[Paper Review] X-ray and radio observations of RX J1826.2-1450/LS 5039

M. Ribó, P. Reig+2 more|RECERCAT (Consorci de Serveis Universitaris de Catalunya)|May 26, 1999

Astrophysical Phenomena and Observations10 citations

TL;DR

This paper presents X-ray and radio observations of RX J1826.2-1450/LS 5039 using RXTE and the GBI-NASA monitoring program, finding no periodic X-ray emission over 0.02–2000 s or 2–200 d, a power-law X-ray spectrum with a strong 6.6 keV iron line, and no high-energy cut-off up to 30 keV. The system shows moderate, non-thermal radio variability without strong outbursts, supporting its classification as a high-mass X-ray binary with a compact object and massive companion star.

ABSTRACT

RX J1826.2-1450/LS 5039 has been recently proposed to be a radio emitting high mass X-ray binary. In this paper, we present an analysis of its X-ray timing and spectroscopic properties using different instruments on board the RXTE satellite. The timing analysis indicates the absence of pulsed or periodic emission on time scales of 0.02-2000 s and 2-200 d, respectively. The source spectrum is well represented by a power-law model, plus a Gaussian component describing a strong iron line at 6.6 keV. Significant emission is seen up to 30 keV, and no exponential cut-off at high energy is required. We also study the radio properties of the system according to the GBI-NASA Monitoring Program. RX J1826.2-1450/LS 5039 continues to display moderate radio variability with a clearly non-thermal spectral index. No strong radio outbursts have been detected after several months.

Motivation & Objective

• To investigate the X-ray timing and spectroscopic properties of RX J1826.2-1450/LS 5039 using data from the RXTE satellite.
• To assess the presence of periodic or pulsed X-ray emission across timescales from 0.02 s to 200 d.
• To characterize the X-ray spectrum, particularly the presence of emission lines and high-energy cutoffs.
• To analyze the radio variability and spectral index of the system using the GBI-NASA monitoring program.
• To evaluate whether the source exhibits strong radio outbursts, which would support a different emission mechanism.

Proposed method

• Analysis of X-ray light curves and power density spectra from RXTE instruments to detect periodic or pulsed emission.
• Fitting the X-ray spectrum with a power-law model plus a Gaussian component to model the iron Kα line at 6.6 keV.
• Assessment of high-energy spectral behavior by testing for exponential cutoffs above 30 keV.
• Use of the GBI-NASA monitoring program to track radio flux density and spectral index over time.
• Comparison of radio variability patterns with known outburst behavior in high-mass X-ray binaries.
• Application of statistical tests to determine significance of detected features, such as the iron line and non-thermal radio spectrum.

Experimental results

Research questions

• RQ1 Is there evidence of periodic or pulsed X-ray emission in RX J1826.2-1450/LS 5039 on timescales from 0.02 s to 200 d?
• RQ2 What is the shape of the X-ray spectrum, and does it require a high-energy cutoff?
• RQ3 What is the strength and energy of the iron Kα emission line in the X-ray spectrum?
• RQ4 Does the system exhibit strong radio outbursts, as seen in some other X-ray binaries?
• RQ5 What is the radio spectral index, and does it indicate non-thermal emission?

Key findings

• No pulsed or periodic X-ray emission was detected in the range 0.02–2000 s or over 2–200 d.
• The X-ray spectrum is well described by a power-law model with a photon index consistent with a hard spectrum, plus a strong Gaussian emission line at 6.6 keV.
• No significant exponential cut-off in the X-ray spectrum was required up to 30 keV, indicating a hard, non-thermal spectrum to high energies.
• The source exhibits moderate radio variability with a non-thermal spectral index, indicating non-thermal emission processes.
• No strong radio outbursts were detected over several months of monitoring, suggesting steady or low-amplitude radio activity.
• The combination of X-ray and radio properties supports the classification of RX J1826.2-1450/LS 5039 as a high-mass X-ray binary with a compact object and massive stellar companion.