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A new hard X-ray transient discovered by INTEGRAL: IGR J18179-1621

ATel #3947; M. Tuerler (ISDC, Univ. of Geneva, Switzerland), J. Chenevez (DTU Space, Denmark); E. Bozzo, C. Ferrigno, A. Tramacere (ISDC, U. of Geneva, Switzerland); I. Caballero, J. Rodriguez (CEA Saclay, France); M. Cadolle-Bel, C. Sanchez-Fernandez (ESA/ESAC, Spain); M. Del Santo, M. Fiocchi, A. Tarana (INAF/IAPS, Roma, Italy), P. R. den Hartog (Stanford Univ. HEPL-KIPAC, USA), I. Kreykenbohm, M. Kuehnel (Dr. Karl Remeis Obs. and ECAP, Germany), A. Paizis (INAF/IASF-Milano, Italy), G. Puehlhofer (IAA-Tuebingen, Germany), K. Watanabe (Florida Gulf Coast Univ., USA), G. Weidenspointner (MPE and MPI HLL, Germany), S. Zhang (IHEP, China)
on 1 Mar 2012; 14:59 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Carlo Ferrigno (Carlo.Ferrigno@unige.ch)

Subjects: X-ray, Gamma Ray, Binary, Black Hole, Neutron Star, Transient

Referred to by ATel #: 3949, 3950, 3988

INTEGRAL discovered a new hard X-ray transient, IGR J18179-1621, during the inner Galactic disk observations performed on 2012-02-29 from 02:20 to 15:41 UTC.

The source was detected in the IBIS/ISGRI mosaic at a significance level of 16 σ (effective exposure time 30 ks) in the 20-40 keV energy band. The corresponding flux was 16±1 mCrab (1.2±0.1 × 10-10 erg/s/cm2) (uncertainties are 68% c.l.).

The source was also detected by JEM-X at a significance level of 8 σ in the 3-10 keV energy band and 10 σ in the 10-25 keV energy band. The corresponding fluxes were 17.7±2.2 mCrab (3.0±0.4 × 10-10 erg/s/cm2) and 36.4±3.6 mCrab (4.4±0.4 × 10-10 erg/s/cm2), respectively (effective exposure time 11.9 ks). The best source position determined with the two JEM-X instruments is
RA=274.467 (18h17m52s);
DEC=-16.357 (-16d21'25")
(J2000) with an associated uncertainty of 1.5 arcmin.

The combined JEM-X and IBIS/ISGRI spectrum can be well described (χ2red/d.o.f.=0.4/12) by a cut-off power-law (Γ=-0.5 ± 0.5, Ecutoff=4.9-0.9+1.5 keV) plus a broad Gaussian absorption line (Ecentroid=20.8-1.8+1.4 keV, σ=3.0-1.3+1.8 keV, τ=10-4+5, model uncertainties at 90% c.l.). The 3-50 keV flux estimated from the spectral fit is 1.0 × 10-9 erg/s/cm2. If the absorption line is interpreted as due to cyclotron scattering, this new source would be a high mass X-ray binary pulsar with a magnetic field in the emitting region of ~1.7 × 1012 Gauss. However, the non-detection of a higher harmonic might indicate that a model with two emission components could also be used (see also the case of X-Per, Doroshenko et al., 2012, arXiv:1202.6271).

Multiwavelength follow-up observations are encouraged to unveil the nature of this transient.