Fifteen Years of M31* X-Ray Variability and Flares
Abstract
We append an additional 15 yr (2009─2024) to the Chandra X-ray light curve of M31*, the supermassive black hole (SMBH) at the center of M31, the Andromeda galaxy. Extending and expanding on the work in Z. Li et al., we show that M31* has remained in an elevated X-ray state from 2006 through at least 2016 (when regular Chandra monitoring ceased) and likely through 2024, with the most recent observations still showing an elevated X-ray flux. We identify one moderate flare in 2013 where the other nuclear X-ray sources are in low-flux states, making that flare a valuable target for follow-up with multiwavelength and multimessenger archival data. We extract a mostly uncontaminated spectrum for M31* from this observation, showing that its X-ray properties are similar to those observed at Sgr A* in its quiescent state by Baganoff et al. Furthermore, we find no substantial change in the source's hardness ratio in the 2006 and 2013 flares compared to the post-2006 elevated state, suggesting the these flares are increases in the regular X-ray emission mechanisms instead of entirely new emission modes. Our extended light curve for M31* provides valuable context for multimessenger or multiwavelength observations of nearby SMBHs.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 2025
- DOI:
- arXiv:
- arXiv:2502.01365
- Bibcode:
- 2025ApJ...981...50D
- Keywords:
-
- X-ray sources;
- X-ray astronomy;
- Supermassive black holes;
- Andromeda Galaxy;
- High energy astrophysics;
- Black holes;
- 1822;
- 1810;
- 1663;
- 39;
- 739;
- 162;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 8 pages, 7 figures, 1 table. Accepted for publication in ApJ
