scholarly journals The missing compact star of SN1987A: a solid quark star?

2012 ◽  
Vol 8 (S291) ◽  
pp. 448-450
Author(s):  
X. W. Liu ◽  
J. D. Liang ◽  
R. X. Xu ◽  
J. L. Han ◽  
G. J. Qiao
Keyword(s):  
Compact Star ◽  
Compact Object ◽  
The Other ◽  
Quark Star ◽  
Cooling Process ◽  
Cluster Star ◽  
X Ray ◽  
Supernova 1987A ◽  
Upper Limit ◽  
Parameter Constraints

AbstractTo investigate the missing compact star of Supernova 1987A, we analyzed the cooling and heating processes of a possible compact star based on the upper limit of observational X-ray luminosity. From the cooling process, we found that a solid quark-cluster star (SQS), having a stiffer equation of state than that of a conventional liquid quark star, has a heat capacity much smaller than a neutron star. The SQS can cool down quickly, naturally explaining the non-detection of a point source in X-ray wavelengths. On the other hand, we considered the heating processes due to magnetospheric activity and possible accretion and obtained some constraints on the parameters of a possible pulsar. Therefore, we concluded that a SQS can explain the observational limit in a confident parameter space. As a possible central compact object, the pulsar parameter constraints can be tested for SN1987A with advanced, future facilities.

scholarly journals GRB 130603B: No Compelling Evidence for Neutron Star Merger

2015 ◽  
Vol 2015 ◽  
pp. 1-5
Author(s):  
Shlomo Dado ◽  
Arnon Dar
Keyword(s):  
Neutron Star ◽  
Near Infrared ◽  
Gamma Ray ◽  
Hubble Space Telescope ◽  
Compact Star ◽  
Compact Object ◽  
Late Time ◽  
Quark Star ◽  
X Ray ◽  
Relativistic Jet

The near infrared (NIR) flare/rebrightening in the afterglow of the short hard gamma ray burst (SHB) 130603B measured with the Hubble Space Telescope (HST) and an alleged late-time X-ray excess were interpreted as possible evidence of a neutron star merger origin of SHBs. However, the X-ray afterglow that was measured with the Swift XRT and Newton XMM has the canonical behaviour of a synchrotron afterglow produced by a highly relativistic jet. The H-band flux observed with HST 9.41 days after burst is that expected from the measured late-time X-ray afterglow. The late-time flare/rebrightening of the NIR-optical afterglow of SHB 130603B could have been produced also by jet collision with an interstellar density bump. Moreover, SHB plus a kilonova can be produced also by the collapse of a compact star (neutron star, strange star, or quark star) to a more compact object due to cooling, loss of angular momentum, or mass accretion.

scholarly journals X-Ray Determination of the Black-Hole Mass in Cygnus X-1

1998 ◽  
Vol 188 ◽  
pp. 388-389
Author(s):  
A. Kubota ◽  
K. Makishima ◽  
T. Dotani ◽  
H. Inoue ◽  
K. Mitsuda ◽  
...  
Keyword(s):  
Black Hole ◽  
Compact Object ◽  
Optical Observations ◽  
Black Hole Mass ◽  
X Ray ◽  
Upper Limit ◽  
Supergiant Star ◽  
X Ray Binaries ◽  
Two Bodies

About 10 X-ray binaries in our Galaxy and LMC/SMC are considered to contain black hole candidates (BHCs). Among these objects, Cyg X-1 was identified as the first BHC, and it has led BHCs for more than 25 years(Oda 1977, Liang and Nolan 1984). It is a binary system composed of normal blue supergiant star and the X-ray emitting compact object. The orbital kinematics derived from optical observations indicates that the compact object is heavier than ~ 4.8 M⊙ (Herrero 1995), which well exceeds the upper limit mass for a neutron star(Kalogora 1996), where we assume the system consists of only two bodies. This has been the basis for BHC of Cyg X-1.

scholarly journals X-ray variability of the HMXB Cen X-3: evidence for inhomogeneous accretion flows.

