NuSTAR observation of the Be/X-ray binary IGR J06074+2205
ATel #17458; Birendra Chhotaray (PRL, Ahmedabad, India), Sachindra Naik (PRL, Ahmedabad, India) Gaurava K. Jaisawal (DTU Space, Denmark), Arghajit Jana (SRM University AP, India), Manoj Mandal (PRL, Ahmedabad, India)
on 28 Oct 2025; 11:57 UT
Credential Certification: Birendra Chhotaray (rsbirendra786@gmail.com)
Subjects: X-ray, Binary, Neutron Star, Transient
Referred to by ATel #: 17714
IGR J06074+2205 is a Be/X-ray binary consisting of a B0.5e donor star and a strongly magnetized neutron star with a rotation period of ~374 s. The system has an orbital period of ~80 days (Mihara et al. 2023, ATel, 16351,1; Chhotaray et al., 2024, MNRAS, 534, 2830). Nesci et al., (2025) (ATel #17424) reported strong H-alpha emission, so enhanced accretion was expected near the periastron passage around 2025-09-24. Their Swift/XRT monitoring between 2025-09-19 and 2025-09-27 showed the count rate rising from 0.03 to 1.9 c s^-1 (Nesci et al., 2025, ATel, 17424, 1). Hence, for a broadband timing and spectral study of the source, we requested a NuSTAR ToO DDT observation, which was performed on 14 October 2025 with an exposure of ~40 ks.
We detected coherent X-ray pulsations at a period of ~374.68 s from the NuSTAR light curve. The pulse profile is dominated by a single-peak-like structure. We performed a detailed spectral analysis in the energy range of 3-30 keV, as the count statistics were poor beyond this energy range. The simultaneous FPMA and FPMB spectra are well described by an absorbed power law plus a blackbody model. The best-fit parameters are gamma = 0.8 +/- 0.2, kT = 1.21 +/- 0.04 keV, and blackbody radius R = 291 +/- 25 m (for D = 5.99 kpc). During the fit, the line-of-sight absorption column density was fixed at 0.43 × 10^22 cm^-2 (Galactic value; HI4PI). Uncertainties are quoted at 90% confidence.
The 3-30 keV luminosity is estimated to be 4.1 × 10^34 erg s^-1 (assuming a source distance of 5.99 kpc). The lowest luminosity at which pulsations were previously detected with XMM-Newton was 1.8 × 10^34 erg s^-1 in the 0.2-12 keV band, assuming a distance of 4.5 kpc (Reig et al. 2018, A&A, 613, A52). For comparison, we estimate the 0.2-12 keV luminosity at 4.5 kpc from our model to be 1.6 × 10^34 erg s^-1, which may be closer to the propeller regime of the pulsar. We have been monitoring the system in the optical band.
We thank the NuSTAR PI for approving our ToO request.
