The giant outburst of 4U 0115+634 in 2011 with Suzaku and RXTE

We present an analysis of X-ray spectra of the high-mass X-ray binary 4U 0115+634 as observed with Suzaku and RXTE in 2011 July, during the fading phase of a giant X-ray outburst. We used a continuum model consisting of an absorbed cutoff power law and an ad hoc Gaussian emission feature centered around 8.5 keV, which we attribute to cyclotron emission. Our results are consistent with a fundamental cyclotron absorption line centered at ∼10.2 keV for all observed flux ranges. At the same time we rule out significant influence of the 8.5 kev Gaussian on the parameters of the cyclotron resonant scattering feature, which are not consistent with the cyclotron line energies or the depths of previously reported flux-dependent descriptions. We also show that some continuum models can lead to artificial line-like residuals in the analyzed spectra, which are then misinterpreted as unphysically strong cyclotron lines. Specifically, our results do not support the existence of a previously claimed additional cyclotron feature at ∼15 keV. Apart from these features, we find for the first time evidence for a He-like Fe XXV emission line at ∼6.7 keV and weak H-like Fe XXVI emission close to ∼7.0 keV.

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Multiple cyclotron line-forming regions in GX 301−2

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732132 ◽

2018 ◽

Vol 620 ◽

pp. A153 ◽

Cited By ~ 8

Author(s):

F. Fürst ◽

S. Falkner ◽

D. Marcu-Cheatham ◽

B. Grefenstette ◽

J. Tomsick ◽

...

Keyword(s):

Relativistic Effects ◽

Resonant Scattering ◽

The Other ◽

High Mass ◽

Good Resolution ◽

Gaussian Shape ◽

X Ray ◽

Cyclotron Line ◽

First Time ◽

The Continuum

We present two observations of the high-mass X-ray binary GX 301−2 with NuSTAR, taken at different orbital phases and different luminosities. We find that the continuum is well described by typical phenomenological models, like a very strongly absorbed NPEX model. However, for a statistically acceptable description of the hard X-ray spectrum we require two cyclotron resonant scattering features (CRSF), one at ∼35 keV and the other at ∼50 keV. Even though both features strongly overlap, the good resolution and sensitivity of NuSTAR allows us to disentangle them at ≥99.9% significance. This is the first time that two CRSFs have been seen in GX 301−2. We find that the CRSFs are very likely independently formed, as their energies are not harmonically related and, if the observed feature were due to a single line, the deviation from a Gaussian shape would be very large. We compare our results to archival Suzaku data and find that our model also provides a good fit to those data. We study the behavior of the continuum as well as the CRSF parameters as function of pulse phase in seven phase bins. We find that the energy of the 35 keV CRSF varies smoothly as a function of phase, between 30 and 38 keV. To explain this variation, we apply a simple model of the accretion column, taking into account the altitude of the line-forming region, the velocity of the in-falling material, and the resulting relativistic effects. We find that in this model the observed energy variation can be explained as being simply due to a variation of the projected velocity and beaming factor of the line-forming region towards us.

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

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3477 ◽

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.

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

International Astronomical Union Colloquium ◽

10.1017/s0252921100152546 ◽

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.

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Cyclotron lines in highly magnetized neutron stars

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834479 ◽

2019 ◽

Vol 622 ◽

pp. A61 ◽

Cited By ~ 34

Author(s):

R. Staubert ◽

J. Trümper ◽

E. Kendziorra ◽

D. Klochkov ◽

K. Postnov ◽

...

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Neutron Stars ◽

Direct Measurement ◽

Resonant Scattering ◽

Electron Cyclotron ◽

X Ray ◽

Cyclotron Line ◽

The Magnetic Field ◽

Proton Cyclotron

Cyclotron lines, also called cyclotron resonant scattering features are spectral features, generally appearing in absorption, in the X-ray spectra of objects containing highly magnetized neutron stars, allowing the direct measurement of the magnetic field strength in these objects. Cyclotron features are thought to be due to resonant scattering of photons by electrons in the strong magnetic fields. The main content of this contribution focusses on electron cyclotron lines as found in accreting X-ray binary pulsars (XRBP) with magnetic fields on the order of several 1012Gauss. Also, possible proton cyclotron lines from single neutron stars with even stronger magnetic fields are briefly discussed. With regard to electron cyclotron lines, we present an updated list of XRBPs that show evidence of such absorption lines. The first such line was discovered in a 1976 balloon observation of the accreting binary pulsar Hercules X-1, it is considered to be the first direct measurement of the magnetic field of a neutron star. As of today (end 2018), we list 35 XRBPs showing evidence of one ore more electron cyclotron absorption line(s). A few have been measured only once and must be confirmed (several more objects are listed as candidates). In addition to the Tables of objects, we summarize the evidence of variability of the cyclotron line as a function of various parameters (especially pulse phase, luminosity and time), and add a discussion of the different observed phenomena and associated attempts of theoretical modeling. We also discuss our understanding of the underlying physics of accretion onto highly magnetized neutron stars. For proton cyclotron lines, we present tables with seven neutron stars and discuss their nature and the physics in these objects.

