POSSIBLE SIGNATURES OF THE CONVERSION OF A NEUTRON STAR TO A STRANGE STAR

1994 ◽  
Vol 03 (03) ◽  
pp. 653-664
Author(s):  
O.G. BENVENUTO ◽  
M.I. KRIVORUCHENKO ◽  
B.V. MARTEMYANOV
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
High Recurrence Rate ◽  
Massive Quark ◽  
Pulsar Emission ◽  
Strange Stars ◽  
X Ray ◽  
Supernova Explosions ◽  
Low Mass ◽  
Step Mechanism

The problem of the identification of strange stars is discussed. We suggest some characteristic signatures for the search for strange stars: a two-step mechanism for supernova explosions accompanied by the occurrence of strange stars and two neutrino bursts; microstructure analysis in the profile of pulsar emission; and unusual stability in the rotation of millisecond pulsars due to the absence of internal crust in strange stars. The cooling of strange stars is faster than the cooling of ordinary neutron stars, so low surface temperature of pulsars can indicate the existence of massive quark cores in observed pulsars. Low mass strange stars as bursters and/or X-ray sources have peculiar observable features: low luminosity and (for bursters) high recurrence rate, large duration of bursts, low ratio of energy emitted between two bursts and energy emitted during the burst.

scholarly journals Crust cooling of the neutron star in Aql X-1: different depth and magnitude of shallow heating during similar accretion outbursts

2019 ◽  
Vol 488 (4) ◽  
pp. 4477-4486 ◽  
Author(s):  
N Degenaar ◽  
L S Ootes ◽  
D Page ◽  
R Wijnands ◽  
A S Parikh ◽  
...  
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
Thermal Evolution ◽  
Unknown Origin ◽  
X Ray ◽  
Low Mass ◽  
Different Sources

ABSTRACT The structure and composition of the crust of neutron stars plays an important role in their thermal and magnetic evolution, hence in setting their observational properties. One way to study the properties of the crust of a neutron star, is to measure how it cools after it has been heated during an accretion outburst in a low-mass X-ray binary (LMXB). Such studies have shown that there is a tantalizing source of heat, of currently unknown origin, that is located in the outer layers of the crust and has a strength that varies between different sources and different outbursts. With the aim of understanding the mechanism behind this ‘shallow heating’, we present Chandra and Swift observations of the neutron star LMXB Aql X-1, obtained after its bright 2016 outburst. We find that the neutron star temperature was initially much lower, and started to decrease at much later time, than observed after the 2013 outburst of the source, despite the fact that the properties of the two outbursts were very similar. Comparing our data to thermal evolution simulations, we infer that the depth and magnitude of shallow heating must have been much larger during the 2016 outburst than during the 2013 one. This implies that basic neutron star parameters that remain unchanged between outbursts do not play a strong role in shallow heating. Furthermore, it suggests that outbursts with a similar accretion morphology can give rise to very different shallow heating. We also discuss alternative explanations for the observed difference in quiescent evolution after the 2016 outburst.

scholarly journals R-mode constraints from neutron star equation of state

2019 ◽  
Vol 23 ◽  
pp. 100
Author(s):  
Ch. C. Moustakidis ◽  
M. C. Papazoglou
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Neutron Stars ◽  
Gravitational Radiation ◽  
Mode Instability ◽  
X Ray ◽  
Long Time ◽  
Low Mass ◽  
X Ray Binaries

The gravitational radiation has been proposed a long time before, as an explana- tion for the observed relatively low spin frequencies of young neutron stars and of accreting neutron stars in low-mass X-ray binaries as well. In the present work we studied the effects of the neutron star equation of state on the r-mode instability window of rotating neutron stars.

scholarly journals Some Constraints on Neutron Star Properties from Gamma Ray Burster Observations

1987 ◽  
Vol 125 ◽  
pp. 489-500
Author(s):  
K. Hurley
Keyword(s):  
Neutron Star ◽  
Low Temperature ◽  
Neutron Stars ◽  
Binary Systems ◽  
Main Sequence ◽  
Gamma Ray ◽  
Cooling Curves ◽  
X Ray ◽  
Upper Limits ◽  
Low Mass

