scholarly journals Hard X-ray properties of NuSTAR blazars

2018 ◽  
Vol 619 ◽  
pp. A93 ◽  
Author(s):  
Gopal Bhatta ◽  
Maksym Mohorian ◽  
Illya Bilinsky
Keyword(s):  
Power Law ◽  
Primary Objective ◽  
Emission Region ◽  
X Ray ◽  
Bl Lacertae ◽  
Central Engine ◽  
Spectrum Radio ◽  
Cross Correlation Analysis ◽  
The Magnetic Field ◽  
Radio Quasar

Context. Investigation of the hard X-ray emission properties of blazars is key to the understanding of the central engine of the sources and associated jet process. In particular, simultaneous spectral and timing analyses of the intraday hard X-ray observations provide us a means to peer into the compact innermost blazar regions that are not accessible to our current instruments. Aims. The primary objective of the work is to associate the observed hard X-ray variability properties in blazars with their flux and spectral states, thereby, based on the correlation among these states, extract the details about the emission regions and processes occurring near the central engine. Methods. We carried out timing, spectral, and cross-correlation analysis of 31 NuSTAR observations of 13 blazars. We investigated the spectral shapes of the sources using single power-law, broken power-law, and log-parabola models. We also studied the co-relation between the soft and hard emission using z-transformed discrete correlation function. In addition, we attempted to constrain the smallest emission regions using minimum variability timescales derived from the light curves. Results. We found that, for most of the sources, the hard X-ray emission can be well represented by the log-parabola model and that the spectral slopes for different blazar subclasses are consistent with the so-called blazar sequence. We also report the steepest spectra (Γ ∼ 3) in the BL Lacertae PKS 2155–304 and the hardest spectra (Γ ∼ 1.4) in the flat-spectrum radio quasar PKS 2149–306. In addition, we noted a close connection between the flux and spectral slope within the source subclass in the sense that high flux and/or flux states tend to be harder in spectra. In BL Lacertae objects, assuming particle acceleration by diffusive shocks and synchrotron cooling as the dominant processes governing the observed flux variability, we constrain the magnetic field of the emission region to be a few Gauss; whereas in flat-spectrum radio quasars, using external Compton models, we estimate the energy of the lower end of the injected electrons to be a few Lorentz factors.

scholarly journals Statistical properties of magnetar bursts and FRB 121102

2019 ◽  
Vol 491 (1) ◽  
pp. 1498-1505 ◽  
Author(s):  
Yingjie Cheng ◽  
G Q Zhang ◽  
F Y Wang
Keyword(s):  
Power Law ◽  
Time Distribution ◽  
Statistical Properties ◽  
Occurrence Rate ◽  
Waiting Time Distribution ◽  
X Ray ◽  
Central Engine ◽  
Fast Radio Burst ◽  
Soft Gamma Repeater ◽  
Critical Process

ABSTRACT In this paper, we present statistics of soft gamma repeater (SGR) bursts from SGR J1550−5418, SGR 1806−20, and SGR 1900+14 by adding new bursts from Kırmızıbayrak et al. detected with the Rossi X-ray Timing Explorer. We find that the fluence distributions of magnetar bursts are well described by power-law functions with indices 1.84, 1.68, and 1.65 for SGR J1550−5418, SGR 1806−20, and SGR 1900+14, respectively. The duration distributions of magnetar bursts also show power-law forms. Meanwhile, the waiting time distribution can be described by a non-stationary Poisson process with an exponentially growing occurrence rate. These distributive features indicate that magnetar bursts can be regarded as a self-organizing critical process. We also compare these distributions with the repeating fast radio burst (FRB) 121102. The statistical properties of repeating FRB 121102 are similar with magnetar bursts, combining with the large required magnetic field (B ≥ 1014 G) of neutron star for FRB 121102, which indicates that the central engine of FRB 121102 may be a magnetar.

scholarly journals Thermal and non-thermal connection in radio mini-halos

2018 ◽  
Vol 14 (S342) ◽  
pp. 137-140
Author(s):  
A. Ignesti ◽  
G. Brunetti ◽  
M. Gitti ◽  
S. Giacintucci
Keyword(s):  
Magnetic Field ◽  
Surface Brightness ◽  
X Rays ◽  
X Ray ◽  
Point Analysis ◽  
Spectrum Radio ◽  
Point To Point ◽  
The Magnetic Field ◽  
Relativistic Particles ◽  
Open Issues

