INTEGRAL and Swift/XRT observations on IGR J18179-1621

TL;DR

This paper presents detailed timing and spectral analysis of the X-ray transient IGR J18179-1621 using INTEGRAL and Swift data, revealing pulsations, spectral features, and magnetic field estimates.

Contribution

It provides the first detailed timing and spectral characterization of IGR J18179-1621, including pulsation detection and cyclotron line identification, indicating a neutron star with a strong magnetic field.

Findings

Detected 11.82 s pulsation with high confidence

Identified a cyclotron resonant scattering feature at 21.5 keV

Estimated magnetic field strength of approximately 2.4 x 10^12 Gauss

Abstract

IGR J18179-1621 is a hard X-ray binary transient discovered recently by INTEGRAL. Here we report on detailed timing and spectral analysis on IGR J18179-1621 in X-rays based on available INTEGRAL and Swift data. From the INTEGRAL analysis, IGR J18179-1621 is detected with a significance of 21.6 sigma in the 18-40 keV band by ISGRI and 15.3 sigma in the 3-25 keV band by JEM-X, between 2012-02-29 and 2012-03-01. We analyze two quasisimultaneous Swift ToO observations. A clear 11.82 seconds pulsation is detected above the white noise at a confidence level larger than 99.99%. The pulse fraction is estimated as 22+/-8% in 0.2-10 keV. No sign of pulsation is detected by INTEGRAL/ISGRI in the 18-40 keV band. With Swift and INTEGRAL spectra combined in soft and hard X-rays, IGR J18179-1621 could be fitted by an absorbed power law with a high energy cutoff plus a Gaussian absorption line centered at 21.5 keV. An additional absorption intrinsic to the source is found, while the absorption line is evidence for most probably originated from cyclotron resonant scattering and suggests a magnetic field in the emitting region of \sim 2.4 \times 10^12 Gauss.