scholarly journals NuSTAR observations of wind-fed X-ray pulsar GX 301–2 during unusual spin-up event

2019 ◽  
Vol 629 ◽  
pp. A101 ◽  
Author(s):  
Armin Nabizadeh ◽  
Juhani Mönkkönen ◽  
Sergey S. Tsygankov ◽  
Victor Doroshenko ◽  
Sergey V. Molkov ◽  
...  
Keyword(s):  
Accretion Disk ◽  
Recent Observation ◽  
High Luminosity ◽  
Line Energy ◽  
Fed State ◽  
X Ray ◽  
Positive Correlation ◽  
Temporal Properties ◽  
Cyclotron Line ◽  
Strong Spin

We report on NuSTAR observations of the well-known wind-accreting X-ray pulsar GX 301–2 during a strong spin-up episode that took place in January–March 2019. A measurement of high luminosity of the source in the most recent observation allowed us to detect a positive correlation of the cyclotron line energy with luminosity. Beyond that, only minor differences in spectral and temporal properties of the source during the spin-up, presumably associated with the formation of a transient accretion disk, and the normal wind-fed state could be detected. Finally, we discuss conditions for the formation of the disk and possible reasons for lack of any appreciable variations in most of the observed source properties induced by the change of the accretion mechanism, and conclude that the bulk of the observed X-ray emission is still likely powered by direct accretion from the wind.

scholarly journals Positive correlation between the cyclotron line energy and luminosity in sub-critical X-ray pulsars: Doppler effect in the accretion channel

2015 ◽  
Vol 454 (3) ◽  
pp. 2714-2721 ◽  
Author(s):  
Alexander A. Mushtukov ◽  
Sergey S. Tsygankov ◽  
Alexander V. Serber ◽  
Valery F. Suleimanov ◽  
Juri Poutanen
Keyword(s):  
Doppler Effect ◽  
Line Energy ◽  
X Ray ◽  
Positive Correlation ◽  
Cyclotron Line

scholarly journals Evidence for the radiation-pressure dominated accretion disk in bursting pulsar GRO J1744−28 using timing analysis

2019 ◽  
Vol 626 ◽  
pp. A106 ◽  
Author(s):  
Juhani Mönkkönen ◽  
Sergey S. Tsygankov ◽  
Alexander A. Mushtukov ◽  
Victor Doroshenko ◽  
Valery F. Suleimanov ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Accretion Disk ◽  
Radiation Pressure ◽  
Compact Objects ◽  
Disk Radius ◽  
Line Energy ◽  
X Ray ◽  
Inner Radius ◽  
Cyclotron Line ◽  
The Magnetic Field

The X-ray pulsar GRO J1744−28 is a unique source that shows both pulsations and type-II X-ray bursts, allowing studies of the interaction of the accretion disk with the magnetosphere at huge mass-accretion rates exceeding 1019 g s−1 during its super-Eddington outbursts. The magnetic field strength in the source, B ≈ 5 × 1011 G, is known from the cyclotron absorption feature discovered in the energy spectrum around 4.5 keV. Here, we have explored the flux variability of the source in context of interaction of its magnetosphere with the radiation-pressure dominated accretion disk. Specifically, we present the results of the analysis of noise power density spectra (PDS) using the observations of the source in 1996–1997 by the Rossi X-ray Timing Explorer (RXTE). Accreting compact objects commonly exhibit a broken power-law PDS shape with a break corresponding to the Keplerian orbital frequency of matter at the innermost disk radius. The observed frequency of the break can thus be used to estimate the size of the magnetosphere. We find, however, that the observed PDS of GRO J1744−28 differs dramatically from the canonical shape. The observed break frequency appears to be significantly higher than expected based on the magnetic field estimated from the cyclotron line energy. We argue that these observational facts can be attributed to the existence of the radiation-pressure dominated region in the accretion disk at luminosities above ∼2 × 1037 erg s−1. We discuss a qualitative model for the PDS formation in such disks, and show that its predictions are consistent with our observational findings. The presence of the radiation-pressure dominated region can also explain the observed weak luminosity dependence of the inner radius, and we argue that the small inner radius can be explained by a quadrupole component dominating the magnetic field of the neutron star.