2020 ◽  
Author(s):  
G Sanjurjo-Ferrín ◽  
J M Torrejón ◽  
K Postnov ◽  
L Oskinova ◽  
J J Rodes-Roca ◽  
...  
Keyword(s):  
Equivalent Width ◽  
Compact Star ◽  
Timing Analysis ◽  
Roche Lobe ◽  
The Other ◽  
Emission Lines ◽  
High Mass ◽  
X Ray ◽  
Accretion Flows ◽  
Inner Radius

Abstract Cen X-3 is a compact high mass X-ray binary likely powered by Roche lobe overflow. We present a phase-resolved X-ray spectral and timing analysis of two pointed XMM-Newton observations. The first one took place during a normal state of the source, when it has a luminosity LX ∼ 1036 erg s−1. This observation covered orbital phases φ = 0.00 − 0.37, i.e. the egress from the eclipse. The egress lightcurve is highly structured, showing distinctive intervals. We argue that different intervals correspond to the emergence of different emitting structures. The lightcurve analysis enables us to estimate the size of such structures around the compact star, the most conspicuous of which has a size ∼0.3R*, of the order of the Roche lobe radius. During the egress, the equivalent width of Fe emission lines, from highly ionized species, decreases as the X-ray continuum grows. On the other hand, the equivalent width of the Fe Kα line, from near neutral Fe, strengthens. This line is likely formed due to the X-ray illumination of the accretion stream. The second observation was taken when the source was 10 times X-ray brighter and covered the orbital phases φ = 0.36 − 0.80. The X-ray lightcurve in the high state shows dips. These dips are not caused by absorption but can be due to instabilities in the accretion stream. The typical dip duration, of about 1000 s, is much longer than the timescale attributed to the accretion of the clumpy stellar wind of the massive donor star, but is similar to the viscous timescale at the inner radius of the accretion disk.

scholarly journals Models of high-frequency quasi-periodic oscillations and black hole spin estimates in Galactic microquasars

2020 ◽  
Vol 643 ◽  
pp. A31
Author(s):  
A. Kotrlová ◽  
E. Šrámková ◽  
G. Török ◽  
K. Goluchová ◽  
J. Horák ◽  
...  
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Neutron Star ◽  
High Frequency ◽  
Accretion Disc ◽  
The Other ◽  
Periodic Oscillations ◽  
X Ray ◽  
Upper Limit ◽  
Oscillation Modes

We explore the influence of nongeodesic pressure forces present in an accretion disc on the frequencies of its axisymmetric and nonaxisymmetric epicyclic oscillation modes. We discuss its implications for models of high-frequency quasi-periodic oscillations (QPOs), which have been observed in the X-ray flux of accreting black holes (BHs) in the three Galactic microquasars, GRS 1915+105, GRO J1655−40, and XTE J1550−564. We focus on previously considered QPO models that deal with low-azimuthal-number epicyclic modes, |m| ≤ 2, and outline the consequences for the estimations of BH spin, a ∈ [0, 1]. For four out of six examined models, we find only small, rather insignificant changes compared to the geodesic case. For the other two models, on the other hand, there is a significant increase of the estimated upper limit on the spin. Regarding the falsifiability of the QPO models, we find that one particular model from the examined set is incompatible with the data. If the spectral spin estimates for the microquasars that point to a >  0.65 were fully confirmed, two more QPO models would be ruled out. Moreover, if two very different values of the spin, such as a ≈ 0.65 in GRO J1655−40 and a ≈ 1 in GRS 1915+105, were confirmed, all the models except one would remain unsupported by our results. Finally, we discuss the implications for a model that was recently proposed in the context of neutron star (NS) QPOs as a disc-oscillation-based modification of the relativistic precession model. This model provides overall better fits of the NS data and predicts more realistic values of the NS mass compared to the relativistic precession model. We conclude that it also implies a significantly higher upper limit on the microquasar’s BH spin (a ∼ 0.75 vs. a ∼ 0.55).

scholarly journals Black hole magnetosphere with small-scale flux tubes – II. Stability and dynamics

2019 ◽  
Vol 487 (3) ◽  
pp. 4114-4127 ◽  
Author(s):  
Yajie Yuan ◽  
Anatoly Spitkovsky ◽  
Roger D Blandford ◽  
Dan R Wilkins
Keyword(s):  
Black Hole ◽  
Compact Star ◽  
Dynamical Evolution ◽  
Compact Object ◽  
Accretion Disc ◽  
Small Scale ◽  
X Rays ◽  
Flux Tubes ◽  
X Ray ◽  
Central Object

ABSTRACT In some Seyfert galaxies, the hard X-rays that produce fluorescent emission lines are thought to be generated in a hot corona that is compact and located at only a few gravitational radii above the supermassive black hole. We consider the possibility that this X-ray source may be powered by small-scale magnetic flux tubes attached to the accretion disc near the black hole. We use three-dimensional, time-dependent, special relativistic, force-free simulations in a simplified setting to study the dynamics of such flux tubes as they get continuously twisted by the central compact star/black hole. We find that the dynamical evolution of the flux tubes connecting the central compact object and the accretion disc is strongly influenced by the confinement of the surrounding field. Although differential rotation between the central object and the disc tends to inflate the flux tubes, strong confinement from surrounding field quenches the formation of a jet-like outflow, as the inflated flux tube becomes kink unstable and dissipates most of the extracted rotational energy relatively close to the central object. Such a process may be able to heat up the plasma and produce strong X-ray emission. We estimate the energy dissipation rate and discuss its astrophysical implications.

