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

Abstract

Recent observations of Her X-1 with NuSTAR and INTEGRAL in 2016 have provided evidence that the 20-year decay of the cyclotron line energy found between 1996 and 2015 has ended and that an inversion with a new increase, possibly similar to the one observed around 1990-1993, has started. We consider this a strong motivation for further observations and for enhanced efforts to significantly improve our theoretical understanding of the accretion process in binary X-ray pulsars. We speculate about the physics behind the long-term decay and its inversion, a possible cyclic behavior, and correlations with other variable observables.

5 pages, 1 figure, accepted by A&A

References in corpus (9)

• Discovery of a flux-related change of the cyclotron line energy in Her X-1
• A model for cyclotron resonance scattering features
• Luminosity dependence of the cyclotron line and evidence for the accretion regime transition in V 0332+53
• Long-term change in the cyclotron line energy in Hercules X-1
• Luminosity-dependent changes of the cyclotron line energy and spectral hardness in Cep X-4
• Discovery and Modeling of a Flattening of the Positive Cyclotron Line/Luminosity Relation in GX 304-1 with RXTE
• The Swift-BAT monitoring reveals a long term decay of the cyclotron line energy in Vela X-1
• Swift/BAT measurements of the cyclotron line energy decay in the accreting neutron star Her X-1: indication of an evolution of the magnetic field?
• Two giant outbursts of V 0332+53 observed with INTEGRAL

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• The Galactic LMXB Population and the Galactic Centre Region
• The First NuSTAR Observation of 4U 1538-522: Updated Orbital Ephemeris and A Strengthened Case for an Evolving Cyclotron Line Energy
• Relation of cyclotron resonant energy and luminosity in a strongly magnetized neutron star GRO J1008-57 observed by Insight-HXMT
• The cyclotron line energy in Her X-1: stable after the decay
• Time Evolution Of Cyclotron Line of Her X-1; A Detailed StatisticalAnalysis Including New ASTROSAT Data
• A broad-band X-ray view of the precessing accretion disk and pre-eclipse dip in the pulsar Her X-1 with NuSTAR and XMM-Newton
• Variations of cyclotron resonant scattering features in Vela X-1 revealed with Insight-HXMT
• Observations of Her X-1 in low states during SRG/eROSITA all-sky survey
• Possible detection of a new cyclotron feature in 4U 1700-37
• A peculiar cyclotron line near 16 keV detected in the 2015 outburst of 4U 0115+63?
• Studying the variations of the cyclotron line in Cen X-3 using Insight-HXMT
• Cyclotron lines in subcritical X-ray pulsars: Monte Carlo simulations reveal the origin of the observed variability
• Timing and spectral studies of the Be/X-ray binary EXO 2030+375 using Insight-HXMT observations