Zifan Zhou

We have conducted further analysis of the LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S240422ed (GCN Circular 36236). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby. offline0. multiorder. fits, 0, distributed via GCN Notice, is available for retrieval from the GraceDB event page: https://gracedb. ligo. org/superevents/S240422ed Based on posterior support from parameter estimation [1], under the assumption that the candidate S240422ed is astrophysical in origin, the probability that the lighter compact object is consistent with a neutron star mass (HasNS) is> 99%.[2] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is> 99%.[2] Both HasNS and HasRemnant consider the support of …

We describe a generalized algorithm for evaluating the steady-state solution of the density matrix equation of motion, for the pump-probe scheme, when two fields oscillating at different frequencies couple the same set of atomic transitions involving an arbitrary number of energy levels, to an arbitrary order of the harmonics of the pump-probe frequency difference. We developed a numerical approach and a symbolic approach for this algorithm. We have verified that both approaches yield the same result for all cases studied, but require different computation time. The results are further validated by comparing them with the analytical solution of a two-level system to first order. We have also used both models to produce results up to the third order in the pump-probe frequency difference, for two-, three- and four-level systems. In addition, we have used this model to determine accurately, for the first time, the gain profile for a self-pumped Raman laser, for a system involving 16 Zeeman sublevels in the D1 manifold of 87Rb atoms. We have also used this model to determine the behavior of a single-pumped superluminal laser. In many situations involving the applications of multiple laser fields to atoms with many energy levels, one often makes the approximation that each field couples only one transition, because of the difficulty encountered in accounting for the effect of another field coupling the same transition but with a large detuning. The use of the algorithm presented here would eliminate the need for making such approximations, thus improving the accuracy of numerical calculations for such schemes.

We identified the compact binary merger candidate S240104bl during real-time processing of data from LIGO Hanford Observatory (H1) at 2024-01-04 16: 49: 32.629 UTC (GPS time: 1388422190.629). The candidate was found by the GstLAL [1] analysis pipeline. S240104bl is an event of interest because its false alarm rate, as estimated by the online analysis, is 3.6 e-17 Hz, or about one in 1e9 years. The event's properties can be found at this URL: https://gracedb. ligo. org/superevents/S240104bl The classification of the GW signal, in order of descending probability, is BBH (> 99%), Terrestrial (< 1%), NSBH (< 1%), or BNS (< 1%). Assuming the candidate is astrophysical in origin, the probability that the lighter compact object is consistent with a neutron star mass (HasNS) is< 1%.[2] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is< 1 …

The trigger S240420aw is no longer considered to be a candidate of interest. There was a high rate of noise transients (glitches) in the LIGO Hanford detector, which created spurious false alarms in the minutes surrounding the time of this candidate.

The second Gravitational-Wave Transient Catalog, GWTC-2, reported on 39 compact binary coalescences observed by the Advanced LIGO and Advanced Virgo detectors between 1 April 2019 15∶ 00 UTC and 1 October 2019 15∶ 00 UTC. Here, we present GWTC-2.1, which reports on a deeper list of candidate events observed over the same period. We analyze the final version of the strain data over this period with improved calibration and better subtraction of excess noise, which has been publicly released. We employ three matched-filter search pipelines for candidate identification, and estimate the probability of astrophysical origin for each candidate event. While GWTC-2 used a false alarm rate threshold of 2 per year, we include in GWTC-2.1, 1201 candidates that pass a false alarm rate threshold of 2 per day. We calculate the source properties of a subset of 44 high-significance candidates that have a …

We have conducted further analysis of the LIGO Hanford Observatory (H1) data around the time of the compact binary merger (CBC) candidate S240104bl (GCN Circular 35480). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby. multiorder. fits, 0, distributed via GCN Notice, is available for retrieval from the GraceDB event page: https://gracedb. ligo. org/superevents/S240104bl After parameter estimation by RapidPE-RIFT [2], the updated classification of the GW signal, in order of descending probability, is BBH (> 99%), Terrestrial (< 1%), NSBH (< 1%), or BNS (< 1%). For the Bilby. multiorder. fits, 0 sky map, the 90% credible region is 27949 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1978+/-618 Mpc (a posteriori mean+/-standard deviation). For further information about analysis methodology and the contents of this alert, refer to the LIGO …

