Multi-wavelength observations investigate behavior of blazar S5 0716+714

Astronomers from Bulgaria and Egypt have performed multi-wavelength observations of a well-known blazar designated S5 0716+714. Results of the observational campaign, published June 23 in the Monthly Notices of the Royal Astronomical Society, provide important insights into the behavior of this object.

Blazars are very compact quasars with relativistic jets along our line of sight, associated with supermassive black holes (SMBHs) at the centers of active, giant elliptical galaxies. They are the most numerous extragalactic gamma-ray sources.

In general, blazars belong to a larger group of active galaxies that host active galactic nuclei (AGN), and based on their optical emission properties, they are divided into two classes: flat-spectrum radio quasars (FSRQs) that feature prominent and broad optical emission lines, and BL Lacertae objects (BL Lacs), which do not.

Discovered in 1981, S5 0716+714 is one of the brightest and extensively studied blazars in the sky due to its extreme variability in all measured energy bands. It is classified as an intermediate-frequency synchrotron-peaked BL Lac type object and exhibits quasi-periodic oscillations (QPOs) in optical, radio and gamma-ray bands.

However, although S5 0716+714 has been observed for decades, its redshift is still uncertain due to the blazar’s featureless optical continuum and bright optical nucleus. Moreover, many aspects of its variability behavior are still not well investigated.

That is why a team of astronomers, led by Boyko Mihov of the Bulgarian Academy of Sciences, decided to take a closer look at S5 0716+714. For this purpose, they mainly used the 1.88-m Cassegrain telescope at the Kottamia Astronomical Observatory in Egypt, and the 2-m Ritchey-Chrétien telescope at the Rozhen National Astronomical Observatory in Bulgaria.

The observations found that on the long-term time scales, the variability amplitude of the combined V-band light curve is estimated to be 388.5% and that the activity of S5 0716+714 shows a gradual decrease. In the optical band, the variability amplitude decreases down to 97.59% and in the gamma-rays, the fractional variability decreases from 0.64 to 0.49.

On short-term time scales, the percentage variability amplitude for S5 0716+714 is 97.59 in the V-band, and it was found to decrease from B to R bands. The individual optical light curves turned out to be strongly correlated with each other and no time lags were identified. Moreover, a transient QPO was detected, with a period of 43.5 days, and the astronomers interpret this oscillation in terms of the helical motion of two blobs within the blazar’s jet.

When it comes to intranight time scales, the researchers detected smooth variability with no signs of flares and estimated a duty cycle in the range of 10–20%, which is among the lowest ever derived for S5 0716+714.

In general, the authors of the paper concluded that S5 0716+714 manifested low activity on all the time scales they investigated during the observation period.

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