Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userX-ray Flux Related Timing and Spectral Features of 2S 1417-62
74
0
0.0
(
0
)
Authors
S.C. Inam
Ask ChatGPT about the research
No Arabic abstract
RXTE observations of the X-ray transient pulsar 2S 1417-62 between 1999 November and 2000 August with a total exposure of $sim 394$ ksec were analyzed. Observations include a main outburst followed by a series of mini outbursts. Changes in pulse morphology and pulse fraction were found to be related to the changes in X-ray flux. Particularly low X-ray flux regions were found to have significantly lower pulse fractions with different pulse morphologies. The 3-60 keV PCA-HEXTE main outburst spectrum was modeled with an absorbed power law model with high energy cut-off and a Gaussian Iron line complex feature. Using the same spectral model, individual 3-20 keV PCA spectra were found to be softer and less absorbed in low X-ray flux regions between outbursts. Spectral studies showed that hydrogen column density was correlated, and the power law index was anti-correlated with the 3-20 keV X-ray flux. X-ray flux related spectral and timing features in 2S 1417-62 except for low X-ray flux regions were interpreted as a sign of disc accretion with a similar accretion geometry with a varying mass accretion rate ($dot{M}$), whereas spectral and timing features of the low X-ray flux regions were interpreted as a sign of possible temporary accretion geometry change prior to the next periastron where $dot{M}$ increases again to restore the original accretion geometry.
rate research
Read More
We have studied the evolution of different timing and spectral properties of the X-ray pulsar 2S 1417--624 during the recent outburst in January 2021 based on the Neutron Star Interior Composition Explorer (NICER) observations. The spin period during the outburst is $P sim$17.3622 s based on the NICER data and the period decreases slowly with time. The evolution of the spin period and pulsed flux is studied with Fermi/GBM during the outburst and the spin-up rate was found to be varied between $simeq$(0.8--1.8)$times$10$^{-11}$ Hz s$^{-1}$. The pulse profile shows strong energy dependence and variability. The pulse profile shows multiple peaks and dips which evolve significantly with energy. The pulsed fraction shows a positive correlation with energy. The evolution of the spectral state is also studied. The NICER energy spectrum is well described with a composite model of -- power-law and a blackbody emission along with a photo-electric absorption component. An iron emission line is detected near 6.4 keV in the NICER spectrum with an equivalent width of about 0.05 keV. During the recent outburst, the flux was relatively low compared to the 2018 outburst and the mass accretion rate was also low. The mass accretion rate is estimated to be $simeq$1.3 $times$ 10$^{17}$ g s$^{-1}$ near the peak of the outburst. We have found a positive correlation between the pulse frequency derivatives and luminosity. The GL model was applied to estimate the magnetic field in low mass accretion rate and different spin-up rates, which is compared to the earlier estimated magnetic field at a relatively high mass accretion rate. The magnetic field is estimated to be $simeq$10$^{14}$ G from the torque-luminosity model, which is comparatively higher than most of the other Be/XBPs.
We investigate timing and spectral characteristics of the transient X-ray pulsar 2S 1417$-$624 during its 2018 outburst with emph{NICER} follow up observations. We describe the spectra with high-energy cut-off and partial covering fraction absortion (PCFA) model and present flux-dependent spectral changes of the source during the 2018 outburst. Utilizing the correlation-mode switching of the spectral model parameters, we confirm the previously reported sub-critical to critical regime transitions and we argue that secondary transition from the gas-dominated to the radiation pressure-dominated disc do not lead to significant spectral changes below 12 keV. Using the existing accretion theories, we model the spin frequency evolution of 2S 1417$-$624 and investigate the noise processes of a transient X-ray pulsar for the first time using both polynomial and luminosity-dependent models for the spin frequency evolution. For the first model, the power density spectrum of the torque fluctuations indicate that the source exhibits red noise component ($Gamma sim -2$) within the timescales of outburst duration which is typical for disc-fed systems. On the other hand, the noise spectrum tends to be white on longer timescales with high timing noise level that indicates an ongoing accretion process in between outburst episodes. For the second model, most of the red noise component is eliminated and the noise spectrum is found to be consistent with a white noise structure observed in wind-fed systems.
We present a study of timing properties of the accreting pulsar 2S 1417-624 observed during its 2018 outburst, based on Swift/BAT, Fermi/GBM, Insight-HXMT and NICER observations. We report a dramatic change of the pulse profiles with luminosity. The morphology of the profile in the range 0.2-10.0keV switches from double to triple peaks at $sim2.5$ $rm times 10^{37}{it D}_{10}^2 erg s^{-1}$ and from triple to quadruple peaks at $sim7$ $rm times 10^{37}{it D}_{10}^2 erg s^{-1}$. The profile at high energies (25-100keV) shows significant evolutions as well. We explain this phenomenon according to existing theoretical models. We argue that the first change is related to the transition from the sub to the super-critical accretion regime, while the second to the transition of the accretion disc from the gas-dominated to the radiation pressure-dominated state. Considering the spin-up as well due to the accretion torque, this interpretation allows to estimate the magnetic field self-consistently at $sim7times 10^{12}$G.
We present analysis of RXTE--PCA observations of GX 1+4 between March 3, 2001 and January 31, 2003 together with the CGRO--BATSE X-ray flux and frequency derivative time series between 1991 and 1999. From the timing analysis of RXTE-PCA observations, we are able to phase connect pulse arrival times of the source within two different time intervals and obtain corresponding timing solutions. Using these pulse arrival times, we contribute to long term pulse frequency history of the source. We look for episodic correlations and anti-correlations between torque and X-ray luminosity using CGRO--BATSE X-ray flux and frequency derivative time series and find that correlation state of GX 1+4 seems to change on $sim$ 100-200 days long intervals. We estimate torque noise of the source and observe flickering noise ($f^{-1}$). We achieve to measure the longest observed timescale for a noise process among accretion powered X-ray pulsars by extending the noise estimate for a time scale ranging from 31 days to 44 years. Spectral analysis of individual RXTE-PCA observations indicates a significant correlation between iron line flux and unabsorbed X-ray flux. Pulse phase resolved spectra of the source indicate a broadening of iron line complex at the bin corresponding to the pulse minimum.
We studied the X-ray properties of the Hickson Compact Group HCG62, in order to determine the properties and dynamic and evolutionary state of its hot gaseous halo. Our analysis reveals that the X-ray diffuse halo has an extremely complex morphological, thermal and chemical structure. Two deep cavities, due to the presence of the AGN hosted by the central galaxy NGC 4778, are clearly visible in the group X-ray halo. The cavities appear to be surrounded by ridges of cool gas. The group shows a cool core associated with the dominant galaxy. In the outer regions the temperature structure is quite regular, while the metal abundance shows a more patchy distribution, with large Si/O and Si/Fe ratios.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
