SVOM/ECLAIRs detection of a possible new outburst onset from the black hole 4U 1630-472

ATel #18030; F. Cangemi (APC, France), S. Le Stum (APC, F), A. Coleiro (APC, F), O. Godet (IRAP, F), J. Rodriguez (CEA, F), Y.-H. I. Yin (HKU, China), R.-C. Chen (NJU, C), L. Tao (IHEP, C), L. Zhang (IHEP, C)
on 4 Sep 2026; 13:05 UT
Credential Certification: Floriane Cangemi (cangemi@apc.in2p3.fr)

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On 2026 September 2 at 01:59:31.116 UT, the onboard trigger software of the SVOM/ECLAIRs telescope (4-150 keV) detected and localized a source at R.A. = 248.506 deg and Dec. = -47.393 deg (J2000), with an uncertainty radius of 4.63 arcmin (90% confidence level), in the 8-50 keV energy band (S/N = 18.43). The source position is consistent with that of the black-hole X-ray binary 4U 1630-472.

A preliminary spectral analysis of the ECLAIRs data, with an exposure of 1996 s, shows that the 4-120 keV spectrum is well described (chi2/dof = 18.73/19) by a cutoff power-law model, with a photon index of Gamma = (0.5 +/- 0.4) and a cutoff energy of E_cut = 17 (+7 / - 4) keV. The corresponding observed flux in the 4-120 keV energy band is (7.8 +0.3 /- 1.1) e-9 erg/cm2/s. All uncertainties are reported at the 90% confidence level.

The source was briefly active in 2025, May, and was then detected and followed with MAXI and detected with ECLAIRs, last time on May 18, 2025. Since then, it was apparently in quiescence (see the MAXI long term light-curve at https://maxi.riken.jp/star_data/J1634-473/J1634-473.html). The ECLAIRs detection may therefore indicate the onset of a new outburst from 4U 1630-472. We remark the flux increase is also visible over the last fews days in MAXI. This source is a recurrent black-hole X-ray binary that can undergo strong and long-lasting outbursts, with the most recent major outbursts occurring in 2018 (ATels, #11722, #11771), and 2020 (ATels #13564, #13572, #13592, #13623).

The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. ECLAIRs was developed jointly by APC, CEA, CNES and IRAP.