Einstein Probe confirms the unprecedented low luminosity state of GRS 1915+105
ATel #17869; A. Marino, N. Rea, F. Coti Zelati (ICE-CSIC), S. Motta (INAF-OAB), R. Fender (Univ. Oxford), K. J. Zhang, D. Zhu (YNU), J. P. Chen (SYSU), W. Chen, Y. Liu (NAO, CAS)
on 3 Jul 2026; 06:08 UT
Credential Certification: Alessio Marino (marino@ice.csic.es)
Subjects: X-ray, Binary, Black Hole, Transient
GRS 1915+105 is one of the most extensively studied Galactic black-hole X-ray binaries (see, e.g., Mirabel & Rodriguez 1994, Belloni et al. 2000, Motta et al. 2025, and references therein). After remaining active for 34 years, the source has recently undergone an unusual fading of its L-band radio emission, down to its lowest level ever recorded (Motta et al., 2026; Atel #17865).
In order to check the X-ray status of the source, we performed a 2.5 ks observation with the Follow-up X-ray Telescope (FXT) on board Einstein Probe (Yuan et al., 2025) on June 27th. No source is detected within 1-arcmin of the source coordinates. By assuming a highly absorbed (NH=1024 cm-2) power-law (of spectral index Gamma=1.7), we pose a (preliminary) 3-σ upper limit on the unabsorbed flux of 4×10-13 erg cm-2 s-1 (0.3-10 keV), corresponding to X-ray luminosity LX ≲ 4 × 1033 erg s-1. Such a non-detection is consistent with the radio fading of the source and may indicate that GRS 1915+105 is entering a low-accretion state never probed before for this source, although a further increase in the intrinsic obscuration can not be excluded at the moment. Multi-wavelength follow-up is encouraged to investigate such an unprecedented regime in this historical source.
Launched on January 9, 2024, EP is a space X-ray observatory designed to monitor the soft X-ray sky with rapid X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). EP is a mission of the Chinese Academy of Sciences in collaboration with ESA, MPE, and CNES.
