Ultra-long Period Research Articles

Apparently Ultralong Period Radio Signals from Self-lensed Pulsar–Black Hole Binaries

Pulsar–black hole (BH) close binary systems, which have not been found yet, are unique laboratories for testing theories of gravity and understanding the formation channels of gravitational-wave sources. We study the self-gravitational lensing effect in a pulsar–BH system on the pulsar’s emission. Because this effect occurs once per orbital period for almost edge-on binaries, we find that it could generate apparently ultralong period (minutes to hours) radio signals when the intrinsic pulsar signal is too weak to detect. Each of such lensed signals, or “pulse,” is composed of a number of amplified intrinsic pulsar pulses. We estimate that a radio telescope with a sensitivity of 10 mJy could detect a few systems that emit such signals in our Galaxy. The model is applied to three recently found puzzling long-period radio sources: GLEAM-X J1627, PSR J0901-4046, and GPM J1839-10. To explain their observed signal durations and periods, the masses of their lensing components are estimated as ∼104 M ⊙, ∼4 M ⊙, and 103−6 M ⊙, respectively, with their binary coalescence times ranging from a few tens to thousands of years. However, the implied merger rates (as high as ∼103−4 Myr−1 per galaxy) and the large period decay rates (>10−8 s s−1) tend to disfavor this self-lensing scenario for these three sources. Despite this, our work still provides observational characteristics for self-lensed pulsar–BH binaries, which could help the detection of related sources in the future. Finally, for a binary containing a millisecond pulsar and a stellar-mass BH, the Shapiro delay effect would cause a ≥10% variation of the profile width for the subpulses in such lensed signals.

Simultaneous bending and temperature measurement based on a superimposed fiber grating sensor

A compact and novel superimposed fiber grating (SI-FG) sensor for simultaneous measurement of temperature and bending based on UV-induced FBG cascaded with a multimode fiber (MMF) embedded ultra-long period fiber grating (MMF-EULPFG) has been proposed and experimentally validated. The MMF-EULPFG acts as a temperature and bending sensing unit and was fabricated by periodically splicing a non-UV-non-photosensitive MMF and a UV-photosensitive single-mode fiber (SMF) which is so called cleaving-splicing method. Due to the periodic refractive index modulation, the 6-period SMF-MMF structure based MMF-EULPFG with a total length of 2.7 mm forms transmission spectra with a −17 dB dip. The proposed SI-FG sensor exhibits high bending and temperature sensitivities of 17.096 nm/m−1 and −0.238 nm/℃, respectively. The UV-induced FBG is fabricated in the initial segment of UV-sensitive fibers within EULPFG by UV exposure method. The dip of FBG transmission spectra also shows response to bending and temperature. By utilizing a matrix obtained from the experimental results, simultaneous measurement of temperature and bending can be achieved. Due to its compact structure and high sensitivity, the proposed novel SI-FG sensor can be used as a competitive all-fiber sensor for structural health monitoring and 3D-shape sensing.Index Terms: Optical fiber sensor, long period fiber grating, superimposed fiber grating, simultaneous measure.

Evolutionary Origin of Ultralong-period Radio Transients

Abstract Recently, two ultralong-period radio transients, GLEAM-X J162759.5-523504.3 (J1627) and GPM J1839-10 (J1839), were discovered with spin periods longer than 1000 s. The origin of these two ultralong-period radio transients is intriguing in understanding the spin evolution of neutron stars (NSs). In this work, we examine whether the interaction between strong magnetized NSs and fallback disks can spin NSs down to the observed ultralong period. Our simulations found that the magnetar + fallback disk model can account for the observed period, period derivative, and X-ray luminosity of J1627 in the quasi-spin-equilibrium stage. To evolve to the current state of J1627, the initial mass-accretion rate of the fallback disk and the magnetic field of the NS are in the range of (1.1–30) × 1024 g s−1 and (2–5) × 1014 G, respectively. In the active lifetime of the fallback disk, it is impossible for J1839 to achieve the observed upper limit of the period derivative. Therefore, we propose that J1839 may be in the second ejector phase after the fallback disk becomes inactive. Those NSs with a magnetic field of (2–6) × 1014 G and a fallback disk with an initial mass-accretion rate of ∼1024–1026 g s−1 are possible progenitors of J1839.

