高能暂现源 · 每日文献综述

We have recently shown evidence that the most relativistic jets (with Lorentz factor <inline-formula><tex-math>$\gt 2$</tex-math></inline-formula>) from stellar-mass black holes in X-ray binary systems may be locked to a fixed axis, likely the spin axis of the black hole. Slower, mildly relativistic jets (with velocities typically <inline-formula><tex-math>${\sim} 0.3c$</tex-math></inline-formula>) are often seen to precess and can be associated with both neutron stars and black holes. In this paper, we demonstrate an additional clear link between highly obscured systems and these lower velocity, precessing jets. We speculate that this link may be due to mass-loading of the jets close to their launch sites, since these obscured systems are likely to be examples of (sometimes persistent, other times transient) super-Eddington accretion. The fastest relativistic jets are now seen to be both locked to a fixed direction, likely the black hole spin axis, and to be launched in low-density environments, while jets launched in dense environments are generally slower and very likely to precess.

We report on NICER and MAXI observations of a long-duration thermonuclear X-ray burst and a subsequent outburst-like X-ray flare from the neutron star low-mass X-ray binary MAXI J0911─655. Prior to the burst, the source was in a persistent low/hard state with a power-law-dominated spectrum (Γ ∼ 1.7) and a mass accretion rate of ∼1% of the Eddington limit. The long burst, detected by MAXI on 2020 May 22 (MJD 58991.7101), was rapidly followed up by NICER. From time-resolved spectroscopy of the cooling tail, we estimate an exponential decay time of ≍43 minutes, the ignition column depth of ≍0.1 × 10<SUP>12</SUP> g cm<SUP>−2</SUP>, the burst fluence of ≍1.1 × 10<SUP>−4</SUP> erg cm<SUP>−2</SUP>, and the total energy release of ≍1.2 × 10<SUP>42</SUP> erg. Approximately 1 day after the burst onset, the 0.5─10 keV light curve unexpectedly rebrightened, initiating an outburst-like flare. During the peak of this flare, the persistent power-law flux increased from its preburst level of ∼0.27 × 10<SUP>−9</SUP>─1.4 × 10<SUP>−9</SUP> erg cm<SUP>−2</SUP> s<SUP>−1</SUP>. This flux enhancement was accompanied by significant spectral softening, with the photon index increasing to Γ ∼ 2.2. Subsequently, the flux decayed and the source returned to its baseline low/hard state. The observed timescales and energetics suggest that intense irradiation from the long burst amplified the ongoing thermal─viscous accretion process. This heating drove an inside-out heating front that temporarily enhanced the mass accretion rate, providing compelling observational evidence of a thermonuclear burst directly modulating the accretion dynamics of its surrounding disk.

We report the discovery of a new X-ray transient, EP J175257.3─351923 (EP250916a), by the Einstein Probe (EP) near the galactic plane. The outburst lasted for at least 250 days and reached a peak 2─10 keV flux of ∼4 × 10<SUP>−10</SUP> erg cm<SUP>−2</SUP> s<SUP>−1</SUP>, exhibiting a fast-rise exponential-decay (FRED) profile typical of X-ray binary outbursts. The source remained in the hard state throughout the outburst, with only modest variations in the photon index (∼1.6 − 2.2) and no evidence of a spectral state transition. Broadband spectral modeling suggests a truncated disk, a weak reflection component, and a high-energy cutoff at ∼217 keV, consistent with hard-state accretion in black-hole systems. No reliable optical or radio counterpart has been detected within the Swift/XRT error circle. The inferred X-ray-to-optical and X-ray-to-radio flux ratios are consistent with a low-mass X-ray binary (LMXB) classification. Neither pulsations nor significant aperiodic variability were detected. Although the compact object cannot yet be firmly identified, the timing, spectral, and multiwavelength evidence favors the classification of EP J175257.3─351923 as a black-hole (BH) LMXB candidate, highlighting EP's potential to uncover a faint, previously hidden population of X-ray binaries.

Persistent, low-luminosity low-mass X-ray binaries offer a unique opportunity to study accretion in this poorly understood regime as well as to unveil new members of the ultracompact X-ray binary (UCXB) family, which are characterised by orbital periods (P<SUB>orb</SUB>) shorter than ∼80 min. We report on a NuSTAR archival observation that, for the first time above 10 keV, spatially resolves the Galactic Centre pair SLX 1744−299 and SLX 1744−300. We find SLX 1744−300 to be slightly brighter, with a flux ratio of ∼1.15, increasing to ∼1.3 when extrapolated to 0.5─10 keV. Both the timing (root-mean-square variability) and spectral properties (well described in both cases by a thermal Comptonisation model) indicate that the systems were in the hard state. The two sources, however, display markedly different behaviour throughout the observation. SLX 1744−299 shows a gradual flux decline consistent with a decrease in the mass-accretion rate, whereas SLX 1744−300 remains steady but exhibits two short-recurrence Type-I X-ray bursts indicative of mixed H and He burning. Combining our results with previously reported upper limits on the distance, we derived low persistent X-ray luminosities of L<SUB>X</SUB> ≲ 1.1 × 10<SUP>36</SUP> erg s<SUP>−1</SUP> and L<SUB>X</SUB> ≲ 2.6 × 10<SUP>36</SUP> erg s<SUP>−1</SUP> (3─78 keV) for SLX 1744−299 and SLX 1744−300, respectively. The corresponding mass-accretion rates, when compared with the critical values from the disc instability model, favour P<SUB>orb</SUB> ≲ 90 min and P<SUB>orb</SUB> ≲ 105─155 min. Although both limits are formally compatible with the UCXB regime, the case of SLX 1744−299 appears significantly more compelling, also considering the previously reported intermediate-duration burst.