XTE J1906+090 is a persistent low-luminosity Be X-ray binary, study suggests

Utilizing INTEGRAL and Swift spacecraft, European astronomers have noticed an unidentified X-ray supply referred to as XTE J1906+090. Outcomes of the observational marketing campaign, offered Could 11 on the arXiv preprint server, recommend that this supply belongs to the small and uncommon group of persistent low-luminosity Be X-ray binaries.

X-ray binaries are composed of a traditional star or a white dwarf transferring mass onto a compact neutron star or a black hole. Primarily based on the mass of the companion star, astronomers divide them into low-mass X-ray binaries (LMXB) and high-mass X-ray binaries (HMXB).

Of particular curiosity are Be/X-ray binaries (BeXRBs), a subclass of HMXBs by which the optical star is a dwarf, subgiant or big OBe star. Finding out X-ray outbursts from BeXRBs could possibly be important so as to enhance our understanding of the character of X-ray binaries and their habits.

XTE J1906+090 was first detected in 1996 with the Rossi X-ray Timing Explorer (RXTE) spacecraft and initially categorized as an unidentified transient X-ray pulsar with a spin interval of about 89 seconds. Earlier research of XTE J1906+090 have prompt that it could be a BeXRB system at a distance of some 33,000 light years, nonetheless because of the lack of optical and infrared spectroscopy, it was troublesome to verify this.

Now, based mostly on the information from the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) and from the Neil Gehrels Swift Observatory, a workforce of astronomers led by Vito Sguera of the Astrophysics and Area Science Observatory of Bologna, Italy, has supplied additional proof supporting the BeXRB state of affairs for XTE J1906+090.

In response to the examine, XTE J1906+090 has been constantly detected by Swift at a persistent low X-ray luminosity worth of about 10 to 40 decillion erg/s, with restricted variability. Subsequently, the X-ray traits of this supply, along with its lengthy spin interval, strongly resemble these of persistent low-luminosity BeXRBs, that are a small and uncommon subgroup of strange BeXRBs.

“Such properties recommend that the compact object orbits the donor Be star in a large (orbital periods longer than ∼ 30 days) and practically round (e<0.2) orbit, not often or by no means crossing the decretion disk star and repeatedly accreting materials from the decrease density outer areas of the stellar wind,” the researchers defined.

The observations additionally detected 4 X-ray outbursts of XTE J1906+090 characterised by an identical X-ray luminosity of about 1,000 decillion erg/s. The astronomers famous that comparable sporadic variability has been already noticed in all of the BeXRBs that are historically thought of as persistent sources.

Furthermore, the researchers discovered that the utmost to minimal luminosity ratio of XTE J1906+090 is totally in line with that noticed in a lot of the persistent BeXRBs. Nevertheless, they added that a lot deeper X-ray spectral investigation of this supply is required so as to draw remaining conclusions relating to its nature.

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