Spectro-temporal evolution of 4U 1702-429 using AstroSat-NICER

Abstract

We present the broadband spectral and timing properties of the atoll source 4U 1702-429 using two observations of AstroSat with the second one having simultaneous NICER data. For both observations, the spectra can be represented by a Comptonizing medium with a black body seed photon source which can be identified with the surface of the neutron star. A disk emission along with a distant reflection is also required for both spectra. For the first observation, the coronal temperature ($\sim 7$ keV) is smaller than the second ($\sim 13$ keV), and the disk is truncated at a larger radius, $\sim 150$ km, compared to the second, $\sim 25$ km, for an assumed distance of 7 kpc. A kHz QPO at $\sim 800$ Hz is detected in the first and is absent in the second observation. Modeling the energy-dependent r.m.s and time lag of the kHz QPO reveals a corona size of $\le$ 30 km. A similar model can explain the energy dependence of the broadband noise at $\sim 10$ Hz for the second observation. The results suggest that kHz QPOs are associated with a compact corona surrounding the neutron star and may occur when the disk is truncated at large distances. We emphasize the need for more wide-band observations of the source to confirm these results.

12 Pages, 7 Figures, Accepted for publication in The Astrophysical Journal

References in corpus (31)

• On the Absorption of X-rays in the Interstellar Medium
• Thermonuclear (type-I) X-ray bursts observed by the Rossi X-ray Timing Explorer
• Improved Reflection Models of Black-Hole Accretion Disks: Treating the Angular Distribution of X-rays
• Broad iron lines in Active Galactic Nuclei
• A review of quasi-periodic oscillations from black hole X-ray binaries: observation and theory
• Calibration of the Large Area X-ray Proportional Counter (LAXPC) instrument on-board AstroSat
• X-ray Reflection By Photoionized Accretion Discs
• Spectral and temporal properties of Compton scattering by mildly relativistic thermal electrons
• X-ray reflection in accreting stellar-mass black hole systems
• Light Curves of Rapidly Rotating Neutron Stars
• The Comptonising medium of the neutron star in 4U 1636-53 through its lower kilohertz Quasi-Periodic Oscillations
• AstroSat/LAXPC reveals the high energy variability of GRS 1915+105 in the chi class
• vKompth: A variable Comptonisation model for low-frequency quasi-periodic oscillations in black-hole X-ray binaries
• Comptonization and QPO Origins in Accreting Neutron Star Systems
• NuSTAR Observations of the Accreting Atolls GX 3+1, 4U 1702-429, 4U 0614+091, and 4U 1746-371
• A Compton Up-scattering Model for Soft Lags in the Lower Kilohertz QPO in 4U1608-52
• Energy Dependent Time Delays of kHz Oscillations due to Thermal Comptonization
• An explanation of the Z-track sources
• The X-ray Spectrum of Cyg X-2
• The Ephemeris and Dipping Spectral Behavior of X1624-490
• Soft lags in neutron star kHz Quasi Periodic Oscillations: evidence for reverberation?
• The Compton hump and variable blue wing in the extreme low-flux NuSTAR observations of 1H0707-495
• Time lags of the kilohertz quasi-periodic oscillations in the low-mass X-ray binaries 4U 1608--52 and 4U 1636--53
• Physical changes during Z-track movement in Sco X-1 on the flaring branch
• A NuSTAR observation of the low mass X-ray binary GX 349+2 throughout the Z-track
• Study of the reflection spectrum of the LMXB 4U 1702-429
• The spectral-timing properties of upper and lower kHz QPOs
• A Systematic Spectral-Timing Analysis of Kilohertz Quasi-Periodic Oscillations in the Rossi X-ray Timing Explorer Archive
• Constraining the size of the Comptonizing medium by modeling the energy dependent time-lags of kHz QPOs of Neutron star system
• Probing the accretion geometry of the atoll source 4U 1702-429 in different spectral states with NICER, NuSTAR, and AstroSat
• Kilohertz quasi-periodic oscillations in neutron-star X-ray binaries: Flattening of the lag spectrum with increasing luminosity

Cited by in corpus (1)

• QPO signatures of disk restoration after type-I X-ray bursts from 4U~1636$-$536