Spica and the annual cycle of PKS B1322–110 scintillations

Abstract

PKS B1322−110 is a radio quasar that is located only 8 .5 in angular separation from the bright B star Spica. It exhibits intra-day variability in its flux density at GHz frequencies attributed to scintillations from plasma inhomogeneities. We have tracked the rate of scintillation of this source for over a year with the Australia Telescope Compact Array, recording a strong annual cycle that includes a near-standstill in August and another in December. The cycle is consistent with scattering by highly anisotropic plasma microstructure, and we fit our data to that model in order to determine the kinematic parameters of the plasma. Because of the low ecliptic latitude of PKS B1322−110 , the orientation of the plasma microstructure is poorly constrained. Nonetheless at each possible orientation our data single out a narrow range of the corresponding velocity component, leading to a one-dimensional constraint in a twodimensional parameter space. The constrained region is consistent with a published model in which the scattering material is associated with Spica and consists of filaments that are radially oriented around the star. This result has a 1% probability of arising by chance.

Extreme intra-hour variability of the radio source J1402+5347 discovered with Apertif

“…This method models the observed variations as a GP with a judiciously chosen functional form for the temporal covariance function. Although this method assumes an analytic form of the covariance function, it can effectively determine the decorrelation timescale and uncertainties even in epochs near the standstills (Bignall et al 2019). The decorrelation timescales from both methods are tabulated in Table 1 and agree with each other within the errors for all the epochs to which both methods could be applied.…”

“…2). An annual modulation of the scintillation properties has been observed in the other known IHVs (Dennett-Thorpe & de Bruyn 2003;Walker et al 2009;Bignall et al 2019) and is caused by the annual change in the relative velocity of the Earth with respect to the plasma clouds that is due to the orbital motion of the Earth around the Sun. Motivated by this, we continued monitoring the source with a cadence of about one month.…”

“…Our second approach was to model the temporal scintillation as a GP with a covariance function given by a damped exponential: K(∆t) = K 0 exp(c∆t) cos(d∆t), where ∆t is the temporal lag and K 0 , c, and d are model parameters (Bignall et al 2019). This choice for the covariance function is motivated by the shape of the ACF, which shows a steep roll-off at small lags, follows by oscillatory behaviour due to the dominant spectral mode in the light curves (see Fig.…”

“…This allows us to estimate the scintillation timescale and the associated uncertainty even for epochs close to the standstill by employing our knowledge of the covariance function from epochs of rapid variability. We determined the parameters K 0 , c, and d from the April 2019 light curve alone instead of using a fit using the entire annual data set (Bignall et al 2019). With these parameter values fixed, we determined the temporal scale factor k for each epoch with a single-parameter Gaussian regression.…”

Intra-Day Variability Observations of Two Dozens of Blazars at 4.8 GHz

“…Today, it becomes clear that the IDV at centimeter wavelengths is not AGN-intrinsic, but caused by the interstellar scintillation (ISS) effect in our Galaxy [17]. The evidence is from the annual modulations of IDV timescales discovered in a couple of IDV sources that had been monitored for years, which can be well fitted by the Earth orbiting around the Sun and annually across the scintillation pattern (e.g., [18][19][20], see a summary on this in [21]).…”