scholarly journals Study of long-term flux and photon index distributions of blazars using RXTE observations

2019 ◽  
Vol 491 (2) ◽  
pp. 1934-1940 ◽  
Author(s):  
Rukaiya Khatoon ◽  
Zahir Shah ◽  
Ranjeev Misra ◽  
Rupjyoti Gogoi
Keyword(s):  
Gaussian Distribution ◽  
Lognormal Distribution ◽  
Flux Distribution ◽  
High Energy ◽  
X Rays ◽  
Photon Index ◽  
Double Gaussian Distribution ◽  
The Difference ◽  
Anderson Darling ◽  
Bl Lacs

ABSTRACT We present a detailed study of flux and index distributions of three blazars [one flat-spectrum radio quasar (FSRQ) and two BL Lacertae objects (BL Lacs)] by using 16 yr of Rossi X-ray Timing Explorer (RXTE) archival data. The three blazars were chosen such that their flux and index distributions have sufficient number of data points (≥90) with relatively less uncertainty $\left(\overline{\sigma _{\rm err}^{2}}/\sigma ^{2} < 0.2\right)$ in light curves. Anderson–Darling (AD) test and histogram fitting show that flux distribution of FSRQ 3C 273 is lognormal, while its photon index distribution is Gaussian. This result is consistent with linear Gaussian perturbation in the particle acceleration time-scale, which produces lognormal distribution in flux. However, for two BL Lacs, viz. Mrk 501 and Mrk 421, AD test shows that their flux distributions are neither Gaussian nor lognormal, and their index distributions are non-normal. The histogram fitting of Mrk 501 and Mrk 421 suggests that their flux distributions are more likely to be a bimodal, and their index distributions are double Gaussian. Since, Sinha et al. had shown that Gaussian distribution of index produces a lognormal distribution in flux, double Gaussian distribution of index in Mrk 501 and Mrk 421 indicates that their flux distributions are probably double lognormal. Observation of double lognormal flux distribution with double Gaussian distribution in index reaffirms two flux states hypothesis. Further, the difference observed in the flux distribution of FSRQ (3C 273) and BL Lacs (Mrk 501 and Mrk 421) at X-rays suggests that the low-energy emitting electrons have a single lognormal flux distribution, while the high-energy ones have a double lognormal flux distribution.

Fricke dosimetry: the difference betweenG(Fe3+) for60Co gamma-rays and high-energy x-rays

1999 ◽  
Vol 44 (7) ◽  
pp. 1609-1624 ◽  
Author(s):  
N V Klassen ◽  
K R Shortt ◽  
J Seuntjens ◽  
C K Ross
Keyword(s):  
Gamma Rays ◽  
High Energy ◽  
X Rays ◽  
The Difference

scholarly journals Modelling the Soft X-ray Excess in E1615+061

1994 ◽  
Vol 159 ◽  
pp. 317-317
Author(s):  
M. Bałucińska-Church ◽  
L. Piro ◽  
H. Fink ◽  
F. Fiore ◽  
M. Matsuoka ◽  
...  
Keyword(s):  
Power Law ◽  
Column Density ◽  
High Energy ◽  
X Rays ◽  
Hard Component ◽  
X Ray ◽  
Simple Power ◽  
High Energy Tail ◽  
Photon Index ◽  
Best Fit

