Studying Polarization in Blazars: A Focus on FSRQs

Blazars are a unique type of active galactic nuclei (AGNs) known for their powerful jets that are aimed nearly towards Earth. These jets are made up of charged particles moving at very high speeds, which causes them to emit a strong amount of light across various wavelengths. Blazars can be categorized into two main types: Flat Spectrum Radio Quasars (FSRQs) and BL Lacertae Objects. FSRQs typically show strong emission lines in their light spectra, while BL Lacs either lack these lines or show them very faintly.

#Importance of Spectropolarimetry

Spectropolarimetry is a method used to study the light emitted by astronomical objects, including blazars. By analyzing how light is polarized, scientists can learn more about the magnetic fields, particle physics, and the physical processes occurring within these objects. The linear Polarization of the light emitted by blazars is usually more than a few percent, suggesting that the light is mainly produced by non-thermal synchrotron radiation, which is a type of radiation emitted when charged particles move through magnetic fields.

#Study Focus

This study focuses on two specific FSRQs, PKS 0637-75 and PKS 1510-089. The goal is to investigate how the orientation of the jets and the main processes that generate the light affect changes in polarization in both the broad lines and the overall light spectrum. Observations were conducted regularly over a two-year period using a specialized instrument on the Southern African Large Telescope.

#Observational Techniques

Observations involved capturing light using a spectrograph that divides incoming light into its various wavelengths while also measuring the polarization at each wavelength. This setup allows scientists to see how polarized the light is and to detect small changes in polarization over time. A series of observations were conducted bi-weekly for both PKS 0637-75 and PKS 1510-089.

#Observation Details

For PKS 0637-75, observations were conducted from February 2019 to March 2020, while for PKS 1510-089, observations took place from March 2019 to August 2021. During these observations, both objects showed variability in their continuum polarization levels.

#Data Collection

Data was obtained in both polarized and non-polarized formats across a defined range of wavelengths. The polarization levels were found to vary, with PKS 0637-75 having an average polarization of about 2.5% and PKS 1510-089 showing a higher average of around 7.5%.

#Analysis of Observations

#Continuum Polarization

In the study, continuum polarization refers to the general level of polarization exhibited by the blazars outside of their specific emission lines. For PKS 0637-75, polarization levels ranged from about 1.4% to 4.0%, whereas PKS 1510-089 exhibited a much broader range from 1.8% to 21.4%.

#Emission Lines

Emission lines are specific regions in the spectrum where light is strongly emitted at certain wavelengths. The study focused particularly on the Mg II line in PKS 0637-75 and the broad H and H lines in PKS 1510-089. In both cases, there was no clear evidence of polarization in these broad emission lines, indicating that the processes generating these emissions are different from those affecting the continuum polarization.

#The Role of Gamma Rays

Blazars are often monitored for gamma-ray emissions, which are high-energy photons. The connection between optical emissions and gamma-ray activity can provide insights into the behavior of the jets and the processes happening in these extreme environments. PKS 1510-089, for instance, is known as a gamma-ray loud blazar, meaning it frequently emits high levels of gamma rays, while PKS 0637-75 does not exhibit this type of activity as often.

#Comparison of FSRQs

The study emphasizes the differences between the two FSRQs. PKS 1510-089, being more active and showing variability, can switch between thermal and non-thermal emission processes more dramatically than the quieter PKS 0637-75. This variability is reflected in their polarization levels, which change alongside their brightness and emission characteristics.

#Implications of Findings

#Polarization Mechanisms

The findings suggest that the polarization mechanisms at play differ between the continuum and emission lines. For PKS 0637-75, the low levels of polarization indicate that thermal processes from the accretion disk primarily drive the emissions. In contrast, PKS 1510-089 shows indications of both thermal and non-thermal processes, particularly during flaring events when the jet's emission dominates.

#Understanding Blazar Emission

The study enhances our grasp of how blazars emit light and how the properties of that light, such as polarization, can be influenced by their internal structures and the orientations of their jets. This knowledge is significant for understanding the more extensive behaviors of AGNs and their role in the cosmos.

#Future Research Directions

Further research is likely to focus on gathering more spectropolarimetric data from various blazars to get a broader understanding of how polarization behaves across this class of objects. Investigating different wavelengths may yield additional insights into the physical conditions within the jets and the accretion disks.

#Conclusion

In summary, the study of PKS 0637-75 and PKS 1510-089 through spectropolarimetry provides valuable insights into the polarization characteristics of blazars. While both objects are FSRQs, they exhibit differing behaviors in terms of emission processes and polarization. Understanding these differences is crucial for piecing together the broader picture of how active galactic nuclei operate and interact with their surroundings in the universe.