TITLE: GCN CIRCULAR NUMBER: 41193 SUBJECT: GRB 250727A: SVOM/ECLAIRs refined analysis DATE: 25/07/29 08:16:33 GMT FROM: SVOM_group svomgroup@bao.ac.cn

M. G. Bernardini (INAF-OAB, LUPM), N. Dagoneau, D. Turpin (CEA), J.-L. Atteia, M. Brunet (IRAP), L. P. Xin (NAOC), J. X. Cao (GXU)

Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 250727A (SVOM burst-id sb25072701).

The burst that triggered ECLAIRs onboard (Cao et al. GCN 41176) consists of a long soft bump detected mainly below 30 keV, with a duration of T90 = (115.1 -8.2 +14.2) s in the 4-30 keV energy band.

The time-averaged spectrum from T0-10 s to T0+100 s (T0 = 2025-07-27T10:55:41.923s) in the energy range 5-50 keV is best fitted by a powerlaw model with index 2.3+/-0.4. With this model, the total 4-50 keV fluence is (1.4+/-0.1)e-7 erg/cm^2.

The spectrum can be equally fit by a blackbody model with temperature 2.4+/-0.5 keV. With this model, the total 4-50 keV fluence is (1.1+/-0.1)e-7 erg/cm^2.

All the quoted errors are at the 68% confidence level.

We note that the calibration of SVOM/ECLAIRs is undergoing thus these results are preliminary.

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

The SVOM/ECLAIRs point of contact for this burst is: Maria Grazia Bernardini (INAF-OAB, LUPM) (maria.bernardini at inaf.it)

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