Abstract

Aims. In this paper, we characterize the first γ-ray flaring episode of the flat-spectrum radio quasar PKS 0346−27 (z = 0.991), as revealed by Fermi-LAT monitoring data, and the concurrent multi-wavelength variability observed from radio through X-rays. Methods. We studied the long- and short-term flux and spectral variability from PKS 0346−27 by producing γ-ray light curves with different time binning. We complement the Fermi-LAT data with multi-wavelength observations from the Atacama Large Millimeter Array (radio mm-band), the Rapid Eye Mount telescope (near-infrared) and Swift (optical-UV and X-rays). This quasi-simultaneous multi-wavelength coverage allowed us to construct time-resolved spectral energy distributions (SEDs) of PKS 0346−27 and compare the broadband spectral properties of the source between different activity states using a one-zone leptonic emission model. Results. PKS 0346−27 entered an elevated γ-ray activity state starting from the beginning of 2018. The high-state continued throughout the year, displaying the highest fluxes in May 2018. We find evidence of short-time scale variability down to approximately 1.5 h, which constrains the γ-ray emission region to be compact. The extended flaring period was characterized by a persistently harder spectrum with respect to the quiescent state, indicating changes in the broadband spectral properties of the source. This was confirmed by the multi-wavelength observations, which show a shift in the position of the two SED peaks by approximately two orders of magnitude in energy and peak flux value. As a result, the non-thermal jet emission completely outshines the thermal contribution from the dust torus and accretion disk during the high state. The broadband SED of PKS 0346−27 transitions from a typical Low-Synchrotron-Peaked (LSP) to the Intermediate-Synchrotron-Peaked (ISP) class, a behavior previously observed in other flaring γ-ray sources. Our one-zone leptonic emission model of the high-state SEDs constrains the γ-ray emission region to have a lower magnetic field, larger radius, and higher maximum electron Lorentz factors with respect to the quiescent SED. Finally, we note that the bright and hard γ-ray spectrum observed during the peak of flaring activity in May 2018 implies that PKS 0346−27 could be a promising target for future ground-based Cherenkov observatories such as the Cherenkov Telescope Array (CTA). The CTA could detect such a flare in the low-energy tail of its energy range during a high state such as the one observed in May 2018.

Highlights

  • Radio-loud active galactic nuclei (AGN) are the most common astrophysical source class in the γ-ray sky

  • In this paper we reported on the γ-ray flaring activity from the flatspectrum radio quasars (FSRQs) PKS 0346−27, and the associated multi-wavelength follow-up observations

  • PKS 0346−27 entered an elevated activity state between the end of 2017 and the beginning of 2018, with the flaring activity continuing over the whole year

Read more

Summary

Introduction

Radio-loud active galactic nuclei (AGN) are the most common astrophysical source class in the γ-ray sky. FSRQs and blazar-like NLS1s are typically LSP, while the peak synchrotron frequency in BL Lacs can range across the three classes (Abdo et al 2010a) While this is true when considering archival multi-wavelength data, some sources have shown extreme changes in their broadband spectral properties during flaring states. The source was found in an elevated state, reaching a daily γ-ray (>100 MeV) flux more than 100 times larger than the average flux reported in the 3FGL, and a significantly harder spectrum with respect to the one reported in the 3FGL This prompted multi-wavelength follow-up observations which revealed enhanced activity in the optical-NIR (Nesci 2018a; Vallely et al 2018), ultraviolet (UV) and X-ray (Nesci 2018b).

Fermi-LAT
Time-resolved SEDs
SED modeling
B99 CTA sensitivity 50h ATCA Planck
Findings
Summary and conclusions
Full Text
Paper version not known

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.