The Blazar Emission Environment: Insight from Soft X-ray Absorption

TL;DR

This study investigates the presence of intrinsic gas in TeV blazars using soft X-ray spectral analysis, finding evidence in one case and none in others, which impacts understanding of their emission environments.

Contribution

It introduces a spectral analysis method to detect intrinsic gas in blazars and applies it to three sources, providing new insights into their emission environments.

Findings

Evidence for intrinsic gas in 1ES 1959+650.

No evidence for intrinsic gas in RGB J0710+591 and W Comae.

Spectral analysis helps distinguish between absorption and spectral curvature.

Abstract

Collecting experimental insight into the relativistic particle populations and emission mechanisms at work within TeV-emitting blazar jets, which are spatially unresolvable in most bands and have strong beaming factors, is a daunting task. New observational information has the potential to lead to major strides in understanding the acceleration site parameters. Detection of molecular carbon monoxide (CO) in TeV emitting blazars, however, implies the existence of intrinsic gas, a connection often found in photo-dissociated region models and numerical simulations. The existence of intrinsic gas within a blazar could provide a target photon field for Compton up-scattering of photons to TeV energies by relativistic particles. We investigate the possible existence of intrinsic gas within the three TeV emitting blazars RGB J0710+591, W Comae and 1ES 1959+650 which have measurements or upper limits on molecular CO line luminosity using an independent technique which is based on the spectral analysis of soft X-rays. Evidence for X-ray absorption by additional gas beyond that measured within the Milky Way is searched for in Swift X-ray Telescope (XRT) data between 0.3 and 10 keV. Without complementary information from another measurement, additional absorption could be misinterpreted as an intrinsically curved X-ray spectrum since both models can frequently fit the soft X-ray data. After breaking this degeneracy, we do not find evidence for intrinsically curved spectra for any of the three blazars. Moreover, no evidence for intrinsic gas is evident for RGB J0710+591 and W Comae, while the 1ES 1959+650 XRT data support the existence of intrinsic gas with a column density of $\sim1\times10^{21}$cm$^{-2}$.