We propose that the rapid cooling of the neutron star following its X-ray superburst in MAXI J1752$-$457 over a period of 4 days, observed by two Japanese satellites, MAXI and NinjaSat, is due to enhanced neutrino emission from cycles of electron capture and $β^{-}$ decay involving odd-$A$ nuclei (or Urca pairs) in the ocean. Hence, this work provides the first indication of the possible existence of such a ``nuclear Urca process". The observation of MAXI J1752$-$457 implies a hot ignition layer with a maximum temperature of $\sim4~{\rm GK}$, located near the Urca shell in the ocean, such that the nuclear Urca process becomes dominant for up to $\sim2$ days after the superburst. This behavior is distinct from that of normal Type-I X-ray bursts, which are triggered by hydrogen or helium burning in much shallower layers than those of superbursts. Our findings enable probing of superburst ashes through Urca pairs via long-term monitoring of crust cooling on day-long timescales.
For the first time in nearly a decade, a bright transient was detected in the central parsec (pc) of the Galaxy. MAXI J1744-294, or -- as it was known in its previous life -- Swift J174540.2-290037, was discovered in outburst by the MAXI telescope in January 2025. We present the results of a broadband, multi-wavelength study of MAXI J1744-294, including data from the NuSTAR, Chandra, XMM-Newton, Swift, and NICER X-ray telescopes, as well as complementary radio and near-infrared observations. We analyze the changing X-ray emission as the outburst evolved from the high/soft to the low/hard state. Using relativistic reflection features in the data, we estimate a spin of $a>0.92$ and viewing inclination $θ=28^{+3}_{-4}$ deg, consistent with the parameters measured for Swift J174540.2-290037. Based on the spectral and temporal characteristics of MAXI J1744-294, we reaffirm its classification as a candidate black hole (BH) low-mass X-ray binary (LMXB) -- the third candidate BH transient discovered within 20 arcsec of the Galactic supermassive black hole Sgr~A*. This work provides further evidence for a cusp of BH-LMXBs in the central pc of our Galaxy, as argued for in previous observa
An uncatalogued bright X-ray transient was detected with MAXI on November 9, 2024, named MAXI J1752$-$457. The NinjaSat X-ray observatory promptly observed the source from November 10 to 18 while the small angular separation from the Sun hampered follow-up campaigns by other X-ray observatories. The MAXI and NinjaSat light curves in the 2-10 keV band showed first and second decaying components at the early and late phases, approximated by exponential functions with e-folding constants of 1.2 $\pm$ 0.2 and 14.9 $\pm$ 0.9 hours (1$σ$ errors), respectively. A single blackbody model reproduces the X-ray spectrum with a softening trend of its temperature decreasing from 1.8 $\pm$ 0.1 keV to 0.59 $\pm$ 0.06 keV. Assuming the unknown source distance at 8 kpc, at which the initial X-ray luminosity roughly corresponds to the Eddington limit, the shrinking blackbody radius was estimated at 5-11 km. This X-ray brightening is interpreted as a superburst in a Galactic low-mass X-ray binary, which is powered by thermonuclear burning triggered presumably by carbon ignition close to the outer crust of the neutron star. The transition between two decaying components occurred at 5.5-7.7 hours, corre
We present Atacama Large Millimeter/Submillimeter Array (ALMA) observations aimed at identifying potential jet-ISM interaction sites in the vicinity of the transient black hole X-ray binaries MAXI J1348-630 and MAXI J1820+070, both of which have recently undergone an outburst, and displayed powerful large scale jets. Using this dataset, we construct molecular line emission maps. By analyzing the morphological, spectral, and kinematic properties of the detected emission, we identify a molecular structure that provides compelling evidence for a jet-driven cavity in the local environment of MAXI J1348-630 but find no significant emission in the local environment of MAXI J1820+070. We use the properties of the detected molecular emission surrounding MAXI J1348-630 to constrain the jet power, finding our results to be consistent with other independent studies of this source, and further validating the utility of astrochemistry for constraining jet energetics. Additionally, our findings provide the first assessment on the formation timescales for jet-ISM interaction regions in the transient black hole X-ray binary population.
