AstroSat observation of GX 5-1: Spectral and timing evolution

Abstract

We report on the first analysis of AstroSat observation of the Z-source GX 5- 1 on February 26-27, 2017. The hardness-intensity plot reveals that the source traced out the horizontal and normal branches. The 0.8-20 keV spectra from simultaneous SXT and LAXPC data at different locations of the hardness-intensity plot can be well described by a disk emission and a thermal Comptonized component. The ratio of the disk flux to the total i.e. the disk flux ratio increases monotonically along the horizontal to the normal one. Thus, the difference between the normal and horizontal branches is that in the normal branch, the disk dominates the flux while in the horizontal one it is the Comptonized component which dominates. The disk flux scales with the inner disk temperature as T_{in}^{5.5} and not as T_{in}{4} suggesting that either the inner radii changes dramatically or that the disk is irradiated by the thermal component changing its hardness factor. The power spectra reveal a Quasi Periodic Oscillation whose frequency changes from \sim 30 Hz to 50 Hz. The frequency is found to correlate well with the disk flux ratio. In the 3-20 keV LAXPC band the r.m.s of the QPO increases with energy (r.m.s \prop E0.8), while the harder X-ray seems to lag the soft ones with a time-delay of a milliseconds. The results suggest that the spectral properties of the source are characterized by the disk flux ratio and that the QPO has its origin in the corona producing the thermal Comptonized component.

References in corpus (41)

• Millisecond Oscillations in X-Ray Binaries
• The broad-band power spectra of X-ray binaries
• Calibration of the Large Area X-ray Proportional Counter (LAXPC) instrument on-board AstroSat
• Boundary layer, accretion disk and X-ray variability in luminous LMXBs
• Mechanisms for High-frequency QPOs in Neutron Star and Black Hole Binaries
• X-ray bursts at extreme mass accretion rates from GX 17+2
• An abrupt drop in the coherence of the lower kilohertz QPO in 4U 1636-536
• Precise Measurements of the Kilohertz Quasi-Periodic Oscillations in 4U 1728-34
• RXTE observations of the first transient Z source XTE J1701-462: shedding new light on mass accretion in luminous neutron star LMXBs
• Large Area X-ray Proportional Counter (LAXPC) Instrument on AstroSat and Some Preliminary Results from its performance in the orbit
• The Amplitude of the Kilohertz Quasi-periodic Oscillations in 4U 1728-34, 4U 1608-52, and Aql X-1, as a Function of X-ray Intensity
• AstroSat/LAXPC reveals the high energy variability of GRS 1915+105 in the chi class
• Measurements of accretion disc corona size in LMXB: consequences for Comptonization and LMXB models
• Disc-jet coupling in an atoll-type neutron star X-ray binary: 4U 1728-34 (GX 354-0)
• Low and high frequency variability as a function of spectral properties in the bright X-ray binary GX 5-1
• Discovery of KiloHertz Quasi-Periodic Oscillations in the Z source GX 5-1
• Spectral Investigations of the nature of the Sco X-1 like sources
• AstroSat/LAXPC observation of Cygnus X-1 in the hard state
• Magnetic Field Evolution of Accreting Neutron Stars - III
• The nature of the Island and Banana States in Atoll sources and a Unified Model for Low Mass X-ray Binaries
• Heating in an Extended Accretion Disk Corona along the Z-Pattern in Cyg X-2
• Spectral and Timing Properties of Atoll Source 4U 1705-44 : LAXPC/AstroSat Results
• X-ray spectral evolution of low-mass X-ray binary GX 349+2
• Accretion Geometry of the Low-Mass X-ray Binary Aquila X-1 in the Soft and Hard States
• Disappearance of Hard X-ray Emission in the Last BeppoSAX Observation of the Z Source GX 349+2
• AstroSat/LAXPC detection of milli-second phenomena in 4U 1728-34
• A model for the Z-track phenomenon in GX 5-1 and observational evidence for the physical origins of the kHz QPO
• ALMA observations of 4U 1728-34 and 4U 1820-30: first detection of neutron star X-ray binaries at 300 GHz
• Stability of the photon indices in Z-source GX 340+0 for spectral states
• Absence of reflection features in NuSTAR spectra of the luminous neutron star X-ray binary GX 5-1
• NuSTAR view of the Z-type neutron star low-mass X-ray binary Cygnus~X--2
• Normal Branch Quasi-Periodic Oscillations in Sco X-1: Viscous Oscillations of a Spherical Shell Near the Neutron Star
• X-ray spectral evolution of the extragalactic Z-source, LMC X-2
• Simultaneous X-ray/optical observations of GX 9+9 (4U 1728-16)
• Effects of thermonuclear X-ray bursts on non-burst emissions in the soft state of 4U 1728--34
• A precise measurement of the orbital period parameters of Cygnus X-3
• Anti-correlated time lags in the Z source GX 5-1: Possible evidence for a truncated accretion disk
• Evolution of cross-correlation and time lag of 4U 1735-44 along the branches
• Extensive broadband X-ray monitoring during the formation of a giant radio jet base in Cyg X-3 with AstroSat
• Coupled HBO and NBO variations in the Z source GX 5-1: inner accretion disk as the location of QPOs
• Correlated X-ray timing and spectral behavior of GX 349+2: RXTE PCA data

Cited by in corpus (6)

• AstroSat view of LMC X-2: Evolution of broadband X-ray spectral properties along a complete Z-track
• Fe K$\alpha$ and Fe K$\beta$ line detection in the NuSTAR spectrum of the ultra-bright Z-source Scorpius X-1
• Broadband X-ray properties of black holes GRS 1758-258 and 1E 1740.7-2942: AstroSat and NuSTAR results
• Spectral and Timing evolution of GX 340+0 along its Z-track
• Anti-Correlated lags in a Neutron star Z source GX 5-1: AstroSat's View
• Detection of the thermonuclear X-ray bursts and dips from the X-ray binary 4U 1323-62 with AstroSat/LAXPC