Study of the X-ray pulsar IGR J19294+1816 with NuSTAR: Detection of cyclotron line and transition to accretion from the cold disk

¹ Department of Physics and Astronomy, University of Turku, 20014 Turku, Finland
e-mail: sergey.tsygankov@utu.fi
² Space Research Institute of the Russian Academy of Sciences, Profsoyuznaya Str. 84/32, 117997 Moscow, Russia
³ Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, 72076 Tübingen, Germany
⁴ Leiden Observatory, Leiden University, 2300 RA Leiden, The Netherlands
⁵ Pulkovo Observatory of the Russian Academy of Sciences, 196140 Saint Petersburg, Russia

Received: 6 July 2018
Accepted: 19 November 2018

Abstract

In the work we present the results of two deep broadband observations of the poorly studied X-ray pulsar IGR J19294+1816 obtained with the NuSTAR observatory. The source was observed during Type I outburst and in the quiescent state. In the bright state a cyclotron absorption line in the energy spectrum was discovered at E_cyc = 42.8 ± 0.7 keV. Spectral and timing analysis prove the ongoing accretion also during the quiescent state of the source. Based on the long-term flux evolution, particularly on the transition of the source to the bright quiescent state with luminosity around 10³⁵ erg s⁻¹, we conclude that IGR J19294+1816 switched to the accretion from the “cold” accretion disk between Type I outbursts. We also report the updated orbital period of the system.