We present two NuSTAR observations of the X-ray transient, MAXI J1752-457, following a superburst which was observed by MAXI/GSC in November, 2024. NuSTAR follow-up confirmed that MAXI J1752-457 is coincident with the previously observed Einstein Probe source, EP240809a. We performed a spectral analysis of the source during both NuSTAR observations, and we find that the hard X-ray spectra are consistent with the inclusion of a spherical blackbody component and a steep, non-thermal, power law component. At about 79 hours after the onset of the superburst, we find a blackbody temperature of $kT_\mathrm{bb}=0.60\pm0.1$ keV and $R_\mathrm{bb}/D_{8}=6.0^{+0.4}_{-0.3}$ km (not including corrections for scattering in the neutron star atmosphere), where $D_{8}$ is the source distance, which is not yet known, in units of 8 kpc. We found that the blackbody temperature did not change significantly in the one day interval between successive NuSTAR observations, and we performed an energy-resolved timing analysis which showed that the source variability was dominated by red noise in the power law component, suggesting coupling with an accretion disk. We infer that the source had entered an accr
On the second of November 2019 the black hole X-ray binary MAXI J0637$-$430 went into outburst, at the start of which it was observed in a thermal ``disc-dominated'' state. High photon energy (extending above 10 keV) observations taken by the NuSTAR telescope reveal that this thermal spectrum can not be fit by conventional two-component (disc plus corona) approaches which ignore disc emission sourced from within the plunging region of the black hole's spacetime. Instead, these models require a third ``additional'' thermal component to reproduce the data. Using new disc solutions which extend classical models into the plunging region we show that this ``additional'' thermal emission can be explained self-consistently with photons emitted from the accretion flow at radii within the innermost stable circular orbit of the black hole. This represents the second low mass X-ray binary, after MAXI J1820+070, with a detection of plunging region emission, suggesting that signatures of this highly relativistic region may well be widespread but not previously widely appreciated. To allow for a detection of the plunging region, the black hole in MAXI J0637$-$430 must be at most moderately spinn
Bicoherence is a way to measure the phase coupling of triplets of Fourier frequencies. We use this method to analyze quasi-periodic oscillations (QPOs) in the black hole X-ray binary MAXI J1535$-$571 during its 2017 September-October outburst. The bicoherence provides an interesting new diagnostic to uncover QPO behaviour and the relationships between QPO harmonics and broadband noise. The bicoherence pattern of type-C QPOs starts as a 'web' pattern and changes to a 'hypotenuse' pattern after the presence of type-B QPOs, indicating that MAXI J1535$-$571 is a low-inclination source. The intensity of bicoherence also exhibits variations across different energy bands. We try to explain the bicoherence results in the scenario of a dual-corona geometry.
We report the results of fitting Insight-HXMT data to the black hole X-ray binary MAXI J1348-430, which was discovered on January 26th, 2019, with the Gas Slit Camera (GSC) on-board MAXI. Several observations at the beginning of the first burst were selected, with a total of 10 spectra. From the residuals of fits using disk plus power law models, X-ray reflection signatures were clearly visible in some of these observations. We use the state-of the-art relxill series reflection model to fit six spectra with distinct reflection signatures and a joint fit to these spectra. In particular, we focus on the results for the black hole spin values. Assuming Rin = RISCO, the spin parameter is constrained to be 0.82+0.04-0.03 with 90% confidence level (statistical only).
