Cyclotron Resonance Energies and Orbital Elements of Accretion Pulsar 4U 0115+63 During the Giant Outburst in 2008

Abstract

We present both timing and spectral analysis of the outburst of 4U 0115+63 in April -- May 2008 with INTEGRAL and RXTE observations. We have determined the spin period of the neutron star at $\sim 3.61430\pm 0.00003$ s, and a spin up rate during the outburst of $\dot{P}=(-7.24\pm 0.03)\times 10^{-6}\mathrm{s}{\mathrm{d}}^{-1}$, the angle of periapsis $\omega =48.67^{\circ }\pm 0.04^{\circ }$ in 2008 and its variation (apsidal motion) $\dot{\omega }=0.048^{\circ }\pm 0.003^{\circ }{\mathrm{yr}}^{-1}$. We also confirm the relation of spin-up torque versus luminosity in this source during the giant outburst. The hard X-ray spectral properties of 4U 0115+63 during the outburst are studied with INTEGRAL and RXTE. Four cyclotron absorption lines are detected using the spectra from combined data of IBIS and JEM-X aboard INTEGRAL in the energy range of 3 -- 100 keV. The 5 -- 50 keV luminosities at an assumed distance of 7 kpc are determined to be in the range of $(1.5-12)\times 10^{37}\mathrm{ergs}{\mathrm{s}}^{-1}$ during the outburst. The fundamental absorption line energy varies during the outburst: around 15 keV during the rising phase, and transiting to $\sim 10$ keV during the peak of the outburst, and further coming back to $\sim 15$ keV during the decreasing phase. The variations of photon index show the correlation with the fundamental line energy changes: the source becomes harder around the peak of the outburst and softer in both rising and decreasing phases. This correlation and transition processes during the outburst need further studies in both observations and theoretical work. The known relation of the fundamental line energy and X-ray luminosity is confirmed by our results, however, our discoveries suggest that some other factors besides luminosity play the important role in fundamental line energy variations and spectral transitions.

14 pages, 13 figures, 6 tables, accepted for the publication in MNRAS

References in corpus (4)

• 4U 0115+63 from RXTE and INTEGRAL Data: Pulse Profile and Cyclotron Line Energy
• Study of the accreting pulsar 4U 0115+634 with a bulk and thermal Comptonization model
• A Further Study of the Luminosity-Dependent Cyclotron Resonance Energies of the Binary X-ray Pulsar 4U0115+63 with RXTE
• Cyclotron Line Variability

Cited by in corpus (24)

• Cyclotron lines in highly magnetized neutron stars
• Patterns of variability in Be/X-ray pulsars during giant outbursts
• The gas-to-extinction ratio and the gas distribution in the Galaxy
• On Timing and Spectral Characteristics of the X-ray Pulsar 4U 0115+63: Evolution of the Pulsation Period and the Cyclotron Line Energy
• The Ups & Downs of Accreting X-Ray Pulsars: Decade-long observations with the Fermi Gamma-Ray Burst Monitor
• No anti-correlation between cyclotron line energy and X-ray flux in 4U 0115+634
• Swift observations of SMC X-3 during its 2016-2017 super-Eddington outburst
• Insight-HXMT observations of Swift J0243.6+6124 during its 2017-2018 outburst
• Variations in the Cyclotron Resonant Scattering Features during 2011 outburst of 4U 0115+63
• Relation of cyclotron resonant energy and luminosity in a strongly magnetized neutron star GRO J1008-57 observed by Insight-HXMT
• LAXPC / AstroSat Study of ~ 1 and ~ 2 mHz Quasi-periodic Oscillations in the Be/X-ray Binary 4U 0115+63 During its 2015 Outburst
• AstroSat observations of GRO J2058+42 during the 2019 outburst
• Timing analysis of EXO 2030+375 during its 2021 giant outburst observed with Insight-HXMT
• Catalog of the Galactic population of X-ray pulsars in High-mass X-ray binary systems
• Variations and Correlations in Cyclotron Resonant Scattering Features of Vela X-1 Studied by INTEGRAL
• The giant outburst of 4U 0115+634 in 2011 with Suzaku and RXTE
• Variations of cyclotron resonant scattering features in Vela X-1 revealed with Insight-HXMT
• Discovery of X-ray pulsations in the Be/X-ray binary IGR J21343+4738
• Temporal Variations And Spectral Properties of Be/X-ray Pulsar GRO J1008-57 Studied by INTEGRAL
• Pulse phase-resolved analysis of SMC X-3 during its 2016--2017 super-Eddington outburst
• Long-term evolution of Cyclotron Line energy in an eclipsing pulsar 4U 1538-522
• A peculiar cyclotron line near 16 keV detected in the 2015 outburst of 4U 0115+63?
• Studies of Cepheus X-4 during 2018 outburst observed with AstroSat
• Flux variability of the "10 keV feature" of 4U 0115+63