Inversion of the decay of the cyclotron line energy in Hercules X-1

Staubert, R.; Klochkov, D.; Fürst, Felix; Wilms, J.; Rothschild, R. E.; Harrison, Fiona A.

doi:10.1051/0004-6361/201731927

Cited by 29 publications

(42 citation statements)

References 33 publications

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“…The assumption is that the line energy depends both on time and flux and there is an explicit rise of E cyc with time after T c = 57341. This is equivalent to the model described in Staubert et al (2017). With this model we find the χ 2 /d.o.f to be 22/22, with b 2 =−8.64 +4.05 −4.15 .…”

Section: Of T C (=54487 +515mentioning

confidence: 60%

“…Further observations with INTEGRAL, Suzaku and NuSTAR fit well with a model assuming a continued decay of E cyc until 2015, with a decay rate of 0.260 ± 0.14 keV/yr (Staubert et al 2016). However in 2016 NuSTAR and INTEGRAL observations of Her X-1 began to indicate a possible upward trend in line energy (Staubert et al 2017) (which is not confirmed so far), possi- Xiao et al 2019).…”

Section: Introductionmentioning

confidence: 63%

“…We have also used emcee, (a Goodman and Weare's Affine Invariant Markov chain Monte Carlo (MCMC) Ensemble sampler (Foreman-Mackey et al 2013)) for Bayesian parameter estimation with some suitable flat priors (Table-3). In this work, we have used all the data previously used in Staubert et al (2014) and Staubert et al (2017) and our recent AstroSat results. We use the cyclotron line energies derived without any flux or temporal correction.…”

Section: Variation Of the Cyclotron Line Energy With Luminosity And Timementioning

confidence: 99%

See 2 more Smart Citations

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

Bala

Bhattacharya

Staubert

et al. 2020

Monthly Notices of the Royal Astronomical Society

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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 $54487^{+515}_{-469}$.

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Section: Of T C (=54487 +515mentioning

confidence: 60%

Section: Introductionmentioning

confidence: 63%

Section: Variation Of the Cyclotron Line Energy With Luminosity And Timementioning

confidence: 99%

See 1 more Smart Citation

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

Bala

Bhattacharya

Staubert

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…An intriguing aspect of this issue is the behavior of Her X-1's CRSF energy between 1991 and 1994, when it appears to have jumped by ∼7 keV. Staubert et al (2014) suggested that this indicates that Her X-1's CRSF energy has a natural "floor" of ∼37 keV, and indeed Staubert et al (2017) report evidence that the decay has reversed and the CRSF energy has begun to increase. This is interesting in comparison to the behavior of 4U 1538−522's CRSF, which is certainly consistent with a relatively short-timescale increase.…”

Section: Ingress Eclipse and Egress Spectramentioning

confidence: 99%

The First NuSTAR Observation of 4U 1538–522: Updated Orbital Ephemeris and a Strengthened Case for an Evolving Cyclotron Line Energy

Hemphill

Rothschild

Cheatham

et al. 2019

ApJ

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We have performed a comprehensive spectral and timing analysis of the first NuSTAR observation of the high-mass X-ray binary 4U 1538−522. The observation covers the X-ray eclipse of the source, plus the eclipse ingress and egress. We use the new measurement of the mid-eclipse time to update the orbital parameters of the system and find marginally-significant evolution in the orbital period, withṖ orb /P orb = (−0.95 ± 0.37) × 10 −6 yr −1 . The cyclotron line energy is found approximately 1.2 keV higher than RXTE measurements from 1997-2003, in line with the increased energy observed by Suzaku in 2012 and strengthening the case for secular evolution of 4U 1538−522's CRSF. We additionally characterize the behavior of the iron fluorescence and emission lines and line-of-sight absorption as the source moves into and out of eclipse.

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“…The CRSF properties of X-ray pulsars are found to be variable for different reasons (Maitra 2017). The CRSF line energy evolves with time in sources like Her X-1 (Staubert et al 2017) and 4U 1538-522 (Hemphill et al 2019). Line energy also shows dependence on X-ray luminosity, for example, in V0332+53 (Doroshenko et al 2017).…”

Section: Introductionmentioning

confidence: 99%

Pulse Phase Variation of the Cyclotron Line in HMXB 4U 1907+09 with AstroSat LAXPC

Varun

Pradhan

Maitra

et al. 2019

ApJ

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We present timing and spectral analysis of data from an observation of the High Mass X-ray Binary pulsar 4U 1907+09 with the LAXPC instrument onboard AstroSat. The light curve consisted of a flare at the beginning of the observation, followed by persistent emission. The pulsar continues to spin down, and the pulse profile is found to be double-peaked up to 16 keV with the peaks separated by a phase of ∼ 0.45. Significant energy dependence of the pulse profile is seen with diminishing amplitude of the secondary peak above 16 keV, and increasing amplitude of the main peak upto 40 keV and a sharp decline after that. We confirm earlier detections of the Cyclotron Resonance Scattering Feature (CRSF) in 4U 1907+09 at ∼ 18.5 ± 0.2 keV in the phase-averaged spectrum with a high detection significance. An intensity resolved spectral analysis of the initial flare in the light curve shows that the CRSF parameters do not change with a change in luminosity by a factor of 2.6. We also performed pulse phase-resolved spectral analysis with ten independent phase bins. The energy and the strength of the cyclotron line show pulse phase dependence that is in agreement with previous measurements. Two features from the current observation: different energy dependence of the two pulse peaks and a strong CRSF only around the secondary peak, both indicate a deviation from a dipole geometry of the magnetic field of the neutron star, or complex beaming pattern from the two poles.

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Inversion of the decay of the cyclotron line energy in Hercules X-1

Cited by 29 publications

References 33 publications

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

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

The First NuSTAR Observation of 4U 1538–522: Updated Orbital Ephemeris and a Strengthened Case for an Evolving Cyclotron Line Energy

Pulse Phase Variation of the Cyclotron Line in HMXB 4U 1907+09 with AstroSat LAXPC

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