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MAXI and NuSTAR Observations of the Faint X-Ray Transient MAXI J1848-015 in the GLIMPSE-C01 Cluster

Journal
Date Issued
2022
Author(s)
Pike, Sean N.
•
Negoro, Hitoshi
•
Tomsick, John A.
•
•
Brumback, McKinley
•
Connors, Riley M.T.
•
García, Javier A.
•
Grefenstette, Brian
•
Hare, Jeremy
•
Harrison, Fiona A.
•
Jaodand, Amruta
•
Ludlam, R. M.
•
•
Mihara, Tatehiro
•
Shidatsu, Megumi
•
Sugizaki, Mutsumi
•
Takagi, Ryohei
DOI
Abstract
We present the results of Monitor of All-sky X-ray Image (MAXI) monitoring and two Nuclear Spectroscopic Telescope Array (NuSTAR) observations of the recently discovered faint X-ray transient MAXI J1848015. Analysis of the MAXI light curve shows that the source underwent a rapid flux increase beginning on 2020 December 20, followed by a rapid decrease in flux after only ∼5 days. NuSTAR observations reveal that the source transitioned from a bright soft state with unabsorbed, bolometric (0.1-100 keV) flux F = 6.9 ± 0.1 × 10-10 erg cm-2 s-1, to a low hard state with flux F = 2.85 ± 0.04 × 10-10 erg cm-2 s-1. Given a distance of 3.3 kpc, inferred via association of the source with the GLIMPSE-C01 cluster, these fluxes correspond to an Eddington fraction of the order of 10-3 for an accreting neutron star (NS) of mass M = 1.4M ⊙, or even lower for a more massive accretor. However, the source spectra exhibit strong relativistic reflection features, indicating the presence of an accretion disk that extends close to the accretor, for which we measure a high spin, a = 0.967 ± 0.013. In addition to a change in flux and spectral shape, we find evidence for other changes between the soft and hard states, including moderate disk truncation with the inner disk radius increasing from R in ≈ 3 R g to R in ≈ 8 R g, narrow Fe emission whose centroid decreases from 6.8 ± 0.1 keV to 6.3 ± 0.1 keV, and an increase in low-frequency (10-3-10-1 Hz) variability. Due to the high spin, we conclude that the source is likely to be a black hole rather than an NS, and we discuss physical interpretations of the low apparent luminosity as well as the narrow Fe emission.
Volume
927
Issue
2
Start page
190
Uri
Url
Issn Identifier
0004-637X
Rights
open.access
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