Magnetar X-ray emission mechanisms

AbstractSoft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs) are peculiar X-ray sources which are believed to be magnetars: ultra-magnetized neutron stars which emission is dominated by surface fields (often in excess of 1E14 G, i.e. well above the QED threshold).Spectral analysis is an important tool in magnetar astrophysics since it can provide key information on the emission mechanisms. The first attempts at modelling the persistent (i.e. outside bursts) soft X-ray (¡10 keV) spectra of AXPs proved that a model consisting of a blackbody (kT 0.3-0.6 keV) plus a power-law (photon index 2-4) could successfully reproduce the observed emission. Moreover, INTEGRAL observations have shown that, while in quiescence, magnetars emit substantial persistent radiation also at higher energies, up to a few hundreds of keV. However, a convincing physical interpretation of the various spectral components is still missing.In this talk I will focus on the interpretation of magnetar spectral properties during quiescence. I will summarise the present status of the art and the currents attempts to model the broadband persistent emission of magnetars (from IR to hard Xrays) within a self consistent, physical scenario.

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Prolonged sub-luminous state of the new transitional pulsar candidate CXOU J110926.4−650224

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834835 ◽

2019 ◽

Vol 622 ◽

pp. A211 ◽

Cited By ~ 10

Author(s):

Francesco Coti Zelati ◽

Alessandro Papitto ◽

Domitilla de Martino ◽

David A. H. Buckley ◽

Alida Odendaal ◽

...

Keyword(s):

Gamma Ray ◽

Broad Band ◽

Optical Emission ◽

Bimodal Distribution ◽

X Ray ◽

The Past ◽

Upper Limits ◽

Photon Index ◽

Multi Wavelength ◽

Absorbed Power

We report on a multi-wavelength study of the unclassified X-ray source CXOU J110926.4−650224 (J1109). We identified the optical counterpart as a blue star with a magnitude of ∼20.1 (3300–10500 Å). The optical emission was variable on timescales from hundreds to thousands of seconds. The spectrum showed prominent emission lines with variable profiles at different epochs. Simultaneous XMM-Newton and NuSTAR observations revealed a bimodal distribution of the X-ray count rates on timescales as short as tens of seconds, as well as sporadic flaring activity. The average broad-band (0.3–79 keV) spectrum was adequately described by an absorbed power law model with photon index of Γ = 1.63 ± 0.01 (at 1σ c.l.), and the X-ray luminosity was (2.16 ± 0.04) × 1034 erg s−1 for a distance of 4 kpc. Based on observations with different instruments, the X-ray luminosity has remained relatively steady over the past ∼15 years. J1109 is spatially associated with the gamma-ray source FL8Y J1109.8−6500, which was detected with Fermi at an average luminosity of (1.5 ± 0.2) × 1034 erg s−1 (assuming the distance of J1109) over the 0.1–300 GeV energy band between 2008 and 2016. The source was undetected during ATCA radio observations that were simultaneous with NuSTAR, down to a 3σ flux upper limit of 18 μJy beam−1 (at 7.25 GHz). We show that the phenomenological properties of J1109 point to a binary transitional pulsar candidate currently in a sub-luminous accretion disk state, and that the upper limits derived for the radio emission are consistent with the expected radio luminosity for accreting neutron stars at similar X-ray luminosities.

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Gamma-ray-emitting narrow-line Seyfert 1 galaxies: the Swift view

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1580 ◽

2020 ◽

Vol 496 (2) ◽

pp. 2213-2229 ◽

Cited By ~ 1

Author(s):

F D’Ammando

Keyword(s):

