TITLE: GCN CIRCULAR NUMBER: 40595 SUBJECT: EP#01709177494: SVOM/VT optical observations DATE: 25/06/01 00:30:31 GMT FROM: Liping Xin at NAOC, SVOM xlp@nao.cas.cn

L. P. Xin, Y. L. Qiu, H. L. Li, C. Wu, Z. H. Yao, Y. N. Ma, X. H. Han, J. Wang, Y. Liu report on behalf of the SVOM and EP mission teams:

SVOM performed a Target of Opportunity observation of he EP-WXT trigger Einstein Probe/WXT-detected source EP#01709177494 (Wu et al., ATEL #17212). SVOM/VT began observing the field at 2025-05-31T02:37:05 UTC, 50.7 min after the trigger in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The exposure time for each frame is 70 seconds.

A cataloged source was identified during the outburst in VT_B and VT_R band images during our 2 orbit observations, compared to the DSS catalog. The position is RA=257.37661 deg, DEC=-26.65560 deg, corresponding to RA(J2000) = 17:09:30.39 DEC(J2000) = -26:39:20.15 Error = 0.5 arcseconds,

The position is consistent with the location of XRT Source 1 (SWIFT J170930.3-263917) (Evens et al., GCN 40592).

Preliminary analysis shows that the brightness of the source was VT_B=19.44+/-0.05 and VT_R=18.81+/-0.05, respectively.

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. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC),CAS.

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