Photometric analysis of the dwarf nova SU UMa based on TESS

We report the photometric analysis of SU UMa based on the observations of the Transiting Exoplanet Survey Satellite (TESS). TESS has released a large amount of data, which contains the light curves of a complete superoutburst and three normal outbursts of SU UMa. Based on the observations, the evolution of superhumps during the superoutburst was analyzed. By using the O - C method, the three stages were determined, and the superhump period for each stage was calculated. The mass ratio q=0.137(1) was estimated based on the stage A superhump method. A periodic oscillation with a period of 2.17(9) days was found in the superhump minimum O - C diagram, which is related to the precession of the accretion disk. We investigated the frequency information of quasiperiodic oscillations (QPOs) in the light curves. An ultralong period QPO of 0.18 days at the time of normal outburst and two ultralong periods QPOs of 0.19 days and 0.285 days in quiescence were found. No QPO was found in the superoutburst.

A mysterious object in our Galaxy pulses every 76 seconds

The discovery of an ultra-long period neutron star, emitting unusual radio signals is rewriting our understanding of these unique star systems. The source has been found to reside in a neutron star graveyard and yet still produce radio emission (zombie stars!). It exhibits highly unusual and chaotic pulse shapes quite unlike anything seen in known neutron stars.

Analysis of optical propagation characteristics of the ultra-long period grating using RCWA.

There have been significant research and analyses on the diffraction efficiency and characteristics of spectral grating with a wavelength-scale period. However, thus far an analysis on a diffraction grating with an ultra-long pitch over several hundred times of the wavelength (>100µm) and a very deep groove over dozens of micrometers has not been performed. We analyzed the diffraction efficiency of these gratings by using the rigorous coupled-wave analysis (RCWA) method and confirmed that the RCWA analytic results correspond well to the actual experimental results on the wide-angle beam-spreading phenomenon. In addition, because a long-period grating with a deep groove results in a small diffraction angle with relatively uniform efficiency, it is possible to convert a point-like distribution to a linear distribution for a short working distance and a discrete distribution for a very long working distance. We believe that a wide-angle line laser with a long grating period can be used in various applications, such as level detectors, precision measurements, multi-point light detecting and ranging (LiDAR) light sources, and security systems.

Seven-core fiber embedded ultra-long period grating for curvature, torsion or temperature sensing

We have proposed and experimentally demonstrated a novel seven-core fiber (SCF) embedded ultra-long period grating (EU-LPFG) structure for curvature, torsion or temperature sensing. The EU-LPFG is fabricated by periodically splicing a SCF and a single mode fiber (SMF) just by using a fusion splicer and a microscope. Due to the periodic refractive index modulation, the EU-LPFG forms two resonant peaks in only 8-period SMF-SCF structure with a total length of 5.0 mm, has high curvature, torsion or temperature sensitivity of 31.26 nm/m−1, 0.19 nm/(rad/m) and 0.53 nm/°C in the range of 0.36–1.61 nm/m−1, 0–57.12 rad/m, 30–100 °C, respectively. According to the compact structure, simple fabricated method, high curvature and torsion sensitivity and ability to measure temperature, the proposed novel SCF-embedded EU-LPFG can be used as the competitive all-fiber sensor in harsh environment applications.

Evidence for an abundant old population of Galactic ultra-long period magnetars and implications for fast radio bursts

ABSTRACT Two recent discoveries, namely PSR J0901−4046 and GLEAM-X J162759.5−523504.3 (hereafter GLEAM-X J1627), have corroborated an extant population of radio-loud periodic sources with long periods (76 and 1091 s, respectively) whose emission can hardly be explained by rotation losses. We argue that GLEAM-X J1627 is a highly magnetized object consistent with a magnetar (an ultra-long period magnetar, ULPM), and demonstrate it is unlikely to be either a magnetically or a rotationally powered white dwarf. By studying these sources together with previously detected objects, we find there are at least a handful of promising candidates for Galactic ULPMs. The detections of these objects imply a substantial number, N ≳ 13 000 and N ≳ 500 for PSR J0901−4046 like and GLEAM-X J1627 like objects, respectively, within our Galaxy. These source densities, as well as cooling age limits from non-detection of thermal X-rays, Galactic offsets, timing stability and dipole spin-down limits, all imply the ULPM candidates are substantially older than confirmed Galactic magnetars and that their formation channel is a common one. Their existence implies widespread survival of magnetar-like fields for several Myr, distinct from the inferred behaviour in confirmed Galactic magnetars. ULPMs may also constitute a second class of FRB progenitors which could naturally exhibit very long periodic activity windows. Finally, we show that existing radio campaigns are biased against detecting objects like these and discuss strategies for future radio and X-ray surveys to identify more such objects. We estimate that ${\cal O}(100)$ more such objects should be detected with SKA-MID and DSA-2000.

