ORCID Profile
0000-0002-1568-7461
Current Organisations
University of California, Berkeley
,
Princeton University
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Publisher: Springer Science and Business Media LLC
Date: 30-11-2022
DOI: 10.1038/S41586-022-05465-8
Abstract: Tidal disruption events (TDEs) are bursts of electromagnetic energy that are released when supermassive black holes at the centres of galaxies violently disrupt a star that passes too close
Publisher: American Astronomical Society
Date: 09-2022
Abstract: We present X-ray, UV, optical, and radio observations of the nearby (≈78 Mpc) tidal disruption event AT2021ehb/ZTF21aanxhjv during its first 430 days of evolution. AT2021ehb occurs in the nucleus of a galaxy hosting a≈10 7 M ⊙ black hole ( M BH inferred from host galaxy scaling relations). High-cadence Swift and Neutron Star Interior Composition Explorer (NICER) monitoring reveals a delayed X-ray brightening. The spectrum first undergoes a gradual soft → hard transition and then suddenly turns soft again within 3 days at δ t ≈272 days during which the X-ray flux drops by a factor of 10. In the joint NICER+NuSTAR observation ( δ t = 264 days, harder state), we observe a prominent nonthermal component up to 30 keV and an extremely broad emission line in the iron K band. The bolometric luminosity of AT2021ehb reaches a maximum of 6.0 − 3.8 + 10.4 % L Edd when the X-ray spectrum is the hardest. During the dramatic X-ray evolution, no radio emission is detected, the UV/optical luminosity stays relatively constant, and the optical spectra are featureless. We propose the following interpretations: (i) the soft → hard transition may be caused by the gradual formation of a magnetically dominated corona (ii) hard X-ray photons escape from the system along solid angles with low scattering optical depth (∼a few) whereas the UV/optical emission is likely generated by reprocessing materials with much larger column density—the system is highly aspherical and (iii) the abrupt X-ray flux drop may be triggered by the thermal–viscous instability in the inner accretion flow, leading to a much thinner disk.
Publisher: Springer Science and Business Media LLC
Date: 09-01-2023
Publisher: American Astronomical Society
Date: 05-06-2020
Publisher: American Chemical Society (ACS)
Date: 22-06-2023
Publisher: Springer Science and Business Media LLC
Date: 10-11-2022
Publisher: Oxford University Press (OUP)
Date: 19-08-2020
Abstract: We present the discovery with Keck of the extremely infrared (IR) luminous transient AT 2017gbl, coincident with the Northern nucleus of the luminous infrared galaxy (LIRG) IRAS 23436+5257. Our extensive multiwavelength follow-up spans ∼900 d, including photometry and spectroscopy in the optical and IR, and (very long baseline interferometry) radio and X-ray observations. Radiative transfer modelling of the host galaxy spectral energy distribution and long-term pre-outburst variability in the mid-IR indicate the presence of a hitherto undetected dust obscured active galactic nucleus (AGN). The optical and near-IR spectra show broad ∼2000 km s−1 hydrogen, He i, and O i emission features that decrease in flux over time. Radio imaging shows a fast evolving compact source of synchrotron emission spatially coincident with AT 2017gbl. We infer a lower limit for the radiated energy of 7.3 × 1050 erg from the IR photometry. An extremely energetic supernova would satisfy this budget, but is ruled out by the radio counterpart evolution. Instead, we propose AT 2017gbl is related to an accretion event by the central supermassive black hole, where the spectral signatures originate in the AGN broad line region and the IR photometry is consistent with re-radiation by polar dust. Given the fast evolution of AT 2017gbl, we deem a tidal disruption event (TDE) of a star a more plausible scenario than a dramatic change in the AGN accretion rate. This makes AT 2017gbl the third TDE candidate to be hosted by a LIRG, in contrast to the so far considered TDE population discovered at optical wavelengths and hosted preferably by post-starburst galaxies.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 20-10-2023
Publisher: American Association for the Advancement of Science (AAAS)
Date: 18-03-2022
Abstract: The polarization of fast radio bursts (FRBs), which are bright astronomical transient phenomena, contains information about their environments. Using wide-band observations with two telescopes, we report polarization measurements of five repeating FRBs and find a trend of lower polarization at lower frequencies. This behavior is modeled as multipath scattering, characterized by a single parameter, σ RM , the rotation measure (RM) scatter. Sources with higher σ RM have higher RM magnitude and scattering time scales. The two sources with the highest σ RM , FRB 20121102A and FRB 20190520B, are associated with compact persistent radio sources. These properties indicate a complex environment near the repeating FRBs, such as a supernova remnant or a pulsar wind nebula, consistent with their having arisen from young stellar populations.