The results of recent soft X-ray and optical searches for quiescent gamma ray burster counterparts are used to constrain the properties of the neutron stars responsible for bursters. Ages are restricted to the range 2×105 y and above based on temperature upper limits and theoretical cooling curves, or 107 y and above if bursters have evolved from pulsars. Velocities are greater than 20 km/s if the neutron stars are unmagnetized. Practically no main sequence star could have escaped detection in the optical/IR searches, so if the neutron stars are in binary systems, the companion is most likely a degenerate, low mass, low temperature object.

scholarly journals Nuclear equation of state effects on the r-mode instability of neutron stars

2012 ◽  
Vol 20 ◽  
pp. 27
Author(s):  
Ch. C. Moustakidis
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Neutron Stars ◽  
Nuclear Symmetry Energy ◽  
Mode Instability ◽  
X Ray ◽  
Nuclear Equation Of State ◽  
Theoretical Predictions ◽  
Low Mass ◽  
X Ray Binaries

We study the effect of nuclear equation of state on the r-mode instability of a rotating neutron star. We consider the case where the crust of the neutron star is perfectly rigid and we employ the related theory. The effects of the density dependence of the nuclear symmetry energy on r-mode instability properties are presented and analyzed. A comparison of theoretical predictions with observed neutron stars in low-mass X-ray binaries is also performed and analyzed.

scholarly journals Enhanced optical activity 12 d before X-ray activity, and a 4 d X-ray delay during outburst rise, in a low-mass X-ray binary

2020 ◽  
Vol 498 (3) ◽  
pp. 3429-3439 ◽  
Author(s):  
A J Goodwin ◽  
D M Russell ◽  
D K Galloway ◽  
M C Baglio ◽  
A S Parikh ◽  
...  
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
Optical Activity ◽  
Accretion Disc ◽  
Observational Evidence ◽  
X Ray ◽  
Viscous Instability ◽  
Low Mass ◽  
Space Observatories ◽  
Multiwavelength Observations

ABSTRACT X-ray transients, such as accreting neutron stars, periodically undergo outbursts, thought to be caused by a thermal-viscous instability in the accretion disc. Usually outbursts of accreting neutron stars are identified when the accretion disc has undergone an instability, and the persistent X-ray flux has risen to a threshold detectable by all sky monitors on X-ray space observatories. Here, we present the earliest known combined optical, UV, and X-ray monitoring observations of the outburst onset of an accreting neutron star low-mass X-ray binary (LMXB) system. We observed a significant, continuing increase in the optical i′-band magnitude starting on July 25, 12 d before the first X-ray detection with Swift/XRT and NICER (August 6), during the onset of the 2019 outburst of SAX J1808.4−3658. We also observed a 4 d optical to X-ray rise delay, and a 2 d UV to X-ray delay, at the onset of the outburst. We present the multiwavelength observations that were obtained, discussing the theory of outbursts in X-ray transients, including the disc instability model, and the implications of the delay. This work is an important confirmation of the delay in optical to X-ray emission during the onset of outbursts in LMXBs, which has only previously been measured with less sensitive all sky monitors. We find observational evidence that the outburst is triggered by ionization of hydrogen in the disc.

Quiescent luminosities of accreting neutron stars-possibility of neutrino losses due to strong pion condensations

2018 ◽  
Vol 27 (08) ◽  
pp. 1850067 ◽  
Author(s):  
Yasuhide Matsuo ◽  
HeLei Liu ◽  
Masa-aki Hashimoto ◽  
Tsuneo Noda
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
Accretion Rate ◽  
Cooling Process ◽  
X Ray ◽  
Mass Accretion Rate ◽  
Star Models ◽  
Low Mass ◽  
X Ray Binaries

We construct the quiescent neutron star models in the evolutionary calculations. The X-ray luminosities have been derived in terms of the time-averaged mass accretion rate for various neutron star masses and surface compositions. We compare the quiescent luminosities observed from X-ray transients in low mass X-ray binaries, where the stellar evolutionary calculations of accreting neutron stars include neutrino cooling due to strong pion condensations. Our results based on the evolutionary calculations suggest that stronger cooling process would be necessary to be consistent with observations.

scholarly journals Search for intermittent X-ray pulsations from neutron stars in low-mass X-ray binaries

