skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Impacts of the Direct Urca and Superfluidity inside a Neutron Star on Type I X-Ray Bursts and X-Ray Superbursts
Abstract We investigate the impacts of the neutrino cooling mechanism inside the neutron star (NS) core on the light curves of type I X-ray bursts and X-ray superbursts. From several observations of NS thermal evolution, physical processes of fast neutrino cooling, such as the direct Urca (DU) process, are indicated. They significantly decrease the surface temperature of NSs, though the cooling effect could be suppressed by nucleon superfluidity. In the present study, focusing on the DU process and nucleon superfluidity, we investigate the effects of NS cooling on the X-ray bursts using a general-relativistic stellar-evolution code. We find that the DU process leads to a longer recurrence time and higher peak luminosity, which could be obstructed by the neutrons’ superfluidity. We also apply our burst models to the comparison with Clocked burster GS 1826−24, and to the recurrence time of a superburst triggered by carbon ignition. These effects are significant within a certain range of binary parameters and the uncertainty of the NS equation of state.  more » « less
Award ID(s):
1927130
PAR ID:
10464897
Author(s) / Creator(s):
; ; ; ; ; ;
Date Published:
Journal Name:
The Astrophysical Journal
Volume:
937
Issue:
2
ISSN:
0004-637X
Page Range / eLocation ID:
124
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; (, The Astrophysical Journal)
    Abstract Type I X-ray bursts are rapidly brightening phenomena triggered by thermonuclear burning on the accreting layers of a neutron star (NS). The light curves represent the physical properties of NSs and the nuclear reactions on the proton-rich nuclei. The numerical treatments of the accreting NS and physics of the NS interior are not established, which shows uncertainty in modeling for observed X-ray light curves. In this study, we investigate theoretical X-ray burst models compared with burst light curves with GS 1826-24 observations. We focus on the impacts of the NS mass and radius and base heating on the NS surface using the MESA code. We find a monotonic correlation between the NS mass and the parameters of the light curve. The higher the mass, the longer the recurrence time and the greater the peak luminosity. While the larger the radius, the longer the recurrence time, the peak luminosity remains nearly constant. In the case of increasing base heating, both the recurrence time and peak luminosity decrease. We also examine the above results with a different numerical code, HERES , based on general relativity and consider the central NS. We find that the burst rate, energy, and strength are almost the same in two X-ray burst codes by adjusting the base heat parameter in MESA (the relative errors ≲5%), while the duration and rise times are significantly different between (the relative error is possibly ∼50%). The peak luminosity and the e-folding time change irregularly between two codes for different accretion rates. 
    more » « less
  2. ; ; ; ; ; (, The Astrophysical Journal)
    Abstract Type I X-ray bursts are rapid-brightening transient phenomena on the surfaces of accreting neutron stars (NSs). Some X-ray bursts, called clocked bursters, exhibit regular behavior with similar light-curve profiles in their burst sequences. The periodic nature of clocked bursters has the advantage of constraining X-ray binary parameters and physics inside the NS. In the present study, we compute numerical models, based on different equations of state and NS masses, which are compared with the observations of a recently identified clocked burster, 1RXS J180408.9−342058. We find that the relation between the accretion rate and the recurrence time is highly sensitive to the NS mass and radius. We determine, in particular, that 1RXS J180408.9−342058 appears to possess a mass less than 1.7M⊙and favors a stiffer nuclear equation of state (with an NS radius ≳12.7 km). Consequently, the observations of this new clocked burster may provide additional constraints for probing the structure of NSs. 
    more » « less
  3. ; ; ; ; ; ; ; ; ; ; et al (, Nature Astronomy)
    Galactic nuclei showing recurrent phases of activity and quiescence have recently been discovered. Some have recurrence times as short as a few hours to a day and are known as quasi-periodic X-ray eruption (QPE) sources. Others have recurrence times as long as hundreds to a thousand days and are called repeating nuclear transients. Here we present a multiwavelength overview of Swift J023017.0+283603 (hereafter Swift J0230+28), a source from which repeating and quasi-periodic X-ray flares are emitted from the nucleus of a previously unremarkable galaxy at ∼165 Mpc. It has a recurrence time of approximately 22 days, an intermediary timescale between known repeating nuclear transients and QPE sources. The source also shows transient radio emission, likely associated with the X-ray emission. Such recurrent soft X-ray eruptions, with no accompanying ultraviolet or optical emission, are strikingly similar to QPE sources. However, in addition to having a recurrence time that is ∼25 times longer than the longest-known QPE source, Swift J0230+28’s eruptions exhibit somewhat distinct shapes and temperature evolution compared to the known QPE sources. Scenarios involving extreme mass ratio inspirals are favoured over disk instability models. The source reveals an unexplored timescale for repeating extragalactic transients and highlights the need for a wide-field, time-domain X-ray mission to explore the parameter space of recurring X-ray transients. 
    more » « less
  4. ; ; ; ; ; ; ; ; ; ; et al (, Nature)
    Abstract Quasi-periodic eruptions (QPEs) are luminous bursts of soft X-rays from the nuclei of galaxies, repeating on timescales of hours to weeks1–5. The mechanism behind these rare systems is uncertain, but most theories involve accretion disks around supermassive black holes (SMBHs) undergoing instabilities6–8or interacting with a stellar object in a close orbit9–11. It has been suggested that this disk could be created when the SMBH disrupts a passing star8,11, implying that many QPEs should be preceded by observable tidal disruption events (TDEs). Two known QPE sources show long-term decays in quiescent luminosity consistent with TDEs4,12and two observed TDEs have exhibited X-ray flares consistent with individual eruptions13,14. TDEs and QPEs also occur preferentially in similar galaxies15. However, no confirmed repeating QPEs have been associated with a spectroscopically confirmed TDE or an optical TDE observed at peak brightness. Here we report the detection of nine X-ray QPEs with a mean recurrence time of approximately 48 h from AT2019qiz, a nearby and extensively studied optically selected TDE16. We detect and model the X-ray, ultraviolet (UV) and optical emission from the accretion disk and show that an orbiting body colliding with this disk provides a plausible explanation for the QPEs. 
    more » « less
  5. ; ; ; ; ; ; ; ; ; ; et al (, The Astrophysical Journal Letters)
    Abstract We present the first comprehensive search for high-energy neutrino emission from high- and low-mass X-ray binaries conducted by IceCube. Galactic X-ray binaries are long-standing candidates for the source of Galactic hadronic cosmic rays and neutrinos. The compact object in these systems can be the site of cosmic-ray acceleration, and neutrinos can be produced by interactions of cosmic rays with radiation or gas, in the jet of a microquasar, in the stellar wind, or in the atmosphere of the companion star. We study X-ray binaries using 7.5 yr of IceCube data with three separate analyses. In the first, we search for periodic neutrino emission from 55 binaries in the Northern Sky with known orbital periods. In the second, the X-ray light curves of 102 binaries across the entire sky are used as templates to search for time-dependent neutrino emission. Finally, we search for time-integrated emission of neutrinos for a list of 4 notable binaries identified as microquasars. In the absence of a significant excess, we place upper limits on the neutrino flux for each hypothesis and compare our results with theoretical predictions for several binaries. In addition, we evaluate the sensitivity of the next generation neutrino telescope at the South Pole, IceCube-Gen2, and demonstrate its power to identify potential neutrino emission from these binary sources in the Galaxy. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email