High-Resolution X-ray Spectroscopy of Hercules X-1 with the XMM-Newton RGS: CNO Element Abundance Measurements and Density Diagnostics of a Photoionized Plasma

Abstract

We analyze the high-resolution X-ray spectrum of Hercules X-1, an intermediate-mass X-ray binary, which was observed with the XMM-Newton Reflection Grating Spectrometer. We measure the elemental abundance ratios by use of spectral models, and we detect material processed through the CNO-cycle. The CNO abundances, and in particular the ratio N/O > 4.0 times solar, provide stringent constraints on the evolution of the binary system. The low and short-on flux states of Her X-1 exhibit narrow line emission from C VI, N VI, N VII, O VII, O VIII, Ne IX, and Ne X ions. The spectra show signatures of photoionization. We measure the electron temperature, quantify photoexcitation in the He alpha lines, and set limits on the location and density of the gas. The recombination lines may originate in the accretion disk atmosphere and corona, or on the X-ray illuminated face of the mass donor (HZ Her). The spectral variation over the course of the 35 d period provides additional evidence for the precession of the disk. During the main-on state, the narrow line emission is absent, but we detect excesses of emission at ~10--15 A, and also near the O VII intercombination line wavelength.

23 pages, 10 figures; accepted for publication in ApJ

References in corpus (5)

• Evolutionary Binary Sequences for Low- and Intermediate-Mass X-ray Binaries
• Line ratios for Helium-like ions: Applications to collision-dominated plasmas
• Double-Peaked X-Ray Lines from the Oxygen/Neon-Rich Accretion Disk in 4U1626-67
• High-Resolution X-Ray Spectroscopy of the Accretion Disk Corona Source 4U 1822-37
• X-ray Line Emission from Evaporating and Condensing Accretion Disk Atmospheres

Cited by in corpus (25)

• X-ray Absorption Line Spectroscopy of the Galactic Hot Interstellar Medium
• The Structure and X-ray Recombination Emission of a Centrally Illuminated Accretion Disk Atmosphere and Corona
• Chandra Grating Spectroscopy of the X-ray Binary 4U 1700-37 in a Flaring State
• "Hiccup" accretion in the swinging pulsar IGR J18245-2452
• XMM-Newton observations of High Mass X-ray Binaries in the SMC
• Identification of an Extended Accretion Disk Corona in the Hercules X-1 Low State: Moderate Optical Depth, Precise Density Determination, and Verification of CNO Abundances
• XMM-Newton EPIC observations of Her X-1
• Discrete X-ray Signatures of a Photoionized Plasma Above the Accretion Disk of the Neutron Star EXO 0748-676
• XMM-Newton EPIC & OM observations of Her X-1 over the 35 day beat period
• Chandra Spectroscopy of MAXI J1305-704: Detection of an Infalling Black Hole Disk Wind?
• The Photoionized Accretion Disk in Her X-1
• An ionised accretion disc wind in Hercules X-1
• Spectroscopic Signatures of the Superorbital Period in the Neutron Star Binary LMC X-4
• X-Ray Spectra of The High-Mass X-RAY Binary 4U~1700-37 using BeppoSAX, Suzaku and RXTE Observations
• XMM-Newton observations of UW CrB -- detection of X-ray bursts and evidence for accretion disc evolution
• Phase-resolved optical and X-ray spectroscopy of low-mass X-ray binary X1822-371
• FUSE Observations of a Full Orbit of Hercules X-1: Signatures of Disk, Star, and Wind
• Vertical wind structure in an X-ray binary revealed by a precessing accretion disk
• Ionized Reflection Spectra from Accretion Disks Illuminated by X-ray Pulsars
• CNO Line Radiation and the X-ray Bowen Fluorescence Mechanism in Optically-Thick, Highly-Ionized Media
• The long stare at Hercules X-1 -- I. Emission lines from the outer disk, the magnetosphere boundary and the accretion curtain
• X-ray He-like ions diagnostics: New Computations for Photoionized Plasmas: I. preliminary considerations
• A strong emission line near 24.8 angstrom in the X-ray binary system MAXI J0556--332: gravitational redshift or unusual donor?
• CIELO-RGS: a catalogue of soft X-ray ionized emission lines
• Accretion disc winds in X-ray binaries