Iron Lines in Swift J0243.6+6124 X-ray Pulsar

Swift J0243.6+6124 is an interesting X-ray source located in our galaxy. It is classified as an ultraluminous X-ray pulsar. This means it shines very brightly in X-ray light and shows periodic signals, known as pulsations. These pulsars are unique because they can produce a lot of energy from the process called Accretion, where material falls into them from a companion star.

In this study, we focused on the behavior of iron lines, which are specific signals we can see in the spectrum of the X-rays emitted by this pulsar. The iron lines tell us about the conditions surrounding the pulsar and how matter behaves near it. By examining these lines, we aim to learn more about the inner workings of Swift J0243.6+6124, especially during its brightest states.

#Observations

Swift J0243.6+6124 was first detected in October 2017 by the Neil Gehrels Swift Observatory. It became exceptionally bright, with a flux that was quite noticeable. The discovery of its pulse period, around 9.86 seconds, pointed to its classification as a Be X-ray binary pulsar. This type of pulsar has a companion star, often a Be star, that contributes to the material it accretes.

For our observations, we used the Hard X-ray Modulation Telescope (HMXT), which has a wide energy range and sensitivity to X-rays. Throughout the outburst period from 2017 to 2018, the telescope collected a lot of data on Swift J0243.6+6124, allowing us to analyze its behavior in detail.

#Iron Line Emissions

When the material surrounding the pulsar is illuminated by X-ray radiation, it can emit fluorescent iron lines. These lines appear in the spectra as peaks at certain energies, which correspond to the energies where iron atoms can emit light. The behavior of these lines can provide crucial insights into the physical conditions near the pulsar.

For the first time, our observations detected a pulsed Broad Iron Line emission from Swift J0243.6+6124. This means that as the pulsar rotates, the intensity and width of the iron line changes, showing a clear link to its pulse phase. We found that the pulse phase shifts the variation of the width and intensity of this iron line by about a quarter of the pulse period.

#Analyzing the Spectral Data

To analyze the spectral data, we created different models to account for the continuum spectrum, which is the base level of X-ray emission before considering specific features like the iron lines. We applied several models to see how they affected our understanding of the iron lines, and we consistently found that the results remained similar.

The broad iron line exhibited different characteristics compared to the narrow line that was also detected. The broad line was linked to the inner regions of the accretion disk, where the conditions are more extreme, while the narrow line originated from farther out in the disk.

#Phase-Resolved Spectral Analysis

One of the key aspects of our analysis was to look at how the spectral parameters changed during different phases of the pulsar's rotation. By breaking down the data according to these phases, we were able to see how the iron line emissions behaved.

We observed that the broad iron line's width varied depending on the phase of the pulse, indicating that different regions of the accretion disk were being illuminated differently as the pulsar rotated. In contrast, the narrow iron line showed a more stable behavior, suggesting that it was less affected by the pulsar's rotation.

#Understanding the Accretion Process

The results we obtained highlight the importance of understanding the accretion process in pulsars. In Swift J0243.6+6124, the accretion column formed by the material falling onto the pulsar plays a critical role in shaping the X-ray emissions we observe.

The accretion disk surrounding the pulsar can be complex, with different regions responding differently to the pulsar's rotation. The illumination of these regions affects the emission of iron lines, leading to the variations in observed spectra.

#Implications for Stellar Physics

These findings contribute to the broader understanding of how pulsars interact with their environments. The behavior of the iron lines can give clues to the physical conditions in the accretion disk, which is critical for modeling the dynamics of matter in extreme environments.

By studying Swift J0243.6+6124, we gain valuable insights not only into this specific pulsar but also into the broader category of Ultraluminous X-ray Pulsars. Exploring these phenomena enhances our knowledge of stellar evolution, accretion processes, and the complexities of matter under extreme gravitational and magnetic fields.

#Conclusion

In summary, the study of Swift J0243.6+6124 has revealed significant details about the behavior of iron line emissions in a pulsar. Our analysis has shown that the behavior of these emissions is closely linked to the pulse phase of the pulsar, providing critical insights into the accretion process and the conditions surrounding the pulsar.

This work highlights the importance of continued research in this field, as each discovery adds to our understanding of the fascinating behavior of pulsars and their interactions with the matter in their vicinity. Future studies will no doubt expand upon these findings and further illuminate the complex dynamics at play in such extreme cosmic environments.