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Suzaku View of the Neutron Star in the Dipping Source 4U 1822-37

Abstract

The dipping X-ray source 4U 1822-37 was observed by Suzaku on 2006 Octrober 20 for a net exposure of 37 ks. The source was detected with the XIS at a 1-10 keV flux of 5.5×1010\times10^{-10} erg cm2^{-2} s1^{-1}, and with the HXD (HXD-PIN) at a 10-50 keV flux of 8.9×1010\times10^{-10} erg cm2^{-2} s1^{-1}. With HXD-PIN, the pulsation was detected at a barycentric period of 0.592437 s, and its change rate was reconfirmed as 2.43×-2.43\times1012^{-12} s s1^{-1}. The 1-50 keV spectra of 4U 1822-37 were found to be very similar to those of Her X-1 in the slopes, cutoff and iron lines. Three iron lines (Fe Kα\alpha, Fe XXV, and Fe XXVI) were detected, on top of a 1-50 keV continuum that is described by an NPEX model plus a soft blackbody. In addition, a cyclotron resonance scattering feature was detected significantly (>99%>99\% confidence), at an energy of 33±\pm2 keV with a depth of 0.40.3+0.6^{+0.6}_{-0.3}. Therefore, the neutron star in this source is concluded to have a strong magnetic field of 2.8×1012\times10^{12} G. Further assuming that the source has a relatively high intrinsic luminosity of several times 1037^{37} erg s1^{-1}, its spectral and timing properties are consistently explained

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