Motoki Kino

ENERGETICS OF TeV BLAZARS AND PHYSICAL CONSTRAINTS ON THEIR EMISSION REGIONS

Using multifrequency spectra from TeV blazars in quiescent states, we obtain the physical parameters of the emission region of blazars within the framework of the one-zone synchrotron self-Compton model. We numerically calculate the steady state energy spectra of electrons by self-consistently taking into account the effects of radiative cooling with a proper account of the Klein-Nishina effect. Here electrons are assumed to be injected with a power-law spectrum and to escape on a finite timescale, which naturally leads to the existence of a break energy scale. Although we do not use time variabilities but use a model of electron escape to constrain the size of the emission region, the resultant size turns out to be similar to that obtained based on time variabilities. Through detailed comparison of the predicted emission spectra with observations, we find that for Mrk 421, Mrk 501, and PKS 2155-304, the energy density of relativistic electrons is about an order of magnitude larger than that of magnetic fields with an uncertainty within a factor of a few.

Radiation Spectra from Advection-dominated Accretion Flows in a Global Magnetic Field

We calculate the radiation spectra from advection-dominated accretion flows (ADAFs), taking into account the effects of a global magnetic field. Our calculation is based on the analytic model for magnetized ADAFs proposed by Kaburaki, in which a large-scale magnetic field controls the accretion process. Adjusting a few parameters, we find that our model can well reproduce the observed spectrum of Sagittarius A*. The result is discussed in comparison with those of well-known ADAF models, in which the turbulent viscosity controls the accretion process.

A short-term flare on a time scale of 20 days in the BL Lac object OT 081

We have conducted daily monitoring of the BL Lac object OT 081 at 8.4 GHz with the Yamaguchi 32 m radio telescope from February to June 2010. Based on these data, we detected a short-time flare with a duration of 19.3 days and an amplitude of 0.73 Jy, overlapped on a long-term trend with a time scale of about 200 days. This short-term flare was also observed in the University of Michigan data at 4.8, 8.0, and 14.5 GHz. Subtracting the long-term trend allowed us to study the short-term flare in details. The flare was found to occur synchronously at 8.4 and 14.5 GHz, with no significant delays between the two frequencies. This suggests that the flaring region was optically thin, as otherwise the radio emission would have peaked with a delay at the lower frequency. The duration of the flare indicates that the emitting region is smaller than 0.01 pc.

VLBI follow-up observations for the large X-ray flares of Mrk 421

In February 2010 and September 2011, the large X-ray flares of Mrk 421 were reported by the Astronomer’s Telegram. Mrk 421 is one of the best sources for studying the most compact regions in blazars, because of its proximity. In order to examine the behavior inside the sub-pc region by densely VLBI monitor soon after the large flare, we carried out quick and multi-epoch follow-up observations for these flares using JVN (the Japanese VLBI network) array at an interval of two weeks to three weeks. As results of our VLBI observations for these large X-ray flares, we present the possibility of a structural change that occurred within ∼ 1.2 mas from the core after the large high-energy flares.

Multi-epoch and multi-frequency VLBI observation of X-ray to gamma-ray flare in TeV blazar Mrk 421

In early 2013, large X-ray and GeV gamma-ray flares occurred in TeV blazar Mrk 421. To investigate the spectral behavior in the radio core region of Mrk 421 after the large high-energy flare phenomenon, we carried out quasi-simultaneous multi-frequency (2–43 GHz) dense monitor of Mrk 421 by using the very long baseline array (VLBA) immediately after the flare. During these VLBA observations, we detected not only flux variation but also clear spectral change. Especially VLBI spectra in 2013 June 16, which corresponds to the 1st X-ray flare seen in the period of our follow-up observation shows relatively flat spectrum compared with the one in 2013 May 22. In the high-energy active state of this source, we have found that there are two periods when the synchrotron self-absorption (SSA) turnover is seen at∼ 8 GHz and at less than∼2 GHz.

The first scientific experiment using Global e-VLBI observations: a multiwavelength campaign on the gamma-ray Narrow-Line Seyfert 1 PMN J0948+0022

The detection of gamma-ray emission by Fermi-LAT from the radio loud Narrow Line Seyfert 1 PMN J0948+0022 (Abdo et al. 2009, ApJ 699, 976) triggered a multi-wavelength campaign between March and July 2009. Given its high compactness (Doi et al. 2006, PASJ 58, 829), inverted spectrum, and 0deg declination, the source was an ideal target to observe at 22 GHz with a Global VLBI array extending from Europe to East Asia and Australia. In order to deliver prompt results to be analysed in combination with the other instruments participating in the campaign, the observations were carried out with real time VLBI, for the first time on a Global scale. Indeed, the main results have been published just a few months after the campaign (Abdo et al. 2009, ApJ 707, 727). Here we present additional details about the e-VLBI observations.

Physical parameters of TeV blazars

Using multi-frequency spectra from TeV blazars at quiescent states, we obtain the physical parameters of the emission region of blazars, based on the synchrotron self-Compton model. We numerically calculate the steady-state electron energy spectrum by self-consistently taking into account radiative cooling effects with a proper account of the Klein-Nishina effects. We find that for Mrk 421, Mrk 501, and PKSu200a2155−304, the energy density of magnetic fields is about one order of magnitude less than that of relativistic electrons, which confirms the previous claim made analytically.