INTEGRAL observations of renewed activity from IGR J18483-0311 and of the unusual dimming trend of GRS 1915+105

ATel #12772; Onori F., Fiocchi M. (INAF-IAPS Roma, Italy), Chenevez J. (DTU Space, Denmark), Sguera V. (INAF-OAS, Bologna, Italy), Bazzano A. Natalucci, L., Ubertini P. (INAF-IAPS Roma, Italy), Bird A. J., Lepingwell V. A. (Univ. of Southampton, UK), Bassani L., Malizia A., Masetti N. (INAF-OAS, Bologna, Italy)
on 17 May 2019; 09:40 UT
Credential Certification: Francesca Onori (francesca.onori@inaf.it)

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During the recent INTEGRAL observations of the Galactic Plane Scan (PI: Dr. A. Bazzano), the IBIS/ISGRI instrument detected a X-ray flare from the supergiant fast X-ray transient and HMXB neutron star system IGR J18483-0311 and the low luminosity state of the micro-quasar GRS 1915+105.

IGR J18483-0311 was detected by IBIS/ISGRI during scans performed in revolution 2089 (between 2019-05-10 11:29:26 UTC and 2019-05-11 08:58:16 UTC) in the 22-60 keV energy range. The flux measured over the whole revolution is F_22-60 = 23.8 +-1.5 mCrab for an effective exposure time of 7.3 ks.
From the analysis of the single science windows we report the detection of two X-ray flares from IGR J18483-0311. The first flare starts on MJD 58613.76 and ends on MJD 58613.83 with an average flux of F_22-60 = 50.9 +-3.7 mCrab and an effective exposure time of 1.1 ks. The second flare starts on MJD 58613.99 and ends on MJD 58614.09 with an average flux of F_22-60 = 58.4 +-5.4 mCrab and an effective exposure time of 0.6 ks.
IGR J18483-0311 was within the field of view of the JEM-X instruments. The averaged fluxes measured with JEM-X in the 3-10 keV and 10-25 keV energy bands are F_3-10 = 20 +/-2 mCrab and F_10_25 = 23 +/-7 mCrab, respectively. The source showed a peak of emission on MJD 58613.82 during which the average fluxes reached F_3-10 = 44 +/-4 mCrab and F_10-25 = 52 +/-9 mCrab.

Recently, the X-ray transient GRS 1915+105 was observed in an unusual low state in the X-rays (see ATels #12771, #12770, #12769, #12765, #12761, #12755, #12743, #12742). During this phase, the source was detected by IBIS/ISGRI in revolutions 2085 (between 2019-04-29 19:55:50 UTC and 2019-04-30 21:44:40 UTC), 2087 (between 2019-05-05 03:37:44 UTC and 2019-05-06 10:45:55 UTC) and 2089. During the whole scanning period GRS 1915+105 showed a dimming trend in the flux at 22-60 keV. In particular, in revolution 2085 the flux of GRS 1915+105 was F_22-60 = 106.9 +-1.5 mCrab for an effective exposure time of 7.3 ks, in revolution 2087 the flux was F_22-60= 74.2 +-1.5 mCrab for an effective exposure time of 8.0 ks, while in revolution 2089 the flux was F_22-60=60.0 +-1.5 mCrab for an effective exposure time of 7.8 ks.
GRS 1915+105 was also within the field of view of JEM-X instruments. The fluxes measured in the 3-10 keV and in the 10-25 keV energy bands during the revolution 2089 are F_3-10 =25 +/-1 mCrab and F_10-25 = 30 +/-3 mCrab, respectively. The effective source exposure time in the combined JEM-X 1+2 instrument is 24.5 ks. During revolution 2085 these fluxes were: F_3-10 =94 +/-1 mCrab and F_10-25 = 114 +/-3 mCrab, while during revolution 2087 they were: F_3-10 =48 +/-1 mCrab and F_10-25 = 59 +/-3 mCrab.

All the data have been analyzed using the Offline Software Analysis version 11.0 (OSA11). The source field will be observed again during the next days in the framework of the Galactic Plane Scan program (PI: Dr. A. Bazzano).
Results from the Galactic Plane Scanning are made publicly available at: http://gps.iaps.inaf.it