NICER Observes the Effects of an X-Ray Burst on the Accretion Environment in Aql X-1

Keek, L.; Arzoumanian, Zaven; Bult, Peter; Cackett, E.; Chakrabarty, Deepto; Chenevez, J.; Fabian, A. C.; Gendreau, Keith C.; Guillot, Sebastien; Güver, T.; Homan, J.; Jaisawal, Gaurava K.; Lamb, Frederick K.; Ludlam, R. M.; Mahmoodifar, Simin; Markwardt, C. B.; Miller, J. M.; Prigozhin, G.; Soong, Yang; Strohmayer, Tod E.; Wolff, M. T.

doi:10.3847/2041-8213/aab104

Cited by 45 publications

(62 citation statements)

References 42 publications

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“…Moreover, significant soft excesses with respect to the hardstate persistent emission were measured in the burst spectra of EXO 0748-676 (Asai & Dotani 2006), SAX J1808. 4-3658 (in 't Zand et al 2013;Bult et al 2019), and Aql X-1 (Keek et al 2018). These excesses suggest a temporary enhancement of the accretion rate induced by the burst, probably via Poynting-Robsertson drag of the accretion flow (Ballantyne & Everett 2005).…”

Section: Introductionmentioning

confidence: 92%

Burst-induced coronal cooling in GS 1826–24

Sánchez–Fernández

Kajava

Poutanen

et al. 2020

A&A

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Type I X-ray bursts in GS 1826-24, and in several other systems, may induce cooling of the hot inner accretion flow that surrounds the bursting neutron star. Given that GS 1826-24 remained persistently in the hard state over the period 2003-2008 and presented regular bursting properties, we stacked the spectra of the X-ray bursts detected by INTEGRAL (JEM-X and ISGRI) and XMM-Newton (RGS) during that period to study the effect of the burst photons on the properties of the Comptonizing medium. The extended energy range provided by these instruments allows the simultaneous observation of the burst and persistent emission spectra. We detect an overall change in the shape of the persistent emission spectrum in response to the burst photon shower. For the first time, we observe simultaneously a drop in the hard X-ray emission, together with a soft X-ray excess with respect to the burst blackbody emission. The hard X-ray drop can be explained by burst-induced coronal cooling, while the bulk of the soft X-ray excess can be described by fitting the burst emission with an atmosphere model, instead of a simple blackbody model. Traditionally, the persistent emission was assumed to be invariant during X-ray bursts, and more recently to change only in normalization but not in spectral shape; the observed change in the persistent emission level during X-ray bursts may thus trigger the revision of existing neutron star massradius constraints, as the derived values rely on the assumption that the persistent emission does not change during X-ray bursts. The traditional burst fitting technique leads to up to a 10% overestimation of the bolometric burst flux in GS 1826-24, which significantly hampers the comparisons of the KEPLER and MESA model against this 'textbook burster'.

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Section: Introductionmentioning

confidence: 92%

Burst-induced coronal cooling in GS 1826–24

Sánchez–Fernández

Kajava

Poutanen

et al. 2020

A&A

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“…Instead the velocity field is connected to Eqs. (38) for determining (dν/dτ, dψ/dτ, dα/dτ ). We note that using Eq.…”

Section: General Relativistic Equations Of Motionmentioning

confidence: 99%

Three-dimensional general relativistic Poynting-Robertson effect: Radial radiation field

et al. 2019

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In this paper we investigate the three-dimensional (3D) motion of a test particle in a stationary, axially symmetric spacetime around a central compact object, under the influence of a radiation field. To this aim we extend the two-dimensional (2D) version of the Poynting-Robertson effect in General Relativity (GR) that was developed in previous studies. The radiation flux is modeled by photons which travel along null geodesics in the 3D space of a Kerr background and are purely radial with respect to the zero angular momentum observer (ZAMO) frames. The 3D general relativistic equations of motion that we derive are consistent with the classical (i.e. non-GR) description of the Poynting-Robertson effect in 3D. The resulting dynamical system admits a critical hypersurface, on which radiation force balances gravity. Selected test particle orbits are calculated and displayed, and their properties described. It is found that test particles approaching the critical hypersurface at a finite latitude and with non-zero angular moment are subject to a latitudinal drift and asymptotically reach a circular orbit on the equator of the critical hypersurface, where they remain at rest with respect to the ZAMO. On the contrary, test particles that have lost all their angular momentum by the time they reach the critical hypersurface do not experience this latitudinal drift and stay at rest with respects to the ZAMO at fixed non-zero latitude. * vittorio.defalco@physics.cz † pavel.bakala@fpf.slu.cz ‡ emmanuelebattista@gmail.com 1 Note however that Robertson mentions general relativistic corrections to inertial terms in describing the perihelion shift in the quasi-Newtonian orbits [2].

