Sains Malaysiana 53(4)(2024): 893-905

http://doi.org/10.17576/jsm-2024-5304-13

Evolusi Pancaran Sinar-X Sagittarius A* antara Tahun 1999 dan 2019 Berdasarkan Pemerhatian Observatori Sinar-X Chandra

(Evolution of Sagittarius A* X-Ray Emission between 1999 and 2019 Based on Chandra X-Ray Observatory Observations)

AIMI AZIZAN¹, MUHAMMAD EZZAT ABDUL HAMID^1,2 & ADLYKA ANNUAR^1,*

¹Jabatan Fizik Gunaan, Fakulti Sains dan Teknologi, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia

²Jabatan Fizik Perubatan, Pusat Perubatan Universiti Malaya, Lembah Pantai, 59100 Kuala Lumpur, Malaysia

Diserahkan: 26 Oktober 2023/Diterima: 27 Februari 2024

Abstrak

Kertas ini membentangkan pemerhatian Observatori Sinar-X Chandra terhadap Sagittarius A* (Sgr A*) yang diambil sepanjang dua dekad pertama operasi observatori tersebut antara tahun 1999 dan 2019. Spektrum sinar-X bagi 143 pemerhatian dianalisis untuk mengkaji evolusi sinar-X Sgr A* sepanjang 20 tahun melalui ciri utamanya, iaitu kecerahan (luminositi), ketumpatan gas dan debu (N_H) dan indeks foton (Γ). Secara amnya, Sgr A* berada dalam keadaan stabil sepanjang tempoh pemerhatian, dengan purata luminositi sinar-X intrinsik dalam julat tenaga 2 – 8 keV iaitu, L2-8 keV,int,kes = (3.69 ± 4.25) ×10³³ erg s^–1. Nilai ini tekal dengan purata luminositi sinar-X cerapan dalam jangka masa yang sama, L2-8 keV,cer,kes = (2.24 ± 2.12) ×10³³ erg s^–1. Walau bagaimanapun, terdapat tujuh pemerhatian (~5%) yang mempunyai luminositi intrinsik melebihi nilai purata yang dianggarkan. Nilai N_H dan Γ yang diukur bagi kesemua pemerhatian dilihat tekal sepanjang tempoh kajian dengan nilai purata, N_H ukur = 0.90 ± 0.35 ×10²³ cm^–2 dan Γ ukur = 1.90 ± 0.68. Ini mencadangkan bahawa kebolehubahan dalam luminositi yang diperhatikan bukan disebabkan oleh pengaburan atau perubahan besar dalam kadar penokokan. Selain itu, kajian ini juga mengukur luminositi sinar-X tertinggi bagi Sgr A*, L2-8 keV,int = 3.84 ± 4.25 0.37 ×10³⁴  erg s^–1, yang berlaku pada 14 September 2013. Keputusan ini sejajar dengan suar yang paling terang pernah dikesan dalam kajian terdahulu. Ini diikuti dengan pemerhatian pada 19 Ogos 2019 dengan luminositi, L2-8 keV,int = 2.40 ± 0.52 0.36 ×10³⁴  erg s^–1. Kajian ini memberikan gambaran menyeluruh terhadap evolusi pancaran Sgr A* selama dua dekad pertama pengoperasian Chandra dan meningkatkan lagi pemahaman terhadap lohong hitam ini.

Kata kunci: Pusat Galaksi; Sgr A*; sinar-X; spektroskopi

Abstract

This paper presents observations made by the Chandra X-ray Observatory on Sagittarius A* (Sgr A*) from 1999 to 2019. The X-ray spectra from 143 observations were analysed to investigate the X-ray evolution of Sgr A* throughout 20 years focusing on its key characteristics, i.e., the luminosities, column density (N_H), and photon index (Γ). In general, this study found that Sgr A* remained in a stable state throughout the observation period, with an average intrinsic X-ray luminosity in the 2 – 8 keV energy range of L2-8 keV,int,all = (3.69 ± 4.25) ×10³³ erg s^-1. This is consistent with the average observed X-ray luminosity, L2-8 keV,obs,all = (2.24 ± 2.12) ×10³³ erg s^–1. However, there were seven observations (~5%) that had intrinsic luminosities exceeding the estimated average value. The measured values of N_H and Γ for all observations, remained consistent throughout the study with average values of N_H meas = 0.90 ± 0.35 ×10²³ cm^–2 and Γmeas= 1.90 ± 0.68 . This suggests that the variability in the observed luminosity was not caused by obscuration or significant changes in accretion rate. Additionally, this study also measured the highest X-ray luminosity for Sgr A*, L2-8 keV,int = (3.69 ± 4.25) ×10³³ erg s^–1 on 14th September 2013. This finding is in line with the brightest flare ever observed in past studies. This was followed by an observation on 19th August 2019, with a luminosity of L2-8 keV,int = 2.40 ± 0.52 0.36 ×10³⁴ erg s^–1. This analysis provides a comprehensive overview of the evolution of Sgr A*’s emissions during the first two decades of Chandra's operation and further enhances our understanding of this black hole.

Keywords: Galactic center; Sgr A*; spectroscopy; X-rays

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*Pengarang untuk surat-menyurat; email: adlyka@ukm.edu.my