7 research outputs found
The First Polarimetric View on Quasi-Periodic Oscillations in a Black Hole X-ray Binary
We present the first polarimetric analysis of Quasi-Periodic Oscillations
(QPO) in a black hole binary utilizing \textit{IXPE} data. Our study focuses on
Swift J1727.8--1613, which experienced a massive outburst that was observed by
various telescopes across different wavelengths. The \textit{IXPE} observation
we studied was conducted during the Hard-Intermediate state. The polarization
degree (PD) and polarization angle (PA) were measured at 4.280.20\% and
, respectively. Remarkably, significant QPO signals
were detected during this observation, with a QPO frequency of approximately
1.34 Hz and a fractional root-mean-square (RMS) amplitude of about 12.3\%.
Furthermore, we conducted a phase-resolved analysis of the QPO using the
Hilbert-Huang transform technique. The photon index showed a strong modulation
with respect to the QPO phase. In contrast, the PD and PA exhibit no
modulations in relation to the QPO phase, which is inconsistent with the
expectation of the Lense-Thirring precession of the inner flow. Further
theoretical studies are needed to conform with the observational results.Comment: Accepted for publication in APJ
In-orbit background simulation of a type-B CATCH satellite
The Chasing All Transients Constellation Hunters (CATCH) space mission plans
to launch three types of micro-satellites (A, B, and C). The type-B CATCH
satellites are dedicated to locating transients and detecting their
time-dependent energy spectra. A type-B satellite is equipped with lightweight
Wolter-I X-ray optics and an array of position-sensitive multi-pixel Silicon
Drift Detectors. To optimize the scientific payloads for operating properly in
orbit and performing the observations with high sensitivities, this work
performs an in-orbit background simulation of a type-B CATCH satellite using
the Geant4 toolkit. It shows that the persistent background is dominated by the
cosmic X-ray diffuse background and the cosmic-ray protons. The dynamic
background is also estimated considering trapped charged particles in the
radiation belts and low-energy charged particles near the geomagnetic equator,
which is dominated by the incident electrons outside the aperture. The
simulated persistent background within the focal spot is used to estimate the
observation sensitivity, i.e. 4.2210 erg cm s
with an exposure of 10 s and a Crab-like source spectrum, which can be
utilized further to optimize the shielding design. The simulated in-orbit
background also suggests that the magnetic diverter just underneath the optics
may be unnecessary in this kind of micro-satellites, because the dynamic
background induced by charged particles outside the aperture is around 3 orders
of magnitude larger than that inside the aperture.Comment: 24 pages, 13 figures, 7 tables, accepted for publication in
Experimental Astronom
The mHz quasi-regular modulations of 4U 1630--47 during its 1998 outburst
We present the results of a detailed timing and spectral analysis of the
quasi-regular modulation (QRM) phenomenon in the black hole X-ray binary 4U
1630--47 during its 1998 outburst observed by Rossi X-ray Timing Explore
(RXTE). We find that the 50-110 mHz QRM is flux dependent, and the QRM
is detected with simultaneous low frequency quasi-periodic oscillations
(LFQPOs). According to the behavior of the power density spectrum, we divide
the observations into four groups. In the first group, namely behavior A,
LFQPOs are detected, but no mHz QRM. The second group, namely behavior B, a QRM
with frequency above 88 mHz is detected and the 5 Hz and 7
Hz LFQPOs are almost overlapping. In the third group, namely behavior C, the
QRM frequency below 88 mHz is detected and the LFQPOs are significantly
separated. In the forth group, namely behavior D, neither QRM nor LFQPOs are
detected. We study the energy-dependence of the fractional rms, centroid
frequency, and phase-lag of QRM and LFQPOs for behavior B and C. We then study
the evolution of QRM and find that the frequency of QRM increases with
hardness, while its rms decreases with hardness. We also analyze the spectra of
each observation, and find that the QRM rms of behavior B has a positive
correlation with / . Finally, we give
our understanding for this mHz QRM phenomena.Comment: 14pages, 15 figure
High energy Millihertz quasi-periodic oscillations in 1A 0535+262 with Insight-HXMT challenge current models
We studied the millihertz quasi-periodic oscillation (mHz QPO) in the 2020
outburst of the Be/X-ray binary 1A 0535+262 using Insight-HXMT data over a
broad energy band. The mHz QPO is detected in the 27-120 keV energy band. The
