The radio-bright blazar PKS 1741-03 coincident with the high energy neutrino alert IceCube-220205B

ATel #15215; Y. Y. Kovalev (ASC Lebedev, MIPT, MPIfR), A. V. Plavin (ASC Lebedev, MIPT), S. V. Troitsky (INR), Yu. A. Kovalev (ASC Lebedev), T. Hovatta (FINCA), S. Kiehlmann (IoA FORTH, OVRO), I. Liodakis (FINCA), A. C.S. Readhead (OVRO, Caltech), A. K. Erkenov (SAO RAS), Y. V. Sotnikova (SAO RAS), M. Tornikoski (MRO), A. Lahteenmaki (MRO), S. G. Jorstad (Boston U., SPbSU), A. P. Marscher (Boston U.), J. L. Gómez (IAA-CSIC), M. Giroletti (INAF-IRA), N. Marchili (INAF-IRA), S. Righini (INAF-IRA), A. B. Pushkarev (CrAO, ASC Lebedev, MIPT)
on 8 Feb 2022; 12:45 UT
Credential Certification: Yuri Y. Kovalev (yyk@asc.rssi.ru)

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The recent GOLD neutrino alert IceCube-220205, GCN #31554, with an energy above 200 TeV is suggested to be associated with the blazar PKS 1741-03. We note that this is one of the brightest blazars on the radio sky and is one of only four blazars singled out by Plavin et al. (2020) as the most probable high energy neutrino sources. Since the Plavin et al. (Jan 2020) paper, IceCube has reported 10 neutrino alerts satisfying the selection criteria used in that paper: neutrino energy >200 TeV and the statistical 90% error region smaller than 10 deg^2. We estimate the chance probability that at least one of these events coincides within its statistical uncertainty plus 0.5 deg systematic error (Plavin et al. 2020) with one of the four blazars selected in 2020. The preliminary p-value obtained by scrambling right ascensions of the 10 events is 3.2%. The object is a member of many radio monitoring programs. It has shown a radio flare at millimeter and centimeter wavelengths that reached 8 Jy in the first half of 2021. The object is observed currently at its typical level of 3-5 Jy. VLBA observations in 2021 show a very compact parsec-scale structure with a core dominance of 0.5-0.9 and 7 mm core size of 85 muas or 0.7 pc. Being one of the brightest radio blazars in the sky, PKS 1741-03 is a modest gamma-ray source; no current gamma-ray flare was reported. This confirms previous observations that the relation between radio, gamma-ray and neutrino luminosities of blazars is nontrivial. We encourage the community to monitor PKS 1741-03 in the whole electromagnetic spectrum. We summarize below results of its recent observations by radio monitoring programs which will continue observations of the blazar. The blazar is observed monthly by the VLBA at 43 GHz within the BEAM-ME program, images are made public. PKS 1741-03 is monitored regularly with the VLBA at 15 GHz by the MOJAVE team, see images at the following link. Metsahovi Radio Observatory has observed this source regularly since 1988 as part of its long-term radio monitoring program. The historical data for PKS 1741-03 show three bright flares exceeding 7 Jy at 37 GHz. The last one peaked from Jan to Mar 2021, and since then the flux density has been dropping from 7.7 Jy in Apr 2021 to below 3 Jy in Feb 2022. RATAN-600 instantaneous spectra of PKS 1741-03 at 1.2, 2.3, 4.7, 8.2, 11.2 and 22 GHz are monitored since 1995 and show a typical behavior for blazars: variable, mostly inverted or flattened near 22 GHz. The 25-years historical spectral maximum of 8.5+-0.2 Jy was observed at 22 GHz on 19 Mar 2021. Flux density decreased to 3.4+-0.2 Jy at 22 GHz in Nov 2021. The OVRO 40-m Telescope has been regularly monitoring the source since 2008 at 15 GHz. In 2021, the blazar was flaring, reaching its highest flux density of 7.6 Jy on 20 Apr 2021. It continued to be in a high state until Jun 2021. The latest observation on 19 Jan 2022 shows a flux density of 5.0+-0.06 Jy. The telescope is used to regularly monitor a large number of AGN at 15 GHz. It is currently supported by private funding from Caltech and MPIfR. The Medicina 32-m radio telescope regularly observes the source with monthly cadence at 8.3 and 24.1 GHz. The latest measurements were obtained on 14 Jan 2022 with a flux density of 5.21+-0.07 Jy and 4.22+-0.15 Jy at 8.3 and 24 GHz, respectively, and a spectral index -0.2. This is markedly different from the most recent peak radio state from 19 Mar 2021 with a flux density of 6.44+-0.04 Jy and 8.2+-0.2 Jy at 8.3 and 24.1 GHz, spectral index +0.2.