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 identified thus 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 can 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 identified stellar course of.

Astronomers usually consider that resulting from their brightness, most ULXs are black holes. Nevertheless, latest observations have discovered that some ULXs showcase coherent pulsations. These sources, often known as ultra-luminous X-ray pulsars (ULXPs), are neutron stars usually much less huge than black holes. The record of identified ULPs remains to be comparatively brief; thus, learning objects of this class is crucial 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 to date detected. It’s positioned some 56 million light years away within the Knife Edge Galaxy (also referred to as NGC 5907). NGC 5907 ULX1 has a spin period of roughly 1.14 seconds and is understood for its quick spin-up throughout the on-state. Nevertheless, nonetheless little or no is understood concerning the magnetic field of this pulsar as some research recommend that it has a multipolar magnetic discipline with a power reaching 100 trillion Gauss, whereas the others level to a magnetic discipline occasion 1,000 instances weaker.

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

The examine 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 development reversed, and the neutron star rotational interval slowed down considerably. After the off-state ended, spin-up resumed, nevertheless, at a decrease price than earlier than.

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

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

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

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