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The 2025 Failed Outburst of IGR J17091−3624: Spectral Evolution and the Role of Ionized Absorbers

Adegoke OK, García JA, Mastroserio G, Kammoun E, Connors RM, Steiner JF, Harrison FA, Buisson DJ, Coley JB, Coughenour BM, Dauser T, Ewing M, Ingram A, Kara E, Nathan E, Parra M, Stern D, Tomsick JA (2025)

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Publication Type: Journal article

Publication year: 2025

Journal

Book Volume: 995

Article Number: 143

Journal Issue: 2

DOI: 10.3847/1538-4357/ae1471

Abstract

IGR J17091−3624 is the only black hole X-ray binary candidate—aside from the well-studied black hole system GRS 1915+105—observed to exhibit a wide range of structured variability patterns in its light curves. In 2025, the source underwent a “failed” outburst: it brightened in the hard state but did not transition to the soft state before returning to quiescence within a few weeks. During this period, IGR J17091−3624 was observed by multiple ground- and space-based facilities. Here, we present results from six pointed NuSTAR observations obtained during the outburst. None of the NuSTAR light curves showed the exotic variability classes typical of the soft state in this source; however, we detected, for the first time, strong dips in the count rate during one epoch, with a total duration of ∼4 ks as seen by NuSTAR. Through spectral and timing analysis of all six epochs, we investigate the hard-state spectral evolution and the nature of the dips. A clear evolution of the coronal properties with luminosity is observed over all six epochs, with clear signatures of relativistic disk reflection that remain largely unchanged across the first five epochs. The first five epochs also show a strong and stable quasiperiodic oscillation feature in the power spectra. The dips observed in Epoch 5 are consistent with partial obscuration by ionized material with a column density NH ≈ 2.0 × 10²³ cm⁻². We discuss possible origins for this material and place constraints on the orbital parameters and distance of the system.

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How to cite

APA:

Adegoke, O.K., García, J.A., Mastroserio, G., Kammoun, E., Connors, R.M., Steiner, J.F.,... Tomsick, J.A. (2025). The 2025 Failed Outburst of IGR J17091−3624: Spectral Evolution and the Role of Ionized Absorbers. Astrophysical Journal, 995(2). https://doi.org/10.3847/1538-4357/ae1471

MLA:

Adegoke, Oluwashina K., et al. "The 2025 Failed Outburst of IGR J17091−3624: Spectral Evolution and the Role of Ionized Absorbers." Astrophysical Journal 995.2 (2025).

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