Curious Case of CGRaBS J0211+1051: Observational Evidence of Lepto-Hadronic Origin of High-Energy Emission?

Abstract

We present an extensive analysis of the multi-wavelength data of the low-synchrotron-peaked BL Lac object CGRaBS J0211+1051, which has been gathered over more than ten years with many observatories. Two major gamma-ray flares have been observed during the Fermi era: one in January 2011 and other in June 2019. During these events, CGRaBS J0211+1051 was also bright in other energy bands. On the other hand, there are also examples of optical activity that do not exhibit any comparable gamma-ray variability. Here, we study the temporal and spectral characteristics of the object in an attempt to understand the emission mechanisms operating in this source. A peculiar feature in its spectrum is the X-ray domain, which is unusually soft considering its object class. Interestingly, the relatively soft UV and optical spectrum does not extrapolate well to the X-rays. To mimic the observed SEDs during quiescent and flaring periods, we use both a purely leptonic and a hadro-leptonic modeling approach to reproduce four broadband SEDs from various epochs. When taking into account the steep optical-UV spectrum, we find that the hadro-leptonic scenarios better explains the SEDs compared to the purely leptonic model. The hadro-leptonic interpretation of the two gamma-ray flares suggests that CGRaBS J0211+1051 could be both a potential neutrino emitter and TeV-bright (E>10 TeV). Thus, it may offer a unique test bed to check for hadro-leptonic contributions to the multi-messenger emission in blazar jets.