The Radio/X-Ray Burst from SGR 1935+2154: Radiation Mechanisms and the Possible QPOs

Excluding single stars, star systems with very strong X-ray sources, thermally radiating winds and circumstellar envelopes, marginal detections, and binary systems that are far from “normal”, there are about 21 close binary systems that show clear signs of stellar activity in the form of variable radio emission. Sixteen of these are RS CVn binaries. Typical events are smoothly varying with time scales of from a few hours to a few days. In the RS CVn binaries UX Ari and V711 Tau variable circular polarization is sometimes observed, with occasional appearence of components with only one frequency and one circular polarization, part of which shows “oscillations” with “periods” of about 4 minutes. Different stars and different events typically have inferred electron energies of about 5 MeV and inferred magnetic fields of 1 - 30 Gauss. The radiation mechanisms are usually assumed to be synchrotron or gyro-synchrotron; however, radiation from plasma processes cannot be ruled out in some cases, and it will be very important to establish or rule out this possibility. Most radio binary events show clear signs of self-absorption, so the variations appear most strongly at the higher frequencies. Typical rise times of events are about 30% of decay times. Maximum radio luminosities range from 1013 to a few times 1017 ergs s-1 Hz-1. Most radio flares are mainly at cm-wavelenghts and have observable and inferred energies 104 - 106 times those for the largest solar events, a scaling which is similar to that for X-ray emission measures of these stars when compared to solar coronal loop emission measures. Most importantly, VLBI measurements of Algol indicate that the sizes of the radio emitting regions for very strong events are of the order of 2 - 3 stellar radii. Single stars appear to be active at radio wavelengths much less commonly than close binary systems. In many cases this may be due to the way dynamo action and convection near the surface are affected by increased rotation forced by the synchronization induced by the binary system.

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Statistical Analyses of the Energies of X-Ray Plateaus and Flares in Gamma-Ray Bursts

The Astrophysical Journal ◽

10.3847/1538-4357/ac35e7 ◽

2022 ◽

Vol 924 (2) ◽

pp. 69

Author(s):

Shuang-Xi Yi ◽

Mei Du ◽

Tong Liu

Keyword(s):

Gamma Ray ◽

Gamma Ray Bursts ◽

Physical Origin ◽

Radiation Mechanisms ◽

Gaussian Distributions ◽

Emission Energy ◽

X Ray ◽

Central Engine ◽

Positive Correlations ◽

Prompt Emission

Abstract Distinct X-ray plateau and flare phases have been observed in the afterglows of gamma-ray bursts (GRBs), and most of them should be related to central engine activities. In this paper, we collect 174 GRBs with X-ray plateau phases and 106 GRBs with X-ray flares. There are 51 GRBs that overlap in the two selected samples. We analyze the distributions of the proportions of the plateau energy E plateau and the flare energy E flare relative to the isotropic prompt emission energy E γ,iso. The results indicate that they well meet the Gaussian distributions and the medians of the logarithmic ratios are ∼−0.96 and −1.39 in the two cases. Moreover, strong positive correlations between E plateau (or E flare ) and E γ,iso with slopes of ∼0.95 (or ∼0.80) are presented. For the overlapping sample, the slope is ∼0.80. We argue that most of X-ray plateaus and flares might have the same physical origin but appear with different features because of the different circumstances and radiation mechanisms. We also test the applicabilities of two models, i.e., black holes surrounded by fractured hyperaccretion disks and millisecond magnetars, on the origins of X-ray plateaus and flares.

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On X-ray Pulsar Radiation Mechanisms

Symposium - International Astronomical Union ◽

10.1017/s0074180900092998 ◽

1981 ◽

Vol 95 ◽

pp. 255-261

Author(s):

V. V. Zheleznyakov

Keyword(s):

Neutron Star ◽

Binary Systems ◽

Hot Spot ◽

Inhomogeneous Magnetic Field ◽

X Rays ◽

Radiation Mechanisms ◽

X Ray ◽

Pulsar Radiation ◽

Cyclotron Emission ◽

Fraunhofer Spectrum

In this report we shall discuss the origin of radiation from the neutron star component of X-ray binary systems whose spectra contain cyclotron lines (Her X-1 and 4U0115+63). A relevant model of the polar region of a neutron star is presented in Figure 1. According to this model the observed X-rays (continuum + cyclotron lines) are generated in the dense plasma atmosphere of a star (in its hot spot heated by accreting matter). The problem of heating the neutron star atmosphere due to accretion has been earlier investigated by Zeldovich and Shakura (1969). Cyclotron lines are formed similarly to the Fraunhofer spectrum of ordinary stars and are absorption lines. For objects such as Her X-1 and 4U0115+63 the cyclotron emission and absorption in the extended accreting column with an inhomogeneous magnetic field should be unessential. Otherwise the accreting column will produce an X-ray continuum devoid of any line type features.

