Swift observations of MAXI J1810-222

ATel #16016; Nathan Morrow, McKinley Brumback, Anna Gaishin, Elise Kesler, Matthew Wanink (University of Michigan)
on 27 Apr 2023; 14:58 UT
Credential Certification: McKinley Brumback (brumback@umich.edu)

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We report on three recent Swift Observatory observations of the source MAXI J1810-222. This object is likely an accreting black hole at an undetermined distance of either 730 pc (ATel #12487) or 6 kpc (Russell et al. 2022) away. All reported value ranges reflect 1 sigma errors.

A 1.2 ks exposure was carried out on 4 April 2023 (OBSID 00011105089) which detected 2549 net photons using the Swift X-ray Telescope. We fit the data with a power-law model with an absorption of N_H = 7.1x10^21 cm^-2 (5.6*1021 - 8.9*1021 cm^-2) and a photon index of 1.8 (1.58 - 2.03). The flux based on this model is 7.56x10^-11 ergs/cm^2/s (5.04x10^-11 - 1.01x10-^10) in the 0.7-8.0 keV band which results in a luminosity of either 4.82x10^33 erg/s (3.21x10^33 - 6.44x10^33) if the object is at a distance of 730 pc, or 3.25x10^35 erg/s (2.17x10^35 - 4.35x10^35) if the object is 6 kpc away. Additionally, we detect emission at 6.4 keV from the iron Kalpha line, which we modeled with a Gaussian.

Another exposure was carried out on 7 April 2023 (OBSID 00011105090) which lasted 1.4 ks, where 2469 net photons were detected. Another absorbed power-law model was used, with N_H = 4.6x10^21 cm^-2 (3.6x10^21 - 5.7x10^21 cm^-2) and a photon index of 1.55 (1.4 - 1.71) in the same energy band. The flux in this case is 8.7x10^-11 ergs/cm^2/s (6.8x10^-11 - 1.1x10^-10) which results in a luminosity of either 5.52x10^33 erg/s (4.34x10^33 - 7.02x10^33) at 730 pc or 3.73*10^35 erg/s (2.93x10^35 - 4.74x10^35) at 6 kpc.

The final exposure was carried out on 10 April 2023 (OBSID 00011105091) which lasted 1.6 ks with 3240 net photons detected. Another power-law model was used, this time with N_H = 6.2x10^21 cm^-2 (5.0x10^21 - 7.5x10^21 cm^-2) and a photon index of 1.75 (1.59 - 1.93) in the same energy band. The flux for this observation is 7.46x10^-11 ergs/cm^2/s (5.6x10^-11 - 9.3x10^-11) which gives a luminosity of 4.76x10^33 erg/s (3.57x10^33 - 5.93x10^33) at 730 pc or 3.21x10^35 (2.41x10^35 - 4.0x10^35) at 6 kpc.

MAXI J1810-222 did not vary strongly in luminosity over the course of the observations, and all observed luminosities are consistent within their errors. However, iron lines are only present in the first of these observations which may indicate a change in the spectral state of the object. We encourage follow up observations to better ascertain the change in luminosity over time.

References
Kennea J. A., Negoro H., 2019, The Astronomer’s Telegram, 12487, 1
Russell, T.D., Del Santo, M., Marino, A., et al. (2022). MNRAS 513(4), 6196-6209

12487