Using the INTEGRAL and Swift spacecraft, European astronomers have observed an unknown X-ray source known as XTE J1906+090. Results of the observation campaign, presented May 11 on arXiv Prepress server, indicates that this source belongs to a small and rare group of continuous low brightness Be X-ray diodes.
X-ray binaries formed by a normal star or white dwarf transferring mass to a compact neutron star or black hole. Based on the companion star’s mass, astronomers divide it into low-mass X-ray binaries (LMXB) and high-mass X-ray binaries (HMXB).
Of particular interest are Be/X-ray binaries (BeXRBs), a subclass of HMXBs in which the optical star is an OBe dwarf, supergiant or supergiant star. Studying X-ray bursts from BeXRBs may be necessary to improve our understanding of the nature and behavior of X-ray binaries.
XTE J1906+090 was first discovered in 1996 using the Rossi X-ray Timing Explorer (RXTE) spacecraft and was initially classified as an unknown X-ray transiting pulsar with a rotation period of about 89 seconds. Previous studies of XTE J1906+090 suggested that it may be a BeXRB system at a distance of about 33,000 light yearsbut because of the lack of visual and infrared spectrometerIt was hard to confirm.
Now, based on data from the International Gamma-Ray Astrophysics Laboratory (INTEGRAL) and from the Neil Gehrels Swift Observatory, a team of astronomers led by Vito Sguera of the Astrophysical and Space Sciences Observatory in Bologna, Italy, has presented more evidence supporting the BeXRB scenario for XTE J1906+. 090.
According to the study, XTE J1906+090 was consistently detected by Swift at a constant low X-ray brightness value of about 10 to 40 dErg/s, with limited contrast. Therefore, the X-ray properties of this source, together with its long rotation period, are very similar to those of continuous low-light BeXRBs, which are a small and rare subset of exotic BeXRBs.
“These properties indicate that the compact object orbiting the donor can be a star of a wide range (tropical periods The researchers explained.
The observations also revealed four X-ray bursts of XTE J1906+090 featuring an X-ray-like illumination of about 1,000 dv erg/s. The astronomers note that a similar intermittent asymmetry has already been observed in all BeXRBs that are traditionally considered stationary sources.
Moreover, the researchers found that the maximum-to-minimum brightness ratio of XTE J1906+090 is fully consistent with that observed for most stable BeXRBs. However, they added that a much deeper X-ray spectral investigation of this source is needed in order to draw definitive conclusions regarding its nature.
V. Sguera et al, XTE J1906+090: Continuous Low Brightness Be X-ray Binary, arXiv (2023). DOI: 10.48550/arxiv.2305.06689
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