SummaryWe report results of an international UV – X-ray campaign in 1990–1992 involving the IUE, Rosat and Ginga satellites to observe E1615+061, a Seyfert 1 galaxy with peculiar spectral and intensity behaviour over the last 20 years. The source has been found to be stable in its medium state during the observations. The Ginga (1–20 keV) spectrum of E1615+061 is adequately represented by a simple power law with a photon index α = 1.8 ± 0.1. However, α ∼ 2, as expected for the intrinsic power law component in a reflection model, cannot be ruled out statistically. The Rosat PSPC (0.1–2 keV) spectra collected during the All Sky Survey and the AO-1 phase can be well-described by a simple power law (α = 2.2 ± 0.1) with cold absorber (NH = 3.5 ± 0.3 · 10λ20 H/cmλ2). Both the photon index being significantly different than that obtained from the Ginga spectrum and the column density being smaller than the galactic column (NH ∼ 4.2 · 10λ20 H/cmλ2) give an indication of a soft excess over and above the hard component seen in the Ginga spectrum. E1615+061 has been observed with IUE in 1990 and in 1992. The source was stable and the colour excess E(B-V) derived from the data = 0.1 is in good agreement with that expected from the galactic absorption.To parameterise the soft excess we fitted the Rosat data with a two-component model consisting of a power law, and a blackbody or thermal bremsstrahlung, with a single galactic absorption term. The column density and the slope of the power law were kept constant. The blackbody temperature was 80 ± 6 eV and 63 ± 12 eV for photon index equal to 1.8 and 2.0, respectively, whereas the bremsstrahlung temperature was 220 ± 40 eV and 115 ± 30 eV for the two cases.An attempt to model the soft excess seen in the Rosat PSPC spectrum has been made assuming that the soft excess is the high energy tail of a disc spectrum which peaks in the UV part of the spectrum. Additionally it was assumed that there is a hard component contributing to the spectrum from UV to X-rays with parameters as described by the Ginga spectrum. The best fit parameters: the mass of the central source and the mass accretion rate were around 5 ± 1 · 10λ6 M⊙ and 0.2 ± 0.04 M⊙/yr, respectively.Our modelling shows that the soft X-ray excess can be described (χredλ2 < 1.2) as the high energy tail of an accretion disk spectrum if the intrinsic power law is quite steep (α = 2). The main contribution to the residuals in the Rosat PSPC range comes from 0.3–0.6 keV, with a tendency for these residuals to increase when the slope gets flatter. The accretion luminosity is ∼ 6.5 · 10λ44 erg/s for the best fit parameters, i.e. about the Eddington luminosity.

scholarly journals ROSAT Spectra and Lightcurves of Bright BL Lacertae Objects at Low Interstellar Absorption

1994 ◽  
Vol 159 ◽  
pp. 384-384
Author(s):  
H.-C. Thomas ◽  
H. H. Fink
Keyword(s):  
Power Law ◽  
Clear Correlation ◽  
X Rays ◽  
Additional Absorption ◽  
Bl Lacertae ◽  
Slow Decline ◽  
Low Energies ◽  
Photon Index ◽  
Hardness Ratio ◽  
The Difference

A programme to obtain soft X-ray spectra of bright BL Lac's from pointed observations with ROSAT has been started. So far 13 objects have been observed and another 6 have been accepted for observation. Available data for the following sources were reduced: OQ 530, OJ 287, B2 0912+29, GB 1011+496, ON 231, B2 1215+30, B2 1308+32, and Mrk 421.In this sample the most outstanding observation clearly is that of Mrk 421. This source was observed with the ROSAT PSPC for a total of 34 ksec between May 5 and May 7, 1992, at a mean countrate of 159 cts/s (see Fink et al., 1991, A&A246, L6 for ROSAT survey results). At the time of the observations Mrk 421 was also very luminous in the optical bands (see poster by S. Kikuchi, this conference). Within the ROSAT band the spectrum is flatter at the soft end (photon index for broken power law model between −2.2 and −2.0) than at the hard end (photon index between −2.6 and −2.4). The countrate increases during the first 5 orbits with a maximum e-folding time of 1.5 days, reaching a maximum luminosity of 4 × 1045erg/s in the energy range of 0.1 to 2.4 keV (for H0 = 75km/s/Mpc). It is followed by a slow decline until a second rise starts which is much stronger in harder X-rays than at low energies. Plotting the hardness ratio (defined as the difference in the countrates above and below 0.5 keV divided by the total countrate) versus the total countrate the second rise displays a much steeper gradient than the first one (see figure 1a).For most of the other BL Lac's the countrates are too low to detect variability on these timescales of hours to days, except for B2 1215+30 and OQ 530, where the chance probability for the observed variations is 4 × 10−4 and 10−10, respectively. Also no clear correlation between hardness ratio and countrate could be found. Spectral fits of single power law models with absorption result in photon indizes ranging from −3.1 to −1.9 with no detectable absorption above the galactic value for 5 of these sources, and some additional absorption for GB 1011+496 and B2 1215+30 (see figure 1b).

