Temperature Profiles of Accretion Disks around Rapidly Rotating Neutron Stars in General Relativity and the Implications for Cygnus X‐2

Bhattacharyya, Sudip; Thampan, Arun V.; Misra, Ranjeev; Datta, Bithin

doi:10.1086/309502

Cited by 26 publications

(63 citation statements)

References 35 publications

(43 reference statements)

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“…(6) The two different situations, viz., rISCO > R and rISCO < R (rISCO is ISCO radius) have important consequences for observed X-ray features, and hence on the measurements of compact star parameters (e.g., Bhattacharyya (2011)). In the former situation, the length of the gap between rISCO and R is also very important for the X-ray emission, because the boundary layer emission to the accretion disc emission ratio depends on this length (e.g., Bhattacharyya et al (2000)). We find that rISCO is greater than R for the maximum mass and maximum angular momentum configurations, and the gap-length for EoS 1-2 is somewhat lower than that for EoS 3.…”

Section: Discussionmentioning

confidence: 99%

“…Besides, a measurement of I of the binary pulsar J0737-3039A with 10% accuracy has been talked about (Morrison et al 2004). Apart from R/rg, R and I, [r orb − R] of LMXBs, which can be inferred from spectral and timing studies of observed X-ray emission (e.g., Bhattacharyya et al (2000)), also has a significant difference (≈ 98%) between EoS 2 and EoS 3. Therefore, since MG and ν have been measured for a number of compact stars (see § 1), B eff could be constrained from observations, within the ambit of our EoS models.…”

Section: Discussionmentioning

confidence: 99%

“…But R is the absolute lower limit of the disc radius. Therefore, if the star extends beyond the ISCO, we set r orb = R (Bhattacharyya et al 2000;Bhattacharyya 2011). …”

Section: Computation Of Rapidly Spinning Stellar Structuresmentioning

confidence: 99%

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Fast spinning strange stars: possible ways to constrain interacting quark matter parameters

Bhattacharyya

Bombaci

Logoteta

et al. 2016

Mon. Not. R. Astron. Soc.

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For a set of equation of state (EoS) models involving interacting strange quark matter, characterized by an effective bag constant (B eff ) and a perturbative QCD corrections term (a 4 ), we construct fully general relativistic equilibrium sequences of rapidly spinning strange stars for the first time. Computation of such sequences is important to study millisecond pulsars and other fast spinning compact stars. Our EoS models can support a gravitational mass (M G ) and a spin frequency (ν) at least up to ≈ 3.0M ⊙ and ≈ 1250 Hz respectively, and hence are fully consistent with measured M G and ν values. This paper reports the effects of B eff and a 4 on measurable compact star properties, which could be useful to find possible ways to constrain these fundamental quark matter parameters, within the ambit of our EoS models. We confirm that a lower B eff allows a higher mass. Besides, for known M G and ν, measurable parameters, such as stellar radius, radius-to-mass ratio and moment of inertia, increase with the decrease of B eff . Our calculations also show that a 4 significantly affects the stellar rest mass and the total stellar binding energy. As a result, a 4 can have signatures in evolutions of both accreting and non-accreting compact stars, and the observed distribution of stellar mass and spin and other source parameters. Finally, we compute the parameter values of two important pulsars, PSR J1614-2230 and PSR J1748-2446ad, which may have implications to probe their evolutionary histories, and for constraining EoS models.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Fast spinning strange stars: possible ways to constrain interacting quark matter parameters

Bhattacharyya

Bombaci

Logoteta

et al. 2016

Mon. Not. R. Astron. Soc.

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“…We take the temperature of the accretion disk to decrease with radius as (e.g., LyndenBell 1969; Bhattacharyya et al 2000):…”

Section: Numerical Modelmentioning

confidence: 99%

Anisotropy of X-Ray Bursts From Neutron Stars With Concave Accretion Disks

Keek

2016

ApJ

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Emission from neutron stars and accretion disks in low-mass X-ray binaries is anisotropic. The non-spherical shape of the disk as well as blocking of the neutron star by the disk make the observed flux dependent on the inclination angle of the disk with respect to the line of sight. This is of importance for the interpretation of thermonuclear X-ray bursts from neutron stars. Because part of the X-ray burst is reflected off the disk, the observed burst flux depends on the anisotropies for both direct emission from the neutron star and reflection off the disk. This influences measurements of source distance, mass accretion rate, and constraints on the neutron star's equation of state. Previous predictions of the anisotropy factors assumed a geometrically flat disk. Detailed observations of two so-called superbursts allowed for the direct and the reflected burst fluxes to each be measured separately. The reflection fraction was much higher than what the anisotropies of a flat disk can account for. We create numerical models to calculate the anisotropy factors for different disk shapes, including concave disks. We present the anisotropy factors of the direct and reflected burst fluxes separately, as well as the anisotropy of the persistent flux. Reflection fractions substantially larger than unity are produced in the case where the inner accretion disk increases steeply in height, such that part of the star is blocked from view. Such a geometry could possibly be induced by the X-ray burst if X-ray heating causes the inner disk to puff up.

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“…Sibgatullin & Sunyaev (1998) analyzed the effect of the quadrupole component in the mass distribution of a rapidly rotating neutron star, on the energy release in the equatorial (or boundary) layer on the surface of the accreting star and in the accretion disc in the cases where the stellar radius is smaller (or larger) than the radius of the last stable circular orbit. The temperature profiles of (thin) accretion discs around rapidly rotating neutron stars (with low surface magnetic fields), taking into account the full effects of general relativity were obtained in Bhattacharyya et al (2000). The calculations suggest that the neutron star in Cygnus X-2 rotates close to the centrifugal mass-shed limit.…”

Section: Introductionmentioning

confidence: 99%

Thin accretion discs around neutron and quark stars

Kovács

Cheng

Harkó

2009

A&A

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Context. The possibility of observationally discriminating between various types of neutron stars, described by different equations of state of the nuclear matter, as well as differentiating neutron stars from other types of exotic objects, for example, quark stars, is one of the fundamental problems in contemporary astrophysics. Aims. We consider and investigate carefully the possibility that different types of rapidly rotating neutron stars, as well as other type of compact general-relativistic objects, can be identified reliably by the study of the emission properties of the accretion discs around them. Methods. We obtain the energy flux, temperature distribution, and emission spectrum from the accretion discs around several classes of rapidly rotating neutron stars, described by different equations of state for neutron matter, and for quark stars, described by the MIT bag model equation of state, and in the CFL (Color-Flavor-Locked) phase, respectively. Results. Particular signatures appear in the electromagnetic spectrum, implying that the equation of state of the dense matter can be tested directly by using astrophysical observations of the emission spectra from accretion discs.

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Temperature Profiles of Accretion Disks around Rapidly Rotating Neutron Stars in General Relativity and the Implications for Cygnus X‐2

Cited by 26 publications

References 35 publications

Fast spinning strange stars: possible ways to constrain interacting quark matter parameters

Fast spinning strange stars: possible ways to constrain interacting quark matter parameters

Anisotropy of X-Ray Bursts From Neutron Stars With Concave Accretion Disks

Thin accretion discs around neutron and quark stars

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