Radio variability of the blazar AO 0235 + 164

Abstract

view Abstract Citations (36) References (54) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Radio Variability of the Blazar AO 0235+164 O'Dell, S. L. ; Dennison, B. ; Broderick, J. J. ; Altschuler, D. R. ; Condon, J. J. ; Payne, H. E. ; Mitchell, K. J. ; Aller, H. D. ; Aller, M. F. ; Hodge, P. E. Abstract The high-redshift (z = 0.940) blazar AO 0235+164 has been monitored for 5 yr at 0.318, 0.430, 0.606, 0.880, 1.40, 4.8, 8.0, and 14.5 GHz. The flux-density variations are correlated over the entire factor-of-50 range of radio frequencies, demonstrating that they are, even at the lowest frequencies, primarily intrinsic to the blazar. (In contrast, low-frequency (ν < 1 GHz] variations in other sources are generally uncorrelated with highfrequency (ν > 1 GHz] variations and may result from extrinsic modulation.) Variations at the lower frequencies lag, with diminished amplitude, those at the higher radio frequencies. This behavior agrees gualitatively, but not guantitatively, with the predictions of the simplest expanding-cloud model. The radio flux-density variations are interpreted in terms of synchrotron emission from adiabatically evolving structures in a compact jet. The data at the two highest radio frequencies are used to establish the time-dependent injection at the base of the jet. The behavior of the source at all other radio frequencies is entirely determined by these two empirically determined time series and four constant parameters (a transparent spectral index, an apparent transit time scale, a tapering exponent, and a magnetic-field index). The data, independent of the details of the model, imply a rather flat transparent spectral index α = -d ln S/d ln ν ~ 0.3 (much flatter than that of extended radio sources), and prolonged injection-i.e., the duration of an active phase (typically about a year) exceeds rise and fall times (a few weeks), identified with an apparent transit time scale. The adiabatic jet model agrees reasonably well with the observations only if the jet is nearly conical (for conservation of magnetic flux transverse to the jet axis) or if it is nearly parabolic (for conservation of magnetic flux longitudinal to the jet axis), and if there is essentially no contribution from a steep-spectrum component (consistent with the absence of significant extended structure). Several arguments indicate that the jet's bulk Lorentz factor {GAMMA} >= 25. Essentially all the radio variability of AO 0235+164 can be understood in terms of adiabatically evolving structures in a relativistic, compact jet. Any extrinsic modulation-e.g., by refractive (slow) scintillation-is less than 7% (rms) at each frequency monitored. Publication: The Astrophysical Journal Pub Date: March 1988 DOI: 10.1086/166126 Bibcode: 1988ApJ...326..668O Keywords: Bl Lacertae Objects; Blazars; Radiant Flux Density; Radio Jets (Astronomy); Radio Sources (Astronomy); Radio Spectra; Variability; Very Long Base Interferometry; Astrophysics; RADIO SOURCES: VARIABLE; BL LACERTAE OBJECTS; GALAXIES: JETS; RADIATION MECHANISMS full text sources ADS | data products SIMBAD (1) NED (1)