Simultaneous Measurement of Dual Parameters Based on Periodically Embedding MMF-Induced Ultralong-Period Fiber Grating

In this article, an ultralong period fiber grating (ULPFG) based on periodically embedding multimode fiber into single mode fiber (PEM-ULPFG) is proposed to simultaneously measure the liquid refractive index (RI) and temperature with high sensitivity. Five resonant dips belong to different cladding modes, and diffraction mode orders appear in the transmission spectrum. The responses of the dips to RI and temperature are different. Therefore, high sensitivity and dual-parameter measurement are realized. Numerical simulation based on the beam propagation method (BPM) is also carried out to design and optimize the parameters of the device. Experimental results show that the maximum RI sensitivity of −1230 nm/RIU in the range of 1.4021–1.4383 RIU is achieved by tracing the target dip (dip 4). The temperature response of dip 4 is also characterized to be as low as 52.6 pm/°C. Another dip (dip 5) is used for measuring temperature with the temperature sensitivity of 92.3 pm/°C. Different responses to the external changes of the dips obtained by the PEM-ULPFG make the proposed sensor competitive in the field of high sensitivity and dual-parameter sensing.

In Situ Synthesis of Cathode Materials for Aqueous High-Rate and Durable Zn–I2 Batteries

Rechargeable aqueous zinc–iodine batteries are considered as one of strong contenders for next-generation energy storage systems by virtue of their low cost and high safety. However, the shuttle effect of highly soluble I3– in zinc–iodine batteries leads to a rapid decrease in capacity and Coulomb efficiency during cycling, which seriously hinders their further development and application. Here, we developed an in situ synthesis of an aqueous fast-charging and ultrastable Zn–I2 battery cathode materials composed of mesoporous carbon and I2. Compounding I2 with highly conductive carbon is an effective method to facilitate electron and ion transport and confine polyiodides/I– conversion reaction inside pores, thereby eliminating polyiodides shuttle effect, which greatly improves cycling stability of Zn–I2 batteries. The developed Zn–I2 battery provides a specific capacity of 90 mAh g–1 at 5 A g–1, excellent multiplicative performance, and retains a capacity retention of 80.6% over an ultralong period of 39 000 cycles at 10 A g–1, superior to previously reported Zn–I2 batteries. Furthermore, Zn–I2 pouch cell retained 89% capacity retention over 1000 cycles at 0.5 A g–1. This work undoubtedly sets a precedent for ultralong cycle life Zn–I2 battery cathode materials and provides an important solution and pathway for the assembly of I2-based materials suitable for high-performance aqueous energy technologies.

Discovery of a radio emitting neutron star with an ultra-long spin period of 76 seconds.

The radio-emitting neutron star population encompasses objects with spin periods ranging from milliseconds to tens of seconds. As they age and spin more slowly, their radio emission is expected to cease. We present the discovery of an ultra-long period radio-emitting neutron star, PSR J0901-4046, with spin properties distinct from the known spin and magnetic-decay powered neutron stars. With a spin-period of 75.88 s, a characteristic age of 5.3 Myr, and a narrow pulse duty-cycle, it is uncertain how radio emission is generated and challenges our current understanding of how these systems evolve. The radio emission has unique spectro-temporal properties such as quasi-periodicity and partial nulling that provide important clues to the emission mechanism. Detecting similar sources is observationally challenging, which implies a larger undetected population. Our discovery establishes the existence of ultra-long period neutron stars, suggesting a possible connection to the evolution of highly magnetized neutron stars, ultra-long period magnetars, and fast radio bursts.

In-Situ Implant Formulation of Laurate and Myristate Prodrugs of Dolutegravir for Ultra-Long Delivery

The focus of present work was to synthesize prodrugs of dolutegravir (DTG) for ultra-long delivery purpose. The prodrug was synthesized by esterification of hydroxyl group with carboxyl group of fatty acid (lauric or myristic acid). The prodrugs were characterized by differential scanning calorimetry, X-ray powder diffraction, nuclear magnetic resonance, Fourier transformed infrared, near infrared-chemical imaging, pH-solubility, partition coefficient, and stability (solid and liquid). Stability studies were performed by exposing the powder drugs to 40°C/75% RH for three months and buffer solutions at room temperature for 72 h. The prodrugs and drug were formulated into in-situ implant using biodegradable polymer. Thermal, spectral, and diffractometric data indicated formation of new chemical and solid forms. Formation of prodrugs resulted in lowering of melting point of DTG from 191.1°C to 163.7 and 140.7°C for DTG-Laurate and DTG-Myristate prodrugs, respectively. A decrease in solubility of 18.2-115.9 and 124.5-1594.9 folds was observed for DTG-Laurate and DTG-Myristate, respectively compared to DTG. Similarly, the prodrugs were highly lipophilic compared to DTG. Solid-state and pH-stability profiles of DTG and prodrugs were comparable. Implant formulation released 60.1% in 77 days compared to 95.6% in 35 days in the case of DTG-Myristate and DTG, respectively. In summary, combining prodrug and drug delivery approaches can be utilized for delivering drug for ultra-long period.

