Letter to the Editor

A redshifted excess in the broad emission lines after the flare of the γ-ray narrow-line Seyfert 1 PKS 2004−447

¹ European Southern Observatory, Alonso de Córdova 3107, Casilla 19, Santiago 19001, Chile
e-mail: whon@student.unimelb.edu.au
² School of Physics, University of Melbourne, Parkville, Victoria 3010, Australia
³ Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia
⁴ Centre for Gravitational Astrophysics, Australian National University, Canberra, ACT 2611, Australia
⁵ Centro de Astronomía (CITEVA), Universidad de Antofagasta, Avenida Angamos 601, Antofagasta, Chile
⁶ Núcleo de Astronomía de la Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército Libertador 441, Santiago 22, Chile
⁷ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁸ Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Quantum, Vesilinnantie 5, 20014 Turku, Finland
⁹ Department of Physics and Astronomy, University of Turku, Quantum, Vesilinnantie 5, 20014 Turku, Finland
¹⁰ , Camino del Observatorio 1515, Las Condes, Santiago, Chile

Received: 11 October 2022
Accepted: 20 March 2023

Abstract

PKS 2004−447 is a narrow-line Seyfert 1 (NLS1) harbouring a relativistic jet with γ-ray emission. On 2019 October 25, the Fermi-Large Area Telescope captured a γ-ray flare from this source, offering a chance to study the broad-line region (BLR) and jet during such violent events. This can provide insights into the BLR structure and jet interactions, which are important for active galactic nuclei (AGN) and host galaxy co-evolution. We report X-shooter observations of enhancements in the broad line components of Balmer, Paschen, and He I lines seen only during the post-flare and vanishing 1.5 years after. These features are biased redwards up to ∼250 km s⁻¹ and are narrower than the pre-existing broad line profiles. This indicates a connection between the relativistic jet and the BLR of a young AGN, and how γ-ray production can lead to localised addition of broad emission lines.