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“…For example, several studies of bursts in the low/hard state 10-12 detected both a simultaneous rise in soft X-rays (owing to the burst itself) and drop in hard X-rays (attributed to cooling of a geometrically thick corona). On the other hand, bursts from other sources in the low/hard state produced reflection features in the X-ray spectra [13][14][15][16] , indicating the presence of an optically thick inner disc.Recently, we presented the first numerical simulation of an accretion disc subject to the sudden, intense radiation field of an X-ray burst 17 . That simulation focused on a hot, geometricallythick disc, and found that strong Compton cooling of the accreting plasma by the burst photons caused the disc temperature to drop by three orders of magnitude, the height to be reduced by one order of magnitude, and the accretion rate to increase by a factor of a few.…”

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confidence: 99%

Interactions of type I X-ray bursts with thin accretion disks

2020

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We perform a set of numerical experiments studying the interaction of Type I X-ray bursts with thin, Shakura-Sunyaev type accretion discs. Careful observations of X-ray spectra during such bursts have hinted at changes occurring in the inner regions of the disc. We now clearly demonstrate a number of key effects that take place simultaneously, including: evidence for weak, radiation-driven outflows along the surface of the disc; significant levels of Poynting-Robertson (PR) drag, leading to enhanced accretion; and prominent heating in the disc, which increases the height, while lowering the density and optical depth. The PR drag causes the inner edge of the disc to retreat from the neutron star surface toward larger radii and then recover on the timescale of the burst. We conclude that the rich interaction of an X-ray burst with the surrounding disc provides a novel way to study the physics of accretion onto compact objects. 1 arXiv:2001.01032v1 [astro-ph.HE] 4 Jan 2020Thermonuclear explosions on the surface of neutron stars, commonly known as Type I X-ray bursts, can be used to study the behavior of matter under extreme conditions 1-3 . Careful analysis of the burst spectrum and luminosity may even provide constraints on the neutron star equation of state 1, 4-6 , one of the most important unsolved problems in high-energy astrophysics. In addition, it has recently been recognized that X-ray bursts are a potentially powerful probe of accretion physics, as the intense release of radiative energy in the burst over a short timescale (seconds for Type I bursts; hours for superbursts) could significantly impact the structure of both the disc and corona 7-9 .Observational evidence for the interaction of bursts with the accretion disc indicates a range of behaviors that signal a strong dependence on the accretion flow geometry, even for sources in the same spectral state. For example, several studies of bursts in the low/hard state 10-12 detected both a simultaneous rise in soft X-rays (owing to the burst itself) and drop in hard X-rays (attributed to cooling of a geometrically thick corona). On the other hand, bursts from other sources in the low/hard state produced reflection features in the X-ray spectra [13][14][15][16] , indicating the presence of an optically thick inner disc.Recently, we presented the first numerical simulation of an accretion disc subject to the sudden, intense radiation field of an X-ray burst 17 . That simulation focused on a hot, geometricallythick disc, and found that strong Compton cooling of the accreting plasma by the burst photons caused the disc temperature to drop by three orders of magnitude, the height to be reduced by one order of magnitude, and the accretion rate to increase by a factor of a few. All of these changes −7/2 K ρ cgs cm 2 g −1 and κ a R = 1.6 × 10 21 T −7/2 K ρ cgs cm 2 g −1 34 , respectively, where T K is the ideal gas temperature of the fluid in Kelvin and ρ cgs is the density in g cm −3 . In this work, we assume the flux mean, κ a F , is the same as the Rosseland me...

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NICER Observes the Effects of an X-Ray Burst on the Accretion Environment in Aql X-1

Cited by 45 publications

References 42 publications

Burst-induced coronal cooling in GS 1826–24

Burst-induced coronal cooling in GS 1826–24

Three-dimensional general relativistic Poynting-Robertson effect: Radial radiation field

Interactions of type I X-ray bursts with thin accretion disks

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