Publisher: Springer Science and Business Media LLC
Date: 21-09-2022
DOI: 10.1038/S41586-022-05071-8
Abstract: Fast radio bursts (FRBs) are highly dispersed, millisecond-duration radio bursts
Publisher: American Astronomical Society
Date: 26-11-2021
Abstract: We present the full panchromatic afterglow light-curve data of GW170817, including new radio data as well as archival optical and X-ray data, between 0.5 and 940 days post-merger. By compiling all archival data and reprocessing a subset of it, we have evaluated the impact of differences in data processing or flux determination methods used by different groups and attempted to mitigate these differences to provide a more uniform data set. Simple power-law fits to the uniform afterglow light curve indicate a t 0.86±0.04 rise, a t −1.92±0.12 decline, and a peak occurring at 155 ± 4 days. The afterglow is optically thin throughout its evolution, consistent with a single spectral index (−0.584 ± 0.002) across all epochs. This gives a precise and updated estimate of the electron power-law index, p = 2.168 ± 0.004. By studying the diffuse X-ray emission from the host galaxy, we place a conservative upper limit on the hot ionized interstellar medium density, .01 cm −3 , consistent with previous afterglow studies. Using the late-time afterglow data we rule out any long-lived neutron star remnant having a magnetic field strength between 10 10.4 and 10 16 G. Our fits to the afterglow data using an analytical model that includes Very Long Baseline Interferometry proper motion from Mooley et al., and a structured jet model that ignores the proper motion, indicates that the proper-motion measurement needs to be considered when seeking an accurate estimate of the viewing angle.
Publisher: Research Square Platform LLC
Date: 16-11-2021
DOI: 10.21203/RS.3.RS-1059119/V1
Abstract: Fast radio bursts (FRBs) are highly dispersed radio bursts prevailing in the universe. The recent detection of FRB~200428 from a Galactic magnetar suggested that at least some FRBs originate from magnetars, but it is unclear whether the majority of cosmological FRBs, especially the actively repeating ones, are produced from the magnetar channel. Here we report the detection of 1863 polarised bursts from the repeating source FRB~20201124A during a dedicated radio observational c aign of Five-hundred-meter Aperture Spherical radio Telescope (FAST). The large s le of radio bursts detected in 88 hr over 54 days indicate a significant, irregular, short-time variation of the Faraday rotation measure (RM) of the source during the first 36 days, followed by a constant RM during the later 18 days. Significant circular polarisation up to 75\\% was observed in a good fraction of bursts. Evidence suggests that some low-level circular polarisation originates from the conversion from linear polarisation during the propagation of the radio waves, but an intrinsic radiation mechanism is required to produce the higher degree of circular polarisation. All of these features provide evidence for a more complicated, dynamically evolving, magnetised immediate environment around this FRB source. Its host galaxy was previously known. Our optical observations reveal that it is a Milky-Way-sized, metal-rich, barred-spiral galaxy at redshift z=0.09795+-0.00003, with the FRB residing in a low stellar density, interarm region at an intermediate galactocentric distance, an environment not directly expected for a young magnetar formed during an extreme explosion of a massive star.
Publisher: American Astronomical Society
Date: 12-2022
Abstract: Some hydrogen-poor superluminous supernovae are likely powered by a magnetar central engine, making their luminosity larger than common supernovae. Although a significant amount of X-ray flux is expected from the spin-down of the magnetar, direct observational evidence is still to be found, giving rise to the “missing energy” problem. Here we present NuSTAR observations of nearby SN 2018hti 2.4 yr (rest frame) after its optical peak. We expect that, by this time, the ejecta have become optically thin for photons more energetic than ∼15 keV. No flux is detected at the position of the supernova down to F 10–30 keV = 9.0 × 10 −14 erg cm −2 s −1 , or an upper limit of 7.9 × 10 41 erg s −1 at a distance of 271 Mpc. This constrains the fraction of bolometric luminosity from the putative spinning down magnetar to be f X ≲ 36% in the 10–30 keV range in a conservative case, f X ≲ 11% in an optimistic case.
Location: United States of America
Location: United States of America
No related grants have been discovered for Wenbin Lu.