Twenty-year light curve of NGC 2403 XMM4 obtained from observations of Swift (blue boxes), Chandra (magenta diamonds), XMM-Newton (green circles) and NuSTAR (red triangles). The observed luminosity is reported in the energy band 0.3 to 10 keV, with the Chandra and NuSTAR values extrapolated to this band from their best-fit parameters. Credit: Luangtip and Roberts, 2023.
By analyzing data from various space telescopes, astronomers have carried out a detailed study of an ultraluminous X-ray source known as NGC 2403 XMM4. Results of the study, published on January 5 in the Monthly Notices of the Royal Astronomical Society journal, indicate that this source is a neutron star accumulating at super-Eddington rates.
Ultraluminous X-ray (ULX) sources are point sources in the sky with typical X-ray luminosities at a level of 1.0 duodecillion erg/s. They are less luminous than active galactic nuclei (AGN), but more consistently luminous than any known stellar process. Although numerous studies on ULXs have been conducted, the fundamental nature of these sources still remains unresolved.
NGC 2403 XMM4 is a ULX located in the spiral galaxy NGC 2403 located approximately 13.7 million light years away. Previous studies have shown it to be a low-luminosity ULX and suggested it may be an intermediate-mass sub-Eddington black hole.
To shed more light on the properties of NGC 2403 XMM4 that could reveal its true nature, Wasutep Luangtip of Srinakharinwirot University in Bangkok, Thailand, and Timothy P. Roberts of Durham University in Durham, Kingdom -Uni, combed through the archives. Radiological data. They analyzed 20 years of observational data from the XMM-Newton, Chandra, Swift and NuSTAR space telescopes.
“Given that NGC 2403 has been observed several times by various observatories since the beginning of this century, including several observations during the current decade, there is now sufficient archival data to give us the opportunity to “analyze this source in detail,” the researchers said. explain.
By studying the 20-year light curve of NGC 2403 XMM4, Luangtip and Roberts found that most of the time its X-ray luminosity is less than 1.0 duodecillion erg/s. However, because NGC 2403 XMM4 is above the brightness threshold for ultraluminous X-ray sources, its spectral behavior appears markedly similar to that of ULX.
According to the paper’s authors, these results indicate that NGC 2403 XMM4 is accumulating at a super-Eddington rate. This hypothesis is also supported by broadband spectroscopic data showing the presence of a steep high-energy tail.
The time-averaged X-ray luminosity of NGC 2403 XMM4 was estimated to be around 0.5 duodecillion erg/s and the source emission was found to be isotropic. Based on this, astronomers estimate that the object has a mass of less than 3.8 solar masses, suggesting that it is a neutron star, with an accretion of 1.3 to 3, Twice that of Eddington.
In summarizing the results, the astronomers noted that although it does not reach the ULX threshold, NGC 2403 XMM4 exhibits many behaviors and features consistent with a super-Eddington accretion.
Overall, the data collected indicates the presence of a neutron star which is an accumulating object in this system. This is therefore the third super-Eddington neutron star detected in NGC 2403.
More information:
Wasutep Luangtip et al, NGC 2403 XMM4: evidence of a super-Eddington neutron star with a possible transient pulsation, Monthly Notices of the Royal Astronomical Society (2024). DOI: 10.1093/mnras/stae023. On arXiv: DOI: 10.48550/arxiv.2401.02177
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Quote: NGC 2403 XMM4 is a super-Eddington neutron star, according to a study (January 11, 2024) retrieved January 11, 2024 from
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