Hoda Mishra and colleagues presented multi-wavelength photometric and spectroscopic monitoring observations of the blazar, B2 1420+32, focusing on its outbursts in 2018-2020. They found that the object exhibits a large scale spectral variability and is the so-called “changing-look” blazar. Their study recently appeared on journal ArXiv.
Blazars are active galactic nuclei with their relativistic jets pointing toward the observer, with two major sub-classes, the flat spectrum radio quasars and BL Lac objects.
AGNs are subdivided into several broad categories, including Type I (also called quasars, Seyfert I) that show a blue continuum from an accretion disk and broad emission lines created by photoionization and Type II (or Seyfert II), which show only narrow lines and no continuum variability. Some AGNs move from one class to another and therefore are dubbed “changing-look” sources. Studying changing look phenomena in blazars can provide useful insight into understanding the origin and particle acceleration processes of radio jets.
Now, Hora Mishra and colleagues reported the detection of a new changing-look blazar. Using mainly the Las Cumbres Observatory Global Telescope Network (LCOGT), they found that the blazar B2 1420+32, at a redshift of 0.682 and with a black hole mass of about 400 million solar masses, appears to shift back and forth between the optical spectrum of an FSRQ and that of a BL Lac several times, while also developing new spectral features.
They found that B2 1420+32 showcases large-scale spectral variability in both its continuum and line emission, together with dramatic gamma-ray and optical variability, on week to month timescales.
They also found that, between 2016–2019, the gamma-ray and optical ﬂuxes increased by factors of 1500 (8 mags) and 40 (4 mags), respectively. The astronomers noted that observed optical variability amplitude is unprecedented, as the optical ﬂux increases by a factor of 100 (5 mags) compared to the SDSS observations conducted in 1995.
For the first time, we detect components in the optical spectra consistent with single temperature blackbody emission, with 20% of the Eddington luminosity.– Wrote authors of the study.
This extreme variability we describe here has not been observed before. However, it may not be uncommon, because dedicated multi-band and spectroscopic monitoring of blazars are still rare. Dedicated searches for more changing-look blazars will extend the changing-look AGN studies to jetted AGNs and allow us to utilize the dramatic spectral changes to reveal AGN/jet physics.— told Hora, lead author of the study.
Finally, researchers concluded that B2 1420+32 is a changing-look blazar transiting between FSRQ and BL Lac due to dramatic changes in the jet continuum ﬂux diluting the line features. They emphasized that extreme variability, as in the case of B2 1420+32, has not been observed before in any blazar.
Featured image: Multi-band optical LCOGT, ASAS-SN, and Fermi light curves of B2 1420+32 © Mishra et al.
Reference: Hora D. Mishra, Xinyu Dai, Ping Chen, Jigui Cheng, T. Jayasinghe, Michael A. Tucker, Patrick J. Vallely, David Bersier, Subhash Bose, Aaron Do, Subo Dong, Thomas W. S. Holoien, Mark E. Huber, Christopher S. Kochanek, Enwei Liang, Anna V. Payne, Jose Prieto, Benjamin J. Shappee, K.Z. Stanek, Saloni Bhatiani, John Cox, Cora DeFrancesco, Zhiqiang Shen, Todd A. Thompson, Junfeng Wang, “The Changing Look Blazar B2 1420+32”, pp. 1-21, ArXiv, 2021. https://arxiv.org/abs/2103.08707
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