PoS - Proceedings of Science
Volume 395 - 37th International Cosmic Ray Conference (ICRC2021) - GAI - Gamma Ray Indirect
Fast X-ray variability of radio galaxy M87
R. Imazawa*, Y. Fukazawa, H. Takahashi and M. Sasada
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Pre-published on: July 31, 2021
Published on: March 18, 2022
M87 is a radio galaxy and it was detected in the TeV gamma-ray band, but its emission and particle acceleration region are still under debate. We searched for fast X-ray variability of M87 by using X-ray archive data with a long exposure than 10 ksec.
As a result, we found an intraday variability during Suzaku/XIS data in 2006. Suzaku/XIS cannot resolve each component in the jet, but HST-1 knot standing at $\sim$100 pc from the core was the brightest component in the X-ray band in this period. Therefore, this variability is likely attributed to HST-1. A soft photon index of 2.38 in the X-ray band indicates that variability component is synchrotron emission by accelerated electrons in HST-1. Assuming the decay time scale as correspond to synchrotron cooling time, we estimated a magnetic field strength to $B\sim1.94\delta^{1/3}$ mG, which is enough to accelerate particles up to TeV, where $\delta$ is a Doppler factor.
In addition, we also found a possible variability of the core during the Chandra/HRC observation in 2017. In this period, a NuStar X-ray spectrum was represented by a power law with a photon index of 1.96. Therefore we could not distinguish this fast variability is due to synchrotron emission or disk/corona emission. From these results, both of the core and HST-1 are could be the origin of the X-ray variability, and we found that knot HST-1 is a candidate of the location of particle acceleration up to TeV.
DOI: https://doi.org/10.22323/1.395.0845
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