Gamma Ray ◽

Thermal Emission ◽

Optical Emission ◽

X Rays ◽

Narrow Line ◽

X Ray ◽

Relativistic Jet ◽

Photon Index ◽

Γ Ray ◽

Lower Variability

ABSTRACT We report the analysis of all Swift observations available up to 2019 April of γ-ray-emitting narrow-line Seyfert 1 galaxies (NLSy1). The distribution of X-ray luminosities (and fluxes) indicates that the jet radiation significantly contributes to their X-ray emission, with Doppler boosting making values higher than other radio-loud NLSy1. The 0.3–10 keV photon indices are on average harder with respect to radio-quiet and radio-loud NLSy1, confirming a dominant jet contribution in X-rays. However, the lower variability amplitude with respect to blazars and the softening of the spectrum in some periods suggests that also the corona radiation contributes to the X-ray emission. In optical and ultraviolet (UV) significant flux changes have been observed on daily, weekly, and monthly time-scale, providing a clear indication of the significant contribution of the jet radiation in this part of spectrum. A strong correlation between X-ray, UV, and optical emission and simultaneous flux variations have been observed in 1H 0323+342, SBS 0846+513, PMN J0948+0022 as expected in case the jet radiation is the dominant mechanism. Correlated multiband variability favours the jet-dominated scenario also in FBQS J1644+2619 and PKS 2004−447. The summed X-ray Telescope spectra of 1H 0323+342, SBS 0846+513, PMN J0948+0022, and FBQS J1644+2619 are well fitted by a broken power law with a break around 2 keV. The spectrum above 2 keV is dominated by the non-thermal emission from a beamed relativistic jet, as suggested by the hard photon index. A Seyfert-like feature like the soft X-ray excess has been observed below 2 keV, making these γ-ray-emitting NLSy1 different from typical blazars.

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THE INTERPLAY OF PROMPT AND AFTERGLOW EMISSION IN GRB 060418

International Journal of Modern Physics D ◽

10.1142/s0218271808012899 ◽

2008 ◽

Vol 17 (09) ◽

pp. 1343-1349 ◽

Cited By ~ 2

Author(s):

S. D. VERGANI ◽

D. MALESANI ◽

E. MOLINARI

Keyword(s):

Gamma Rays ◽

Spectral Properties ◽

Gamma Ray ◽

Early Time ◽

Lorentz Factor ◽

X Ray ◽

Central Engine ◽

Low Energies ◽

Prompt Emission

We present observations of the early afterglow emission of GRB 060418. Thanks to the simultaneous coverage at optical, X-ray and gamma-ray wavelengths, we can detect and separate the external shock emission (visible in the optical and late X-ray data) and the central engine activity (early X and gamma rays). The two components are clearly distinguished based on temporal and spectral properties. The detection of the afterglow onset (in the optical) allows the determination of the fundamental fireball properties, namely its bulk Lorentz factor and total energy. The early time X-ray flare closely resembles the prompt emission gamma-ray pulses in its temporal profile, being wider at low energies and showing lags between the hard and soft bands. This provides a strong suggestion that X-ray flares are a continuation of the prompt emission.

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Correlations between Spectral Properties and Spin-down Rate in Soft Gamma-Ray Repeaters and Anomalous X-Ray Pulsars

The Astrophysical Journal ◽

10.1086/320025 ◽

2001 ◽

Vol 551 (2) ◽

pp. L155-L158 ◽

Cited By ~ 45

Author(s):

D. Marsden ◽

N. E. White

Keyword(s):

Spectral Properties ◽

Gamma Ray ◽

X Ray

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Revealing x-ray and gamma ray temporal and spectral similarities in the GRB 190829A afterglow

Science ◽

10.1126/science.abe8560 ◽

2021 ◽

Vol 372 (6546) ◽

pp. 1081-1085

Author(s):

◽

H. Abdalla ◽

F. Aharonian ◽

F. Ait Benkhali ◽

E. O. Angüner ◽

...

Keyword(s):

Gamma Rays ◽

Gamma Ray ◽

High Energy ◽

X Ray ◽

Photon Index ◽

Very High Energy ◽

Stereoscopic System ◽

Very High ◽

Intrinsic Energy

Gamma-ray bursts (GRBs), which are bright flashes of gamma rays from extragalactic sources followed by fading afterglow emission, are associated with stellar core collapse events. We report the detection of very-high-energy (VHE) gamma rays from the afterglow of GRB 190829A, between 4 and 56 hours after the trigger, using the High Energy Stereoscopic System (H.E.S.S.). The low luminosity and redshift of GRB 190829A reduce both internal and external absorption, allowing determination of its intrinsic energy spectrum. Between energies of 0.18 and 3.3 tera–electron volts, this spectrum is described by a power law with photon index of 2.07 ± 0.09, similar to the x-ray spectrum. The x-ray and VHE gamma-ray light curves also show similar decay profiles. These similar characteristics in the x-ray and gamma-ray bands challenge GRB afterglow emission scenarios.

