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Fast radio bursts (FRBs) are bright milliseconds-duration radio bursts from cosmological distances. Despite intense observational and theoretical studies, their physical origin is still mysterious. One major obstacle is the lack of identification of multi-wavelength counterparts for FRBs at cosmological distances. So far, all the searches other than in the radio wavelength, including those in the gamma-ray energies, have only left upper limits. Here we report a gigaelectronvolt (GeV) gamma-ray flare lasting 15.6 seconds as well as additional evidence of variable gamma-ray emission in temporal and spatial association with the hyper-active, newly discovered repeating FRB 20240114A, which has been localized to a dwarf galaxy at a redshift of 0.13. The energetic, short GeV gamma-ray flare reached a prompt isotropic luminosity of the order of ${10}^{48}~{\rm ergs~{s}^{-1}}$. The additional less-significant gamma-ray flares, if true, also have similar luminosities; such flares could contribute to a 5-day average luminosity of the order of ${10}^{45}~{\rm ergs~{s}^{-1}}$. These high-luminosity flares challenge the traditional FRB engine scenario involving a seconds-period magnetar. Rather, it suggests a powerful, long-lived, but newborn energy source at the location of this active repeater, either directly powering the bursts or indirectly triggering bursts in the vicinity of the FRB engine., Comment: Comments are welcome

Energy-dependence of X-ray Fourier power spectral states and the characteristic frequencies of the Band-Limited Noise (BLN) components have been seen in the hard state and intermediate states of black hole X-ray binaries. Here we report our analysis of the \emph{Insight}-HXMT observations of the black hole transient MAXI J1820$+$070 during its 2018 outburst when the source was brightest in hard X-rays. We found opposite trends of the low-frequency ($<$ 0.1 Hz) and the high-frequency ($>$ 10 Hz) BLN components, i.e., decreasing vs. increasing in frequency with increasing photon energy up to beyond 200 keV, respectively. This establishes an apparent two-way broadening of the power plateau formed by multiple BLNs in the power spectra towards higher photon energies. The trend of increasing characteristic frequency of the highest BLN component with increasing photon energy has been interpreted as due to that the corresponding seed photons which are up-scatted to relatively higher energies originate in a region relatively more central in the corona previously. Following the same framework, the decreasing trend of the characteristic frequency of the low-frequency BLN component with increasing photon energy can be interpreted as due to that the corresponding seed photons which are up-scattered to higher photon energies originate from further out in the disk flow but on the opposite side of the central corona as to the observer. The opposite trends then implies that the the plateau in the power spectra formed by the multiple BLNs represents the radial extension of the accretion disk that contributes seed photons which produce the observed BLNs; the higher the photon energy is, the wider the power plateau and the smaller the fractional variability are, probably approaching to a Power-Law Noise (PLN) seen in the soft state., Comment: 12 pages, 6 figures, submitted to ApJ

We made use high-cadence observations from the $Insight$-HXMT and $NICER$ to scrutinize the spectral and timing evolution during the 2018 outburst of the black hole X-ray binary (BHXRB) MAXI J1820+070. It's hardness-intensity diagram (HID) displays a ''q''-like track including all the spectral states, along a unique loop in the hard state. The tracks observed in the HID is anticipated in the evolution of the components responsible for Compton and reflection emission. This is substantiated by the relationship between the X-ray luminosity $L_\mathrm{X}$ and photon index $\Gamma$, as well as the relationship between X-ray luminosity $L_\mathrm{X}$ and the ratio of Compton to disk luminosities $L_\mathrm{C}/L_\mathrm{D}$. Both of these relationships exhibit a pattern reminiscent of HID. During the hard state, the hardness (also $\Gamma$) is determined by either reflection component ($R_{f}>1$ ) or Compton component ($R_{f}<1$) depending on the value reflection fraction $R_{f}$. So the distinctive evolution of $R_{f}$ leads to the unique loop in the HID (also in the $L_\mathrm{X}$--$\Gamma$ plane) of hard state. Additionally, we found a negative correlation between frequency of the type-C quasi-periodic oscillation (QPO) ($\nu_{\mathrm{C,QPO}}$) and the optical depth of the Compton emission ($\tau$), and a positive correlation between $\nu_{\mathrm{C,QPO}}$ and $\Gamma$. These correlations strongly suggest a coupling between the QPO properties and the underlying process responsible for Comptonization., Comment: 14 pages, 10 figures, submitted to MNRAS