scholarly journals The Nature of the Compact Object in the Hard X-Ray Source 4U2206+54

2004 ◽  
Vol 194 ◽  
pp. 208-208
Author(s):  
J. M. Torrejón ◽  
I. Kreykenbohni ◽  
A. Orr ◽  
L. Titarchuk ◽  
I. Negueruela
Keyword(s):  
Neutron Star ◽  
Accretion Disk ◽  
Compact Object ◽  
High Energy ◽  
Energy Data ◽  
X Ray ◽  
Hot Plasma ◽  
Cyclotron Line ◽  
First Time

We present an analysis of archival RXTE and BeppoSAX data of the X-ray source 4U2206+54. For the first time, high energy data (≥ 30 keV) is analyzed. The data is well described by comptonization models in which seed photons with temperatures between 1.1 keV arid 1.5 keV are comptonized by a hot plasma at 50 keV thereby producing a hard tail which extends up to 100 keV. From luminosity arguments it is shown that the area of the soft photons source must be small (r ≈ 1 km) and that the presence of an accretion disk in this system is unlikely. Here we report on the possible existence of a cyclotron line around 30 keV . The presence of a neutron star in the system is strongly favored by the available data.

scholarly journals New measurements of the cyclotron line energy in Cen X-3

2020 ◽  
Vol 500 (3) ◽  
pp. 3454-3461
Author(s):  
Gunjan Tomar ◽  
Pragati Pradhan ◽  
Biswajit Paul
Keyword(s):  
Broad Band ◽  
Resonant Scattering ◽  
High Energy ◽  
Emission Lines ◽  
Power Law Model ◽  
Pulse Profile ◽  
Line Energy ◽  
X Ray ◽  
Cyclotron Absorption ◽  
Cyclotron Line

ABSTRACT We report results from the analysis of data from two observations of the accreting binary X-ray pulsar Cen X-3 carried out with the broad-band X-ray observatories Suzaku and NuSTAR. The pulse profile is dominated by a broad single peak and show some energy dependence with two additional weak pulse peaks at energies below 15 and 25 keV, respectively. The broad-band X-ray spectrum for 0.8–60.0 keV for Suzaku  and 3.0–60.0 keV for NuSTAR is fitted well with high-energy cut-off power-law model along with soft-excess, multiple iron emission lines and a cyclotron absorption. The cyclotron line energy is found to be $30.29^{+0.68}_{-0.61}$ and $29.22^{+0.28}_{-0.27}$ keV, respectively, in the Suzaku  and NuSTAR  spectra. We make a comparison of these two measurements with four previous measurements of Cyclotron Resonant Scattering Feature (CRSF) in Cen X-3  obtained with Ginga, BeppoSAX,  and RXTE. We find no evidence for a dependence of the CRSF on luminosity. Except for one CRSF measurement with BeppoSAX , the remaining measurements are consistent with a CRSF energy in the range of 29.5–30.0 keV over a luminosity range of 1.1–5.4 × 1037 erg s−1 different from several other sources that show considerable CRSF variation in the same luminosity range.

scholarly journals Observational properties of relativistic black hole winds

2006 ◽  
Vol 2 (S238) ◽  
pp. 471-472
Author(s):  
Ken-ya Watarai
Keyword(s):  
Black Hole ◽  
Accretion Disk ◽  
High Luminosity ◽  
Disk Thickness ◽  
X Ray ◽  
Mass Outflow ◽  
Wind Velocities

AbstractWe examine observational properties of relativistic black hole winds as an origin of high luminosity sources such as microquasars and ultra-luminous X-ray sources (ULXs). When strong relativistic wind/outflow happens in the vicinity of the black hole, the wind might form the optically-thick photosphere. Therefore the emission observed in ULXs might come from the photosphere of the wind, not from the accretion disk.We found that the location of the photosphere is larger than the disk thickness for super-Eddington mass-outflow rates and sub-relativistic wind velocities (v ∼ 0.1–0.2 c). To understand the radiative structure in the high luminosity sources, we should take into account not only the emission from the accretion disk but also the emission from the outflow at the same time.

scholarly journals Time evolution of cyclotron line of Her X-1: a detailed statistical analysis including new AstroSat data

