Timing and Spectral Study of IGR J19294+1816 with the RXTE: The Discovery of Cyclotron Features

Abstract

Gauss. This is also detected at a lower significance in two other observations. In addition an Fe line emission at 6.4 keV is prominently detected during the highest flux.X-ray pulsations are detected in 9 out of 10 observations; no pulsations were found in the observation with the lowest flux level. During this observation with the lowest flux the pulsation phenomenon becomes detectable only at the soft X-ray bands.

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

“…Another interesting outburst characteristic is the variation of the pulse fraction. RXTE observations (Roy, Choudhury & Agrawal 2017) and LAXPC observations (this work) tend to show an increasing pulse fraction all the way up to ∼30 keV, as expected in most accretion powered X-ray pulsars. However, beyond 30 keV, the PF drops dramatically.…”

“…The detection of a pulse peak and its higher harmonics have been reported in all previous outbursts including in this current work. Notably, the higher harmonics decrease in strength as the outburst progresses from its highest to its lowest flux levels as seen from RXTE observations (Roy, Choudhury & Agrawal 2017). Inhomogeneities in the NS accretion disk also get prominently detected in the form of mHz QPOs in a number of HMXB pulsars during their periastron passage outbursts (for example, 4U 0115+63: Dugair et al 2013, V 0332+53:Caballero-García et al 2016 and IGR 19294+1816 is no exception to this.…”

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

“…On the other hand, we verified that it is indeed possible to model the spectrum with a combination of a power law and cyclabs model, however, not only the fit quality is considerably worse in this case but also the line itself gets unreasonably deep. We conclude, therefore, that the claim of the cyclotron line discovery by Roy et al (2017) is unsupported by the data used by the authors, which has insufficient statistics. On the other hand, NuSTAR data provide much better statistics and allow us to conduct a much more sensitive search for the possible cyclotron lines in the source spectrum.…”

“…Discovery of the cyclotron resonance scattering feature at ∼ 36 keV in the spectrum of the source has been claimed by Roy et al (2017) based on the observed deviation of the RXTE/PCA continuum from a power law above ∼ 30 keV. The choice of the continuum model by the authors appears, however, to be extremely odd, because X-ray spectra of all known XRPs exhibit a cutoff above ∼ 15 − 20 keV (see e.g., Nagase 1989;Filippova et al 2005).…”

“…The relative faintness of IGR J19294+1816 did not allow to make any conclusions regarding the physical properties of the NS in the system up to date. Only tentative detection of the cyclotron absorption line at ∼35.5 keV was reported based on the deviation of the source spectrum from a power law at higher energies using the RXTE data (Roy et al 2017). In this work we use long-term Swift/XRT monitoring observations to characterise accretion regimes in the system as well as two dedicated deep NuSTAR observations to describe properties of the NS in the hard X-ray range for the first time.…”