An international team of astronomers has investigated the recently discovered X-ray transient named Maxi J1348−630, using the Neutron Star Interior Composition Explorer (NICER). The results of the new observations suggest that the source is a black hole X-ray binary. The study is detailed in a paper published on arXiv.org on 16 September.
X-ray binaries (XRB) consist of a normal star or a white dwarf that transfers mass onto a compact neutron star or black hole. Many black holes show XRB transient events characterized by outbursts in the X-ray band.
During these outbreaks, astronomers observe mainly hard and soft spectral states. In the hard state, the spectrum is dominated by a continuum of electric shape, while in the soft state the spectrum is dominated by disk-blackbody emission. However, some black hole XRBs also exhibit an intermediate state in which the hard power-law continuum and a disk thermal emission component contribute almost equally to the total spectrum.
The MAXI J1348I630 is an X-ray transient discovered on January 26, 2019, with the Gas Slit Camera (GSC) of an all-sky X-ray image (MAXI) monitor aboard the International Space Station (ISS). Subsequent observations of this source suggest that it is a black hole candidate in a binary system.
Recently, a group of astronomers led by Liang Zhang of the University of Southampton, UK, has published a new study supporting the black hole landscape. The research is based on the results of NICER monitoring of MAXI J1348 between630 between January 26 and October 8, 2019.
“We studied the external evolution and timing properties of the recently discovered X-ray transient MAXI J1348−630 with NICER. We produced fundamental diagrams commonly used to detect spectral evolution, And power density spectra to rapidly study X-rays. Variability, “the researchers explained.
In general, the researchers found that the spectral evolution of the MAXI J134830630 during its main outbreak was similar to that previously reported for other black hole customers. The source increased from the hard state, through the hard intermediate state and the soft-intermediate state, to the soft state. Later, it went back to a difficult position in the spreading decay. He said that the transition from hard to soft state was very fast.
In addition, he detected two re-flares of the MAXI J134830630. These occurred at the end of the main outbreak and had peak flows of one and two orders of magnitude larger than the main burst event. The results show that the source remained in the hard state during re-flare, never changing to the soft state. Astronomers noted that such behavior resembles so-called “failed outbreaks”, usually less luminous at their peak, showing no evidence of state transitions, and those seen in many black hole transitions .
The study also found half-period oscillations (QPOs) in MAXI J1348−630. They detected di-erent type of low frequency QPO in di p erent stages of the main outbreak.
According to the authors of the paper, all results of NICER monitoring strongly support the hypothesis that MAXI J1348 a630 contains a black hole.
Outbreak of X-ray transient MAXI J1727–203 investigated with NICER
NICER observations suggest that the X-ray transient MAXI J134830630 is a black hole X-ray binary, arXiv: 2009.07749 [astro-ph.HE] arxiv.org/abs/2009.07749
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