Fast radio bursts (FRBs) are bright, millisecond-duration radio bursts of cosmic origin. There have been several dozen FRBs found to repeat. Among them, those precisely localized provide the best opportunity to probe their multi-wavelength counterparts, local environment, and host galaxy that would reveal their origins. Here we report our X-ray, ultraviolet (UV) and optical observations with the $Swift$ satellite that were performed simultaneously in the radio band with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) observations of the repeating FRB 20190520B, aiming at detection of possible multi-wavelength bursts in association with radio bursts and multi-wavelength counterpart of the persistent radio source (PRS). While a total of 10 radio bursts were detected by FAST at the same time of $Swift$ observations, we detected neither X-ray, UV or optical bursts in accompany of the radio bursts, nor persistent multi-wavelength counterpart of the PRS. We obtained the energy upper limits ($3\sigma$) on any multi-wavelength bursts as $5.03 \times 10^{47}$ erg in the hard X-ray band (15-150 keV), $7.98 \times 10^{45}$ erg in the soft X-ray band (0.3-10 keV), and $4.51 \times 10^{44}$ erg in the U band, respectively. The energy ratio between soft X-ray (0.3-10 keV) and radio emission of the bursts is constrained as $<6\times10^{7}$, and the ratio between optical (U band) and radio as $<1.19\times10^{6}$. The 3$\sigma$ luminosity upper limits at the position of PRS are 1.04$\times10^{47}$ (15-150 keV), 8.81$\times10^{42}$ (0.3-10 keV), 9.26$\times10^{42}$ (UVW1), and 2.54$\times10^{42}$ erg s$^{-1}$ (U), respectively. We show that the PRS is much more radio loud than representative pulsar wind nebulae, supernova remnants, extended jet of Galactic X-ray binaries and ultraluminous X-ray sources, suggestive of boosted radio emission of the PRS., Comment: 12 pages, 7 figures, submitted to ApJ

The megajansky radio burst, FRB 20200428, and other bright radio bursts detected from the Galactic source SGR J1935+2154 suggest that magnetars can make fast radio bursts (FRBs), but the emission site and mechanism of FRB-like bursts are still unidentified. Here we report the emergence of a radio pulsar phase of the magnetar five months after FRB 20200428. 795 pulses were detected in 16.5 hours over 13 days by the Five-hundred-meter Aperture Spherical Radio telescope, with luminosities about eight decades fainter than FRB 20200428. The pulses were emitted in a narrow phase window anti-aligned with the X-ray pulsation profile observed by the X-ray telescopes. The bursts, conversely, appear in random phases. This dichotomy suggests that radio pulses originate from a fixed region within the magnetosphere, but bursts occur in random locations and are possibly associated with explosive events in a dynamically evolving magnetosphere. This picture reconciles the lack of periodicity in cosmological repeating FRBs within the magnetar engine model., Comment: published on Science Advances, the authors' version

