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INTEGRAL Observations of MAXI J1836-194

ATel #3652; M. Del Santo (INAF/IASF-Roma, Italy), E. Kuulkers (ESA/ESAC, Spain), J. Rodriguez (CEA Saclay, France), C. Baldovin, E. Bozzo (ISDC/University of Geneva), I. Caballero (CEA Saclay, France), M. Cadolle Bel (ESA/ESAC, Spain), F. Capitanio (INAF/IASF-Roma, Italy), J. Chenevez (DTU Space, Denmark), I. Kreykenbohm (IAA Tuebingen/ISDC), M. Kuehnel (ECAP & Remeis Observatory Bamberg), C. Sanchez-Fernandez (ESA/ESAC, Spain), K. Watanabe (FGCU, USA), G. Weidenspointner (MPE and MPI HLL, Germany)
on 19 Sep 2011; 17:57 UT
Credential Certification: Melania Del Santo (melania.delsanto@iasf-roma.inaf.it)

Subjects: Binary, Black Hole, Transient

Referred to by ATel #: 3689, 3790

MAXI J1836-194 (ATEL #3611) was in the INTEGRAL/IBIS FOV on September 13th from UT 09:15 till 12:56, during the Galactic Bulge monitoring observations (See http://integral.esac.esa.int/BULGE ). It was detected at about 55 mCrab and 50 mCrab (in 18-40 keV) in revolutions 1088 and 1090, respectively. Unfortunately it was not within the JEM-X field of view in any of the pointings for this observation. In the framework of the "inner disk >0" observations, further pointings were performed by INTEGRAL during revolution 1090. Here, we report on preliminary results of these IBIS and JEM-X observations collected on 2011-09-18 since 03:11:34.0 until 14:48:56.0.

MAXI 1836-194 was detected by IBIS/ISGRI at a significance level of 32 sigma and 19 sigma in the 20-40 keV and 40-80 keV bands, respectively (~23 ks effective exposure time). The corresponding fluxes are roughly 48 mCrab and 44 mCrab, respectively. The source was also clearly detected by JEM-X at 23 sigma level in the 3-10 keV energy band with a flux of about 38 mCrab (~5 ks effective exposure time). The simultaneous IBIS/ISGRI+JEM-X 4-300 keV spectrum can be well described (chi2_red/d.o.f=1.0/18) by a power-law model with photon index 2.19+/-0.05. There is no evidence of any high-energy cutoff below 200 keV. No disk black-body component (ATEL #3628) is requested by the JEM-X data. The estimated 3-20 keV and 20-100 keV mean fluxes are 1.0E-9 erg/cm2/s and 6.2E-10 erg/cm2/s, respectively.

RXTE/PCA spectra (power-law slope as 1.7-1.8) on August 31 (ATEL #3618) and September 2 (ATEL #3628) suggested that MAXI J1836-194 was in the hard/intermediate state at that time. Our INTEGRAL spectral fit and the prominent hard X-ray emission observed suggest MAXI J1836-194 being still in an intermediate state, possibly soft/intermediate as reported in the ATEL #3626. Our findings are consistent with the nature of black-hole candidate proposed for this source, definitely strengthened by the last radio (ATEL #3628) and optical (ATEL #3640) observations.

Follow-up observations at multi-wavelengths are strongly encouraged.

Further INTEGRAL observations are planned.

We acknowledge support from the Galactic Bulge group.