| Name: | Kinjal Roy |
| Affiliation: | Raman Research Institute |
| Conference ID : | ASI2024_354 |
| Title : | Two fundamental cyclotron lines detected in 4U 0115+63 during 2023 outburst |
| Authors : | Kinjal Roy, Hemanth Manikantan, and Biswajit Paul |
| Authors Affiliation: | Raman Research Institute, C. V. Raman Avenue, Sadashivanagar, Bengaluru - 560 080, India. |
| Mode of Presentation: | Oral |
| Abstract Category : | High Energy Phenomena, Fundamental Physics and Astronomy |
| Abstract : | The Be X-ray binary 4U 0115+63 underwent a giant outburst in 2023 with X-ray luminosity of the source exceeding ≥10^38 erg s−1. During the outburst, two target of opportunity observations were made with NuSTAR. The 3-79 keV broadband X-ray coverage of NuSTAR allows us to properly model the continuum and investigate the nature of the multiple cyclotron resonance scattering features present in the source spectrum. We detected five cyclotron lines during the 2023 outburst near 12, 16, 24, 34 and 47 keV. The ∼16 keV cyclotron line cannot be harmonically related to two of the other lines at ∼12 keV and 24 keV, indicating the presence of two fundamental lines in the spectrum of 4U 0115+63. Including the two current observations with NuSTAR, we now have information about the CRSF lines across a wide range of luminosity to study the dependence of centroid energy of the cyclotron lines with luminosity. The CRSF line centre showed no anti-correlation with luminosity, unlike previously reported. Instead, a weak positive correlation is found for four of the line energies. We also study the origin of the two fundamental lines using phase resolved spectroscopy of the source. The variation of the two fundamental lines with spin phase favours the two-pole cyclotron line model where the two different cyclotron lines originate from two different poles of the neutron star. |
