Initial X-ray Spectroscopy of SMSS J114447.77-430859.3

ATel #15452; J. M. Miller (Univ. of Michigan), A. C. Fabian (Univ. of Cambridge), E. Kammoun (IRAP, Toulouse)
on 21 Jun 2022; 20:28 UT
Credential Certification: Jon Miller (jonmm@umich.edu)

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A recent observation of the extremely luminous quasar SMSS J1144447.7-430859.3 (Onken et al. 2022) with the Neil Gehrels Swift Observatory detected the source, with an X-ray flux of F_X = 1.1+/- 0.2 E-12 erg/cm^2/s (0.3-10.0 keV; ATEL #15450).

Additional exposure has been obtained, now totaling 3576 seconds in three visits accumulated throughout 21 June 2022. The time-averaged net count rate is 4.5 +/- 0.4 E-2 c/s in the full XRT band. Fits to the binned 0.3-10.0 keV spectrum with an absorbed power-law (minimizing a Cash statistic) give a column density of N_H = 4 +/- 2 E+21 cm^-2, a power-law index of Gamma = 1.6 +/- 0.3, and a flux normalization of K = 6 +/- 2 E-4 ph/cm^2/s/keV at 1 keV (1-sigma errors). The absorption and power-law parameters are both measured in the frame of the source, at a redshift of z = 0.83. The absorption is therefore local to the source. The absorbed flux is F_abs = 1.5 +/- 0.5 E-12 erg/cm^2/s, and the unabsorbed flux is 1.7 +/- 0.5 E-12 erg/cm^2/s. The implied X-ray luminosity of the source is then L_X = 4.7 +/- 1.5 E+45 erg/s.

The large fractional uncertainties in the flux and luminosity values are driven by the uncertainty in the spectral slope. When the power-law index is fixed at its central value, the fractional error on the power-law normalization reduces from 33% to just 10%. The flux and luminosity values reported here are slightly higher than those reported in ATEL #15450 owing to the ability to account for absorption.

We thank Swift for executing these observations.

References

Onken, C., et al., 2022, PASA, submitted, arxiv:2206.04204