AbstractSeveral cool-core clusters are known to host a radio mini-halo, a diffuse, steep-spectrum radio source located in their cores, thus probing the presence of non-thermal components as magnetic field and relativistic particles on scales not directly influenced by the central AGN. The nature of the mechanism that produces a population of radio-emitting relativistic particles on the scale of hundreds of kiloparsecs is still unclear. At the same time, it is still debated if the central AGN may play a role in the formation of mini-halos by providing the seed of the relativistic particles. We aim to investigate these open issues by studying the connection between thermal and non-thermal components of the intra-cluster medium. We performed a point-to-point analysis of the radio and the X-ray surface brightness of a compilation of mini-halos. We find that mini-halos have super-linear scalings between radio and X-rays, with radio brightness declining more steeply than the X-ray brightness. This trend is opposite to that generally observed in giant radio halos, thus marking a possible difference in the physics of the two radio sources. Finally, using the scalings between radio and X-rays and assuming a hadronic origin of mini-halos we derive constraints on the magnetic field in the core of the hosting clusters.

scholarly journals The large gamma-ray flare of the flat-spectrum radio quasar PKS 0346−27

2019 ◽  
Vol 627 ◽  
pp. A140
Author(s):  
R. Angioni ◽  
R. Nesci ◽  
J. D. Finke ◽  
S. Buson ◽  
S. Ciprini
Keyword(s):  
Spectral Properties ◽  
Emission Region ◽  
Short Time Scale ◽  
Quiescent State ◽  
Emission Model ◽  
X Rays ◽  
High State ◽  
Spectrum Radio ◽  
Multi Wavelength ◽  
Radio Quasar

Aims. In this paper, we characterize the first γ-ray flaring episode of the flat-spectrum radio quasar PKS 0346−27 (z = 0.991), as revealed by Fermi-LAT monitoring data, and the concurrent multi-wavelength variability observed from radio through X-rays. Methods. We studied the long- and short-term flux and spectral variability from PKS 0346−27 by producing γ-ray light curves with different time binning. We complement the Fermi-LAT data with multi-wavelength observations from the Atacama Large Millimeter Array (radio mm-band), the Rapid Eye Mount telescope (near-infrared) and Swift (optical-UV and X-rays). This quasi-simultaneous multi-wavelength coverage allowed us to construct time-resolved spectral energy distributions (SEDs) of PKS 0346−27 and compare the broadband spectral properties of the source between different activity states using a one-zone leptonic emission model. Results. PKS 0346−27 entered an elevated γ-ray activity state starting from the beginning of 2018. The high-state continued throughout the year, displaying the highest fluxes in May 2018. We find evidence of short-time scale variability down to approximately 1.5 h, which constrains the γ-ray emission region to be compact. The extended flaring period was characterized by a persistently harder spectrum with respect to the quiescent state, indicating changes in the broadband spectral properties of the source. This was confirmed by the multi-wavelength observations, which show a shift in the position of the two SED peaks by approximately two orders of magnitude in energy and peak flux value. As a result, the non-thermal jet emission completely outshines the thermal contribution from the dust torus and accretion disk during the high state. The broadband SED of PKS 0346−27 transitions from a typical Low-Synchrotron-Peaked (LSP) to the Intermediate-Synchrotron-Peaked (ISP) class, a behavior previously observed in other flaring γ-ray sources. Our one-zone leptonic emission model of the high-state SEDs constrains the γ-ray emission region to have a lower magnetic field, larger radius, and higher maximum electron Lorentz factors with respect to the quiescent SED. Finally, we note that the bright and hard γ-ray spectrum observed during the peak of flaring activity in May 2018 implies that PKS 0346−27 could be a promising target for future ground-based Cherenkov observatories such as the Cherenkov Telescope Array (CTA). The CTA could detect such a flare in the low-energy tail of its energy range during a high state such as the one observed in May 2018.

scholarly journals Detection of TeV Gamma Rays from SN1006

1998 ◽  
Vol 188 ◽  
pp. 121-124 ◽  
Author(s):  
Toru Tanimori
Keyword(s):  
Magnetic Field ◽  
Cosmic Rays ◽  
Gamma Rays ◽  
High Energy ◽  
Shock Acceleration ◽  
Emission Region ◽  
X Ray ◽  
High Energy Electrons ◽  
Tev Gamma Rays ◽  
The Magnetic Field

