The energy spectrum of anomalous X-ray pulsars and soft gamma-ray repeaters

Trümper, J.; Zezas, A.; Ertan, Ünal; Kylafis, N. D.

doi:10.1051/0004-6361/200911834

Cited by 53 publications

(69 citation statements)

References 63 publications

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“…For event B, the most adequate model for describing the burst spectrum was non-thermal: a power law with an index of 0.42. Such non-thermal behavior is also typical for magnetar bursts (van der Horst et al 2012;Lin et al 2013;Şaşmaz Muş et al 2015). Following the burst, we observed the segments Gray and Oscillation, during which clear periodic modulations at 8.7 s could be seen.…”

Section: Discussionmentioning

confidence: 78%

Variation of Spectral and Timing Properties in the Extended Burst Tails From the Magnetar 4u 0142+61

Chakraborty

Göǧüş

Mus

et al. 2016

ApJ

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Extended emission episodes with an intensity above the preburst level are observed following magnetar bursts from a number of soft gamma repeaters and anomalous X-ray pulsars (AXPs). Such extended tail emissions were observed following two events detected from AXP 4U 0142+61. We investigated in detail the evolution of spectral and temporal properties during these two tail segments using Rossi X-ray Timing Explorer/Proportional Counter Array observations, and report distinct variations in the spectral and temporal behavior throughout the tails. In particular, in both cases we observed a sudden enhancement of the pulsation amplitude in conjunction with bursts and a smooth decline of X-ray emission (cooling) during the tail. We suggest that an inefficiently radiating trapped fireball formed during the burst, which can heat up the stellar surface, is able to explain the tail properties and its energetics. We also present the episodic detection of absorption and emission features during tails. One possible mechanism that has been proposed to give rise to such spectral lines is the proton/ion cyclotron resonance process, which has been suggested as offering a valuable tool in probing the complex magnetic field of magnetars.

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Section: Discussionmentioning

confidence: 78%

Variation of Spectral and Timing Properties in the Extended Burst Tails From the Magnetar 4u 0142+61

Chakraborty

Göǧüş

Mus

et al. 2016

ApJ

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“…In the accretion picture presented by Trümper et al (2010Trümper et al ( , 2013, this is a natural consequence of the fact that only about half of the produced hard X-ray luminosity in the radiative shock is observed directly (L h ), while the other half is intercepted by the polar cap and the major fraction of it is reemitted as soft X-rays (L s ). With our reported calculations in Sect.…”

Section: Discussionmentioning

confidence: 99%

“…A detailed model for the formation of the quiescent spectra of AXPs/SGRs has been proposed by Trümper et al (2010Trümper et al ( , 2013 using the fallback disk model. These spectra consist of two components (e.g., den Hartog et al 2008a,b;Enoto et al 2010); a quasi-thermal component at low energies, which is generally attributed to the photospheric emission from the neutron star polar cap, and a hard power-law component.…”

Section: Introductionmentioning

confidence: 99%

“…These spectra consist of two components (e.g., den Hartog et al 2008a,b;Enoto et al 2010); a quasi-thermal component at low energies, which is generally attributed to the photospheric emission from the neutron star polar cap, and a hard power-law component. In the model of Trümper et al (2010Trümper et al ( , 2013, this power-law component is attributed to the emission from the radiative shock, located near the bottom of the accretion column. This component is emitted as a fan beam, which partly hits the surrounding polar cap, where the radiation is absorbed or scattered, leading to the quasi-thermal component.…”

Section: Introductionmentioning

confidence: 99%

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Spectral formation in a radiative shock: application to anomalous X-ray pulsars and soft gamma-ray repeaters

Kylafis

Trümper

Ertan

2014

A&A

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Context. In the fallback disk model for the persistent emission of anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs), the hard X-ray emission arises from bulk-and thermal Comptonization of bremsstrahlung photons, which are generated in the accretion column. The relatively low X-ray luminosity of these sources implies a moderate transverse optical depth to electron scattering, with photons executing a small number of shock crossings before escaping sideways. Aims. We explore the range of spectral shapes that can be obtained with this model and characterize the most important parameter dependencies. Methods. We use a Monte Carlo code to study the crisscrossing of photons in a radiative shock in an accretion column and compute the resulting spectrum. Results. As expected, high-energy power-law X-ray spectra are produced in radiative shocks with photon-number spectral index Γ > ∼ 0.5. We find that the required transverse optical depth is 1 < ∼ τ ⊥ < ∼ 7. Such spectra are observed in low-luminosity X-ray pulsars. Conclusions. We demonstrate here with a simple model that Compton upscattering in the radiative shock in the accretion column can produce hard X-ray spectra similar to those seen in the persistent and transient emission of AXPs and SGRs. In particular, one can obtain a high-energy power-law spectrum, with photon-number spectral-index Γ ∼ 1 and a cutoff at 100−200 keV, with a transverse Thomson optical depth of ∼5, which is shown to be typical in AXPs/SGRs.

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“…In the frame of the disk model, rotational properties and X-ray luminosity of this SGR can be reached simultaneously within the cooling timescale of a neutron star with B 0 10 12 G (Alpar et al 2011). Recently, Trümper et al (2010) showed that the high-energy spectrum of AXP 4U 0142+61 can be produced in the accretion column of this source mainly by the bulk Comptonization process.…”

Section: Introductionmentioning

confidence: 98%

On the X-Ray Outbursts of Transient Anomalous X-Ray Pulsars and Soft Gamma-Ray Repeaters

Çalışkan¹,

Ertan²

2012

ApJ

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We show that the X-ray outburst light curves of four transient anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs), namely, XTE J1810−197, SGR 0501+4516, SGR 1627−41, and CXOU J164710.2−455216, can be produced by the fallback disk model that was also applied to the outburst light curves of persistent AXPs and SGRs in our earlier work. The model solves the diffusion equation for the relaxation of a disk that has been pushed back by a soft gamma-ray burst. The sets of main disk parameters used for these transient sources are very similar to each other and to those employed in our earlier models of persistent AXPs and SGRs. There is a characteristic difference between the X-ray outburst light curves of transient and persistent sources. This can be explained by the differences in the disk surface density profiles of the transient and persistent sources in quiescence indicated by their quiescent X-ray luminosities. Our results imply that a viscous disk instability operating at a critical temperature in the range of ∼1300-2800 K is a common property of all fallback disks around AXPs and SGRs. The effect of the instability is more pronounced and starts earlier for the sources with lower quiescent luminosities, which leads to the observable differences in the X-ray enhancement light curves of transient and persistent sources. A single active disk model with the same basic disk parameters can account for the enhancement phases of both transient and persistent AXPs and SGRs. We also present a detailed parameter study to show the effects of disk parameters on the evolution of the X-ray luminosity of AXPs and SGRs in the X-ray enhancement phases.

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The energy spectrum of anomalous X-ray pulsars and soft gamma-ray repeaters

Cited by 53 publications

References 63 publications

Variation of Spectral and Timing Properties in the Extended Burst Tails From the Magnetar 4u 0142+61

Variation of Spectral and Timing Properties in the Extended Burst Tails From the Magnetar 4u 0142+61

Spectral formation in a radiative shock: application to anomalous X-ray pulsars and soft gamma-ray repeaters

On the X-Ray Outbursts of Transient Anomalous X-Ray Pulsars and Soft Gamma-Ray Repeaters

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