Swift observations of the new outburst of the BH transient 4U 1630-472
ATel #17139; Melania Del Santo, Alberto Segreto, Carlotta Miceli (INAF/IASF Palermo)
on 7 Apr 2025; 23:28 UT
Credential Certification: Melania Del Santo (melania@ifc.inaf.it)
Subjects: X-ray, Black Hole, Transient
Referred to by ATel #: 17164
In the last 10 days, the BH transient 4U 1630-472 has been showing signs of increased activity in the Swift/BAT survey data.
Therefore, we triggered a monitoring campaign with Swift which observed the source on 2025-04-06 (XRT exposure 1.2 ks) and on 2025-04-07 (XRT exposure 1.1 ks). These two observations are consistent in the spectral shape and flux.
We simultaneously fitted the BAT hard X-ray spectrum (15-120 keV) stacked from 2025-03-31 to 2025-04-07 and the XRT spectrum (0.5-10 keV) taken on April 7th with an absorbed thermal Comptonisation model. The best fit results in an absorption column density of N_H=9.4 (+1.3/-1.1) cm^-2, an electron temperature of 30 (+11/-5) keV, a power-law index of 1.65 +/-0.06. Thus, the spectral parameters are consistent with 4U 1630-472 being in the hard state, which is rarely observed in this source.
The estimated absorbed fluxes in the 1-10 keV and 15-100 keV energy bands are roughly 9.3E-10 erg/cm^2/s and 3.4E-9 erg/cm^2/s, respectively.
Future Swift observations are planned in the upcoming days to monitor the outburst evolution. We thank the Swift team for assistance and the quick planning of the observations.