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Do star clusters form in a completely mass-segregated way?

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834265 ◽

2019 ◽

Vol 626 ◽

pp. A79 ◽

Cited By ~ 10

Author(s):

Václav Pavlík ◽

Pavel Kroupa ◽

Ladislav Šubr

Keyword(s):

Star Clusters ◽

Point Of View ◽

High Mass ◽

Orion Nebula ◽

Energy Redistribution ◽

X Ray ◽

Star Forming ◽

Independent Observations ◽

Mass Segregation ◽

Rule Out

Context. ALMA observations of the Serpens South star-forming region suggest that stellar protoclusters may be completely mass segregated at birth. Independent observations also suggest that embedded clusters form segregated by mass. Aims. As the primordial mass segregation seems to be lost over time, we aim to study on which timescale an initially perfectly mass-segregated star cluster becomes indistinguishable from an initially not mass-segregated cluster. As an example, the Orion Nebula Cluster (ONC) is also discussed. Methods. We used N-body simulations of star clusters with various masses and two different degrees of primordial mass segregation. We analysed their energy redistribution through two-body relaxation to quantify the time when the models agree in terms of mass segregation, which sets in only dynamically in the models that are primordially not mass segregated. A comprehensive cross-matched catalogue combining optical, infrared, and X-ray surveys of ONC members was also compiled and made available. Results. The models evolve to a similar radial distribution of high-mass stars after the core collapse (about half a median two-body relaxation time, trh) and become observationally indistinguishable from the point of view of mass segregation at time τv ≈ 3.3 trh. In the case of the ONC, using the distribution of high-mass stars, we may not rule out either evolutionary scenario (regardless of whether they are initially mass segregated). When we account for extinction and elongation of the ONC, as reported elsewhere, an initially perfectly mass-segregated state seems to be more consistent with the observed cluster.

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LMC X–4: Different Types of Long-Term Variability

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318002442 ◽

2017 ◽

Vol 14 (S339) ◽

pp. 146-146

Author(s):

S. Molkov

Keyword(s):

Binary Systems ◽

Noise Model ◽

High Mass ◽

Time Interval ◽

Spin Torque ◽

X Ray ◽

Spin Period ◽

Different Types ◽

First Time

AbstractThis talk presented a summary of our study of different types of long-term variability in the high-mass X-ray binary LMC X-4, by taking advantage of more than 43 years of measurements in the X-ray domain. In particular, we investigated the 30-day cycle of modulation of the X-ray emission from the source (super-orbital or precessional variability), and refined the orbital period and its first derivative. We showed that the precession period in the time-interval 1991–2015 is near its equilibrium value of Psup = 30.370 days, while the observed historical changes in the phase of this variability can be interpreted in terms of the ‘red noise’ model. We obtained an analytical law from which the precession phase can be determined to within 5% throughout the entire time-interval under consideration. Our analysis revealed for the first time that the source is displaying near-periodic variations of its spin period, on a time-scale of roughly 6.8 years, thus making LMC X-4 one of the (few) known binary systems that show remarkable long-term spin–torque reversals.

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New simulation of QSO X-ray heating during the Cosmic Dawn

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317011115 ◽

2017 ◽

Vol 12 (S333) ◽

pp. 34-38

Author(s):

Hannah E. Ross ◽

Keri Dixon ◽

Ilian Iliev ◽

Garrelt Mellema

Keyword(s):

Radiative Transfer ◽

Large Volume ◽

Intergalactic Medium ◽

Temperature Fluctuations ◽

High Mass ◽

X Ray ◽

First Time ◽

X Ray Binaries ◽

Skewness And Kurtosis

AbstractThe upcoming radio interferometer Square Kilometre Array is expected to directly detect the redshifted 21-cm signal from the Cosmic Dawn for the first time. In this era temperature fluctuations from X-ray heating of the neutral intergalactic medium can impact this signal dramatically. Previously, in Ross et al. (2017), we presented the first large-volume, 244 h-1 Mpc=349 Mpc a side, fully numerical radiative transfer simulations of X-ray heating. This work is a follow-up where we now also consider QSO-like sources in addition to high mass X-ray binaries. Images of the two cases are clearly distinguishable at SKA1-LOW resolution and have RMS fluctuations above the expected noise. The inclusion of QSOs leads to a dramatic increase in non-Gaussianity of the signal, as measured by the skewness and kurtosis of the 21-cm signal. We conclude that this increased non-Gaussianity is a promising signature of early QSOs.

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The Remarkable Spin-down and Ultrafast Outflows of the Highly Pulsed Supersoft Source of Nova Herculis 2021

The Astrophysical Journal ◽

10.3847/2041-8213/ac34fd ◽

2021 ◽

Vol 922 (2) ◽

pp. L42

Author(s):

Jeremy J. Drake ◽

Jan-Uwe Ness ◽

Kim L. Page ◽

G. J. M. Luna ◽

Andrew P. Beardmore ◽

...

