INTEGRAL observations of the on-going outburst from the new X-ray transient Swift J1728.9-3613
ATel #12502; L. Ducci (IAAT, Germany; ISDC, Switzerland), V. Grinberg (IAAT, Germany), J. Wilms (ECAP, Germany), L. Sidoli, A. Paizis (INAF-IASF Milano, Italy), J. Chenevez (DTU Denmark), E. Bozzo, C. Ferrigno, V. Savchenko (ISDC, Switzerland)
on 13 Feb 2019; 19:45 UT
Credential Certification: Lorenzo Ducci (lorenzo.ducci@unige.ch)
Subjects: X-ray, Black Hole, Transient
The new X-ray transient source Swift J1728.9-3613
(ATel #12436, ATel #12437, ATel #12443, ATel #12445, ATel #12455, GCN #23800)
has been recently detected by INTEGRAL during the monitoring of the Galactic Center
(INTEGRAL revolution 2056; PI: J. Wilms).
We extracted the IBIS/ISGRI and JEM-X mosaics combining the available near real time (NRT)
INTEGRAL observations
(from 2019-02-12 11:55 to 2019-02-12 13:39 UTC; IBIS/ISGRI exposure time: ~5.7ks; JEM-X exposure time: ~2.7ks)
and found that the source is detected at a significance of 27 σ in the 20-40 keV energy
range and about 12 σ in the 40-80 keV energy range.
The corresponding fluxes are 103 ± 4 mCrab and 96 ± 8 mCrab, respectively.
In the JEM-X mosaics, the source is detected at a significance of 60 σ in the 3-10 keV energy
range and about 16 σ in the 10-25 keV energy range. The corresponding fluxes are
337 ± 9 mCrab and 154 ± 16 mCrab, respectively.
The average preliminary JEM-X + IBIS/ISGRI spectrum (4-100 keV) can be described
(χ2red=1.5, 19 dof) with an absorbed power law
with photon index of 2.9 ± 0.1 and exponential rolloff at 50 (+31, -15) keV.
We fixed the absorption column density at NH=3.4E22 cm-2,
according to the previous measurement in the ATel #12455.
The 4-100 keV flux estimated from the spectral fit is (5.3 ± 0.8)*1E-9 erg/cm2/s
(all unertainties are given at 68% confidence level).
The photon index and flux are consistent with those measured by NICER
about two weeks ago (ATel #12455),
indicating that during this period the source did not change
significantly its spectral state.
A more complete analysis will be carried on the consolidated INTEGRAL data.