scholarly journals Multi-wavelength Behaviour of III Zw2

2002 ◽  
Vol 19 (1) ◽  
pp. 73-76
Author(s):  
Nikita Salvi ◽  
Mat J. Page ◽  
Jason A. Stevens ◽  
Keith O. Mason ◽  
Kinwah Wu
Keyword(s):  
Synchrotron Radiation ◽  
Optical Emission ◽  
High Energy ◽  
X Rays ◽  
X Ray ◽  
High Energy Electrons ◽  
Photon Index ◽  
Multi Wavelength ◽  
Wavelength Light ◽  
Gaussian Line

AbstractIII Zw2 was observed with XMM-Newton in July 2000. Its X-ray spectrum can be described by a power law of photon index Γ≈1.7 with a Gaussian line at 6.7 KeV. There is no significant evidence of intrinsic absorption within the source or of a soft X-ray excess. Multi-wavelength light curves over a period of 25 years show related variations from the radio to X-rays. We interpret the radio to optical emission as synchrotron radiation, self-absorbed in the radio/millimetre region, and the X-rays as mainly due to Compton up-scattering of low energy photons by the population of high energy electrons that give rise to the synchrotron radiation.

scholarly journals NuSTAR observation of Ark 564 reveals the variation of coronal temperature with flux

2020 ◽  
Vol 492 (2) ◽  
pp. 3041-3046 ◽  
Author(s):  
Samuzal Barua ◽  
V Jithesh ◽  
Ranjeev Misra ◽  
Gulab C Dewangan ◽  
Rathin Sarma ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
High Energy ◽  
Quality Data ◽  
X Rays ◽  
Coronal Temperature ◽  
High Quality Data ◽  
Photon Index ◽  
Reflection Component ◽  
Shed Light

ABSTRACT The hard X-ray spectral index of some active galactic nuclei (AGN) has been observed to steepen with the source flux. This has been interpreted in a Comptonization scenario, where an increase in the soft flux decreases the temperature of the corona, leading to steepening of the photon index. However, the variation of the coronal temperature with flux has been difficult to measure due to the presence of complex reflection component in the hard X-rays and the lack of high-quality data at that energy band. Recently, a 200 ks Nuclear Spectroscopic Telescope Array(NuSTAR) observation of Ark 564 in 3–50 keV band revealed the presence of one of the coolest coronae with temperature kTe ∼ 15 keV in the time-averaged spectrum. Here, we reanalyse the data and examined the spectra in four flux levels. Our analysis shows that the coronal temperature decreased from ∼17 to ∼14 keV as the flux increased. The high energy photon index Γ ∼ 2.3 varied by less than 0.1, implying that the optical depth of the corona increased by about 10 per cent as the flux increased. This first reporting of coronal temperature variation with flux shows that further long observation by NuSTAR of this and other sources would shed light on the geometry and dynamics of the inner regions of the accretion flow.

scholarly journals High-Energy Continuum Variability in Active Galactic Nuclei

1994 ◽  
Vol 159 ◽  
pp. 113-122
Author(s):  
Rick Edelson
Keyword(s):  
Accretion Disk ◽  
Thermal Emission ◽  
High Energy ◽  
Thermal Source ◽  
X Rays ◽  
Optical Monitoring ◽  
Bl Lac Objects ◽  
X Ray ◽  
Bl Lac ◽  
Bl Lacs

