A Disk Wind in the Black Hole Candidate MAXI J1803-298
ATel #14650; J. M. Miller, M. T. Reynolds (Univ. of Michigan)
on 21 May 2021; 14:43 UT
Credential Certification: Jon Miller (jonmm@umich.edu)
Subjects: X-ray, Binary, Black Hole, Transient
Referred to by ATel #: 14994
We report on recent observations of the black hole candidate MAXI J1803-298 obtained with the Neil Gehrels Swift Observatory. The source shows strong X-ray flux dips, indicative of a viewing angle close to the plane of the accretion disk (#14609). Accretion disk winds in stellar-mass black holes are known to be equatorial (e.g. Miller et al. 2008, Ponti et al. 2012), so a disk wind is anticipated in this system as it shifts into a soft spectral state.
Swift observations of MAXI J1803-298 obtained on 2021 May 20-21 show evidence of absorption in the Fe K band. We derived windowed timing mode XRT spectra after excluding the central 4-6 pixels in order to limit photon pile-up. The individual spectra were combined in order to improve sensitivity, and binned. The summed 6.3 ks spectrum can be fit with a combination of disk blackbody (kT = 1.1 keV) and power-law components, though the power-law is not strongly required and may partially arise owing to pile-up effects. The 0.5-10 keV absorbed flux is 1.2 E-8 erg/cm2/s (roughly 0.5 Crab).
The Fe K band includes a strong, broad emission line with a blue extent consistent with a high inclination, and unresolved absorption consistent with He-like Fe XXV and H-like Fe XXVI lines. At the resolution afforded by the XRT, the modest velocity shifts typical of disk winds are difficult to measure, and standard corrections for detector effects at high count rates may over-correct the energy scale. The data do not rule out static absorption but it is more likely that the absorption is tied to an outflow that can be confirmed at high resolution. Exploratory fits with photoionized absorption models suggest a column density of N_H = 2-3 E+22 cm^-2 and an ionization of log xi = 4.0-4.5. These values are more consistent with the winds found in H 1743-322, 4U 1630-472, and IGR J17091-3624 than the winds seen in GRO J1655-40, GRS 1915+105, and V404 Cyg (e.g., King et al. 2012, 2015; Miller et al. 2015; Trueba et al. 2019).
We thank Brad Cenko and the Swift team for granting and executing monitoring observations of MAXI J1803-298. In future work, we will examine the multi-wavelength evolution of this source.
References:
King, A. L., et al., 2012, ApJ, 746, L20
King, A. L., et al., 2015, ApJ, 813, L37
Miller, J. M., et al., 2008, ApJ, 680, 1359
Miller, J. M., et al., 2015, ApJ, 814, 87
Ponti, G., et al., 2012, MNRAS, 422, L11
Trueba, N., et al., 2019, ApJ, 886, 104