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Time Resolved Circular Polarimetry of White Dwarf Pulsars

International Astronomical Union Colloquium ◽

10.1017/s0252921100100740 ◽

1982 ◽

Vol 69 ◽

pp. 399-401

Author(s):

W. Krzeminski ◽

J.D. Landstreet ◽

I. Thompson

Keyword(s):

Orbital Period ◽

White Dwarf ◽

White Dwarfs ◽

Radiation Mechanisms ◽

Time Resolved ◽

X Ray ◽

Rotation Periods ◽

Accretion Process ◽

Cataclysmic Binaries ◽

Synchronous Rotation

There are two recognized subsets of cataclysmic binaries that contain white dwarfs: the AM Her stars, whose white dwarf components are sufficiently magnetized to ensure synchronous rotation with the orbital period, and the DQ Her stars, which do not maintain synchronism and probably have been spun up by mass accretion. Both groups of stars, recognized also as X-ray sources, are important as probes of the accretion process, and the radiation mechanisms in the vicinity of the white dwarf. So far, we know five objects belonging to the former group (AM Her, AN UMa, VV Pup, 2A 0311-227, and PG 1550+191), and seven falling into the latter: WZ Sge, AE Aqr, V533 Her, DQ Her, V1223 Sgr, H2252-035, and EX Hya, with the corresponding rotation periods of their white dwarf primaries of 28, 33, 64, 71, 794, 805, and 4020 s, respectively. While the main observational and theoretical efforts have been focussed on the AM Her class, the DQ Her binaries have been investigated to much lesser extent. This is probably because the DQ Her stars have been recognized only very recently as a homogeneous class.

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

International Astronomical Union Colloquium ◽

10.1017/s0252921100078350 ◽

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

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Impact of intrinsic polarization of Sgr A* historical flares on (polarization) properties of their X-ray echoes

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2619 ◽

2020 ◽

Vol 498 (3) ◽

pp. 4379-4385

Author(s):

Ildar Khabibullin ◽

Eugene Churazov ◽

Rashid Sunyaev

Keyword(s):

Primary Source ◽

Molecular Complexes ◽

Line Of Sight ◽

Radiation Mechanisms ◽

Intrinsic Polarization ◽

X Ray ◽

Relative Line ◽

Sgr A ◽

The Moment

ABSTRACT Reflection of X-ray emission on molecular clouds in the inner ∼100 pc of our Galaxy reveals that, despite being extremely quiet at the moment, our supermassive black hole Sgr A* should have experienced bright flares of X-ray emission in the recent past. Thanks to the improving characterization of the reflection signal, we are able to infer parameters of the most recent flare(s) (age, duration, and luminosity) and relative line-of-sight disposition of the brightest individual molecular complexes. We show that combining these data with measurements of polarization in the reflected X-ray continuum will not only justify Sgr A* as the primary source but also allow deriving intrinsic polarization properties of the flare emission. This will help to identify radiation mechanisms and underlying astrophysical phenomena behind them. For the currently brightest reflecting molecular complex, Sgr A, the required level of sensitivity might be already accessible with upcoming X-ray polarimeters.

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High-Energy Radiation From Active Galactic Nuclei

International Astronomical Union Colloquium ◽

10.1017/s0252921100078325 ◽

1994 ◽

Vol 142 ◽

pp. 923-928

Author(s):

Marek Sikora

Keyword(s):

Active Galactic Nuclei ◽

Galactic Nuclei ◽

Seyfert Galaxies ◽

High Energy ◽

Radiation Mechanisms ◽

High Energy Radiation ◽

Energy Radiation ◽

X Ray ◽

Radiation Properties ◽

Galaxies Active

AbstractTwo recent findings concerning high-energy radiation properties of active galactic nuclei—discovery of breaks in hard X-ray spectra of Seyfert galaxies, and discovery of huge fluxes of hard gamma rays from blazars—seem to press us to change our standard views about radiation production in these objects. I review briefly the existing radiation models, confront them with the newest observations, and discuss newly emerging theoretical pictures which attempt to account for the discoveries.Subject headings: galaxies: active — galaxies: nuclei — radiation mechanisms: nonthermal

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X-RAY RADIATION MECHANISMS AND BEAMING EFFECT OF HOT SPOTS AND KNOTS IN ACTIVE GALACTIC NUCLEAR JETS

The Astrophysical Journal ◽

10.1088/0004-637x/710/2/1017 ◽

2010 ◽

Vol 710 (2) ◽

pp. 1017-1031 ◽

Cited By ~ 24

Author(s):

Jin Zhang ◽

J. M. Bai ◽

Liang Chen ◽

Enwei Liang

Keyword(s):

Hot Spots ◽

Radiation Mechanisms ◽

X Ray

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PARAMETRIC X-RAY RADIATION IN THE BACKWARD GEOMETRY

10.46813/2019-122-184 ◽

2019 ◽

pp. 184-186

Author(s):

V.I. Alekseev ◽

A.N. Eliseyev ◽

E.F. Irribarra ◽

I.A. Kishin ◽

A.S. Kubankin ◽

...

Keyword(s):

Spectral Width ◽

Total Radiation ◽

Radiation Yield ◽

Radiation Mechanisms ◽

X Ray

Parametric X-ray Radiation registered in the backward geometry is analysed. The main properties of the radiation for such geometry are discussed. The advantages of the backward geometry over other configurations regarding the intensity, the spectral width and the possibility to discriminate the contributions form different radiation mechanisms to the total radiation yield are presented.

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