We analyzed the spectral shape of the Compton shoulder around the neutral Fe-K line of the Compton-thick type II Seyfert nucleus of the Circinus galaxy. The characteristics of this Compton shoulder ...with respect to the reflected continuum and Fe-K line core intensity are powerful diagnostics tools for analyzing the structure of the molecular tori, which obscures the central engine. We applied our Monte-Carlo-based X-ray reflection spectral model to the Chandra High Energy Transmission Grating data and successfully constrained the various spectral parameters independently, using only the spectral data only around the Fe-K emission line. The obtained column density and inclination angle are consistent with previous observations and the Compton-thick type II Seyfert picture. In addition, we determined the metal abundance of the molecular torus for the case of the smooth and clumpy torus to be and 1.74 0.16 solar abundance, respectively. Such slightly over-solar abundance can be useful information for discussing the star formation rate in the molecular tori of active galactic nuclei.
ABSTRACT We have performed systematic studies of narrow Fe-K line (6.4 keV) flux variability and Ni-K line intensity for Seyfert galaxies, using Suzaku and XMM-Newton archival data. Significant Fe-K ...line variability of several tens of percent was detected for a pair of observations separated by 1000-2000 days (Cen A, IC 4329 A, NGC 3516, and NGC 4151) and 158 days (NGC 3516). These timescales are larger by a factor of 10-100 than the inner radius of the torus, consistent with the view that X-ray reflection by a torus is a main origin for a narrow Fe-K line. The Ni-K line was detected with a >2 level for the Circinus galaxy, Cen A, MRK 3, NGC 4388, and NGC 4151. A mean and variance of the Ni-K to Fe-K line intensity ratios are 0.066 and 0.026, respectively. Comparing this with the Monte-Carlo simulation of reflection, the Ni to Fe abundance ratio is 1.9 0.8 solar. We discuss the results and the possibility of Ni abundance enhancement.
Abstract
We report on the variations of the physical parameters of the jet observed in the blazar Mrk 421, and discuss the origin of X-ray flares in the jet, based on analysis of several spectral ...energy distributions (SEDs). The SEDs are modeled using the one-zone synchrotron self-Compton model, its parameters determined using a Markov chain Monte Carlo method. The lack of data at TeV energies means many of the parameters cannot be uniquely determined and are correlated. These are studied in detail. We find that the optimal solution can be uniquely determined only when we apply a constraint to one of four parameters: the magnetic field (B), the Doppler factor, the size of the emitting region, and the normalization factor of the electron energy distribution. We used 31 sets of SEDs from 2009 to 2014 with optical–UV data observed with UVOT/Swift and the Kanata telescope, X-ray data with XRT/Swift, and γ-ray data with the Fermi Large Area Telescope. The result of our SED analysis suggests that, in the X-ray faint state, the emission occurs in a relatively small area (∼1016 cm) with a relatively strong magnetic field (B ∼ 10−1 G). The X-ray bright state shows a tendency opposite to that of the faint state, that is, a large emitting area (∼1018 cm), probably downstream of the jet, and a weak magnetic field (B ∼ 10−3 G). The high X-ray flux was due to an increase in the maximum energy of electrons. On the other hand, the presence of two kinds of emitting areas implies that the one-zone model is unsuitable for reproducing at least part of the observed SEDs.
Attenuation characteristics of a Ce:Gd3Al2Ga3O12 scintillator Uchida, Nagomi; Takahashi, Hiromitsu; Ohno, Masanori ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/2021, Letnik:
986
Journal Article
Recenzirano
Attenuation characteristics of scintillation photons from Ce-doped Gd3Al2Ga3O12 (Ce:GAGG) scintillators were investigated by measuring samples of various sizes. Scintillation light is attenuated by ...two factors. The first is self-absorption of the Ce:GAGG scintillator itself, and the second is geometrical effects such as reflection properties caused by reflector wrapping. The attenuation coefficient of the Ce:GAGGs was determined as 0.00155±0.00006 mm −1 indicating that the scintillation light decays to 1/e as it passes approximately 645 ± 26 mm through the Ce:GAGG. This attenuation does not affect the entire wavelength range; however, it significantly occurs only in the wavelength range from 460 nm to 510 nm where emission and absorption overlap. In the narrow Ce:GAGG scintillator used in this experiment, the geometrical attenuation effect was in the overall wavelength, and the attenuation coefficient was 0.010 ± 0.001 mm −1. In this setup, the self-absorption effect only occupied 10% of the whole attenuation, while geometrical attenuation significantly affected the number of detected photons.
