B2 1308+326: A Changing-look Blazar or Not?

Abstract In our previous study, we identified a shift in the synchrotron peak frequency of the blazar B2 1308+326 from 10 12.9 to 10 14.8 Hz during a flare, suggesting it could be a changing-look blazar (CLB). In this work, we investigate the changing-look behaviour of B2 1308+326 by analysing a newly acquired optical spectrum and comparing it with an archival spectrum. We find that between the two epochs, the continuum flux increased by a factor of ~4.4, while the Mg ii emission line flux decreased by a factor of 1.4 ± 0.2. Additionally, the equivalent width of the Mg ii line reduced from ~20 to ~3 Å, indicating an apparent shift from a flat-spectrum radio quasar (FSRQ) class to a BL Lacertae (BL Lac) class. Despite this apparent change, the ratio of accretion disk luminosity to Eddington luminosity remains &gt;10 −2 during both epochs, indicating efficient accretion persists in B2 1308+326. The measured black hole mass remains consistent with an average <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">BH</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>8.44</mml:mn> </mml:math> M ⊙ . Our findings suggest that B2 1308+326 is not a genuine CLB but rather an intrinsic FSRQ that emerges as a BL Lac during high-flux states due to enhanced nonthermal emission.