2015A&A...578A..88K


C.D.S. - SIMBAD4 rel 1.7 - 2019.12.10CET12:17:26

2015A&A...578A..88K - Astronomy and Astrophysics, volume 578A, 88-88 (2015/6-1)

Swift/BAT measurements of the cyclotron line energy decay in the accreting neutron star Hercules X-1: indication of an evolution of the magnetic field?

KLOCHKOV D., STAUBERT R., POSTNOV K., WILMS J., ROTHSCHILD R.E. and SANTANGELO A.

Abstract (from CDS):

The magnetic field is a crucial ingredient of neutron stars. It governs the physics of accretion and of the resulting high-energy emission in accreting pulsars. Studies of the cyclotron resonant scattering features (CRSFs) seen as absorption lines in the X-ray spectra of the pulsars permit direct measurements of the field strength. From an analysis of a number of pointed observations with different instruments, the energy of CRSF, Ecyc, has recently been found to decay in Her X-1, which is one of the best-studied accreting pulsars. We present our analysis of a homogeneous and almost uninterrupted monitoring of the line energy with Swift/BAT. We analyzed the archival Swift/BAT observations of Her X-1 from 2005 to 2014. The data were used to measure the CRSF energy averaged over several months. The analysis confirms the long-term decay of the line energy. The downward trend is highly significant and consistent with the trend measured with the pointed observations: dEcyc/dt~-0.3keV per year. The decay of Ecyc either indicates a local evolution of the magnetic field structure in the polar regions of the neutron star or a geometrical displacement of the line-forming region due to long-term changes in the structure of the X-ray emitting region. The shortness of the observed timescale of the decay, -Ecyc/{dot}(E)cyc∼100yr, suggests that trend reversals and/or jumps of the line energy might be observed in the future.

Abstract Copyright:

Journal keyword(s): accretion, accretion disks - stars: neutron - stars: magnetic field

Simbad objects: 3

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Number of rows : 3

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 V* HZ Her LXB 16 57 49.8110797681 +35 20 32.487435684 11.90 14.89 13.63 13.88   B3/6ep 1902 0
2 Granat 1915+105 LXB 19 15 11.54938 +10 56 44.7585           ~ 2237 0
3 HD 226868 HXB 19 58 21.6758193269 +35 12 05.782512305 9.38 9.72 8.91 8.42   O9.7Iabpvar 3851 0

    Equat.    Gal    SGal    Ecl

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2019.12.10-12:17:26

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