X-ray observation of Aql X-1 with the Neil Gehrels Swift Observatory

ATel #16826; Manoj Mandal (MCC), Sabyasachi Pal (MCC)
on 23 Sep 2024; 10:41 UT
Credential Certification: Manoj Mandal (manojmandal@mcconline.org.in)

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Aquila X-1 (Aql X-1) is a neutron-star low-mass X-ray binary (NS LMXB) that undergoes approximately one outburst per year (ATel #16284, #16174, #15401, #14437, #13953, #14079, #13961,# 2871, #2850, #2902, #2742). A new outburst of Aql X-1 was reported in September 2024 in multi-wavelength (ATel #16821, #16822, #16823). To monitor this outburst, we triggered an observation with Neil Gehrels Swift Observatory for Aql X-1. Here, we report preliminary results from a Swift/XRT observation on 2024 Sept 19 at 23:10:15. The observation was performed in Windowed Timing mode with an exposure of ~1 ks.

The preliminary analysis of the X-ray data detects the source, at a count rate of ~16 cnt s^-1 in the 0.5−10 keV range. There was no clear evidence of Type I bursts in the light curve. The XRT spectra can be fitted with an absorbed multi-color blackbody model with a column density N_H = (0.40 ± 0.02) × 10²² cm^-2 and an inner-disk temperature of 2.16 ± 0.01 keV. The best-fit result provides a reduced chi-square of 1.08 for 407 degrees of freedom. The unabsorbed flux is (8.0 ± 0.9) × 10^-10 erg cm^-2 s^-1 in 0.5−10 keV and the corresponding luminosity is (2.58 ± 0.05) × 10³⁶ erg s^-1 for a source distance of 5.2 ± 0.7 kpc. The reported errors in the spectral parameters represent 90% confidence intervals.

Further multi-wavelength observations are encouraged to trace the evolution of this outburst.

We thank the staff of the Neil Gehrels Swift Observatory for rapidly approving and scheduling these observations.