NGC 7793P13: An absorbed line at 1.3 keV, calculated from pulsed spectra of XMM/Newton/pn and NICER/XTI. Credit: Lin et al., 2021.
Astronomers used data from several spacecraft to study NGC 7793P13, an ultra-luminous and X-ray pulser. This new study, which was published on November 1, 2009, on the arXiv preprint server, provides crucial information about timing and spectral characteristics of this source.
Ultra-luminous sources of Xray radiation (ULXs), which are point sources in the sky, emit more radiation in Xrays than any one million suns at all wavelengths. They are less bright than active galactic nuclei but are still more luminous than any other known stellar process.
Astronomers believe most ULXs, because of their brightness, are black holes. Recent observations have shown that some ULXs exhibit coherent pulsations. These sources are known as ultra-luminous Xray pulsars or ULXPs. They are neutron stars that are typically smaller than black holes. It is difficult to find ULPs, so it is important for researchers who are interested in exploring the universe using X-rays.
NGC 7793P13, also known as XMMU X235751.1-323725, is a ULX that can be found in the spiral galaxy NGC 7793 within the Sculptor constellation. It is approximately 12.7 million lightyears from Earth. It hosts a 0.42-second pulser, which is a binary star hosting an accreting neutron and a massive companion of less than 15 solar mass. Previous observations have shown this source to host a 1.4-solar mass pulsar. The orbital period of this system is likely to be approximately 65 days. However, optical modulation may also be due to a super-orbital time sometimes observed in ULXs.
NGC 7793P13 is an important discovery for astronomers. It demonstrated that super-Eddington accretion occurs in at least one ULX where the accretor has a mass less than 15 solar masses. Lupin Chun Che Lin, of the Ulsan National Institute of Science and Technology, Korea, led a team of researchers who took a closer look at the ULP. They wanted to learn more about the modulation of the ULP and how the pulsar properties change as a function of flux and time.
Lin and his team studied NGC 7793P13's evolution from the bright to the dim state, with an order-of-magnitude in flux change. They used Swift, NuSTAR, and XMM–Newton spacecraft data as well as the NICER instrument aboard the International Space Station for this purpose.
Astronomers statistically compared pulsed structures and identified at least three changes in the distribution. The flux evolution seems to be correlated with the change in the pulsed structure.
These results indicate that there is no direct relationship between the orbital phase and the pulsed fraction change. The measured pulsed fraction change of NGC7793 P13 in 3-10keV can be broken down into two groups.
Astronomers also noted that NGC7793 P13 remained in the ultraluminous hard state throughout their observations. The pulsed emission becomes less intense when the source enters a faint stage towards the end of 2019.
More information: Lupin Chhe Lin et. al., Investigation of the timing of an Ultra-luminous Ultra-ray Pulsar NGC7793 P13. arXiv.2111.00769v2 (astro-ph.HE], Lupin Chun-Che Lin, et al. Investigation of the timing of an Ultra-luminous-X-ray Pulsar NGC7793 P13. arXiv:2111.00769v2 [astro-ph.HE], arxiv.org/abs/2111.00769
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