In spite of the recent progress of high energy gamma-ray astronomy, there still remains quite unclear and important problem about the origin of cosmic rays. Supernova remnants (SNRs) are the favoured site for cosmic rays up to 1016 eV, as they satisfy the requirements such as an energy input rate. But direct supporting evidence is sparse. Recently intense non-thermal X-ray emission from the rims of the Type Ia SNR SN1006 (G327.6+14.6) has been observed by ASCA (Koyama et al. 1995)and ROSAT (Willingale et al. 1996), which is considered, by attributing the emission to synchrotron radiation, to be strong evidence of shock acceleration of high energy electrons up to ~100 TeV. If so, TeV gamma rays would also be expected from inverse Compton scattering (IC) of low energy photons (mostly attributable to the 2.7 K cosmic background photons) by these electrons. By assuming the magnetic field strength (B) in the emission region of the SNR, several theorists (Pohl 1996; Mastichiadis 1996; Mastichiadis & de Jager 1996; Yoshida & Yanagita 1997) calculated the expected spectra of TeV gamma rays using the observed radio/X-ray spectra. Observation of TeV gamma rays would thus provide not only the further direct evidence of the existence of very high energy electrons but also the another important information such as the strength of the magnetic field and diffusion coefficient of the shock acceleration. With this motivation, SN1006 was observed by the CANGAROO imaging air Cerenkov telescope in 1996 March and June, also 1997 March and April.

scholarly journals Iron Line Emission from NGC1068

1989 ◽  
Vol 134 ◽  
pp. 167-172
Author(s):  
Katsuji Koyama
Keyword(s):  
Energy Range ◽  
Power Law ◽  
Equivalent Width ◽  
Line Emission ◽  
X Rays ◽  
Iron Line ◽  
X Ray ◽  
Central Engine ◽  
Photon Index ◽  
The Continuum

X-ray emission in the 2–10 keV energy range was observed with the Ginga satellite from the Seyfert 2 galaxy NGC1068. The continuum spectrum can be described by a power-law of photon index about 1.5. An intense iron line at 6.5 keV with an equivalent width of 1.3 keV was clearly noticed. The X-ray flux was about 6 × 10 −12 erg/sec/cm2 or 3 × 1041 erg/sec, assuming a distance of 22 Mpc. The observed spectrum is consistent with the scattering and reprocessing of X-rays by the gas surrounding the central engine. With this picture we estimate that the X-ray flux of the central engine is about 1043 - 1044 erg/sec, a typical value for a Seyfert 1 galaxy.

scholarly journals On Special Features of Non-Thermal Solar X Radiation above 10 keV

1972 ◽  
Vol 14 ◽  
pp. 761-762
Author(s):  
G. Elwert ◽  
E. Haug
Keyword(s):  
Magnetic Field ◽  
Angular Distribution ◽  
Power Law ◽  
Impulsive Phase ◽  
X Rays ◽  
Energetic Electrons ◽  
X Ray ◽  
Preferred Direction ◽  
Field Lines ◽  
The Magnetic Field

The polarization and angular distribution of solar hard X radiation above 10 keV was calculated under the assumption that the X rays originate as bremsstrahlung from energetic electrons moving in a preferred direction. The source electrons are supposed to have a power-law spectrum. These conditions are to be expected in the impulsive phase of an X-ray burst. The spiral orbits of the electrons around the magnetic field lines are taken into account.

scholarly journals Temporal and Spectral Variability of OJ 287 before the April–June 2020 Outburst

Galaxies ◽  
2020 ◽  
Vol 8 (3) ◽  
pp. 58
Author(s):  
Nibedita Kalita ◽  
Alok C. Gupta ◽  
Minfeng Gu
Keyword(s):  
Power Law ◽  
Lower Energy ◽  
X Rays ◽  
Power Law Model ◽  
Energy Bands ◽  
Spectral Variability ◽  
X Ray ◽  
Bl Lacertae ◽  
Inverse Compton ◽  
Absorbed Power

We present the results of a temporal and spectral study of the BL Lacertae object OJ 287 in optical, UV, and X-ray bands with observations performed by Swift satellite during September 2019–March 2020. In this period, the source showed moderate variability characterized by variability amplitude of ∼22–31% in all the wavelengths on a short timescale, except the hard X-ray band which was variable by only ∼8%. We observed that the X-ray flux of the source was significantly dominated by the soft photons below 2 keV. Soft lags of ∼45 days were detected between the optical/UV and soft X-ray emissions, while there is no correlation between the hard X-rays and the lower energy bands indicating the presence of two emission components or electron populations. Although two components contribute to the X-ray emission, most of the 0.3–10 keV spectra were well fitted with an absorbed power-law model which outlines the dominance of synchrotron over inverse Compton (IC) mechanism. The X-ray spectra follow a weak “softer when brighter” trend.

