Study investigates magnetic field of an extremely ultraluminous X-ray pulsar

Utilizing NASA’s Swift spacecraft and ESA’s XMM-Newton satellite, astronomers have noticed NGC 5907 ULX1—essentially the most luminous ultra-luminous X-ray pulsar recognized so far. Outcomes of the observational marketing campaign, printed February 7 on the pre-print server arXiv, shed extra mild on the magnetic discipline of this pulsar.

Extremely-luminous X-ray sources (ULXs) are level sources within the sky which might be so shiny in X-rays that every emits extra radiation than 1 million suns emit in any respect wavelengths. Though they’re much less luminous than active galactic nuclei, they’re extra constantly luminous than any recognized stellar course of.

Astronomers usually imagine that on account of their brightness, most ULXs are black holes. Nevertheless, latest observations have discovered that some ULXs showcase coherent pulsations. These sources, generally known as ultra-luminous X-ray pulsars (ULXPs), are neutron stars usually much less large than black holes. The listing of recognized ULPs remains to be comparatively quick; thus, learning objects of this class is important for researchers exploring the universe in X-rays.

Reaching peak luminosity of about 100 duodecillion erg/s, NGC 5907 ULX1 is essentially the most luminous ULXP thus far detected. It’s situated some 56 million light years away within the Knife Edge Galaxy (also called NGC 5907). NGC 5907 ULX1 has a spin period of roughly 1.14 seconds and is thought for its quick spin-up in the course of the on-state. Nevertheless, nonetheless little or no is thought in regards to the magnetic field of this pulsar as some research counsel that it has a multipolar magnetic discipline with a energy reaching 100 trillion Gauss, whereas the others level to a magnetic discipline occasion 1,000 occasions weaker.

Due to this fact, with the intention to shed extra mild on the magnetic discipline of NGC 5907 ULX1, a crew of astronomers led by Felix Fuerst of the European Area Astronomy Heart (ESAC) in Madrid, Spain, has analyzed the Swift and XMM-Newton knowledge from a long-term monitoring (between 2003 and 2022) of the pulsar’s X-ray flux and pulse interval.

The research discovered that NGC 5907 ULX1 was in an off- or low-state between mid-2017 to mid-2020. Throughout this off-state the secular spin-up pattern reversed, and the neutron star rotational interval slowed down considerably. After the off-state ended, spin-up resumed, nonetheless, at a decrease price than earlier than.

The researchers employed completely different strategies to estimate the magnetic discipline of the neutron star, both primarily based on the spin-up or spin-down energy.

“The best estimate for the magnetic field strength in our knowledge is ≈ 2.5 × 10¹³ G, whereas for the low B-field resolution, we discover values as little as 2 × 10¹² G. Whereas primarily based on these numbers we can’t distinguish which magnetic discipline is current in actuality, we observe that for a ∼10¹² G discipline, we’d anticipate to see a cyclotron resonant scattering function (CRSF) round 12 keV, which thus far has not been noticed within the spectrum,” the authors of the paper defined.

The astronomers additionally estimated the magnetic discipline energy primarily based on the spin-down in the course of the off-state between 2017–2019 and located that it’s at a degree of 25 trillion Gauss. They famous that on the whole, all the outcomes level towards the course of a magnetic discipline with a energy of at the very least a number of trillion Gauss in NGC 5907 ULX1. This means that the pulsar is accreting at very excessive charges.

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