ASASSN-18xx: Discovery of an Unprecedented, Extremely Rapid, ~2 mag Brightening of the AGN 4C +40.01

ATel #12106; K. Z. Stanek (OSU), X. Dai (University of Oklahoma), C. S. Kochanek, T. A. Thompson (OSU), B. J. Shappee (IfA, Hawaii), T. W.-S. Holoien (Carnegie Observatories), J. L. Prieto (Diego Portales; MAS), Subo Dong (KIAA-PKU)
on 12 Oct 2018; 18:20 UT
Credential Certification: Krzysztof Stanek (stanek.32@osu.edu)

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During the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN, Shappee et al. 2014), using data from the quadruple 14-cm "Leavitt" telescope in McDonald Observatory, Texas, we have discovered an unprecedented, factor of at least 5 optical brightening of the Seyfert 1.9 AGN 4C +40.01 (J2000.0 RA,Dec=3.3797092,40.8603178; z=0.25).

4C +40.01, while possibly optically variable in CRTS data , it was never brighter than ~17 mag in these data (photometry might be contaminated by a nearby bright star). Its PS1 brightness is g=19.7, and its Gaia brightness is g=19.1.

In ASAS-SN data, 4C +40.01 rapidly brightened to g~15.4 on UT 2018-10-12.19, while it was fainter than g~17.3 just a day before, UT 2018-10-11.17 (see its full ASAS-SN Sky Patrol light curve here). Such high brightness is unprecedented for this object, which is classified on NED as "Flat-Spectrum Radio Source" and "Seyfert 1.9".

This transient has been named "ASASSN-18xx" and has been posted to TNS. In general, such behavior is very rarely seen for AGN or quasars (e.g, ATel #11110, #12082), so rapid multi-wavelength follow-up observations are strongly encouraged.

We would like to thank Las Cumbres Observatory and its staff for their continued support of ASAS-SN. ASAS-SN is funded in part by the Gordon and Betty Moore Foundation through grant GBMF5490 to the Ohio State University, NSF grant AST-1515927, the Mt. Cuba Astronomical Foundation, the Center for Cosmology and AstroParticle Physics (CCAPP) at OSU, the Chinese Academy of Sciences South America Center for Astronomy (CASSACA), and the Villum Fonden (Denmark).