Keyword(s):

White Dwarf ◽

Emission Lines ◽

Optical Observations ◽

High Mass ◽

X Rays ◽

Pulse Profile ◽

X Ray ◽

Classical Nova ◽

First Time ◽

The Magnetic Field

Abstract Nova Her 2021 (V1674 Her), which erupted on 2021 June 12, reached naked-eye brightness and has been detected from radio to γ-rays. An extremely fast optical decline of 2 magnitudes in 1.2 days and strong Ne lines imply a high-mass white dwarf. The optical pre-outburst detection of a 501.42 s oscillation suggests a magnetic white dwarf. This is the first time that an oscillation of this magnitude has been detected in a classical nova prior to outburst. We report X-ray outburst observations from Swift and Chandra that uniquely show (1) a very strong modulation of supersoft X-rays at a different period from reported optical periods, (2) strong pulse profile variations and the possible presence of period variations of the order of 0.1–0.3 s, and (3) rich grating spectra that vary with modulation phase and show P Cygni–type emission lines with two dominant blueshifted absorption components at ∼3000 and 9000 km s−1 indicating expansion velocities up to 11,000 km s−1. X-ray oscillations most likely arise from inhomogeneous photospheric emission related to the magnetic field. Period differences between reported pre- and post-outburst optical observations, if not due to other period drift mechanisms, suggest a large ejected mass for such a fast nova, in the range 2 × 10−5–2 × 10−4 M ⊙. A difference between the period found in the Chandra data and a reported contemporaneous post-outburst optical period, as well as the presence of period drifts, could be due to weakly nonrigid photospheric rotation.

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Revisiting the spectral and timing properties of 4U 1909+07 with NuSTAR and Astrosat

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2604 ◽

2020 ◽

Vol 498 (4) ◽

pp. 4830-4838 ◽

Cited By ~ 1

Author(s):

Gaurava K Jaisawal ◽

Sachindra Naik ◽

Wynn C G Ho ◽

Neeraj Kumari ◽

Prahlad Epili ◽

...

Keyword(s):

Broad Band ◽

High Energy ◽

High Mass ◽

X Rays ◽

Pulse Profile ◽

X Ray ◽

Beam Geometry ◽

Cyclotron Absorption ◽

Using Data ◽

Wind Distribution

ABSTRACT We present the results obtained from the analysis of high-mass X-ray binary pulsar 4U 1909+07 using NuSTAR and Astrosat observations in July 2015 and 2017, respectively. X-ray pulsations at ≈604 s are clearly detected in our study. Based on the long-term spin-frequency evolution, the source is found to spun-up in the last 17 yr. We observed a strongly energy-dependent pulse profile that evolved from a complex broad structure in soft X-rays into a profile with a narrow emission peak followed by a plateau in energy ranges above 20 keV. This behaviour ensured a positive correlation between the energy and pulse fraction. The pulse profile morphology and its energy evolution are almost similar during both the observations, suggesting a persistent emission geometry of the pulsar over time. The broad-band energy spectrum of the pulsar is approximated by an absorbed high-energy exponential cut-off power-law model with iron emission lines. In contrast to the previous report, we found no statistical evidence for the presence of cyclotron absorption features in the X-ray spectra. We performed phase-resolved spectroscopy using data from the NuSTAR observation. Our results showed a clear signature of absorbing material at certain pulse phases of the pulsar. These findings are discussed in terms of stellar wind distribution and its effect on the beam geometry of this wind-fed accreting neutron star. We also reviewed the subsonic quasi-spherical accretion theory and its implication on the magnetic field of 4U 1909+07 depending on the global spin-up rate.

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Possible detection of a new cyclotron feature in 4U 1700–37

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa437 ◽

2020 ◽

Vol 493 (2) ◽

pp. 3045-3053

Author(s):

Suman Bala ◽

Jayashree Roy ◽

Dipankar Bhattacharya

Keyword(s):

Compact Object ◽

Periodic Oscillation ◽

High Mass ◽

Emission Region ◽

Frequency Range ◽

Quasi Periodic Oscillation ◽

X Ray ◽

Line Feature ◽

Transient Source ◽

Cyclotron Line

ABSTRACT We present a spectral and timing study of the high-mass X-ray binary transient source 4U 1700–37 using NuSTAR and ASTROSAT/LAXPC. The source is observed in two different flux states. A combined spectral analysis of NuSTAR’s focal plane modules A and B shows the possible hint of a cyclotron line feature at ∼16 keV. The line feature is consistently present in different continuum models with at least 3σ confidence level. We do not detect the presence of a previously reported 39 keV cyclotron line in the combined spectra. A ∼16 keV cyclotron feature would suggest that the compact object is a neutron star with a magnetic field strength ∼2.1 × 1012 G in the emission region. We also find the presence of a rare Ni Kα emission line around 7.6 keV in the NuSTAR spectrum. We searched the NuSTAR and ASTROSAT data for coherent or quasi-periodic oscillation signals but found no evidence in the frequency range 0.1 mHz to 103 Hz.

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