CGRO and IUE observations suggest that the strong, aperiodic variability seen in the Exosat long-look observations of AGN extends over a much wider energy band. Some BL Lac objects (but no Seyfert 1 galaxies) have shown X-ray variations which were so rapid that they violate the assumptions of isotropy inherent in the Eddington limit. In the ultraviolet, Seyfert 1s as a class show an anti-correlation between the variability amplitude and luminosity, while BL Lacs show a positive correlation. Furthermore, Seyfert 1s show strong flux-correlated spectral variability, while BL Lacs show little or none. All of this suggests that the high-energy continua of BL Lacs are beamed towards us, while the ultraviolet continua of Seyfert 1s are emitted isotropically.The November 1991 multi-waveband monitoring of the BL Lac PKS 2155−304 showed strong correlated variability, with the soft X-rays leading the ultraviolet by a few hours, and no measurable lag between the ultraviolet and optical down to a limit of ≲ 1.5 hr. This indicates that the X-rays from this BL Lac are not produced by Compton upscattering, and that the ultraviolet does not come directly from a thermal source such as an accretion disk. This also strongly constrains the relativistic jet model, suggesting that all of the radiation is produced in a flattened region like a shock front.Low temporal resolution ultraviolet/optical monitoring of the Seyfert 1 NGC 5548 in 1989 yielded a strong correlation with no measurable lag to a limit of ≲4 days, casting some doubt on the standard model of thermal emission from an accretion disk in Seyfert 1s. Upcoming X-ray/ultraviolet/optical monitoring of the Seyfert 1 NGC 4151 in December 1993 will have much faster sampling, to permit a strong test of both this model and the competing reprocessing model.

The X-ray Albedo from the Earth

1968 ◽  
Vol 1 (3) ◽  
pp. 111-112
Author(s):  
J.R. Harries ◽  
R.J. Francey
Keyword(s):  
Charged Particle ◽  
High Energy ◽  
X Rays ◽  
X Ray ◽  
Diffuse Flux ◽  
The Earth ◽  
Particle Background ◽  
The Difference

An albedo X-ray flux from the Earth was observed by experiments which were flown on Skylark rockets during April 1967. The details of the flights and the equipment have been covered in a previous paper. The celestial X-rays observed from discrete sources are superimposed on a diffuse X-ray flux. Most measurements of this diffuse flux have taken the difference between the number of X-rays observed from an area of sky, which is thought to be free of sources, and the flux from the direction of the Earth. By assuming that there are no X-rays from the direction of the Earth, this method removes the high-energy charged-particle background which should be the same in both cases.

scholarly journals An X-ray Spectral Survey of BL Lac Objects

1989 ◽  
Vol 134 ◽  
pp. 191-193 ◽  
Author(s):  
P. Barr ◽  
P. Giommi ◽  
A. Pollock ◽  
G. Tagliaferri ◽  
D. Maccagni ◽  
...  
Keyword(s):  
High Energy ◽  
Oxygen Absorption ◽  
X Rays ◽  
Bl Lac Objects ◽  
Synchrotron Source ◽  
X Ray ◽  
High Energy Tail ◽  
Bl Lac ◽  
Spectral Survey ◽  
Bl Lacs

A wide variety of X-ray spectral forms has been reported in BL Lac objects. Concave spectra, i.e. a steep soft X-ray spectrum with a flat high energy tail, have been reported in a few of the brightest BL Lacs (e.g Urry 1986). Conversely, convex spectra (steep hard X-rays, flat soft X-ray spectrum) have also been reported, sometimes in the same objects (Madejski 1985, Barr et al 1988, George et al 1988). The high energy tails have usually been invoked as a signature of synchrotron-self-Compton emission. Two conflicting interpretations of the convex spectra have been made. Urry et al (1986) suggest absorption by a partially ionised medium, probably intrinsic to the BL Lac object, following the identification of an Oxygen absorption trough in the Einstein OGS spectrum of PKS 2155-304 by Canizares and Kruper (1984). Conversely, Barr et al (1988) attribute the hard X-ray steepening to energy loss mechanisms operating on a synchrotron source.

