Insight-HXMT scanning survey detections of the new X-ray transient MAXI J0903-531

ATel #14558; C. Wang, J.-Y. Liao, J. Guan, C.-K. Li, Y. Nang, N. Sai, Y. Liu, Y. Chen, X.-L. Cao, C.-Z. Liu, T.-P. Li, F.-J. Lu, L.-M. Song, M. Wu, Y.-P. Xu, S.-N. Zhang, report on behalf of the Insight-HXMT team:
on 17 Apr 2021; 15:43 UT
Credential Certification: Yu-Peng Chen (chenyp@ihep.ac.cn)

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Upon the report of the new X-ray transient MAXI J0903-531 discovered by MAXI /GSC (K. Yamaoka et al. 2021, ATEL #14555), the precise position of the source was obtained with the Swift follow-up observation (J. A. Kennea et al. 2021, ATEL #14557). We carefully inspected the candidate new source list from the regular Galactic plane scanning survey with Insight-HXMT/LE (Sai et al. 2020), and found three positive detections at the locations near MAXI J0903-531, which are listed as follows:

Scanning time: January 7th, 2018; 01:13 UT for 306 s
Candidate new source position: (R.A., Dec) = (135.49 deg, -53.56 deg) (J2000) with 1-sigma error of 0.38 deg.
Average flux: 9.5+/-1.7 mCrab (1-6 keV, 1-sigma error)

Scanning time: March 17th, 2020; 09:54 UT for 428 s
Candidate new source position: (R.A., Dec) = (135.75 deg, -53.51 deg) (J2000) with 1-sigma error of 0.65 deg.
Average flux: 3.1+/-1.5 mCrab (1-6 keV, 1-sigma error)

Scanning time: February 9th, 2021; 11:28 UT for 636 s
Candidate new source position: (R.A., Dec) = (135.90 deg, -53.49 deg) (J2000) with 1-sigma error of 0.51 deg.
Average flux was 4.6+/-1.6 mCrab (1-6 keV, 1-sigma error)

The first detection is consistent with the precise position of (R.A., Dec) = (136.27866 deg, -53.50518 deg) (J2000) reported by Swift (ATEL #14557) within 2-sigma error, and the other two are consistent within 1-sigma error.

Insight-HXMT is the first Chinese astronomy satellite, which was launched in 2017 and funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More detailed information is given on website: http://hxmtweb.ihep.ac.cn/.

References: Sai, N., Liao, j.-Y., Li, C.-K., et al. 2020, JHEAp, 26, 1.