A NuSTAR observation of the low mass X-ray binary GX 349+2 throughout the Z-track

Abstract

Although the most luminous class of neutron star low mass X-ray binaries, known as Z sources, have been well studied, their behavior is not fully understood. In particular, what causes these sources to trace out the characteristic Z-shaped pattern on color-color or hardness-intensity diagrams is not well known. By studying the physical properties of the different spectral states of these sources, we may better understand such variability. With that goal in mind, we present a recent NuSTAR observation of the Z source GX 349+2, which spans approximately 2 days, and covers all its spectral states. By creating a hardness-intensity diagram we were able to extract five spectra and trace the change in spectral parameters throughout the Z-track. GX 349+2 shows a strong, broad Fe K$\alpha$ line in all states, regardless of the continuum model used. Through modeling of the reflection spectrum and Fe K$\alpha$ line we find that in most states the inner disk radius is consistent with remaining unchanged at an average radius of 17.5 $R_g$ or 36.4 km for a canonical 1.4 $M_{\odot }$ neutron star. During the brightest flaring branch, however, the inner disk radius from reflection is not well constrained.

12 pages, 7 figures, accepted by ApJ

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Cited by in corpus (17)

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• Highly Significant Detection of X-Ray Polarization from the Brightest Accreting Neutron Star Sco X-1
• NICER-NuSTAR Observations of the Neutron Star Low-Mass X-ray Binary 4U 1735-44
• Relativistic X-Ray Reflection and Photoionised Absorption in the Neutron-Star Low-Mass X-ray Binary GX 13+1
• StrayCats: A catalog of NuSTAR Stray Light Observations
• AstroSat view of IGR J17091-3624 and GRS 1915+105: decoding the 'pulse' in the 'Heartbeat State'
• Constraining the Coronal Heights and Readjustment Velocities Based on the Detection of a Few Hundred Seconds Delays in the Z Source GX 17+2
• Iron Line from Neutron Star Accretion Disks in Scalar Tensor Theories
• Fe K$\alpha$ and Fe K$\beta$ line detection in the NuSTAR spectrum of the ultra-bright Z-source Scorpius X-1
• Spectral and Timing evolution of GX 340+0 along its Z-track
• Broadband spectro-temporal investigation of neutron star low-mass X-ray binary GX 349+2
• X-ray polarization of Z-type neutron star low-mass X-ray binaries -- I. Model-independent, time-resolved X-ray polarimetry
• Modeling the upper kHz QPOs of 4U 1728-34 with X-ray reverberation
• AstroSat View of Transient Low-mass X-ray Binary XTE J1701-462: Spectral and Temporal Evolution along the Z-track
• Spectro-temporal evolution of 4U 1702-429 using AstroSat-NICER
• IXPE view of the Sco-like source GX 349+2 in the normal branch
• X-ray polarization of Z-type neutron star low-mass X-ray binaries -- II. Spectropolarimetric analysis