| Autor: |
Hadrien Paugnat, Tuan Do, Abhimat K. Gautam, Gregory D. Martinez, Andrea M. Ghez, Shoko Sakai, Grant C. Weldon, Matthew W. Hosek Jr., Zoë Haggard, Kelly Kosmo O’Neil, Eric E. Becklin, Gunther Witzel, Jessica R. Lu, Keith Matthews |
| Jazyk: |
angličtina |
| Rok vydání: |
2024 |
| Předmět: |
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| Zdroj: |
The Astrophysical Journal, Vol 977, Iss 2, p 228 (2024) |
| Druh dokumentu: |
article |
| ISSN: |
1538-4357 |
| DOI: |
10.3847/1538-4357/ad8ac6 |
| Popis: |
In this work, we measure the spectral index of Sagittarius A* (Sgr A*) between the H (1.6 μ m) and $K^{\prime} $ (2.2 μ m) broadband filters in the near-infrared (NIR), sampling over a factor ∼40 in brightness, the largest range probed to date by a factor ∼3. Sgr A*-NIR is highly variable, and studying the spectral index α (with F _ν ∝ ν ^α ) is essential to determine the underlying emission mechanism. For example, variations in α with flux may arise from shifts in the synchrotron cutoff frequency, changes in the distribution of electrons, or multiple concurrent emission mechanisms. We investigate potential variations of ${\alpha }_{H-K^{\prime} }$ with flux by analyzing seven epochs (2005–2022) of Keck Observatory imaging observations from the Galactic Center Orbits Initiative. We remove the flux contribution of known sources confused with SgrA*-NIR, which can significantly impact color at faint flux levels. We interpolate between the interleaved H and $K^{\prime} $ observations using multi-output Gaussian processes. We introduce a flexible empirical model to quantify α variations and probe different scenarios. The observations are best fit by an ${\alpha }_{H-K^{\prime} }=-0.50\pm {0.08}_{\mathrm{stat}}\pm {0.17}_{\mathrm{sys}}$ that is constant from ∼1 mJy to ∼40 mJy (dereddened 2 μ m flux). We find no evidence for a flux dependence of Sgr A*'s intrinsic spectral index. In particular, we rule out a model explaining NIR variability purely by shifts in the synchrotron cutoff frequency. We also constrain the presence of redder, quiescent emission from the black hole, concluding that the dereddened 2 μ m flux contribution must be ≤0.3 mJy at 95% confidence level. |
| Databáze: |
Directory of Open Access Journals |
| Externí odkaz: |
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