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

Abstract

In the work we present the results of two deep broad-band 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 $E_{\rm cyc}=42.8\pm0.7$ 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 $10^{35}$ erg s$^{-1}$, we concluded that IGR J19294+1816 switched to the accretion from the "cold" accretion disc between Type I outbursts. We also report the updated orbital period of the system.