scholarly journals Soft X-rays and photoelectrons from nickel at different temperatures

1937 ◽  
Vol 159 (897) ◽  
pp. 283-294 ◽  
Keyword(s):  
Secondary Electron ◽  
Secondary Electron Emission ◽  
High Energy ◽  
Secondary Emission ◽  
X Rays ◽  
Secondary Electrons ◽  
X Ray ◽  
Different Temperatures ◽  
The Difference ◽  
The One

The photoelectric method of investigating the intensity of soft X-rays was first employed independently and at about the same time by Richardson and Bazzoni (1921), Kurth (1921), Mohler and Foote (1922), Holweck (1922) and Hughes (1922). A large number of investigators (Rudberg 1929) have since adapted the method for the study of soft X-ray critical potentials on the one side (Thomas 1925; Compton and Thomas 1926; Richardson and Andrewes 1930; Richardson and Rao 1930; Richardson and Chalklin 1926, 1928 a , b ; Andrewes, Davies and Horton 1926, 1928; Horton, Andrewes and Davies 1923; Davies and Horton 1926), and the efficiency of soft X-ray excitation from metallic elements on the other (Richardson and Robertson 1927, 1929; Davies 1928; Nakaya 1929). The problem of the photoelectric efficiency of metals in the region of soft X-rays has also received some attention (Davies 1928; Bandopadhyaya 1928). Nakaya (1929) has studied the relation between the intensity of soft X-rays and the photoelectric current as a function of the nature of the photoelectric detector. Closely allied to the excitation of soft X-rays is the phenomenon of secondary electron emission from metal faces. The critical potentials in the secondary emission have been investigated by Petry (1925, 1926), Farns­ worth (1928, 1929), Krefft (1927, 1928), Ahearn (1931), Rao (1930) and others (cf. Hyatt and Smith 1928). Richardson (1930) has drawn attention to the similarity of the phenomena of the excitation of soft X-rays and the emission of secondary electrons and the approximate coincidence of the critical potentials in the two cases. To explain these and other properties, he has suggested that when a metal surface is bombarded with electrons, the first act is the excitation of a structure electron by the primary, which is returned as part of the high-energy group of secondaries. When the excited structure electrons return to the ground state, the low-energy secondary electrons and soft X-rays result as a consequence. This hypothesis accounts for the agreement between the soft X-ray and secondary electron breaks. In an earlier paper (1928) he has drawn attention to the difference in the order of efficiency of the two phenomena, the coefficient of the secondary emission being about a million times that of the soft X-ray excitation.

The Basic Physical Principles of Ion, Electron, and X-Ray Detectors and Their Application to Microanalysis

1985 ◽  
Vol 43 ◽  
pp. 154-157
Author(s):  
A.J. Tousimis
Keyword(s):  
Ion Beam ◽  
Depth Resolution ◽  
Sample Surface ◽  
High Energy ◽  
X Rays ◽  
X Ray ◽  
Electrons And Ions ◽  
Spatial Depth ◽  
Minimum Surface Area ◽  
Physical Principles

An integral and of prime importance of any microtopography and microanalysis instrument system is its electron, x-ray and ion detector(s). The resolution and sensitivity of the electron microscope (TEM, SEM, STEM) and microanalyzers (SIMS and electron probe x-ray microanalyzers) are closely related to those of the sensing and recording devices incorporated with them.Table I lists characteristic sensitivities, minimum surface area and depth analyzed by various methods. Smaller ion, electron and x-ray beam diameters than those listed, are possible with currently available electromagnetic or electrostatic columns. Therefore, improvements in sensitivity and spatial/depth resolution of microanalysis will follow that of the detectors. In most of these methods, the sample surface is subjected to a stationary, line or raster scanning photon, electron or ion beam. The resultant radiation: photons (low energy) or high energy (x-rays), electrons and ions are detected and analyzed.

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