The evolution of the current outburst of the low mass X-ray binary IGR J17091-3624

ATel #8761; Victoria Grinberg (MIT), Felix Fuerst (CalTech), Ralf Ballhausen (Remeis/FAU/ECAP), Wiebke Eikmann (Remeis/FAU/ECAP), Joern Wilms (Remeis/FAU/ECAP), Carlo Ferrigno (ISDC), Enrico Bozzo (ISDC), Marion Cadolle Bel (MPCDF), Elise Egron (INAF-OA), Thierry Favre (ISDC), Felicia Krauss (Remeis/FAU/ECAP), Ingo Kreykenbohm (Remeis/FAU/ECAP), Michael A. Nowak (MIT), Katja Pottschmidt (CRESST/GSFC/UMBC), Jerome Rodriguez(AIM/CEA)
on 2 Mar 2016; 04:31 UT
Credential Certification: Victoria Grinberg (grinberg@space.mit.edu)

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The transient low mass X-ray binary IGR J17091-3624 is a key source to understanding accretion/ejection processes in X-ray binaries. Observations during its best studied outburst in 2011 have shown that the source shows variability patterns that have so far been unique to GRS 1915+105 (Altamirano et al., 2011, ApJ, 742, L17). It also does not follow the standard track on the X-ray-radio correlation plane and transits into the soft state at comparatively low radio luminosities (Rodriguez et al., 2011, A&A, 533, L4).

After being in quiescence since ~2013, a steady rise in the Swift/BAT and a 1ks Swift/XRT snapshot have been reported by Miller et al. in ATel #8742. Here we report on results from the INTEGRAL monitoring of the Galactic Center region and further Swift/XRT pointings.

INTEGRAL/JEM-X (3-20 keV) & INTEGRAL/IBIS (20-80 keV) fluxes in mCrab:

revolution start--end 3-10 keV flux 10-20 keV flux 20-40 keV flux 40-80 keV flux
1645 2016-02-14--15 <14 <24 < 7 12+/-2
1646 2016-02-18--19 out of FOV out of FOV 12+/-2 19+/-3
1647 2016-02-20--22 <10 <17 15.9+/-1.6 20+/-2
1648 2016-02-22 <10 <17 20+/-2 34+/-3
1649 2016-02-25--27 out of FOV out of FOV 32+/-2 42+/-3

All uncertainties are only statistical and quoted at 1 sigma c.l. Maximal upper values denote 5 sigma upper limits. Note that observations in revolutions 1647 and 1649 were not continuous.

We fit four Swift/XRT observations obtained mainly in the WT mode with an absorbed power law model, with absorption tied between the four observations, but norm and slope of the power law free to vary between observations:

date power law slope 2-10 keV flux [10e-10 erg/cm2/s]
2016-02-26 1.22+/-0.13 (PC mode, observation presented in ATel #8742)
2016-02-27 1.41+/-0.10 1.85+/-0.12
2016-02-29 1.49+/-0.09 2.4+/-0.12
2016-03-01 1.52+/-0.08 2.75+/-11

The source shows a clear softening as expected during the rising phase of the outburst but is still clearly in the hard state.

(Coordinated) Multiwavelength observations of the source are highly encouraged.

We thank the Swift PI and team for the quick organization of the pointed Swift observations.