ABSTRACT We present multi-epoch X-ray spectral observations of three Type IIn supernovae (SNe), SN 2005kd, SN 2006jd, and SN 2010jl, acquired with Chandra, XMM-Newton, Suzaku, and Swift. Previous ...extensive X-ray studies of SN 2010jl have revealed that X-ray spectra are dominated by thermal emission, which likely arises from a hot plasma heated by a forward shock propagating into a massive circumstellar medium (CSM). Interestingly, an additional soft X-ray component was required to reproduce the spectra at a period of ∼1-2 years after the SN explosion. Although this component is likely associated with the SN, its origin remained an open question. We find a similar, additional soft X-ray component from the other two SNe IIn as well. Given this finding, we present a new interpretation for the origin of this component; it is thermal emission from a forward shock essentially identical to the hard X-ray component, but directly reaches us from a void of the dense CSM. Namely, the hard and soft components are responsible for the heavily and moderately absorbed components, respectively. The co-existence of the two components with distinct absorptions as well as the delayed emergence of the moderately absorbed X-ray component could be evidence for asphericity of the CSM. We show that the X-ray spectral evolution can be qualitatively explained by considering a torus-like geometry for the dense CSM. Based on our X-ray spectral analyses, we estimate the radius of the torus-like CSM to be on the order of ∼5 × 1016 cm.
ABSTRACT A bright long gamma-ray burst GRB 141207A was observed by the Fermi Gamma-ray Space Telescope and detected by both instruments onboard. The observations show that the spectrum in the prompt ...phase is not well described by the canonical empirical Band function alone, and that an additional power-law component is needed. In the early phase of the prompt emission, a modified blackbody with a hard low-energy photon index ( = +0.2 to +0.4) is detected, which suggests a photospheric origin. In a finely time-resolved analysis, the spectra are also well fitted by the modified blackbody combined with a power-law function. We discuss the physical parameters of the photosphere such as the bulk Lorentz factor of the relativistic flow and the radius. We also discuss the physical origin of the extra power-law component observed during the prompt phase in the context of different models such as leptonic and hadronic scenarios in the internal shock regime and synchrotron emission in the external forward shock. In the afterglow phase, the temporal and spectral behaviors of the temporally extended high-energy emission and the fading X-ray emission detected by the X-Ray Telescope on-board Swift are consistent with synchrotron emission in a radiative external forward shock.
Suzaku Hard X-ray Detector (HXD) achieved the lowest background level than any other previously or currently operational missions sensitive in the energy range of 10–600 keV, by utilizing PIN ...photodiodes and GSO scintillators mounted in BGO active shields to reject particle background and Compton-scattered events as much as possible. Because it does not have an imaging capability nor rocking mode for the background monitor, the sensitivity is limited by the reproducibility of the non X-ray background (NXB) model. We modeled the HXD NXB, which varies with time as well as other satellites with a low-Earth orbit, by utilizing several parameters, including particle monitor counts and satellite orbital/attitude information. The model background is supplied as an event file in which the background events are generated by random numbers, and can be analyzed in the same way as the real data. The reproducibility of the NXB model depends on the event selection criteria (such as cut-off rigidity and energy band) and the integration time, and the 1
$\sigma$
systematic error is estimated to be less than 3% (PIN 15–40 keV) and 1% (GSO 50–100 keV) for more than 10 ks exposure.
This study presents a background estimation for the CubeSats Applied for MEasuring and LOcalising Transients (CAMELOT), which is a proposed fleet of nanosatellites for the all‐sky monitoring and ...timing‐based localization of gamma ray transients with precise localization capability at low Earth orbits. CAMELOT will allow us to observe and precisely localize short gamma ray bursts (GRBs) associated with kilonovae, long GRBs associated with core‐collapse massive stars, magnetar outbursts, terrestrial gamma ray flashes, and gamma ray counterparts to gravitational wave sources. A fleet of at least nine 3U CubeSats is proposed to be equipped with large and thin CsI(Tl) scintillators read out by multipixel photon counters (MPPC). A careful study of the radiation environment in space is necessary to optimize the detector casing, estimate the duty cycle due to the crossing of the South Atlantic Anomaly and polar regions, and minimize the effect of the radiation damage of MPPCs.
PDF
