NICER Spectroscopy of MAXI J1848-015 in the Stellar Cluster GLIMPSE-C01

ATel #14429; J. M. Miller (Univ. Michigan); A. Sanna, L. Burderi (Univ. Cagliari); T. Di Salvo (Univ. Palermo); D. Chakrabarty, M. Ng (MIT); K. Gendreau (NASA/GSFC)
on 2 Mar 2021; 10:06 UT
Credential Certification: Jon Miller (jonmm@umich.edu)

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We report on a NICER observation of the newly discovered transient, MAXI J1848-015 (ATEL #14282, #14290, #14420, #14424). 11.2 ks of net exposure was obtained starting on 23 Feb 2021 at 14:54:00 UTC.

Fits with an absorbed blackbody describe the continuum well. A blackbody temperature of kT = 1.00(2) keV is measured. When the line-of-sight absorption is described using tbabs with appropriate abundances and cross sections, a column density of N = 5.1 E+22 cm^-2 is measured. For this reason, the spectrum below 2 keV is strongly impacted.

The Fe K band appears to include several lines. The most prominent is an unresolved He-like Fe XXV emission line at 6.70 keV, with a flux of 1.5 E-5 ph cm^-2 s^-1 and an equivalent width of 53 eV. It is possible that intercombination and forbidden lines contribute and that a single Gaussian accounts for the combined line flux. Weaker, tentative emission lines at approximately 6.40 keV, 6.9 keV, and 7 keV may be attributed to neutral (or, low-ionization) Fe, strongly shifted Fe XXV or Fe XXVI, and Fe XXVI. Components of a relativistic line might be able to account for some of the weak lines.

The flux of the source is measured to be F = 2.3 E-11 erg cm^-2 s^-1 (1-10 keV). The unabsorbed flux is F ~ 4.7 E-11 erg cm^2 s^-1. For a source distance of 3.3 kpc (Hare et al. 2018, ApJ, 865, 33), this corresponds to a luminosity of L ~ 6 E+34 erg/s. Even for a 1.4 Msun neutron star, this represents an Eddington fraction of just 3 E-4. It would be extraordinary to detect a broad disk line at such a low Eddington fraction, and it would also be extraordinary if the system is driving a wind. A cluster age above 2 Gyr (Hare et al.) would seem to preclude young stars and strong local diffuse X-ray emission.

Further observations are strongly encouraged.


NICER is a 0.2-12 keV X-ray telescope operating on the International Space Station. The NICER mission and portions of the NICER science team activities are funded by NASA.