The detection of GW170817 (Abbott et al. 2017b) coincident with the short gamma-ray burst GRB 170817A (Goldstein et al. 2017; Savchenko et al. 2017) was a groundbreaking discovery for the multimessenger era. Not only was it the first binary neutron star (BNS) merger detected by the gravitational-wave (GW) instruments Advanced LIGO (Aasi et al. 2015) and Advanced Virgo (Acernese et al. 2014), it was also the first, and to date only, GW detection with a confirmed electromagnetic (EM) counterpart. Since then, the search for EM emission from more of these extreme events has been at the forefront of multimessenger astronomy, particularly in the gamma-ray energy band, since GRB 170817A demonstrated that BNS mergers are a progenitor of short gamma-ray bursts (GRBs; Abbott et al. 2017a). GWs have also been observed from the mergers of other compact objects, such as binary black hole (BBH) and …

We identified the compact binary merger candidate S240107b during real-time processing of data from LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) at 2024-01-07 01: 32: 15.720 UTC (GPS time: 1388626353.720). The candidate was found by the CWB [1], GstLAL [2], MBTA [3], PyCBC Live [4], and SPIIR [5] analysis pipelines. S240107b is an event of interest because its false alarm rate, as estimated by the online analysis, is 5.8 e-08 Hz, or about one in 6 months. The event's properties can be found at this URL: https://gracedb. ligo. org/superevents/S240107b The classification of the GW signal, in order of descending probability, is BBH (97%), Terrestrial (3%), NSBH (< 1%), or BNS (< 1%). There were noise transients (glitches) in the LIGO Hanford and Livingston detectors near the time of the signal which may affect the parameters or the significance of the candidate. Assuming the …

We have conducted further analysis of the LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) data around the time of the compact binary merger (CBC) candidate S240107b (GCN Circular 35493). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby. offline0. multiorder. fits, 0, distributed via GCN Notice, is available for retrieval from the GraceDB event page: https://gracedb. ligo. org/superevents/S240107b After parameter estimation by RapidPE-RIFT [2], the updated classification of the GW signal, in order of descending probability, is BBH (97%), Terrestrial (3%), NSBH (< 1%), or BNS (< 1%). For the Bilby. offline0. multiorder. fits, 0 sky map, the 90% credible region is 4143 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 6089+/-2429 Mpc (a posteriori mean+/-standard deviation). For further information about analysis …

We report the observation of a coalescing compact binary with component masses and (all measurements quoted at the 90% credible level). The gravitational-wave signal GW230529_181500 was observed during the fourth observing run of the LIGO-Virgo-KAGRA detector network on 2023 May 29 by the LIGO Livingston Observatory. The primary component of the source has a mass less than at 99% credibility. We cannot definitively determine from gravitational-wave data alone whether either component of the source is a neutron star or a black hole. However, given existing estimates of the maximum neutron star mass, we find the most probable interpretation of the source to be the coalescence of a neutron star with a black hole that has a mass between the most massive neutron stars and the least massive black holes observed in the Galaxy. We estimate a merger rate density of for compact binary coalescences with properties similar to the source of GW230529_181500; assuming that the source is a neutron star-black hole merger, GW230529_181500-like sources constitute about 60% of the total merger rate inferred for neutron star-black hole coalescences. The discovery of this system implies an increase in the expected rate of neutron star-black hole mergers with electromagnetic counterparts and provides further evidence for compact objects existing within the purported lower mass gap.