Over the past decade, observations of relativistic outflows from outbursting X-ray binaries in the Galactic field have grown significantly. In this work, we present the first detection of moving and decelerating radio-emitting outflows from an X-ray binary in a globular cluster. MAXI J1848-015 is a recently discovered transient X-ray binary in the direction of the globular cluster GLIMPSE-C01. Using observations from the VLA, and a monitoring campaign with the MeerKAT observatory for 500 days, we model the motion of the outflows. This represents some of the most intensive, long-term coverage of relativistically moving X-ray binary outflows to date. We use the proper motions of the outflows from MAXI J1848-015 to constrain the component of the intrinsic jet speed along the line of sight, $β_\textrm{int} \cos θ_\textrm{ejection}$, to be $=0.19\pm0.02$. Assuming it is located in GLIMPSE-C01, at 3.4 kpc, we determine the intrinsic jet speed, $β_\textrm{int}=0.79\pm0.07$, and the inclination angle to the line of sight, $θ_\textrm{ejection}=76^\circ\pm2^{\circ}$. This makes the outflows from MAXI J1848-015 somewhat slower than those seen from many other known X-ray binaries. We also cons
On 2 September 2017 MAXI J1535-571 went into outburst and peaked at ~5 Crab in the 2-20 keV energy range. Early in the flare INTEGRAL performed Target of Opportunity pointings and monitored the source as it transitioned from the hard state to the soft state. Using quasi-simultaneous observations from MAXI/GSC and INTEGRAL/SPI, we studied the temporal and spectral evolution of MAXI J1535-571 in the 2-500 keV range. Early spectra show a Comptonized spectrum and a high-energy component dominant above ~150 keV. CompTT fits to the SPI data found electron temperatures (kTe) evolves from ~31 keV to 18 keV with a tied optical depth (tau ~ 0.85) or tau evolving from ~1.2-0.65 with a tied kTe (~24 keV). To investigate the nature of the high-energy component, we performed a spectral decomposition of the 100-400 keV energy band. The CompTT flux varies significantly during the hard state while the high-energy component flux is consistent with a constant flux. This result suggests that the two components originate from different locations, which favors a jet origin interpretation for the high-energy component over a hybrid corona interpretation. Lastly, two short rebrightenings during the hard-t
The newly discovered galactic black hole candidate (BHC) MAXI~J1348-630 showed two major outbursts in 2019, just after its discovery. Here, we provide a detailed spectral and temporal analysis of the less-studied second outburst using archive data from multiple satellites, namely Swift, MAXI, NICER, NuSTAR and AstroSat. The outburst continued for around two and a half months. Unlike the first outburst from this source, this second outburst was a `failed' one. The source did not transition to soft or intermediate spectral states. During the entire outburst, the source was in the hard state with high dominance of non-thermal photons. The presence of strong shocks are inferred from spectral fitting using a TCAF model. In NuSTAR spectra, weak reflection is observed from spectral fitting. Low-frequency quasi-periodic oscillations are also detected in AstroSat data.
Monitor of All-sky X-ray Image (MAXI) is a Japanese X-ray all-sky monitor onboard the International Space Station (ISS).
MAXI J1305-704 is a transient X-ray binary with a black hole primary. It was discovered on April 9, 2012, during its only known outburst. MAXI J1305-704 is also a high inclination low-mass X-ray binary with prominent dip features in its light curves, so we check the full catalog of 92 \emph{Swift}/XRT continuous observations of MAXI J1305-704, focusing only on the stable spectra. We select 13 ``gold" spectra for which the root mean square RMS <0.075 and the coronal scattered fraction $f_{\mathrm{sc}} \lesssim 25 \%$. These ``gold" data are optimal thermal-state observations for continuum-fitting modeling, in which the disk extends to the innermost-stable circular orbit and is geometrically thin. The black hole spin was unknown for this object before. By utilizing the X-ray continuum fitting method with the relativistic thin disk model \texttt{kerrbb2} and supplying the known dynamical binary system parameters, we find MAXI J1305-704 has a moderate spin ($a_{*}=0.87_{-0.13}^{+0.07}$) at a 68.3\% confidence level. This is the first determination of MAXI J1305-704's spin.