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Spectral Properties of the Prompt X-ray Emission and Afterglow from the Gamma-Ray Burst of 1997 February 28

The Astrophysical Journal ◽

10.1086/311132 ◽

1998 ◽

Vol 493 (2) ◽

pp. L67-L70 ◽

Cited By ~ 44

Author(s):

F. Frontera ◽

E. Costa ◽

L. Piro ◽

J. M. Muller ◽

L. Amati ◽

...

Keyword(s):

Spectral Properties ◽

Gamma Ray ◽

Gamma Ray Burst ◽

X Ray

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A Spatial Study of X-ray Properties in Superbubble 30 Dor C with XMM-Newton

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316006608 ◽

2015 ◽

Vol 11 (A29B) ◽

pp. 737-737

Author(s):

Y. Babazaki ◽

I. Mitsuishi ◽

H. Sano ◽

S. Yoshiike ◽

T. Fukuda ◽

...

Keyword(s):

Spatial Variation ◽

Spatial Resolution ◽

Thermal Model ◽

Spectral Properties ◽

High Spatial Resolution ◽

Cosmic Ray ◽

The West ◽

X Ray ◽

Photon Index ◽

Circumstellar Environment

AbstractThe superbubble (SB) 30 Dor C with the strong non-thermal X-ray emission is one of the best targets for study of the cosmic-ray (CR) acceleration. We investigated X-ray spectral properties of the SB with a high spatial resolution of ~10 pc. Consequently, the spectra in the east regions can be described with a combination of absorbed thermal and non-thermal models while the spectra in the west regions can be fitted with an absorbed non-thermal model. We found that the observed photon index and intensity in 2-10 keV show variations of 2.0-3.5 and (0.6-8.0) × 10−7 erg s−1 cm−2 str−1, respectively. The results are possibly caused by the spatial variation of the CR acceleration efficiency and/or the circumstellar environment.

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A Review of Gamma-Ray Burst Observations

Symposium - International Astronomical Union ◽

10.1017/s007418090016125x ◽

1987 ◽

Vol 125 ◽

pp. 477-487

Author(s):

W. Doyle Evans ◽

John G. Laros

Keyword(s):

Neutron Stars ◽

Spectral Properties ◽

Gamma Ray ◽

Gamma Ray Bursts ◽

Gamma Ray Burst ◽

X Ray

Gamma-ray bursts are generally believed to originate in the vicinity of neutron stars, but the phenomenology is still not understood. In this paper we review the known characteristics of gamma bursts and give new observational results on temporal and spectral properties. We suggest that a class of repeating bursters exists that are spectrally harder than x-ray bursters but significantly softer than “classical” gamma bursts. The March 5, 1979, burst may be the prototype of this class of bursters.

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Revisiting the long term X-ray spectral evolution of Seyfert 1 galaxies

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3217 ◽

2019 ◽

Author(s):

Shan-Shan Weng ◽

Ying Chen ◽

Ting-Ting Wang ◽

Zhen-Yi Cai ◽

Erlin Qiao ◽

...

Keyword(s):

Spectral Analysis ◽

Power Law ◽

Order Effect ◽

Accretion Disc ◽

Spectral Evolution ◽

X Ray ◽

Viscosity Parameter ◽

Photon Index ◽

Gaussian Line

Abstract Characterizing the long-term variability of AGNs is a key legacy of RXTE. We carry out a spectral analysis on a sample of 20 Seyfert 1 galaxies, which had been observed by the RXTE for at least 100 times. All 18,335 spectra are fitted in a uniform way using a power-law component plus an additional Gaussian line when necessary. For any source in our sample, we confirm that the spectrum softens or the photon index, Γ, increases with increasing the 2–10 keV luminosity, LX. However, different source holds distinct Γ − LX/LEdd relation, rather than a common one. We also fit the correlation with a function of Γ = C + β × log (flux), where C is a constant and parameter β is the slope of the correlation. In this way, the increase speed of the Γ − LX/LEdd relation can be depicted with the parameter β. Since our sample contains a large sample of long-term monitored sources, it allows us to explore the second order effect of spectral evolution. We find that there is an anti-correlation between β and the X-ray Eddington ratio, LX/LEdd. That is, the increasing tendency of Γ with increasing X-ray luminosity becomes slower when the source has a larger X-ray Eddington ratio. Our results may indicate changes in the geometry and/or the viscosity parameter of the accretion disc at different Eddington ratios.

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