Measurement of Laser Phase Noise for Ultra-Long Period of 0.8 Seconds With 800-ps Temporal Resolution Using Optical Coherent Detection With FPGA-Implemented Data Acquisition

In this study, we demonstrate laser phase noise measurement with a 0.8-s period and an 800-ps temporal resolution. An optical carrier is received by heterodyne detection, and the detected electrical signals are acquired using field programmable gate array circuits with 1.25-GSample/s analog-to-digital converters and 1-GByte memory. The laser phase noise is visualized using a field spectrogram and a very wide FM noise spectrum from near the DC, which is constructed using our proposed phase-compensating interleaved fast Fourier transformation. We compare the phase noise characteristics of an external cavity laser with those of a distributed feedback semiconductor laser.

Ultra-long acting prodrug of dolutegravir and delivery system – Physicochemical, pharmacokinetic and formulation characterizations

The focus of present work was to characterize ultra-long acting prodrug of dolutegravir (DTG) and develop biodegradable microparticle formulation. Palmitic acid (PA) conjugated prodrug of DTG was prepared by esterification of hydroxyl group of DTG with the carboxyl group of PA. Physicochemical properties of the prodrug was characterize by MS, NMR, FTIR, SEM, DSC, NIR-CI, pH-solubility, and solid and liquid pH-stability. Comparative solid and liquid stability was performed by storing powder DTG and DTG-Palmitate at 40 °C/75% RH for three months and liquid solution pH 2–8 at room temperature for 24 h, respectively. Pharmacokinetic evaluation was performed in white albino New Zealand rabbits by subcutaneous injection (30 mg/Kg). Poly(lactide-co-glycolide) microparticle formulation was prepared by emulsification-evaporation method and characterized for particle size distribution, shape, drug loading and in-vitro release. MS, NMR, FTIR, SEM, DSC, NIR-CI indicated formation of prodrug. Melting point of the prodrug was lower than DTG but higher than PA. Shape of DTG crystals was irregular while DTG-Palmitate crystals was fine-needle. Solid and liquid stability profiles of the prodrug were similar to DTG. Plasma half-life, area under the curve, and mean-residence time of DTG-Palmitate were 8.8, 2.3 and 14.7 folds of DTG. D90 of DTG and DTG-Palmitate microparticles was 107.1 ± 2.7 and 94.3 ± 3.4 µm, respectively. The in-vitro drug release was almost complete in three weeks from DTG microparticles while it was <85% in six months from DTG-Palmitate microparticles. In conclusion, physicochemical and pharmacokinetic properties and biodegradable microparticles of the prodrug suggested that the prodrug has potential of sustaining DTG release for ultra-long period compared to DTG.

Strain, bending, refractive index independent temperature sensor based on a graded index multimode fiber embedded long period fiber grating.

A novel embedded ultra-long period fiber grating (EULPFG) based on a graded index multimode fiber (GI-MMF) is proposed for temperature measurement. Due to the small RI difference of the modes near the GI-MMF self-imaging point, the resonant peak of transmission spectrum is wavelength-insensitive to refractive index (RI), strain and bending. However, the sensor is sensitive to temperature. The experimental results show that the temperature sensitivity of the EULPFG is 90.77 pm/°C. The sensitivities of other physical parameters are suppressed, and the suppressed sensitivities are at least one order of magnitude less than those of similar sensors. The EULPFG with anti-interference from other parameters is expected to be used in ocean monitoring systems to measure the temperature of the seawater.