We demonstrate a slow-light augmented unbalanced Mach-Zehnder interferometer (MZI) which can be used to enhance very significantly the sensitivity of measuring the frequency shift in a laser. The degree of enhancement depends on the group index of the slow-light medium, the degree of imbalance between the physical lengths of the two arms of the MZI, and the spectral width of the laser. For a laser based on a high-finesse cavity, yielding a narrow quantum noise limited spectral width, the group index has to be larger than the finesse in order to achieve enhancement in measurement sensitivity. For the reported results, strong slow-light effect is produced by employing electro-magnetically induced transparency via coherent population trapping in a buffer-gas loaded vapor cell of Rb atoms, with a maximum group index of ~1759. The observed enhancement in sensitivity for a range of group indices agrees well with the theoretical model. The maximum enhancement factor observed is ~22355, and much larger values can be obtained using cold atoms for producing the slow-light effect, for example. The sensitivity of any sensor that relies on measuring the frequency shift of a laser can be enhanced substantially using this technique. These include, but are not limited to, gyroscopes and accelerometers based on a conventional ring laser or a superluminal ring laser, and detectors for virialized ultra-light field dark matter. We also show how similar enhancements can be achieved in a slow-light augmented unbalanced Michelson interferometer.

We have conducted further analysis of the LIGO Hanford Observatory (H1) data around the time of the compact binary merger (CBC) candidate S240109a (GCN Circular 35502). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby. multiorder. fits, 0, distributed via GCN Notice, is available for retrieval from the GraceDB event page: https://gracedb. ligo. org/superevents/S240109a For the Bilby. multiorder. fits, 0 sky map, the 90% credible region is 28048 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1594+/-567 Mpc (a posteriori mean+/-standard deviation). For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow. docs. ligo. org/userguide/.[1] Ashton et al. ApJS 241, 27 (2019) and Morisaki et al. arXiv: 2307.13380 (2023)

We identified the compact binary merger candidate S240426s during real-time processing of data from LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) at 2024-04-26 03: 14: 51.975 UTC (GPS time: 1398136509.975). The candidate was found by the CWB [1], GstLAL [2], MBTA [3], and PyCBC Live [4] analysis pipelines. S240426s is an event of interest because its false alarm rate, as estimated by the online analysis, is 7.6 e-09 Hz, or about one in 4 years. The event's properties can be found at this URL: https://gracedb. ligo. org/superevents/S240426s After parameter estimation by RapidPE-RIFT [5], the classification of the GW signal, in order of descending probability, is BBH (98%), Terrestrial (2%), NSBH (< 1%), or BNS (< 1%). Assuming the candidate is astrophysical in origin, the probability that the lighter compact object is consistent with a neutron star mass (HasNS) is< 1%.[6] Using the …

Gravitational waves are expected to be produced from neutron star oscillations associated with magnetar giant flares and short bursts. We present the results of a search for short-duration (milliseconds to seconds) and long-duration ( 100 s) transient gravitational waves from 13 magnetar short bursts observed during Advanced LIGO, Advanced Virgo and KAGRA's third observation run. These 13 bursts come from two magnetars, SGR 19352154 and Swift J1818.01607. We also include three other electromagnetic burst events detected by Fermi GBM which were identified as likely coming from one or more magnetars, but they have no association with a known magnetar. No magnetar giant flares were detected during the analysis period. We find no evidence of gravitational waves associated with any of these 16 bursts. We place upper bounds on the root-sum-square of the integrated gravitational-wave strain that reach at 100 Hz for the short-duration search and at Hz for the long-duration search, given a detection efficiency of 50%. For a ringdown signal at 1590 Hz targeted by the short-duration search the limit is set to . Using the estimated distance to each magnetar, we derive upper bounds on the emitted gravitational-wave energy of erg ( erg) for SGR 19352154 and erg ( erg) for Swift J1818.01607, for the short-duration (long-duration) search. Assuming isotropic emission of electromagnetic radiation of the burst fluences, we constrain the ratio of gravitational-wave energy to electromagnetic energy for bursts from SGR 19352154 with available fluence …

We identified the unmodeled transient candidate S240421ar during real-time processing of data from LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) at 2024-04-21 05: 29: 35.734 UTC (GPS time: 1397712593.734). The candidate was found by the CWB [1] and GstLAL [2] analysis pipelines. S240421ar is an event of interest because its false alarm rate, as estimated by the online analysis, is 3.6 e-08 Hz, or about one in 10 months. The event's properties can be found at this URL: https://gracedb. ligo. org/superevents/S240421ar The classification of the GW signal, in order of descending probability, is Terrestrial (59%), BBH (41%), BNS (< 1%), or NSBH (< 1%). Assuming the candidate is astrophysical in origin, the probability that the lighter compact object is consistent with a neutron star mass (HasNS) is< 1%.[3] Using the masses and spins inferred from the signal, the probability of matter …

