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

ATel #12704; Fiocchi M., Onori F., Bazzano A. (INAF-IAPS Roma, Italy), Bird A. J., Lepingwell V. A. (Univ. of Southampton, UK), Chenevez J., Khaled Alizai (DTU Space, Denmark), Bassani L., Malizia A., Masetti N. (INAF-OAS, Bologna, Italy)
on 29 Apr 2019; 19:22 UT
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Credential Certification: mariateresa fiocchi (mariateresa.fiocchi@iaps.inaf.it)

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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 http://gps.iaps.inaf.it