Among more than 800 known fast radio bursts (FRBs), only two, namely FRB 20121102A and FRB 20190520B, are confirmed to be associated with a persistent radio sources (PRS). Here we report evidence of apparent temporal variability in the PRS associated with the bursting FRB 20190520B based on the Karl G. Jansky Very Large Array (VLA) observations taken in 2020 and 2021. Based on the analysis of epoch-to-epoch variability of the PRS at L, S, C, and X band in 1-12 GHz, we detected not only overall marginal variability but also a likely radio flux decrease ($\sim$ 3.2 $\sigma$) between the observations taken in 2020 and 2021 at 3 GHz. Assuming no spectral variation in the PRS during these observations, we found the evidence for an overall broadband radio flux decrease by about 20 percent between the 2020 and the 2021 observations, suggesting that the PRS probably evolves on the yearly time scale. If we attribute the marginal variability at 3 GHz as intrinsic or due to scintillation, the size of potential variable component of the PRS is constrained to be sub-parsec. On the other hand, the size of the PRS can be also constrained to be larger than about 0.22 parsec from the averaged radio spectrum and the integrated radio luminosity in the 1-12 GHz band based on equipartition and self-absorption arguments. We discuss potential origins of the PRS and suggest that an accreting compact object origin might be able to explain the PRS's temporal and spectral properties. Confirmation of variability or flux decline of the PRS would be critical to our understanding of the PRS and its relation to the bursting source., Comment: 12 pages, 3 figures, accepted for publication in ApJ

The origin of current angular momentum (AM) of the black hole (BH) in X-ray binary (XRB) is still unclear, which is related with the birth and/or the growth of the BH. Here we collect the spin parameters $a_{*}$ measured in BH XRBs and find an apparent bimodal distribution centered at $\sim$ 0.17 and 0.83. We find a positive relation between the spin parameter and the orbital period/orbital separation through combining distinct XRB categories, including neutron star (NS) low-mass X-ray binaries (LMXBs), Roche-lobe overflow (RLOF) BH XRBs and wind-fed BH XRBs. It seems that the AM of the compact star and the binary orbit correlates by combining the different XRB systems. These positive relations imply that accretion process is a common mechanism for spinning up the compact star in these diverse XRB systems. We infer that the low and high spin BH XRBs may experience different evolution and accretion history, which corresponds to the bimodal distribution of the BH spin parameters. The low spin BHs ($a_{*}<0.3$) are similar to the NS LMXBs, the compact star of which is spun-up by the low-level accretion, and the high spin BHs ($a_{*}>0.5$) had experienced a short hypercritical accretion ($\gg \dot{M}_\mathrm{Edd}$) period, during which, the BH spin dramatically increased., Comment: 13 pages, 7 figures, accepted for publication in MNRAS

X-ray low frequency quasi-periodic oscillations (LFQPOs) of black hole X-ray binaries, especially those type-C LFQPOs, are representative timing signals of black hole low/hard state and intermediate state, which has been suspected as to originate due to Lense-Thirring precession of the accretion flow. Here we report an analysis of one of the \emph{Insight}-HXMT observations of the black hole transient MAXI J1820$+$070 taken near the flux peak of its hard spectral state during which strong type-C LFQPOs were detected in all three instruments up to photon energies above 150 keV. We obtained and analyzed the short-timescale X-ray spectra corresponding to high- and low-intensity phases of the observed LFQPO waveform with a spectral model composed of Comptonization and disk reflection components. We found that the normalization of the spectral model is the primary parameter that varied between the low and high-intensity phases. The variation in the LFQPO flux at the hard X-ray band (> 100 keV) is from the Compton component alone, while the energy-dependent variation in the LFQPO flux at lower energies (< 30 keV) is mainly caused by the reflection component with a large reflection fraction in response to the incident Compton component. The observed X-ray LFQPOs thus should be understood as manifesting the original timing signals or beats in the hard Compton component, which gives rise to additional variability in softer energies due to disk reflection., Comment: 8 pages, 4 figures, accepted for publication in MNRAS

Fast radio bursts (FRBs) are brief, intense flashes of radio waves from unidentified extragalactic sources. Polarized FRBs originate in highly magnetized environments. We report observations of the repeating FRB 20190520B spanning seventeen months , which show its amount of Faraday rotation is highly variable and twice changes its sign. The FRB also depolarizes below radio frequencies around 1 to 3 GHz. We interpret these properties as due to change in the parallel component of the integrated magnetic field along the line-of-sight, including reversals. This could result from propagation through a turbulent, magnetized screen of plasma located between $10^{-5}$ to 100 parsecs of the FRB source. This is consistent with the bursts passing through the stellar wind of a binary companion of the FRB source., Comment: arXiv:2203.08151 has been merged into this