scholarly journals X-Ray Bursts

1977 ◽  
Vol 4 (1) ◽  
pp. 101-110 ◽  
Author(s):  
George W. Clark
Keyword(s):  
Neutron Star ◽  
Compact Star ◽  
Compact Object ◽  
Gravitational Potential Energy ◽  
X Rays ◽  
High Luminosity ◽  
Emission Pattern ◽  
X Ray ◽  
Accretion Rates ◽  
Nuclear Burning

Most of the variable phenomena of high-luminosity (≳1036erg s−1) stellar X-ray sources can be explained, at least qualitatively, within the general framework of binary accretion models in which thermal X-rays are emitted in the vicinity of a neutron star or blackhole by plasma that has flowed downhill from the surface of a nuclear burning companion and been heated by conversion of its gravitational potential energy. The yield of X-ray energy in this process is so high, exceeding in some cases 0.1c2per unit mass, that X-ray luminosities in excess of 104L⊙can be generated with accretion rates of only ˜10−BM⊙per year. Since the transfer process depends strongly on many parameters that specify the relevant properties of two stars and their interaction, one finds a remarkable variety and range of X-ray phenomena. If the compact object is a magnetized neutron star, rotation will cause its X-ray emission pattern to sweep over a distant observer and thereby produce regular pulsations like those observed with periods in the range from 1 to 103seconds. Orbital motions can cause regular eclipses and absorption dips like those observed with periods in the range from hours to days. Changes in the rate of mass loss by the nuclear burning star or in the transfer efficiency can account for the variations in intrinsic X-ray luminosities that appear as flares, novae and on-off transitions. Irregularities in the flow of plasma near the compact star can also affect the intrinsic luminosity and appear as erratic fluctuations, spikes and shot-noise in the observed intensity.

scholarly journals The Origin of Flaring Activity in AE Aquarii

1995 ◽  
Vol 151 ◽  
pp. 272-275
Author(s):  
Nazar Ikhsanov
Keyword(s):  
Main Sequence ◽  
Compact Star ◽  
Compact Object ◽  
Electromagnetic Spectrum ◽  
Thermal Source ◽  
X Rays ◽  
Mass Ratio ◽  
X Ray ◽  
Γ Rays ◽  
Gas Accretion

AE Aqr is a close non-eclipsing binary system with an orbital period Porb ≈ 9.88 hr, eccentricity of the orbit e = 0.02 (Chincarini & Walker 1981) and a mass ratio q = 1.14 (Reinsch & Beuermann 1994), situated at the distance of ∼ 84 pc (Van Paradijs et al. 1989). The secondary is K3 red dwarf on or close to the main sequence (Bruch 1991). The primary cannot be observed directly. However, the stable photometric oscillations at a period of 33 s (and at half this period) in the optical (Patterson 1979), UV (Eracleous et al. 1994), X-rays (Patterson et al. 1980) and, probably, VHE γ-rays (Meintjes et al. 1992, Bowden et al. 1992) leave no doubt that the primary is a rapidly rotating magnetized compact object. The observed rate of deceleration of the primary rotation is Ṗ = 5.64 × 10−14 ss−1 (De Jager et al. 1994), and its mass is m1sin3i (0.56 ± 0.03) M⊙ (Reinsch & Beuermann 1994). The lack of eclipses allows to put a lower limit to the mass of the primary m1 ≥ 0.62M⊙.AE Aqr emits detectable radiation in all parts of the electromagnetic spectrum. In radio and γ-rays it is a powerful non-thermal source. However, in the optical, UV and X-rays the radiation is likely to be thermal and can be well explained by gas accretion onto a compact star (Patterson 1979, Patterson et al. 1980). The observed impulse profile of the pulsating component (Eracleous et al. 1994) looks similar to that of the accreting X-ray pulsars.

scholarly journals Discovery of thermonuclear Type-I X-ray bursts from the X-ray binary MAXI J1807+132

2020 ◽  
Vol 501 (1) ◽  
pp. 261-268
Author(s):  
A C Albayati ◽  
D Altamirano ◽  
G K Jaisawal ◽  
P Bult ◽  
S Rapisarda ◽  
...  
Keyword(s):  
Neutron Star ◽  
Strong Evidence ◽  
Compact Object ◽  
Type I ◽  
Time Resolved ◽  
X Ray ◽  
Upper Limit ◽  
Low Mass ◽  
Photospheric Radius ◽  
Peak Luminosity

