Room temperature solid-state detectors for Gamma ray burst spectroscopy

We have evaluated several solid state detectors which offer excellent energy resolution at room temperature for soft X-rays. For soft X-rays (< 1 keV to 20 keV), silicon P-intrinsic-N (PIN) and avalanche-mode photodiodes (APD's) have been studied. Using commercially available charge sensitive pre-amplifiers, these photodiodes provide 1 keV resolution without cooling. Their detection efficiencies are limited to about 20 keV and 15 keV, respectively. To overcome this constraint, we have studied thick (1.5 mm) PIN detectors made by Micron Semiconductor Ltd., U.K., as well as compound semiconducting materials with high Z constituents such as CZT and PbI₂. PbI₂ allows high detection efficiencies of photons up to 100 keV with detectors 100–300 microns thick. These new detectors offer the capability to study the low-energy spectral evolution of Gamma ray bursts (GRBs). A matrix of these detectors could be used as an image plane detector with moderate spatial resolution for imaging.     

Gamma ray bursts

Gamma-ray bursts have been detected at photon energies up to tens of GeV. We review some recent developments in the X-ray to GeV photon phenomenology in the light of Swift and Fermi observations, and some of the theoretical models developed to explain them, with a view towards implications for C.T.A.     

Quantum gravity with THESEUS

Experimental Astronomy - In this paper we explore the possibility to search for a dispersion law for light propagation in vacuo with a sample of Gamma-Ray Bursts detected by the THESEUS satellite....     

A theory for gamma ray and X-ray burst sources

A common mechanism for both X-ray and-ray bursters is proposed on the basis that a window can be created transiently in the polar cap of a degenerate star, a white dwarf for X-ray bursts and a neutron star for-ray bursts. The window exposes transiently a hot degenerate sub-layer of the star at shallow depth, from which escapes blackbody flux for a source at temperature 3 kev with window radius 10 km in the case of X-ray bursts and for a source at temperature 300 kev with window radius 0.5 km in the case of-ray bursts.     

Nuclear criticality as a contributor to gamma ray burst events

Most gamma ray bursts are able to be explained using supernovae related phenomenon. Some measured results still lack compelling explanations and a contributory cause from nuclear criticality is proposed. This is shown to have general properties consistent with various known gamma ray burst properties. The galactic origin of fast rise exponential decay gamma ray bursts is considered a strong candidate for these types of events.     

Searching for multifractal scaling in gamma ray burst time series

We present a multifractal analysis of GRB time series used to quantify the variability of the light curve. We discuss the advantages and disadvantages of multifractal analysis, including sensitivity to noise, and burst intensity, and present results for a few sample bursts.     

用位相相关方法测量Geminga脉冲星的守时参数

利用γ射线脉冲星Ｇｅｍｉｎｇａ自旋及频率变化的稳定性，采用位相相关的方法分析了ＥＧＲＥＴ对脉冲星Ｇｅｍｉｎｇａ四次观测间隔较长的数据，得到较为准确的守时参数ｆ．位相相关的结果与更长数据段折叠搜索的结果较为接近，表明对于自旋和频率变化都较为稳定的γ射线脉冲星，位相相关分析方法可以作为提高脉冲星参数精度的有效方法．     

Cosmic ray modulation studies with Lead-Free Gulmarg Neutron Monitor

A lead-free neutron monitor operating at High Altitude Research Laboratory (HARL), Gulmarg optimized for detecting 2.45 MeV neutron bursts produced during the atmospheric lightning discharges is also concurrently used for studying background neutron component present in the atmosphere. These background neutrons are produced due to the interaction of primary cosmic rays with the atmospheric constituents. In order to study and extract the information about the yield of the neutron production during transient atmospheric lightning discharges, the system is continuously operated to monitor and record the cosmic ray produced background secondary neutrons in the atmosphere. The data analysis of the background neutrons recorded by Lead-Free Gulmarg Neutron Monitor (LFGNM) has convincingly established that the modulation effects due to solar activity phenomena compare very well with those monitored by the worldwide IGY or NM64 type neutron monitors which have optimum energy response relatively towards the higher energy regime of the cosmic rays. The data has revealed various types of modulation phenomena like diurnal variation, Forbush decrease etc. during its entire operational period. However, a new kind of a periodic/seasonal variation pattern is also revealed in the data from September 2007 to September 2012, which is seen to be significantly consistent with the data recorded by Emilio Segre observatory, Israel (ESOI) Neutron Monitor. Interestingly, both these neutron monitors have comparable latitude and altitude. However, the same type of consistency is not observed in the data recorded by the other conventional neutron monitors operating across the globe.     

Gamma ray spectrum of the crab nebula in the multi TeV region

The THEMISTOCLE array of 18 Cherenkov detectors which has a 3 TeV gamma energy threshold, has detected a signal from the Crab nebula at a 5.8 standard deviation level. Information on the energy spectrum is obtained in the range 3–15 TeV. The integrated flux can be fitted with the form, Φ (> E) = (3.7 ± 0.5) × 10^-12 (E/5)-^{−1.5 ± 0.20} cm⁻² s⁻¹ (E in TeV) compatible with the extrapolation of results at lower energies. The Crab signal is used to measure the angular resolution of the multi-telescope technique. The value obtained is 2.3 mr (0.15°) in agreement with the results of simulations, and confirms the interest of this new method for multi-TeV gamma-ray detection.     

