Discovery of a new X-ray pulsar

Using the ART-XC and eROSITA telescopes aboard the Spectrum Roentgen Gamma (SRG) mission, an international team of astronomers have detected a new pulsar. The newly found object, designated SRGA J204318.2 + 443815, turns out to be a long-lived weak x-ray pulsar in a distant binary system. The discovery is reported in an article published July 12 on arXiv.org.

X-ray pulsars (also called accretion-powered pulsars) are sources displaying strict periodic variations in x-ray intensity, consisting of a magnetized neutron star orbiting with a normal stellar companion. In these binary systems, the X-ray emission is fueled by the release of gravitational potential energy when the material is accreted from a massive companion. X-ray pulsars are among the brightest objects in the X-ray sky.

Now, a team of astronomers led by Alexander Lutovinov from the Institute for Space Research (IKI) of the Russian Academy of Sciences, reports the discovery of another X-ray pulsar. Using the ART- telescope XC, they discovered a relatively bright X-ray source in November 2020, about 26,000 light years from Earth. Follow-up observations from this source, which received the designation SRGA J204318.2 + 443815 (or SRGe J204319.0 + 443820) with space telescopes like XMM-Newton, NICER and NuSTAR allowed the team to confirm the nature pulsar from this source and reveal its properties.

“In this article, we reported the discovery of a novel X-ray pulsar, SRGA J204318.2 + 443815 / SRGe J204319.0 + 443820. The source was found by both instruments, ART-XC and eROSITA, at edge of SRG during the second and third readings all over the sky, “the astronomers wrote in the study.

Observations revealed pulses of SRGA J204318.2 + 443815 with a period of approximately 742 seconds. The source has bolometric luminosity at a level of 400 decillion erg / s, an exponentially cut off hard X-ray spectrum; a number of emission lines have been detected in the optical and infrared spectra of its companion star.

These results suggest that SRGA J204318.2 + 443815 is a novel low-light persistent x-ray pulsar in a distant binary system. The pulsar’s companion is a Be star, most likely of the spectral type B0-B2e. Astronomers speculate that SRGA J204318.2 + 443815 may be a new member of the subclass of persistent low-light Be X-ray binary systems (BeXRB) presumably accreting from the “cold” accretion disk.

Summarizing the results, the researchers noted that the discovery of SRGA J204318.2 + 443815 demonstrates how useful the SRG spacecraft is when it comes to searching for weak sources of such x-rays.

“Considering that the sensitivity of SRG telescopes exceeds all previous and currently active surveying instruments, the SRG Observatory allows us to unveil the hidden population of faint persistent objects, including the population of X-ray pulsars. rotation in BeXRB.of SRG to achieve this goal is demonstrated by this article as well as by the discovery of several other new XRP in the Magellanic Clouds and our Galaxy (see for example, Haberl et al. 2020; Maitra et al. al. 2020; Doroshenko et al. 2021) “, concluded the authors of the article.

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