We identified the compact binary merger candidate S240109a during real-time processing of data from LIGO Hanford Observatory (H1) at 2024-01-09 05: 04: 31.842 UTC (GPS time: 1388811889.842). The candidate was found by the GstLAL [1] analysis pipeline. S240109a is an event of interest because its false alarm rate, as estimated by the online analysis, is 7.3 e-09 Hz, or about one in 4 years. The event's properties can be found at this URL: https://gracedb. ligo. org/superevents/S240109a The classification of the GW signal, in order of descending probability, is BBH (> 99%), Terrestrial (< 1%), NSBH (< 1%), or BNS (< 1%). Assuming the candidate is astrophysical in origin, the probability that the lighter compact object is consistent with a neutron star mass (HasNS) is< 1%.[2] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is< 1%.[2 …

We have conducted further analysis of the LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) data around the time of the compact binary merger (CBC) candidate S231118d (GCN Circular 35090). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby. multiorder. fits, 0, distributed via GCN Notice, is available for retrieval from the GraceDB event page: https://gracedb. ligo. org/superevents/S231118d After parameter estimation by RapidPE-RIFT [2], the updated classification of the GW signal, in order of descending probability, is BBH (> 99%), Terrestrial (< 1%), NSBH (< 1%), or BNS (< 1%). For the Bilby. multiorder. fits, 0 sky map, the 90% credible region is 956 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2110+/-585 Mpc (a posteriori mean+/-standard deviation). For further information about analysis methodology and the …

We identified the compact binary merger candidate S230922g during real-time processing of data from LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) at 2023-09-22 02: 03: 44.886 UTC (GPS time: 1379383442.886). The candidate was found by the CWB [1], GstLAL [2], and MBTA [3] analysis pipelines. S230922g is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.9 e-24 Hz, or about one in 1e16 years. The event's properties can be found at this URL: https://gracedb. ligo. org/superevents/S230922g The classification of the GW signal, in order of descending probability, is BBH (> 99%), NSBH (< 1%), BNS (< 1%), or Terrestrial (< 1%). Assuming the candidate is astrophysical in origin, the probability that the lighter compact object is consistent with a neutron star mass (HasNS) is< 1%.[4] Using the masses and spins inferred from the signal, the probability …

The third Gravitational-Wave Transient Catalog (GWTC-3) describes signals detected with Advanced LIGO and Advanced Virgo up to the end of their third observing run. Updating the previous GWTC-2.1, we present candidate gravitational waves from compact binary coalescences during the second half of the third observing run (O3b) between 1 November 2019, 15∶ 00 Coordinated Universal Time (UTC) and 27 March 2020, 17∶ 00 UTC. There are 35 compact binary coalescence candidates identified by at least one of our search algorithms with a probability of astrophysical origin p astro> 0.5. Of these, 18 were previously reported as low-latency public alerts, and 17 are reported here for the first time. Based upon estimates for the component masses, our O3b candidates with p astro> 0.5 are consistent with gravitational-wave signals from binary black holes or neutron-star–black-hole binaries, and we identify …

We have conducted further analysis of the LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) data around the time of the compact binary merger (CBC) candidate S231119u (GCN Circular 35120). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby. offline0. multiorder. fits, 0, distributed via GCN Notice, is available for retrieval from the GraceDB event page: https://gracedb. ligo. org/superevents/S231119u After parameter estimation by RapidPE-RIFT [2], the updated classification of the GW signal, in order of descending probability, is BBH (95%), Terrestrial (5%), NSBH (0%), or BNS (0%). For the Bilby. offline0. multiorder. fits, 0 sky map, the 90% credible region is 5212 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 6597+/-2556 Mpc (a posteriori mean+/-standard deviation). For further information about analysis methodology …