Unprecedented variability of Sgr A* in NIR
| Autor: | Do, Tuan, Witzel, Gunther, Gautam, Abhimat K., Chen, Zhuo, Ghez, Andrea M., Morris, Mark R., Becklin, Eric E., Ciurlo, Anna, Hosek Jr., Matthew, Martinez, Gregory D., Matthews, Keith, Sakai, Shoko, Schödel, Rainer |
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| Rok vydání: | 2019 |
| Předmět: | |
| Druh dokumentu: | Working Paper |
| DOI: | 10.3847/2041-8213/ab38c3 |
| Popis: | The electromagnetic counterpart to the Galactic center supermassive black hole, Sgr A*, has been observed in the near-infrared for over 20 years and is known to be highly variable. We report new Keck Telescope observations showing that Sgr A* reached much brighter flux levels in 2019 than ever measured at near-infrared wavelengths. In the K$^\prime$ band, Sgr A* reached flux levels of $\sim6$ mJy, twice the level of the previously observed peak flux from $>13,000$ measurements over 130 nights with the VLT and Keck Telescopes. We also observe a factor of 75 change in flux over a 2-hour time span with no obvious color changes between 1.6 $\mu$m and 2.1 $\mu$m. The distribution of flux variations observed this year is also significantly different than the historical distribution. Using the most comprehensive statistical model published, the probability of a single night exhibiting peak flux levels observed this year, given historical Keck observations, is less than $0.3\%$. The probability to observe the flux levels similar to all 4 nights of data in 2019 is less than $0.05\%$. This increase in brightness and variability may indicate a period of heightened activity from Sgr A* or a change in its accretion state. It may also indicate that the current model is not sufficient to model Sgr A* at high flux levels and should be updated. Potential physical origins of Sgr A*'s unprecedented brightness may be from changes in the accretion-flow as a result of the star S0-2's closest passage to the black hole in 2018 or from a delayed reaction to the approach of the dusty object G2 in 2014. Additional multi-wavelength observations will be necessary to both monitor Sgr A* for potential state changes and to constrain the physical processes responsible for its current variability. Comment: 9 pages, 4 figures, accepted to ApJ Letters |
| Databáze: | arXiv |
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