Indian astronomers investigate magnetar CXOU J010043.1−721134

Result of period search using efsearch for observation G of CXOU J010043. Credit: Chatterjee et al., 2021.
Result of period search using efsearch for observation G of CXOU J010043. Credit: Chatterjee et al., 2021.

Astronomers from the Indian Space Research Organization (ISRO) have performed long-term observations of a peculiar magnetar known as CXOU J010043.1−721134. Results of this monitoring campaign shed more light on the nature of this source. The study was presented in a paper published May 19 on

Magnetars are neutron stars with extremely strong magnetic fields, more than quadrillion times stronger than the magnetic field of our planet. Decay of magnetic fields in magnetars powers the emission of high-energy electromagnetic radiation, for instance, in the form of X-rays or radio waves.

CXOU J010043.1−721134 (or CXOU J010043) is an anomalous X-ray pulsar (AXP) in the Small Magellanic Cloud (SMC), which has been classified as a magnetar. It is the only known magnetar in the SMC and has the lowest column density among all other identified magnetars. Given that CXOU J010043 is located far away from the galactic plane and its absorption column is well-constrained, this source can be investigated with higher accuracy compared to other known magnetars.

So a team of astronomers led by Rwitika Chatterjee decided to take a closer look at this magnetar. They have analyzed the results of a 16-year long observational campaign of this source using ESA's XMM-Newton spacecraft.

The researchers wrote, in this paper, we present a detailed analysis of eleven observations of CXOU J010043, spanning 2000 to 2016, carried out with the XMM-Newton telescope. This includes the re-analysis of five older datasets (2000 to 2005; see MG05 and TE08) using the latest calibration files.

The observations found that CXOU J010043 has a spin period of approximately 8.0275 seconds, which is typical for magnetars as such objects have few-second periods. The magnetar appears to exhibit a steady spin-down with a spin-down rate of about 0.0176 nanoseconds/second.

Furthermore, the study found that CXOU J010043 has a dipolar magnetic field of about 380 trillion G and characteristic age of some 7,200 years. These results are in agreement with previous observations of this magnetar.

The XMM-Newton data indicate that CXOU J010043 has a double-peaked pulse profile, shows no significant energy dependence. When it comes to pulse fractions in the soft and hard energy band, they lie in the range 19−47 percent and 18−63 percent respectively. The astronomers noted that both pulse profile, as well as pulse fraction, do not show notable temporal variations.

The researchers said, the thermal comptonization model is able to adequately explain the observed spectra and pulse profile. A cool, optically thick electron plasma acts as the comptonizing medium for thermal seed photons from the magnetar surface. Interestingly, the plasma temperature does not seem to decrease significantly with time, as would be expected if one were to assume a continuously radiating body with no heating sources.

They assume that there may exist an internal source within the CXOU J010043 system that continually provides heat to maintain its temperature over such long timescales.

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