An exact solution of the gamma ray burst arrival time analysis problem

An analytical solution of the GRB arrival time analysis is presented. The errors in the position of the GRB resulting from timing and position errors of different satellites are calculated. A simple method of cross-correlating gamma ray burst time-histories is discussed.     

Gamma ray signatures of ultra high energy cosmic ray accelerators: electromagnetic cascade versus synchrotron radiation of secondary electrons

We discuss the possibility of observing ultra high energy cosmic ray sources in high energy gamma rays. Protons propagating away from their accelerators produce secondary electrons during interactions with cosmic microwave background photons. These electrons start an electromagnetic cascade that results in a broad band gamma ray emission. We show that in a magnetized Universe (B≳10⁻¹² G) such emission is likely to be too extended to be detected above the diffuse background. A more promising possibility comes from the detection of synchrotron photons from the extremely energetic secondary electrons. Although this emission is produced in a rather extended region of size ∼10 Mpc, it is expected to be point-like and detectable at GeV energies if the intergalactic magnetic field is at the nanogauss level.      

Exploration of the high-redshift universe enabled by THESEUS

Experimental Astronomy - At peak, long-duration gamma-ray bursts are the most luminous sources of electromagnetic radiation known. Since their progenitors are massive stars, they provide a tracer...     

Gamma ray astronomy beyond 2001: What instruments for the newt challenges?

In spite of the recent successes of SIGMA, RXTE andCompton GRO, and the launch of INTEGRAL in 2001, a lot ofquestions will stay opened for the next decades in gamma-ray astronomy.In this context we have to think about future instrument concepts whichwill allow a new step in the understanding of high-energy phenomena atwork in many exciting objects: binary systems with compact objects,active galactic nuclei, supernovae and novae, gamma ray bursters...A short overview of these new types of instruments will be given.     

Cosmic ray studies with a gas Cherenkov counter in association with an ionization spectrometer

The results from a ballon-borne gas Cherenkov counter (threshold 16.5 GeV nuc^–1) and an ionization spectrometer are presented. The gas Cherenkov counter provides an absolute energy calibration for the response of the calorimeter for 5Z26 nuclei of cosmic rays. The contribution of scintillation to the gas Cherenkov pulse height has been obtained by independently selecting particles below the gas Cherenkov threshold using the ionization spectrometer. Energy spectra were derived by minimizing the ² between a Monte Carlo simulated data and flight data. Best fit power laws (dN/dE=AE ^–) were determined for C, N, O, Ne, Mg, and Si. The power laws, all consistent withE ^–2.7, are not good fits to the data. A better fit is obtained using the spectrum derived from the spectrometer. The data from the ionization calorimeter (Simonet al., 1979) and the gas Cherenkov are thus completely self-consistent.On sabbatical leave from the University of Maryland.     

BATSEγ射线暴和太阳硬X射线暴的强度和时间特征

本文研究了CGRO卫星上BATSE探测器对硬X天空监测过程中触发和记录到的1 0 0 0多个γ暴和 40 0 0多个太阳硬X射线暴的强度和时间性质 ,发现它们的强度分布相似 ,这也许意味着硬X射线天空中两种主要的爆发现象机制相似 ,同时对将γ暴的强度分布作为其宇宙学起源的证据提出了疑问 .对太阳暴的持续时间分析表明 ,其强度和持续时间呈正相关 ,而γ暴是弱负相关 .太阳暴的强度和持续时间在BATSE运行过程中有长时标变化 ,最近对γ暴的研究也发现了这种现象     

Absorption spectroscopy of gamma‐ray burst afterglows: Probing the GRB line of sight

GRB absorption spectroscopy opened up a new window in the study of the high redshift Universe, especially with the launch of the Swift satellite and the quick and precise localization of the afterglow. Eight‐meter class telescopes can be repointed within a few hours from the GRB, enabling the acquisition of high signal‐to‐noise ratio and high resolution afterglow spectra. In this paper I will give a short review of what we learned through this technique, and I will present some of the first results obtained with the X‐shooter spectrograph (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Gamma ray emitting globular clusters: Possible contribution from relativistic jets of intermediate mass black holes

We developed a method that allows us to estimate the high energy gamma ray luminosity of intermediate mass black holes (IMBH) located in the central regions of globular clusters. Our calculations are based on the relation between the relativistic jet kinetic power and the luminosity of the gamma ray radiation that is produced by the jet itself. The power of a relativistic jet is determined via the Blandford–Znajek mechanism. Our calculations show that the contribution of the central IMBH in gamma ray luminosity is comparable with the contribution of the population of millisecond pulsars.     

Synergies of THESEUS with the large facilities of the 2030s and guest observer opportunities

Experimental Astronomy - The proposed THESEUS mission will vastly expand the capabilities to monitor the high-energy sky. It will specifically exploit large samples of gamma-ray bursts to probe the...     

The THESEUS space mission: science goals,requirements and mission concept

Experimental Astronomy - THESEUS, one of the two space mission concepts being studied by ESA as candidates for next M5 mission within its Comsic Vision programme, aims at fully exploiting Gamma-Ray...