Optical and X-ray Studies of the Be/X-ray Binary IGR J06074+2205

TL;DR

This study combines X-ray and optical observations to analyze the behavior of the Be/X-ray binary IGR J06074+2205 during outbursts, revealing complex emission properties and disc evolution that could lead to future giant outbursts.

Contribution

It provides a comprehensive multi-wavelength analysis of the system's outburst behavior and disc dynamics, which is novel in capturing the evolution before, during, and after outbursts.

Findings

Pulse profiles depend on luminosity and energy.

The circumstellar disc shows increasing emission lines and growth over time.

The disc's growth may trigger future giant X-ray outbursts.

Abstract

We present the results obtained from X-ray and optical analysis of the Be/X-ray binary IGR~J06074+2205, focusing on before, during, and after the X-ray outbursts in October and December 2023. The properties of the neutron star in the binary are investigated using NICER and NuSTAR observations during the X-ray outbursts. The pulse profiles across a broad energy range, are found to be strongly dependent on luminosity and energy, revealing the complex nature of the emitting region. An absorbed power-law can describe each NICER spectrum in the 1-7 keV band. The 3-79 keV NuSTAR spectrum can be well-described by a negative and positive power-law with an exponential cut-off model. Utilizing the MAXI/GSC long-term light curve, we estimate the probable orbital period to be 80 or 80/n (n=2,3,4) days. We investigate the evolution of the circumstellar disc around the Be star by using optical spectroscopic observations of the system between 2022 and 2024. We observe variable H$\alpha$ and FeII emission lines with an increase in equivalent width, indicating the presence of a dynamic circumstellar disc. A distinct variation in the V/R value for H$\alpha$ and FeII lines is also observed. The appearance of additional emission lines, such as HeI (5875.72 \AA), HeI (6678 \AA), and HeI (7065 \AA), during the post-outburst observation in February 2024 suggests the growing of a larger or denser circumstellar disc. The disc continues to grow without any noticeable mass loss, even during the 2023 X-ray outbursts, which may lead to a future giant X-ray outburst.