 MeV, respectively. After a brief description of the experiments, we present some results obtained on solar bursts recorded in 1990 and 1991 June. Special emphasis is given to the results related with particle acceleration during solar flares.The first part of the review is devoted to the constraints obtained on the electron acceleration timescale through the analysis of the temporal characteristics of the bursts. Combined studies of hard X-ray and gamma-ray emissions from PHEBUS and radio emissions from the Nançay Multifrequency Radioheliograph are used to infer constraints on the coronal magnetic topology involved in flares. The characteristics (location, spectrum) of the radio-emitting sources are found to vary within a flare from one hard X-ray peak to the other. Hard X-ray and gamma-ray burst onsets and rapid increases of the > 10 MeV emission are coincident with changes in the associated radio emission pattern. These results will be discussed in the context of the flare energy release.The second part of the paper concerns the heliocentric angle distribution of > 10 MeV events and presents more detailed observations of some of the largest flares in the gamma-ray line and the high-energy domains produced by ultrarelativistic electrons and > 100 MeV nucleon−1 ions. The PHEBUS observations of the gamma-ray line flare of 11 June 1991 have been used to deduce the hardness of the accelerated ion spectrum. The link between the main part of the flare and the late long-lasting >50 MeV emission detected by EGRET/COMPTON is discussed. Finally some observations of the large 1990 May 24 flare which produced a large neutron event at ground level are presented.Subject headings: acceleration of particles — Sun: flares — Sun: radio radiation — Sun: X-rays, gamma rays

scholarly journals High-Energy Gamma and Radio Variability of Blazars in the Model of Non-Stationary Jets

1996 ◽  
Vol 175 ◽  
pp. 419-420
Author(s):  
M.M. Romanova ◽  
R.V.E. Lovelace
Keyword(s):  
Synchrotron Radiation ◽  
Gamma Ray ◽  
High Energy ◽  
Propagation Time ◽  
X Rays ◽  
Infrared Band ◽  
Inverse Compton Scattering ◽  
Wide Range ◽  
Radio Band ◽  
Number Of Particles

A model has been developed for impulsive VLBI jet formation and gamma ray outbursts of Blazars. Propagation of newly expelled matter in the old channel of a jet is calculated supposing that the main driving force is the electromagnetic field. The new outflowing matter overtakes the old matter and forms double, fast or slow magnetosonic shock fronts. In the region of the fronts, the number of particles and their energy increase continuously with propagation time from the central object (Romanova and Lovelace, 1995). Accelerated electrons and positrons in the front interact with a diffuse field of UV photons (inverse Compton scattering), with the magnetic field (synchrotron radiation), and with synchrotron photons (SSC processes), thus creating radiation in a very wide range of bands. The self-consistent relativistic equations for the number of particles, the momentum, energy, and magnetic flux in the front are derived and solved numerically (Lovelace and Romanova, 1995). The time-dependent apparent luminosities in the radio to gamma ray bands are calculated taking into account the Doppler boost of the photons. The model predicts a short outburst of radiation in gamma rays (weeks or so) connected with Compton processes, a sharp (less than a day) outburst in the X-rays with a smooth decrease of the luminosity connected with SSC processes, and synchrotron radiation changing from infrared to radio bands (Fig. 1A). The lepton distribution function was taken as fl = K1/γ2 in the main energy containing range, γ1 ≤ γ ≤ γ2, steeper distribution fl = K2/γ3 for γ2 ≤ γ ≤ γ3, and even steeper for γ ≥ γ3. For γ < γ1, fl is assumed negligible as a result of synchrotron self-absorption. The lowest frequency f(syn1), determined by self-absorption, corresponds initially to the infrared band, and later - to the radio band. From Fig.1B, one can see that radio at 3 mm may start to appear after 2 weeks after outburst. But its maximum may correspond to much later times (months), because f(syn1) decreases slowly with time. The appearance of the new VLBI component in QSO 0528+134, which approximately coincides with the strong gamma-ray flash and with the beginning of the strong mm radio outburst (Krichbaum, et al. 1995; Pohl, et al. 1995), supports the proposed model.Both authors were supported in part by NSF grant AST-9320068. MMR is grateful to RFBR and Organizers of the Symposium for the partial support.

scholarly journals Introducing the HD+B model for pulsar wind nebulae: a hybrid hydrodynamics/radiative approach

2020 ◽  
Vol 494 (3) ◽  
pp. 4357-4370
Author(s):  
B Olmi ◽  
D F Torres
Keyword(s):  
Gamma Ray ◽  
High Energy ◽  
Theoretical Modelling ◽  
X Rays ◽  
Pulsar Wind Nebulae ◽  
New Approach ◽  
Energy Gamma ◽  
Radiative Model ◽  
Pulsar Wind

ABSTRACT Identification and characterization of a rapidly increasing number of pulsar wind nebulae is, and will continue to be, a challenge of high-energy gamma-ray astrophysics. Given that such systems constitute -by far- the most numerous expected population in the TeV regime, such characterization is important not only to learn about the sources per se from an individual and population perspective, but also to be able to connect them with observations at other frequencies, especially in radio and X-rays. Also, we need to remove the emission from nebulae in highly confused regions of the sky for revealing other underlying emitters. In this paper, we present a new approach for theoretical modelling of pulsar wind nebulae: a hybrid hydrodynamic-radiative model able to reproduce morphological features and spectra of the sources, with relatively limited numerical cost.

Detector commissioning and development for PETRA-III

2010 ◽  
Vol 1 (SRMS-7) ◽  
Author(s):  
David Pennicard ◽  
Heinz Graafsma ◽  
Michael Lohmann
Keyword(s):  
High Speed ◽  
Materials Science ◽  
Dynamic Range ◽  
Photon Counting ◽  
High Energy ◽  
X Rays ◽  
Silicon Detectors ◽  
Time Resolved ◽  
Wide Range ◽  
Synchrotron Light

The new synchrotron light source PETRA-III produced its first beam last year. The extremely high brilliance of PETRA-III and the large energy range of many of its beamlines make it useful for a wide range of experiments, particularly in materials science. The detectors at PETRA-III will need to meet several requirements, such as operation across a wide dynamic range, high-speed readout and good quantum efficiency even at high photon energies. PETRA-III beamlines with lower photon energies will typically be equipped with photon-counting silicon detectors for two-dimensional detection and silicon drift detectors for spectroscopy and higher-energy beamlines will use scintillators coupled to cameras or photomultiplier tubes. Longer-term developments include ‘high-Z’ semiconductors for detecting high-energy X-rays, photon-counting readout chips with smaller pixels and higher frame rates and pixellated avalanche photodiodes for time-resolved experiments.

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