NuSTAR observation of recent MAXI transient confirms a new outburst of the black hole X-ray binary MAXI J1543-564

ATel #17569; Benjamin M. Coughenour (Utah Valley University), John A. Tomsick (UCB/SSL), Douglas J. K. Buisson (Independent), Joel B. Coley (Howard, NASA/GSFC, CRESST II), Poshak Gandhi (Southampton), Javier A. García (NASA/GSFC, Caltech), Jeremy Hare (NASA/GSFC), Renee M. Ludlam (Wayne State), Labani Mallick (U of Manitoba & CITA, U of Toronto), Aarran Shaw (Butler)
on 31 Dec 2025; 21:56 UT
Credential Certification: Benjamin Coughenour (bcoughenour@uvu.edu)

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The recent MAXI transient (ATel #17552, #17559, #17560) was observed with NuSTAR on 26-28 December 2025. The source is clearly detected in both FPMs at (R.A., Dec) = (235.818, -56.4115), which is consistent (given NuSTAR's angular resolution of 18") with the Chandra position of the black hole X-ray binary candidate MAXI J1543-564 (ATel #3407). This source last went into outburst in 2011. Here we confirm that MAXI J1543-564 is experiencing renewed activity, rather than the high-mass X-ray binary pulsar XTE 1543-568 (which is 19' away from our source and outside the NuSTAR FOV) or a new transient (which would have been called MAXI J1544-565).

We have carried out a preliminary analysis of the quick-look data (with ~21 ks of exposure for Science Mode 01) and extracted a source spectrum for MAXI J1543-564. The source spectrum is roughly approximated (reduced chi-square < 1.4) by an absorbed thermal disk plus a power-law model (using tbabs*(diskbb+powerlaw) in XSPEC). Our NuSTAR spectrum is unable to constrain the interstellar absorption, and so the column density was fixed to nH = 1.4e22. We find a disk temperature of 0.96+/-0.01 keV and a power-law photon index of 2.34+/-0.02. The observed source flux in the 3-20 keV band is 7.1e-10 ergs/cm^2/s (roughly 30 mCrab). This spectrum is consistent with that of an intermediate-state black hole X-ray binary, with the disk providing ~65% of the source flux below 10 keV. These results are also in-line with those from intermediate state RXTE observations of MAXI J1543-564 during its previous 2011 outburst (Stiele et al. 2012, MNRAS 422, 679). Visual inspection of the residuals suggests reflection signatures with a broad Fe K-alpha line as well as an absorption feature near 6.9 keV.

Additional observations are recommended, particularly when the source is no longer sun-constrained for soft X-ray telescopes. XRISM's ability to distinguish discrete absorption features could be particularly useful.