ABSTRACT MAXI J1807+132 is a low-mass X-ray binary (LMXB) first detected in outburst in 2017. Observations during the 2017 outburst did not allow for an unambiguous identification of the nature of the compact object. MAXI J1807+132 that was detected in outburst again in 2019 and was monitored regularly with Neutron Star Interior Composition Explorer(NICER). In this paper, we report on 5 days of observations during which we detected three thermonuclear (Type-I) X-ray bursts, identifying the system as a neutron star LMXB. Time-resolved spectroscopy of the three Type-I bursts revealed typical characteristics expected for these phenomena. All three Type-I bursts show slow rises and long decays, indicative of mixed H/He fuel. We find no strong evidence that any of the Type-I bursts reached the Eddington Luminosity; however, under the assumption that the brightest X-ray burst underwent photospheric radius expansion, we estimate a <12.4 kpc upper limit for the distance. We searched for burst oscillations during the Type-I bursts from MAXI J1807+132 and found none (<10 per cent amplitude upper limit at 95 per cent confidence level). Finally, we found that the brightest Type-I burst shows a ∼1.6 s pause during the rise. This pause is similar to one recently found with NICER in a bright Type-I burst from the accreting millisecond X-ray pulsar SAX J1808.4–3658. The fact that Type-I bursts from both sources can show this type of pause suggests that the origin of the pauses is independent of the composition of the burning fuel, the peak luminosity of the Type-I bursts, or whether the NS is an X-ray pulsar.

QCD — MOTIVATED QUARK STARS IN THE LIGHT OF RECENT ASTROPHYSICAL OBSERVATIONS

2000 ◽  
Vol 14 (19n20) ◽  
pp. 1939-1952
Author(s):  
MIRA DEY ◽  
IGNAZIO BOMBACI ◽  
JISHNU DEY ◽  
SUBHARTHI RAY ◽  
E. P. J. VAN DEN HEUVEL ◽  
...  
Keyword(s):  
Black Hole ◽  
Gamma Ray ◽  
Observational Evidence ◽  
Gamma Ray Bursts ◽  
Compact Objects ◽  
The Other ◽  
Quark Star ◽  
Burst Source ◽  
X Ray ◽  
Quark Stars

Are there quark stars in nature? We review the question in the light of modern astrophysical observations. Quark stars have properties which are very similar to those of neutron stars. For example they are now known to have the same kind of cooling properties. Their masses may also be similar. On the other hand, gamma ray bursts (GRB), the brightest phenomenon observable at present in the sky, could possibly be conversion of normal or neutron matter on the surface of a quark star. The best observational evidence for the existence of quark stars seems to be some compact objects, the X-Ray burst source 4U 1820-30, the X-ray pulsar Her X-1, the star 4U 1728-34 and SAX J-1808.4-3658, this last one being the stablest and fastest rotating hard X-ray pulsar known to date. The mass of at least these four objects is high and their radius is low, placing them close to the black hole line, in the mass–radius (M–R) plot.

scholarly journals Time-Dependent X-Ray Observations of Wolf-Rayet Binaries with 0-Type and with Suspected Compact Companions

1982 ◽  
Vol 99 ◽  
pp. 577-581 ◽  
Author(s):  
A.F.J. Moffat ◽  
C. Firmani ◽  
I.S. McLean ◽  
W. Seggewiss
Keyword(s):  
Stellar Wind ◽  
Compact Star ◽  
Outer Part ◽  
The Other ◽  
Time Dependent ◽  
Variable Component ◽  
X Rays ◽  
X Ray ◽  
Einstein Observatory

Each of four WR binaries has been observed in the 0.1 −5 keV range on four consecutive days for a total of ∼ 104 sec with the IPC on the Einstein Observatory. One of the stars is the well-known WN5 + 06 binary V444 Cyg; the other three have suspected compact companions; all have periods close to four days.Neither HD 197406 (WN7) nor HD 96548 (WN8) was detected; hence Lx (0.5–3.0 keV) ≲ 1032 erg s−1, which is on the low side, even for 0-stars. EZ CMa (WN5) and V444 Cyg are moderately strong, variable X-ray sources with Lx (0.5–3.0 keV) ≃ 1033 erg s−1, kT ≃ 0.5 keV and NH ≃ 1022 cm−2. These values suggest that the X-ray flux arises in the outer part of the wind. The variable component may be produced by collision of two winds.There is no evidence of harder X-rays coming from accretion onto a compact star. Nevertheless, the presence of a collapsar is not excluded at hv ≲ 5 keV, where absorption in the WR wind would likely reduce the X-ray flux to a level which is masked by the flux coming from the hot stellar wind.

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