your ID: 0317 
First Name: Fukun 
Last Name: Liu 
Affiliation: Peking University 

Title: Harmonic QPOs and thick disk p-mode oscillations in BL Lac object AO 0235+164 
Authors: F.K. Liu, G. Zhao, X.-B. Wu 
Topic: 2 
Session: oral 

Abstract: Periodic outbursts are observed in many AGNs and usually explained with a
 supermassive black hole binary (SMBHB) scenario. However, multiple periods are 
observed in some AGNs and cannot be explained with it. Here we analyze the periodicity
 of the radio light curves of AO 0235+164 at multi-frequencies and report the discovery of 
six QPOs in integer ratio 1:2:3:4:5:6 of QPO frequencies, of which the second with period 
$P_2 = (5.46 \\pm 0.47) {\\rm yr}$ is the strongest. We fit the radio light curves and show
 that the initial phases of six QPOs have zero or $\\pi$ differences relative to each other. 
We suggest a harmonic relationship of QPOs. The centroid frequency, relative strength, 
harmonic relationship and relative initial phases of QPOs are independent of radio frequency. 
The harmonic QPOs are likely due to the quasi-periodic injection of plasma from an oscillating 
accretion disk into the jet. We estimate the supermassive black hole mass 
$M_{\\rm BH} \\simeq (4.72\\pm 2.04) \\times 10^8 M_\\odot$ and the accretion rate 
$\\dot{m}\\simeq 0.007$. With the knowledge of accretion disk, it implies that the inner region 
of accretion disk of AO 0235+164 is a radiatively inefficient accretion flow. The oscillation 
accretion is due to the p-mode oscillation of the thick disk probably excited by a SMBHB. 
The theoretical predications of fundamental oscillation frequency and the harmonics are well 
consistent with the observations. Harmonic QPOs would be absent when the thick disk 
becomes geometrically thin due to the increase of accretion rate. We discuss the observations 
of AO 0235+164 basing on the SMBHB-thick disk oscillation scenario.