INTEGRAL's detection of two Galactic X-ray transient sources: SWIFT J1858.6-0814 and 4U 1901+014

M. Fiocchi*, F. Onori, A. Bazzano, A. J. Bird, V. A. Lepingwell, J. Chenevez, K. Alizai, L. Bassani, A. Malizia, N. Masetti

*Corresponding author for this work

Research output: Other contributionNet publication - Internet publicationResearch


During a recent INTEGRAL observation as part of the Galactic Plane Scan Programme (PI: Dr. A. Bazzano), the IBIS/ISGRI instrument detected two Galactic X-ray transient sources: SWIFT J1858.6-0814 and 4U 1901+014. The sources were detected during scans performed in revolution 2081 between 2019-04-19T08:42:34 UTC and 2019-04-20T01:50:10 UTC in images made in the 22-60 keV energy range.
SWIFT J1858.6-0814 was first detected by Swift/BAT on 2018 October 31 (ATel #12151) and was detected in both soft X-rays (ATel #12158, ATel #12160, ATel #12163, ATel #12164) and hard X-rays (ATel #12167). The source remained active up to 2019 February as observed by NuSTAR (ATel #12512). SWIFT J1858.6-0814 was detected by IBIS/ISGRI in the 22-60 keV energy range with a flux of 14.5±1.9 mCrab, for an effective exposure time of 5.8 ks. From the combined JEM-X1 and JEM-X2 mosaic, we estimated a 3 sigma upper limit of 6 mCrab and 16 mCrab in the 3-10 keV and 10-25 keV energy bands, respectively, for an exposure time of 3.8 ks.
Both SWIFT/BAT and MAXI/GSC detected the fourth X-ray outburst from the binary pulsar 4U 1901+03 on 2019-02-08 (GCN #23882, ATel #12498). A NuSTAR observation which began around 2019-02-08 has shown a hard X-ray emission and a possible detection of a narrow absorption Cyclotron line around 31 keV (ATel #12684). The ISGRI/IBIS observation was performed during the decline of the source´s current outburst and 4U1901+014 was detected with a flux of 45.0±3.4 mCrab, for an effective exposure time of 1.9 ks (in the 22-60 keV energy range). This source was not within the field of view of JEM-X instruments.
All the data have been analyzed using the Offline Software Analysis version 11.0 (OSA11).
Results from the Galactic Plane Scanning are made publicly available at
Original languageEnglish
Publication date29 Apr 2019
Publication statusPublished - 29 Apr 2019
SeriesThe Astronomer's telegram
NumberATel #12704


  • X-ray
  • Gamma ray
  • Binary
  • Transient


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