Observations are examining an X-ray from Vela X-1

Using the X-ray Imaging Polarimetry Explorer (IXPE), an international team of astronomers has made polar X-ray observations of an accretion X-ray pulsar known as Vela X-1. Results of the surveillance campaign presented on 3 March arXiv Prepress server, providing important insights into the properties of X-ray radiation from this pulsar.

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 (LMXBs) and high-mass X-ray binaries (HMXBs).

At a distance of 6500 light years Off the ground, the Vela X-1 is quite loudMass An X-ray binary system (HMXB), formed by an accretion neutron star and giant donor HD 77581 in a tight 9-day orbit. HD 77581 releases strong stellar winds that cause a bow shock as it interacts with the interstellar medium. This makes the Vela X-1 one of only two HMXBs known to suffer bow shock.

Recently, a group of astronomers, led by Sofia Vorsblom of the University of Turku in Finland, investigated Vela X-1 using IXPE, hoping to shed more light on the nature of this pulsar.

“In this paper, we present the first results of X-ray polarimetry observations of Vela X-1 by IXPE conducted on two separate occasions during the year 2022,” the researchers wrote.

First of all, the team measured the spin period of the Vela X-1 using phase conduction technology, which was found to be about 283.4 seconds. The pulse part in the energy range 2–8 keV was determined to be 53.3% for the first note and 48.1% for the second note.

Subsequently, it was found that in the entire IXPE energy range (2–8 keV), the mean polarization degree (PD) and polarization angle (PA) are at a level of about 3.9% and −1.5°, respectively, for the first observation. For the second observation, the mean PD and PA were measured to be 3.7% and 48.9°, respectively. Moreover, polarization spectroscopy of the averaged phase data for Vela X-1 found a PD of 2.3% and a PA of 47.3°.

The astronomers concluded that this lower degree of polarization is consistent with results obtained for other known X-ray stars. They hypothesize that the obtained value of PD may be due to the inverse temperature structure of the neutron star’s atmosphere. However, they added that the lower PD may also be a consequence of the strong differences in PD and PA with energy, or strong differences in PA with the phase of the pulsar.

The study authors note that more studies on Vela X-1 are needed in order to draw definitive conclusions.

“A full and detailed analysis of the complex energy dependence of the polarization properties of Vela X-1 is beyond the scope of this paper and is subject to more extensive future work,” the scientists wrote.

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