2021 ◽  
Vol 38 ◽  
Author(s):  
Yunus Emre Bahar ◽  
Manoneeta Chakraborty ◽  
Ersin Göğüş
Keyword(s):  
Neutron Stars ◽  
Orbital Period ◽  
Oscillation Frequency ◽  
Orbital Motion ◽  
X Rays ◽  
X Ray ◽  
Second Stage ◽  
Corrected Data ◽  
Low Mass ◽  
X Ray Binaries

Abstract We present the results of our extensive binary orbital motion corrected pulsation search for 13 low-mass X-ray binaries. These selected sources exhibit burst oscillations in X-rays with frequencies ranging from 45 to 1 122 Hz and have a binary orbital period varying from 2.1 to 18.9 h. We first determined episodes that contain weak pulsations around the burst oscillation frequency by searching all archival Rossi X-ray Timing Explorer data of these sources. Then, we applied Doppler corrections to these pulsation episodes to discard the smearing effect of the binary orbital motion and searched for recovered pulsations at the second stage. Here we report 75 pulsation episodes that contain weak but coherent pulsations around the burst oscillation frequency. Furthermore, we report eight new episodes that show relatively strong pulsations in the binary orbital motion corrected data.

scholarly journals The study of multipeaked type-I X-ray bursts in the neutron star low-mass X-ray binary 4U 1636 − 536 with RXTE

2020 ◽  
Vol 501 (1) ◽  
pp. 168-178
Author(s):  
Chen Li ◽  
Guobao Zhang ◽  
Mariano Méndez ◽  
Jiancheng Wang ◽  
Ming Lyu
Keyword(s):  
Neutron Star ◽  
Flux Ratio ◽  
Light Curves ◽  
Type I ◽  
X Ray ◽  
Soft State ◽  
Peak Flux ◽  
Low Mass ◽  
Two Peaks ◽  
Second Peak

ABSTRACT We have found and analysed 16 multipeaked type-I bursts from the neutron-star low-mass X-ray binary 4U 1636 − 53 with the Rossi X-ray Timing Explorer (RXTE). One of the bursts is a rare quadruple-peaked burst that was not previously reported. All 16 bursts show a multipeaked structure not only in the X-ray light curves but also in the bolometric light curves. Most of the multipeaked bursts appear in observations during the transition from the hard to the soft state in the colour–colour diagram. We find an anticorrelation between the second peak flux and the separation time between two peaks. We also find that in the double-peaked bursts the peak-flux ratio and the temperature of the thermal component in the pre-burst spectra are correlated. This indicates that the double-peaked structure in the light curve of the bursts may be affected by enhanced accretion rate in the disc, or increased temperature of the neutron star.

scholarly journals A Machine Learning Approach For Classifying Low-mass X-ray Binaries Based On Their Compact Object Nature

2020 ◽  
Author(s):  
R Pattnaik ◽  
K Sharma ◽  
K Alabarta ◽  
D Altamirano ◽  
M Chakraborty ◽  
...  
Keyword(s):  
Machine Learning ◽  
Black Hole ◽  
Neutron Star ◽  
Binary Systems ◽  
Compact Object ◽  
X Ray ◽  
Average Accuracy ◽  
Machine Learning Approach ◽  
Low Mass ◽  
X Ray Binaries

Abstract Low Mass X-ray binaries (LMXBs) are binary systems where one of the components is either a black hole or a neutron star and the other is a less massive star. It is challenging to unambiguously determine whether a LMXB hosts a black hole or a neutron star. In the last few decades, multiple observational works have tried, with different levels of success, to address this problem. In this paper, we explore the use of machine learning to tackle this observational challenge. We train a random forest classifier to identify the type of compact object using the energy spectrum in the energy range 5-25 keV obtained from the Rossi X-ray Timing Explorer archive. We report an average accuracy of 87±13% in classifying the spectra of LMXB sources. We further use the trained model for predicting the classes for LMXB systems with unknown or ambiguous classification. With the ever-increasing volume of astronomical data in the X-ray domain from present and upcoming missions (e.g., SWIFT, XMM-Newton, XARM, ATHENA, NICER), such methods can be extremely useful for faster and robust classification of X-ray sources and can also be deployed as part of the data reduction pipeline.

Sign in / Sign up

Export Citation Format

Share Document