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

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 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 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.

AstroSat detection of a mHz QPO and cyclotron line in IGR J19294+1816 during the 2019 outburst

“…We measure the pulsar's spin period to be 12.485065±0.000015 s. We also report the detection of a 0.032 Hz QPO from the timing analysis of LAXPC light curves. From our spectral analysis results we find the cyclotron line energy to be centered at 42.7±0.9 keV (consistent with NuSTAR report, Tsygankov et al 2019) and estimate the pulsar's magnetic field to be 4.6×10 12 G. From the 0.7-50 keV model flux obtained using our spectroscopy results and assuming a source distance of 11 kpc, we find that during its declining outburst phase, IGR 19294+1816 had a source luminosity of 1.6×10 37 ergs s −1 .…”

“…In our work, we detect the CRSF feature at 42 keV, which indicates (for a z of ∼0.3 and for MNS in the range 1.4-2.0 M : Cottam, Paerels & Mendez 2002) a magnetic field strength of 4.6×10 12 G. Our measurement of ECRSF agrees with the NuSTAR studies of the source (Tsygankov et al 2019). It is also interesting to note that the centroid energy of the cyclotron line has remained steady between the different luminosity states.…”

“…A clear understanding of such anomalies requires a systematic study using of transient pulsars across multiple observations. Tsygankov et al 2019). Our study of this pulsar during its most recent 2019 outburst using AstroSat has additionally strengthened our knowledge about some of the timing and spectral characteristics of this source.…”

“…It is also interesting to note that the centroid energy of the cyclotron line has remained steady between the different luminosity states. Particularly, Tsygankov et al (2019) have conducted their spectral analysis over two luminosity states (LX ∼6.4×10 34 ergs s −1 and LX ∼3.4×10 36 ergs s −1 ) and our work probes a slightly higher luminosity (i.e. LX ∼1.6×10 37 ergs s −1 ) during which the ECRSF has remained fairly steady at ∼42 keV (see Figure 7).…”

“…Corbet & Krimm (2009) inferred an orbital period of 117.2 days using long term Swift-BAT flux modulations. NIR spectroscopy revealed that the system hosts a B1Ve optical companion star and the distance to the system was inferred to be around 11±1 kpc (Tsygankov et al 2019). A cyclotron absorption feature was detected at ∼42 keV using NuSTAR observations (Tsygankov et al 2019).…”