Brightening of the quasar PKS 0420-014 across the electromagnetic spectrum

ATel #15935; D. Elsaesser (TU Dortmund, Germany) S. G. Jorstad, C. Pauley (Institute for Astrophysical Research, Boston University, Boston, MA, USA) A. Scherbantin, L. Kunkel, L. Schneider, M. Kadler, F. Eppel, F. Roesch, K. Mannheim (University of Wurzburg, Germany) M. Heidemann, O. Domann, L. Kimmel, R. Goldbach, F. Wehr, D. Scheuermayer, J. Seufert, B. Horst, R. Steineke, D. Reinhart, N. Zottmann, M. Feige, C. Lorey (FKG - Hans-Haffner-Sternwarte, Wuerzburg, Germany) J. A. Acosta Pulido (Instituto de Astrofisica de Canarias and Universidad de La Laguna, Tenerife, Spain) S. A. Cellone (Complejo Astronomico El Leoncito, CASLEO, San Juan, Argentina) N. Marchili, S. Righini, M. Giroletti (INAF, Istituto di Radioastronomia, Bologna, Italy) V. Vlasyuk, O. Spiridonova, O. Maslennikova (Special Astrophysical Observatory of Rus. Ac. Sci.; Russia) T. Tripathi, A. C. Gupta (Aryabhatta Research Institute of Observational Sciences (ARIES), Manora Peak, Nainital 263001, India) P. Edwards, J. Stevens (CSIRO Space and Astronomy, Australia) M. I. Carnerero, C. M. Raiteri, M. Villata (INAF, Osservatorio Astrofisico di Torino, Italy)
on 7 Mar 2023; 19:38 UT
Credential Certification: Dominik Elsaesser (dominik.elsaesser@tu-dortmund.de)

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Observatories of the Whole Earth Blazar Telescope (WEBT) and the ATCA have detected high state over a broad spectral range of the FSRQ PKS 0420-014 (RA 04 23 15.800 Dec -01 20 33.066, ICRS J2000; z=0,91609 – cf. SIMBAD)
While this AGN showed ca. 18 mag (R-band) in Dec 2022 and Jan 2023, an increase of ca. 2.66 mag was detected in the last weeks, from 17.803 mag on Feb. 13 to a max. of 15.140 mag on Mar. 2 (R-Band).
Previously it reached a comp. brightness in Oct. 2020 (ATel #14106: R: 15.25). Only in 2012 (ATel #4278: R: 14.5 and 14.3 mag) and 2010 (ATel #2395: R: 14.43 mag) higher values were reported in the last 20 yrs.
Optical (R-band):
JD 2459929.8008: 18.194 ± 0.032 (PT)
JD 2459941.4478: 18.059 ± 0.077 (HHO)
JD 2459951.4173: 17.800 ± 0.084 (IAC)
JD 2459961.3768: 17.533 ± 0.061 (IAC)
JD 2459983.3697: 17.462 ± 0.058 (HHO)
JD 2459984.7197: 17.421 ± 0.042 (PT)
JD 2459989.3851: 17.803 ± 0.068 (IAC)
JD 2459994.4207: 17.699 ± 0.065 (IAC)
JD 2459997.2902: 16.968 ± 0.025 (HHO)
JD 2460001.3479: 16.669 ± 0.041 (IAC)
JD 2460002.2798: 16.652 ± 0.024 (HHO)
JD 2460004.2881: 15.980 ± 0.020 (HHO)
JD 2460005.3850: 15.491 ± 0.035 (HHO)
JD 2460006.0861: 15.476 ± 0.001 (AR)
JD 2460006.0901: 15.497 ± 0.002 (AR)
JD 2460006.1904: 15.186 ± 0.012 (SAO)
JD 2460006.2164: 15.166 ± 0.010 (SAO)
JD 2460006.2363: 15.142 ± 0.009 (SAO)
JD 2460006.2444: 15.140 ± 0.010 (SAO)
JD 2460006.2814: 15.242 ± 0.011 (HHO)
JD 2460006.3721: 15.374 ± 0.021 (HHO)
JD 2460006.4076: 15.425 ± 0.039 (IAC)
JD 2460006.4453: 15.516 ± 0.038 (IAC)
JD 2460007.3021: 16.247 ± 0.026 (HHO)
JD 2460007.3829: 16.365 ± 0.045 (HHO)

The optical observations were conducted at Perkins Obs. (PT, 1.82 m telescope), the Hans-Haffner Obs. (HHO, 0.5 m), the Inst. de Astrofisica de Canarias (IAC, 0.82 m), the ARIES Obs. (AR, 1.04 m) and the Special Astrophysical Obs. of Rus.Ac.Sci. (SAO, 1 m).
All data were collected with a standard RC filter and the specifications of the GASP list of the WEBT collaboration.
Gamma-ray: We have calculated the gamma-ray flux of the quasar at 0.1-200 GeV obtained by the Fermi LAT using the data provided by the Fermi Space Science Center from 2023 Feb. 8 to Mar. 1 with 1 day binning. Although the source was mostly undetected at gamma-ray energies (assuming that a detection corresp. to TS>10), it was detected at the end of Feb. with the flux level of (1.2+-0.6)E-7 ph/cm^2/s on JD2460004.
Radio: In the run-up to the increase in brightness, an increase of the flux densities, S, in the radio band was detected with the 32 m radio telescope at Medicina (Italy):
8.5 GHz
JD 2459932.7754: 4.95 ± 0.10
JD 2459972.6721: 5.04 ± 0.10
24 GHz
JD 2459932.8443: 6.4 ± 0.2
JD 2459972.7356: 6.5 ± 0.2

Australia Telescope Compact Array (ATCA) monitoring at radio frequencies between 2.1 GHz and 35 GHz indicates a long-term radio outburst starting in 2018. Data show a flat spectral index with S~2 Jy at all frequencies in 2018, followed by an increase in S at all frequencies with an inverted spectrum between 2.1 GHz and higher frequencies. Latest measured flux densities:

2.1 GHz JD 2459914.5: 2.015 ± 0.046 Jy
5.5 GHz JD 2459961.5: 4.411 ± 0.017 Jy
9 GHz JD 2459961.5: 5.892 ± 0.017 Jy
17 GHz JD 2459812.5: 8.545 ± 0.065 Jy
19 GHz JD 2459812.5: 8.497 ± 0.065 Jy
33 GHz JD 2459893.5: 7.2 ± 0.1 Jy
35 GHz JD 2459893.5: 7.1 ± 0.1 Jy

The ATCA is part of the Australia Telescope National Facility under the direction of the CSIRO, funded by the Australian Government. The Gomeroi people are the traditional owners of the Observatory site.