Ultra-long period and small-amplitude tsunami generated following the July 2020 Alaska Mw7.8 tsunamigenic earthquake

The July 2020 Mw7.8 Alaska tsunamigenic earthquake was a fresh call for potential large tsunamis associated with the Aleutian subduction zone. The second largest ever-recorded earthquake worldwide (Mw 9.2) occurred in this zone in 1964 indicating its massive earthquake and tsunami risk. Our analysis of the July 2020 tsunami revealed that it involves very long period waves (51–64 min) which is unusual for an Mw7.8 earthquake. The tsunami coastal amplitude was small (~0.5 m) which is much smaller than that usually expected from a tsunamigenic earthquake of this size. Here, through numerical simulations and spectral analyses, we explain the ultra-long period and small amplitude waves of the tsunami. Our analysis using an analytical equation showed that the ultra-long period of the tsunami (51–64 min) can be reproduced using the shallow water depth around the source region (100–200 m) and the length of the coseismic deformation area (~100 km). By comparing the coastal amplitude of this event with four other similar-size and similar-mechanism earthquakes (thrust Mw7.8), we attribute the relatively small coastal amplitude of this tsunami to the deep focal depth of the earthquake (28 km) and the extremely shallow water around the source region.

High-sensitivity dual-direction weak magnetic field sensor based on structural modulated ultralong period microfiber grating

A high-sensitivity optical fiber dual-direction weak magnetic field sensor based on a structural modulated ultralong period microfiber grating (SULPMG) is proposed. The SULPMG was fabricated by an electric arc discharge and flame-heating drawing method, and the sensor was fabricated by cascading the SULPMG with a core offset section. By tuning the direction of an applied magnetic field, the refractive index of a magnetic fluid (MF) can be tuned accordingly. The transmission spectral response of the proposed sensor was measured and analyzed. For the weak magnetic field intensity range from 0 mT to 7 mT, the obtained magnetic field sensitivity is −1.759 nm/mT and 1.082 nm/mT when the magnetic field is perpendicular or parallel to the light propagation direction, respectively. Theoretical analysis shows that reducing the waist diameter can further improve the sensitivity of the sensor. The proposed sensor is expected to be applied to weak magnetic field measurements in the aviation, vehicle detection and biomedical fields.

Measuring complex field waveforms of quadrature amplitude modulation optical signals using a spectrally slicing-and-synthesizing coherent optical spectrum analyzer.

We propose a spectrally slicing-and-synthesizing coherent optical spectrum analyzer to measure complex field waveforms of quadrature amplitude modulation (QAM) optical signals with ultralong periods. The optical spectrum of a measured optical signal is divided into multiple narrowband spectral components, called slices. The slices are sequentially measured using low-speed coherent detection. After phase noise suppression and frequency fluctuation compensation on each slice, the measured slices are synthesized to recover the original signal spectrum. Our numerical and experimental results confirm that the proposed method can overcome the limitation of the measurement bandwidth because the signal spectrum can synthesize more than 100 slices. We experimentally demonstrate complex field measurements of 16QAM optical signals. Our method can measure high-speed optical complex field waveforms with no bandwidth limitation.

Periodicity in recurrent fast radio bursts and the origin of ultralong period magnetars

ABSTRACT The recurrent fast radio burst FRB 180916 was recently shown to exhibit a 16-d period (with possible aliasing) in its bursting activity. Given magnetars as widely considered FRB sources, this period has been attributed to precession of the magnetar spin axis or the orbit of a binary companion. Here, we make the simpler connection to a rotational period, an idea observationally motivated by the 6.7-h period of the Galactic magnetar candidate, 1E 161348–5055. We explore three physical mechanisms that could lead to the creation of ultralong period magnetars: (i) enhanced spin-down due to episodic mass-loaded charged particle winds (e.g. as may accompany giant flares), (ii) angular momentum kicks from giant flares, and (iii) fallback leading to long-lasting accretion discs. We show that particle winds and fallback accretion can potentially lead to a sub-set of the magnetar population with ultralong periods, sufficiently long to accommodate FRB 180916 or 1E 161348–5055. If confirmed, such periods implicate magnetars in relatively mature states (ages 1−10 kyr) and which possessed large internal magnetic fields at birth Bint ≳ 1016 G. In the low-twist magnetar model for FRBs, such long period magnetars may dominate FRB production for repeaters at lower isotropic-equivalent energies and broaden the energy distribution beyond that expected for a canonical population of magnetars, which terminate their magnetic activity at shorter periods P ≲ 10 s.

INTEGRAL contributions to magnetars and multimessenger astrophysics

AbstractThe INTEGRAL satellite, in orbit since October 2002, has significantly contributed to the study of magnetars and, thanks to its unique capabilities for the study of transient gamma-ray phenomena, it is now playing an important role in multimessenger astrophysics. The most recent results include the discovery of a peculiar burst from SGR J1935+2154, which gave the first observational evidence for the connection between magnetars and fast radio bursts, and extensive searches for bursting activity in peculiar sources, such as the repeating FRB 20200120E in M81 and the ultra-long period magnetar candidate GLEAMX J162759.5–523504.3.