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
(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.
|Publication date||1 Mar 2012|
|Publication status||Published - 1 Mar 2012|
|Series||The Astronomer's telegram|
- Black hole
- Neutron star
- Gamma ray