Ultraluminous X-ray source in the galaxy NGC 55

[Astronuc]

https://phys.org/news/2021-11-ultraluminous-x-ray-source-galaxy-ngc.html

Using data from NASA's Swift and NuSTAR spacecraft , as well as from ESA's XMM-Newton satellite, Indian astronomers have investigated spectral and temporal properties of an ultraluminous X-ray source (ULX) in the spiral galaxy NGC 55. The study, published November 12 on arXiv.org, sheds more light on the nature of this source.

At a distance of about 5.8 million light years away, NGC 55, also known as the Whale Galaxy, is a magellanic-type, barred spiral galaxy with a mass of around 20 billion solar masses and size of approximately 50,000 light years. NGC 55 is a member of the Sculptor group, where the galaxies are few in number and well separated in space. Due to this NGC 55 is not rich in star-forming regions as it is not interacting with any nearby companion.

NGC 55 hosts a bright, non-nuclear ultraluminous X-ray source, designated NGC 55 ULX1, with a peak X-ray luminosity of about 2 duodecillion (10³⁹) erg/s.

Spectral and Temporal Properties of Ultra-luminous X-ray Source NGC 55 ULX1
https://arxiv.org/abs/2111.06637

The inferred high luminosity is considered as strong evidence for the existence of intermediate-mass black hole (IMBH) in ULXs with a proposed mass range of 10²−10⁵M⊙ (Colbert & Mushotzky 1999;Coleman Miller & Colbert 2004).

Same paper - https://academic.oup.com/mnras/advance-article-abstract/doi/10.1093/mnras/stab3307/6428406

From 2015 - Spectral variability in Swift and Chandra observations of the ultraluminous source NGC 55 ULX1
https://academic.oup.com/mnras/article/448/2/1153/1050404

Abstract: NGC 55 ULX1 is a bright Ultraluminous X-ray source located 1.78 Mpc away. We analysed a sample of 20 Swift observations, taken between 2013 April and August, and two Chandra observations taken in 2001 September and 2004 June. We found only marginal hints of a limited number of dips in the light curve, previously reported to occur in this source, although the uncertainties due to the low counting statistics of the data are large. The Chandra and Swift spectra showed clearly spectral variability which resembles those observed in other ULXs.

 

[lippyka]

The spectra were well fitted with a power-law with exponential cutoff model, with a photon index of between 1.7 and 2.6 and a cutoff energy between 2.5 and 4.5 keV. The cut-off energies are generally higher than previously observed in other ULXs and this source appears to be among the most extreme objects in terms of spectral variability.