A1 Refereed original research article in a scientific journal
Rapid jet ejection from PKS 0215+015 coincident with a high-energy neutrino event
Authors: Eppel, F.; Kadler, M.; Ros, E.; Benke, P.; Debbrecht, L. C.; Eich, J.; Edwards, P. G.; Giroletti, M.; Gokus, A.; Hämmerich, S.; Heßdörfer, J.; Janssen, M.; Kim, S.; Kirchner, D.; Kovalev, Y. Y.; Krichbaum, T. P.; Ojha, R.; Paraschos, G. F.; Rösch, F.; Schulga, W.; Sinapius, J.; Stevens, J.
Publisher: EDP Sciences
Publication year: 2026
Journal: Astronomy and Astrophysics
Article number: A326
Volume: 708
ISSN: 0004-6361
eISSN: 1432-0746
DOI: https://doi.org/10.1051/0004-6361/202558593
Publication's open availability at the time of reporting: Open Access
Publication channel's open availability : Open Access publication channel
Web address : https://doi.org/10.1051/0004-6361/202558593
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/523355027
Self-archived copy's licence: CC BY
Self-archived copy's version: Publisher`s PDF
Aims. We present a new neutrino-blazar multiwavelength-flare coincidence, observed in the blazar PKS 0215+015 that showed a strong multiwavelength outburst in positional and temporal coincidence with the IceCube neutrino track alert IC220225A similar to the case of TXS 0506+056. We investigate the immediate response of the radio jet to the major flare and a possible neutrino association.
Methods. We performed target-of-opportunity observations of PKS 0215+015 with the Very Long Baseline Array (VLBA) at 15 GHz, 23 GHz, and 43 GHz in full polarization for six epochs with a monthly cadence following the neutrino event. We combined the VLBA observations with monitoring data from the Effelsberg 100-m telescope, the Australia Telescope Compact Array, and Fermi/LAT.
Results. Based on our kinematic analysis, we identified a new rapid jet component with an apparent speed of ∼60−80 c, which was ejected around the arrival time of IC220225A. The fast component ejection is traced by a characteristic signature in polarization that suggests a shock–shock interaction with a quasi-stationary feature. By combining the VLBA results with radio variability data, we estimated a bulk Lorentz factor of Γ = 105 ± 56, and a jet viewing angle of ϑ = (1.47 ± 0.31)°.
Conclusions. We note that the properties of the rapid component exceed previously reported maximum apparent jet speeds and Lorentz factors reported by continuous monitoring programs. This is likely only possible because we are observing an exceptional flaring event at high redshift (z = 1.72), with a higher observing cadence than in typical monitoring programs. We suggest that neutrino production in PKS 0215+015 can happen through pγ-interactions with protons possibly accelerated within the fast moving feature. The target photon field could be external to the jet or explained by a multi-layered jet. The latter scenario would be in agreement with the presence of quasi-stationary features revealed in our analysis.
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This work is based on observations with the 100-m telescope of the MPIfR (Max-Planck-Institut für Radioastronomie) at Effelsberg. FE, MK, JH, and FR acknowledge support from the German Science Foundation (DFG, grants 447572188, 434448349, 465409577, 443220636 [FOR5195: Relativistic Jets in Active Galaxies]) and the German Aerospace Center (DLR, grant 50OR2506). SH is partly supported by the German Science Foundation (DFG grant numbers WI 1860/14-1 and 434448349). We acknowledge the M2FINDERS project from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 101018682). YYK was supported by the MuSES project, which has received funding from the European Union (ERC grant agreement No 101142396). Views and opinions expressed are those of the authors only and do not necessarily reflect those of the European Union or ERCEA. Neither the European Union nor the granting authority can be held responsible for them. This research has made use of the Astrophysics Data System, funded by NASA under Cooperative Agreement 80NSSC21M00561. The VLBA is an instrument of the National Radio Astronomy Observatory. The National Radio Astronomy Observatory and Green Bank Observatory are facilities of the U.S. National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This work made use of the Swinburne University of Technology software correlator, developed as part of the Australian Major National Research Facilities Programme and operated under licence (Deller et al. 2011). The Australia Telescope Compact Array is part of the Australia Telescope National Facility (https://ror.org/05qajvd42) which is funded by the Australian Government for operation as a National Facility managed by CSIRO. We acknowledge the Gomeroi people as the Traditional Owners of the Observatory site. This research has made use of data from the MOJAVE database that is maintained by the MOJAVE team (Lister et al. 2018). This study makes use of VLBA data from the VLBA-BU Blazar Monitoring Program (BEAM-ME and VLBA-BU-BLAZAR; http://www.bu.edu/blazars/BEAM-ME.html), funded by NASA through the Fermi Guest Investigator Program.
