INVESTIGATION OF X-RAY SOURCES IN NGC 7552: IDENTIFICATION OF A NEW ULX CANDIDATE

Year 2025, Volume: 26 Issue: 1, 45 - 59, 25.03.2025

Sinan Allak , Aysun Akyüz

https://doi.org/10.18038/estubtda.1551932

Abstract

This study investigates the X-ray and optical properties of 29 X-ray sources within the NGC 7552 galaxy, using Chandra, Swift X-Ray Telescope (Swift-XRT) data, and Hubble Space Telescope (HST). A significant finding was the identification of a new ultraluminous X-ray source (ULX-3) with an X-ray luminosity, LX 〖≈10〗^39 erg s^(-1) making it the third ULX identified in this galaxy. The spectral analysis of ULX-3 suggests it could be a stellar-mass black hole with an estimated mass of around 8 solar masses (M_⊙). Nearly half of the observed X-ray binaries (XRBs) were classified as transient or variable. Variability studies revealed that ULX-1 exhibited significant long-term variability in Chandra data, while ULX-2 remained stable in both Chandra and Swift-XRT observations. ULX-3 showed no significant variability in Chandra data, indicating steady emissions during the observation period. The analysis of the X-ray energy spectra for ULX-1, ULX-2, and ULX-3 showed that power-law models best described their spectra. These findings suggest that the ULXs have a hard spectral structure, commonly linked to X-ray emissions from compact objects such as black holes or neutron stars. Optical counterparts were also identified for several XRBs, including ULX-1, ULX-2, and ULX-3, most of which exhibit faint optical magnitudes (mV >22 mag) characteristic of ULX systems.

Keywords

Ultraluminous X-ray Sources (ULXs), X-ray Binaries, Optical Counterparts of ULXs, NGC 7552

Supporting Institution

Scientific and Technological Research Council of Türkiye (TÜBİTAK)

Project Number

122C183

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