scholarly journals On The Location of the Acceleration and Emission Sites in Gamma-Ray Blazars

1994 ◽  
Vol 142 ◽  
pp. 945-948
Author(s):  
Charles D. Dermer ◽  
Reinhard Schlickeiser
Keyword(s):  
Gamma Rays ◽  
Gamma Ray ◽  
Acceleration Of Particles ◽  
External Radiation ◽  
Radiation Mechanisms ◽  
Bl Lac Objects ◽  
X Ray ◽  
Bl Lacertae ◽  
Central Engine ◽  
Nonthermal Particles

AbstractCompton scattering of external radiation by nonthermal particles in outflowing blazar jets is dominated by accretion-disk photons rather than scattered radiation to distances ~ 0.01-0.1 pc from the central engine for standard parameters, thus clarifying the limits of validity of the model by the present authors and the model of Sikora, Begelman, & Rees. On the basis of contemporaneous Ginga X-ray and EGRET gamma-ray observations, we estimate the radius of 3C 279’s gamma-ray photosphere to be smaller than estimated by Blandford. There is thus no need to require that the acceleration and emission sites of gamma-ray blazars to be located farther than ~ 102 - 103 gravitational radii from the central engine. We argue that lineless BL Lac objects, rather than quasars, are more likely to be detected in the TeV energy range.Subject headings: acceleration of particles — BL Lacertae objects: general — galaxies: jets — gamma rays: theory — radiation mechanisms: nonthermal

scholarly journals PKS 2005-489: A very bright BL Lac object in a nearby galaxy

1986 ◽  
Vol 119 ◽  
pp. 59-60
Author(s):  
J V Wall ◽  
I J Danziger ◽  
M Pettini ◽  
R S Warwick ◽  
W Wamsteker
Keyword(s):  
Radio Source ◽  
Power Law ◽  
Nearby Galaxy ◽  
Bl Lac Objects ◽  
X Ray ◽  
Spectrum Radio ◽  
Bl Lac ◽  
The Galaxy

The galaxy identified with the flat-spectrum radio source PKS 2005-489 has a bright stellar nucleus with V ⋍ 13 mag. Optical, UV and X-ray observations indicate variability and power-law continua in each of these wavebands, leading to the conclusion that PKS 2005-489 is one of the brightest BL Lac objects known.

Ariel 5 hard X-ray observations

1979 ◽  
Vol 366 (1726) ◽  
pp. 295-310
Keyword(s):  
Power Law ◽  
Line Emission ◽  
Galactic Centre ◽  
X Ray ◽  
Upper Limits ◽  
Inverse Compton ◽  
Time Variations ◽  
Cyclotron Line ◽  
Galactic Sources ◽  
The Magnetic Field

Results from the hard X-ray detector (8 cm 2 area, 8° f. w. h. m. field of view, energy range 26–1200 keV) are reviewed in the context of observations by other groups. At least three different classes of galactic sources are studied by this detector. In the first, magnetospheric control of the emission, which seems to be a modified thermal spectrum is dominant. Examples are Cen X-3, Her X-1, A0535 + 26 and GX 301 – 2. So far, only direct evidence on the magnetic field strength from cyclotron line emission has come from Her X-1. In the second, the characteristics are a power law spectrum extending to over about 200 keV and fast a periodic time variations with little evidence of the presence of strong magnetic fields. Inverse Compton production of the X-ray photons seems important here. Examples are Cyg X-1, A0620–00, Ser X-1 and perhaps Cir X-1, although this last object suffers periodic heavy low energy absorption. The third is the white dwarf emitter class, e. g. AM Herculis and possibly AM Canum Venaticorum; sources in this class surprisingly tend to exhibit a power law rather than a thermal spectral shape. Sco X-1 and Sco X-2 are perhaps a fourth class of object. Hard X-ray upper limits obtained from a survey of COS-B γ -ray source positions are discussed. Further attempts to find hard X-ray emission from the galactic centre X-ray burst sources are mentioned.

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