INTEGRAL detection of an outbursts of two supergiant fast X-ray transients
ATel #5402; M. Tuerler, C. Ferrigno (ISDC, Switzerland), A. Bodaghee (SSL - UC Berkeley, USA) , P. Romano (INAF/IASF-PA, Italy)
on 19 Sep 2013; 18:10 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Carlo Ferrigno (Carlo.Ferrigno@unige.ch)
Subjects: X-ray, Neutron Star, Transient
During the observation of parts of the inner Galactic spiral arms performed on 2013-09-18, the INTEGRAL observatory
detected the outbursts from the sources IGR J16418-4532 (see also ATEL #5398 for the Swift detection of an outburst on 2013-09-17 ) and IGR J18483-0311. The former is a supergiant fast X-ray transient (SFXT) with intermediate properties (Sidoli et al., MNRAS., 420, 554-561, 2012; Romano et al., MNRAS, 419, 2695-2702, 2012), the latter a confirmed member of this class (e.g., Romano et al., MNRAS, 401, 1564-1569, 2010).
The region of the Scutum/Sagittarius arms was observed on 2013-09-18 between 15:18 and 19:00 UTC. A new outburst of the SFXT IGR J18483-0311 was detected by the instruments JEM-X and IBIS/ISGRI.
The average fluxes extracted from the composite image of the observation are
4.6±1.3 mCrab (3-10 keV), 16±3 mCrab (10-20 keV), 17.0±1.5 mCrab (20-40 keV), and 12±2 mCrab (40-80 keV) .
The source spectrum above 20 keV (effective exposure 11.7 ks) can be described by a power law with index 1.6±0.5 and 20-80 keV flux 2.7e-10 erg/s/cm2 (reduced χ2=0.4 for 4 degrees of freedom). A visual inspection of the light curve extracted with bins of one minute did not reveal evidence of any remarkable flare.
The region of the Perseus arm was observed on 2013-09-18 between 02:13 and 05:55 UTC. IGR J16418-4532 was detected only in the IBIS/ISGRI summed image in the 20-40 keV energy band at an average flux level of 19±2 mCrab (effective exposure 7.4 ks). Its hard X-ray spectrum can be fitted with a power-law of index 3.7-1.0+1.5 and a 20-40 keV flux 1.3e-10 erg/s/cm2 (reduced χ2=1.3 for 4 degrees of freedom). A visual inspection of the 20-40 keV light curve extracted with bins of one minute showed quasi-persistent emission at the above average flux level and a single flare centred at 17:31 UTC reaching 80±20 mCrab for about two minutes.
Further observations are planned during the coming weeks.
The INTEGRAL spiral arms monitoring program