Swift/XRT Observation of MAXI J1828-249 in the Hard State
ATel #5886; John A. Tomsick (SSL/UCB), Stephane Corbel (Univ. Paris Diderot & CEA Saclay)
on 14 Feb 2014; 08:19 UT
Credential Certification: John A. Tomsick (jtomsick@ssl.berkeley.edu)
Subjects: X-ray, Binary, Black Hole, Transient
Referred to by ATel #: 5911
The black hole candidate X-ray transient MAXI J1828-249 was discovered on 2013 October 15 (ATEL#5474). While it may have briefly been in the hard state (ATEL#5476, ATEL#5483), it soon made a transition to a soft state, and both thermal disk-blackbody and power-law components were detected (ATEL#5479, ATEL#5492). The source has not been observable with Swift since mid-November because of a sun angle constraint, but it just became visible again.
We observed MAXI J1828-249 with the Swift X-ray Telescope (XRT) in photon counting mode starting at 2014 February 14, 0.05 h for an exposure time of 1.46 ks (ObsID 00032997026). The source count rate in the 0.5-10 keV energy band is 0.76 c/s after background subtraction. We extracted the energy spectrum, and it is well-described by an absorbed power-law (reduced-chi2 = 0.8 for 31 degrees of freedom). The column density is (3.0+/-0.9)e21 cm-2 (90% confidence errors, Wilms et al. 2000 abundances), which is comparable to previously reported values for this source. The photon index is Gamma = 1.70+/-0.15, and the absorbed 0.5-10 keV flux is 4.1e-11 erg/cm2/s. This value of the power-law index provides good evidence that the source is now in the hard state.
A radio observation of MAXI J1828-249 is planned for Feb. 16, and we plan to pursue further X-ray observations. Coverage at other wavelengths is also encouraged.
We thank Neil Gehrels for approving the Swift TOO request and the Swift duty scientists for carrying out the observations.