2020 ◽  
Vol 497 (1) ◽  
pp. 1029-1042 ◽  
Author(s):  
S Bala ◽  
D Bhattacharya ◽  
R Staubert ◽  
C Maitra
Keyword(s):  
Statistical Analysis ◽  
Time Evolution ◽  
Temporal Evolution ◽  
Upward Trend ◽  
Line Energy ◽  
X Ray ◽  
Line Feature ◽  
Detailed Statistical Analysis ◽  
Secular Decline ◽  
Cyclotron Line

ABSTRACT The cyclotron line feature in the X-ray spectrum of the accretion-powered pulsar Her X-1 has been observed and monitored for over three decades. The line energy exhibited a slow secular decline over the period 1995–2014, with a possible (not confirmed) indication of a reversal thereafter. Recent works have shown that the temporal evolution of the line energy may be modelled as a flattening after an earlier decrease until MJD 55400 (±200). In this work, we present the results of AstroSat observations in the context of earlier data and offer a common interpretation through a detailed study of temporal and flux dependence. We find that the variation of the line energy does not support an upward trend but is consistent with the reported flattening after an earlier decrease until MJD $54487^{+515}_{-469}$.

scholarly journals No anticorrelation between cyclotron line energy and X-ray flux in 4U 0115+634

2013 ◽  
Vol 551 ◽  
pp. A6 ◽  
Author(s):  
S. Müller ◽  
C. Ferrigno ◽  
M. Kühnel ◽  
G. Schönherr ◽  
P. A. Becker ◽  
...  
Keyword(s):  
Line Energy ◽  
X Ray ◽  
Cyclotron Line

scholarly journals Cyclotron line energy in Hercules X-1: stable after the decay

2020 ◽  
Vol 642 ◽  
pp. A196
Author(s):  
R. Staubert ◽  
L. Ducci ◽  
L. Ji ◽  
F. Fürst ◽  
J. Wilms ◽  
...  
Keyword(s):  
High Precision ◽  
Line Energy ◽  
X Ray ◽  
Average Value ◽  
Pulse Phase ◽  
Flux Level ◽  
Cyclotron Line ◽  
The Continuum

We summarize the results of a dedicated effort made between 2012 and 2019 to follow the evolution of the cyclotron line in Her X-1 through repeated NuSTAR observations. The previously observed nearly 20-year-long decay of the cyclotron line energy has ended in 2012: from then on, the pulse-phase-averaged flux-corrected cyclotron line energy has remained stable and constant at an average value of Ecyc = (37.44 ± 0.07) keV (normalized to a flux level of 6.8 RXTE/ASM-cts s−1). The flux dependence of Ecyc discovered in 2007 is now measured with high precision, giving a slope of (0.675 ± 0.075) keV/(ASM-cts s−1), corresponding to an increase of 6.5% of Ecyc for an increase in flux by a factor of two. We also find that all line parameters as well as the continuum parameters show a correlation with X-ray flux. While a correlation between Ecyc and X-ray flux (both positive and negative) is now known for several accreting binaries with various suggestions for the underlying physics, the phenomenon of a long-term decay has so far only been seen in Her X-1 and Vela X-1, with far less convincing explanations.

scholarly journals Changes in Cyclotron line energy with luminosity in Accreting X-ray pulsars

2012 ◽  
Vol 8 (S290) ◽  
pp. 283-284
Author(s):  
Osamu Nishimura
Keyword(s):  
Beam Pattern ◽  
Polar Cap ◽  
Line Energy ◽  
X Ray ◽  
Cyclotron Line

AbstractI model changes in cyclotron line energy with luminosity, considering the effect of polar cap dimensions and changes in beam pattern as well as shock height. Cyclotron lines are calculated by a superposition of a large number of cyclotron lines formed in different heights of an accretion column. Cyclotron line energy has been observed to change with luminosity in a number of accreting X-ray pulsars. In X0115+63 and V0332+53, the fundamental cyclotron line energy has been observed to decrease with increasing luminosity. This phenomenon has been interpreted as a change in shock height with luminosity. However, the rate of the change seems to be very different, in which the line energy in V0332+53 seems to vary slowly with luminosity compared with that in X0115+63. I found that the changes in the cyclotron line energies with luminosity can be explained by changes in beam pattern and the size of a polar cap rather than a shock height.

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