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INTEGRAL detection of 4U 1630-472 in outburst

ATel #7159; Y. Wang C. Ferrigno (ISDC, University of Geneva, CH) A. Bodaghee (GSU, USA) on behalf of the ISA Collaboration
on 27 Feb 2015; 23:23 UT
Credential Certification: Carlo Ferrigno (Carlo.Ferrigno@unige.ch)

Subjects: X-ray, Binary, Black Hole, Transient

During the observations of Galactic Spiral Arms Norma/Perseus performed on 2015 February 26 from 07:34 to 11:15 UTC, the JEM-X instruments (3-30 keV) on board INTEGRAl detected the black-hole candidate 4U 1630-47. The current outburst started on 25 January 2015, according to the MAXI report (ATeL #6991).

The source is detected in the JEM-X mosaic image with a flux of 315 ± 9 mCrab and 23 ± 13 mCrab in the 3-10 and 10-20 keV energy bands (statistical uncertainty at 1σ level). The source is not detected at higher energy: the 5 σ upper limits in IBIS/ISGRI are 13 and 14 mCrab in the 20-40 and 40-80 keV energy bands.

The average JEM-X spectrum (effective exposure time 13 ks) can be described by an thermal model with column density fixed at 1024cm-2 (Tomsik et al, 2005, ApJ 630,413). We used a disk black-body with kTin = 1.3 ±0.1 keV and Norm=300+200-100 yielding an unabsorbed 2-20 keV model flux of 10-8erg/s//cm2 (chi2_red/d.o.f.=0.7/6). A similar spectral component was present also during the first months of previous source outbursts (e.g., Tomsick et al., 2005, Seifina et al. 2014, ApJ 789, 57), together with a hard tail, which could not be firmly detected with the present INTEGRAL data: adding a power-law to the model provides a fit improvement with a 8% probability of being due to a statistical fluctuation. (Caveat: the spectral parameters could slightly change with a refined energy calibration, not available in the quick-look data used in this analysis.)

Further observations will be performed in the direction of this source during the coming weeks.