SVOM/ECLAIRs sees the rebrightening of the Be/X-ray binary pulsar 1A 0535-668

ATel #18143; S. Le Stum (APC, France), H. Yang (IRAP, F), F. Cangemi (APC, F), A. Coleiro (APC, F), C. Diez (IRAP, F), S. Schanne (CEA, F), L. Tao (IHEP, China), L. Zhang (IHEP, C)
on 6 Nov 2026; 08:55 UT
Credential Certification: Floriane Cangemi (cangemi@apc.in2p3.fr)

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We report the detection of the Be/X-ray binary pulsar 1A 0535-668 with the ECLAIRs telescope onboard the SVOM mission on November 3, between 22:58:40 and November 4, 00:04:05 UTC, with a signal-to-noise ratio of 17.63 in the 4-10 keV energy band, while the source was within the ECLAIRs field of view.

A preliminary spectral analysis of the ECLAIRs data (effective exposure time of 3474 s) shows that the 4-20 keV spectrum is well described by a power-law model (fit statistic = 7.22/6 dof), with a photon index of Gamma = 2.7 +/- 0.3. The corresponding observed flux in the 4-20 keV energy band is (2.3 +/-0.2)e-9 erg/cm2/s. All uncertainties are quoted at the 90% confidence level.

The most recent detection of the source prior to our observations was reported by Swift/XRT (ATel #18051), which indicated that the source was fading on September 9, with a flux of approximately 3e-12 erg/cm2/s. ECLAIRs continued to cover the source between September 11 and October 15, during which the source was not detected. The detection reported here therefore indicates that the source has undergone a renewed increase in X-ray activity, with the onset of the rebrightening occurring after October 15 at the latest.

The source was also within the ECLAIRs field of view later on November 4, when a further increase in the count rate was observed, from 30.82 +/-0.94 cts/s to 39.14 +/- 0.49 cts/s (4-10 keV), between November 3 22:58:40 UTC and November 4 22:16:24 UTC observations, providing additional evidence for the ongoing brightening of the source.

MAXI previously reported the brightest outburst ever detected from this source on 2026 August 28 (ATel #18020). Prior to the current activity, three other outbursts had been reported on 2025 September 30 (MJD 60948; ATels #17455 and #17467), 2026 February 27 (MJD 61098; ATel #17705), and 2026 May 21 (MJD 61181; ATel #17815). SVOM Target of Opportunity observation will be perform to further investigate the ongoing activity of the source.

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.