Fast X-ray variability of radio galaxy M87

Discussion timeslot (ZOOM-Meeting): 16. July 2021 - 18:00
ZOOM-Meeting URL: https://icrc2021.desy.de/pf_access_abstracts
Corresponding Session: https://icrc2021-venue.desy.de/channel/Presenter-Forum-1-Evening-All-Categories/48

■ Executive summary

- What is this contribution about?

In this contribution, we report the results of study the fast X-ray variability of radio galaxy M87.

- Why is relevant / interesting?

M87 is one of the TeV detected radio galaxy and it indicates particle acceleration up to TeV. But the location of acceleration is not known,andthis topic is interesting for origin of very high energy cosmic rays.

- What have we done?

We did study X-ray variabilities with Chandra, Suzaku, NuSTAR telescope.Because X-ray emission with soft spectrum indicates synchrotron radiation, it is able to discuss the magnetic field and particle energy from time scaleof variabilities.

- What is the result?

We found first X-ray intraday variability of M87 in 2006from the Suzaku observation.It is X-ray flaring periodof HST-1 region (~100 pc from the core), it indicates HST-1 is source of thisfastvariability.We calculated the magnetic field strength from the decay time scale, we found it is enough to do particle acceleration up to TeV.

■Abstract:

M87 is one of the nearest radio galaxy. We can study the core, jet, and some components by radio to X-ray observations.

Regarding TeV gamma ray observations, it is known to show an intra-day variability.

Such fast variability may occur at the particle acceleration region. But due to rough angular resolution, we cannot know which component causes this variability.

We searched for fast X-ray variability of the M87 from long-exposure X-ray archive data. As a result, we found an intra-day variability during Suzaku/XIS data in 2006.

Suzaku/XIS cannot resolve each component, but HST-1 was the brightest component in the X-ray band in this period, core had 1/4 of HST-1 flux.

Therefore, this variability possibly comes from HST-1, but we cannot rule out the possibility of large core variability.

A soft photon index larger 2.0 in the X-ray band indicates that variability component is synchrotron emission from accelerated electrons in HST-1 or core.

In addition, we also find a possible variability of core on the Chandra/HRC observation in 2017. In this period, NuSTAR X-ray spectra have a power law with a photon index of 1.8, and thus not likely a synchrotron spectrum from the jet. Here the X-ray emission from the core was dominant in this period.

Also, we find that one NuSTAR observation showed a higher flux than other NuSTAR observations by a factor of 2.5.rnFrom these results, both core and HST-1 can be the origin of the X-ray variability. We will discuss the variability site and emission mechanism.'

(This contribution based on the contents of Imazawa et al., 2021, ApJ; Accepted June 2021.)

Authors: Ryo Imazawa
Co-Authors: Yasushi Fukazawa | Hiromitsu Takahashi | Mahito Sasada
Indico-ID: 896
Proceeding URL: https://pos.sissa.it/395/845