We present the results of MAXI monitoring and two NuSTAR observations of the recently discovered faint X-ray transient MAXI J1848-015. 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 $\sim5$ days. NuSTAR observations reveal that the source transitioned from a bright soft state with unabsorbed, bolometric ($0.1$-$100$ keV) flux $F=6.9 \pm 0.1 \times 10^{-10}\,\mathrm{erg\,cm^{-2}\,s^{-1}}$, to a low hard state with flux $F=2.85 \pm 0.04 \times 10^{-10}\,\mathrm{erg\,cm^{-2}\,s^{-1}}$. 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 order $10^{-3}$ for an accreting neutron star of mass $M=1.4M_\odot$, or even lower for a more massive accretor. However, the source spectra exhibit strong relativistic reflection features, indicating the presence of an accretion disk which extends close to the accretor, for which we measure a high spin, $a=0.967\pm0.013$. In addition to a change in flux and spectral shape, we find evidence for other changes between the soft and hard sta
We present results from radio and X-ray observations of the X-ray transient MAXI J1810-222. The nature of the accretor in this source has not been identified. In this paper, we show results from a quasi-simultaneous radio and X-ray monitoring campaign taken with the Australia Telescope Compact Array (ATCA), the Neil Gehrels Swift observatory X-ray telescope (XRT), and the Swift Burst Alert Telescope (BAT). We also analyse the X-ray temporal behaviour using observations from the Neutron star Interior Composition Explorer (NICER). Results show a seemingly peculiar X-ray spectral evolution of MAXI J1810-222 during this outburst, where the source was initially only detected in the soft X-ray band for the early part of the outburst. Then, ~200 days after MAXI J1810-222 was first detected the hard X-ray emission increased and the source transitioned to a long-lived (~1.5 years) bright, harder X-ray state. After this hard state, MAXI J1810-222 returned back to a softer state, before fading and transitioning again to a harder state and then appearing to follow a more typical outburst decay. From the X-ray spectral and timing properties, and the source's radio behaviour, we argue that the r
The properties of the disk/jet coupling in quiescent black hole low mass X-ray binaries (BH LMXBs) are still largely unknown. In this paper we present the first quasi-simultaneous radio and X-ray detection in quiescence of the BH LMXB MAXI J1348$-$630, which is known to display a hybrid disk/jet connection that depends on the accretion rate. We performed deep X-ray and radio observations using the Chandra X-ray Observatory and the Australia Telescope Compact Array. MAXI J1348$-$630 is detected for the first time in quiescence at an X-ray luminosity $L_{\rm X} = (7.5 \pm 2.9) \times 10^{30} (D/2.2 \ {\rm kpc})^2$ erg s$^{-1}$: one of the lowest X-ray luminosities observed for a quiescent BH LMXB, possibly implying a short orbital period for the system. MAXI J1348$-$630 is also detected in radio at $L_{\rm R} = (4.3 \pm 0.9) \times 10^{26} (D/2.2 \ {\rm kpc})^2$ erg s$^{-1}$. These detections allow us to constrain the location of MAXI J1348$-$630 on the radio/X-ray diagram in quiescence, finding that the source belongs to the standard (radio-loud) track in this phase. This provides a strong confirmation that hybrid-correlation sources follow the standard track at low luminosities and
In black hole X-ray binaries, a non-thermal high-energy component is sometimes detected at energies above 200 keV. The origin of this component is debated and distinct spectral modelizations can lead to different interpretations. High-energy polarimetry measurements with INTEGRAL allow new diagnostics on the physics responsible for the MeV spectral component. In this work, we aim to investigate the high-energy behavior of three bright sources discovered by the MAXI: MAXI J1535-571, MAXI J1820+070 and MAXI J1348-630. We take advantage of their brightness to investigate their soft gamma-ray (0.1-2 MeV) properties with INTEGRAL. We use both spectral and polarimetric approaches to probe their high-energy emission with the aim to bring new constraints on the ~ MeV emission. We first study the spectral characteristics of the sources in the 3-2000 keV using JEM-X, IBIS and SPI with a semi-phenomenological description of the data. We then use IBIS as a Compton telescope in order to evaluate the polarization properties of the sources above 300 keV. A high-energy component is detected during the HIMS and SIMS of MAXI J1535-571, the LHS of MAXI J1820+070 and the LHS of MAXI J1348-630. The com
A new technique could solve one of the biggest challenges in making future computer chips from ultrathin materials。 Researchers found that coating molybdenum disulfide with oxygen or fluorine lets manufacturers remove just the top layer of atoms much more safely during plasma processing。 The result is a cleaner, more controlled path toward smaller