QPO centroid frequency is correlated with the source flux, and evolves in the
35-95 mHz range during the outburst. The QPO is most significant in the 50-65
keV band, with a significance of ~ 8 sigma, but is hardly detectable (<2 sigma)
in the lowest (1-27 keV) and highest (>120 keV) energy bands. Notably, the
detection of mHz QPO above 80 keV is the highest energy at which mHz QPOs have
been detected so far. The fractional rms of the mHz QPO first increases and
then decreases with energy, reaching the maximum amplitude at 50-65 keV. In
addition, at the peak of the outburst, the mHz QPO shows a double-peak
structure, with the difference between the two peaks being constant at ~0.02
Hz, twice the spin frequency of the neutron star in this system. We discuss
different scenarios explaining the generation of the mHz QPO, including the
beat frequency model, the Keplerian frequency model, the model of two jets in
opposite directions, and the precession of the neutron star, but find that none
of them can explain the origin of the QPO well. We conclude that the
variability of non-thermal radiation may account for the mHz QPO, but further
theoretical studies are needed to reveal the physical mechanism.Comment: 13 pages, 7 figures. Accepted for publication in MNRA
Simulation Studies for the First Pathfinder of the CATCH Space Mission
The Chasing All Transients Constellation Hunters (CATCH) space mission is an
intelligent constellation consisting of 126 micro-satellites in three types (A,
B, and C), designed for X-ray observation with the objective of studying the
dynamic universe. Currently, we are actively developing the first Pathfinder
(CATCH-1) for the CATCH mission, specifically for type-A satellites. CATCH-1 is
equipped with Micro Pore Optics (MPO) and a 4-pixel Silicon Drift Detector
(SDD) array. To assess its scientific performance, including the effective area
of the optical system, on-orbit background, and telescope sensitivity, we
employ the Monte Carlo software Geant4 for simulation in this study. The MPO
optics exhibit an effective area of cm at the focal spot for 1 keV
X-rays, while the entire telescope system achieves an effective area of
cm at 1 keV when taking into account the SDD detector's detection
efficiency. The primary contribution to the background is found to be from the
Cosmic X-ray Background. Assuming a 625 km orbit with an inclination of
, the total background for CATCH-1 is estimated to be
counts s in the energy range of 0.5--4 keV. Based on
the background within the central detector and assuming a Crab-like source
spectrum, the estimated ideal sensitivity could achieve erg
cm s for an exposure of 10 s in the energy band of 0.5--4
keV. Furthermore, after simulating the background caused by low-energy charged
particles near the geomagnetic equator, we have determined that there is no
need to install a magnetic deflector
Isolation of a potential probiotic strain Bacillus amyloliquefaciens LPB-18 and identification of antimicrobial compounds responsible for inhibition of food-borne pathogens
This study was carried out to screen a potential probiotic microbe with broad-spectrum antagonistic activity against food-borne pathogens and identify the antimicrobial compounds. Based on morphological and molecular analysis, a new Bacillus strain with the ability to produce effective antimicrobial agents was isolated from the breeding soil of earthworms and identified as having a close evolutionary footprint to Bacillus amyloliquefaciens. The antimicrobial substances produced by B. amyloliquefaciens show effective inhibition of Aspergillus flavus and Fusarium oxysporum in an agar diffusion assay. Antimicrobial agents were identified as a series of fengycin and its isoforms (fengycin A and fengycin B) after being submitted to RT-HPLC and MALDI-TOF MS analyses. To evaluate the probiotic activity of the B. amyloliquefaciens, antibiotic safety and viability of the isolated strain in a simulated gastrointestinal environment were carried out. The safety test result revealed that strain LPB-18 is susceptible to multiple common antibiotics. Moreover, acidic condition and bile salts assay were carried out, and the results revealed that it couble be a potential probiotic microbe B. amyloliquefaciens LPB-18 is good choice for biological strains in agricultural commodities and animal feedstuffs
Identification and functional analysis of non-coding regulatory small RNA FenSr3 in Bacillus amyloliquefaciens LPB-18
Bacillus amyloliquefaciens is an interesting microbe in the food processing and manufacturing industries. Non-coding small RNAs (sRNAs) have been shown to play a crucial role in the physiology and metabolism of bacteria by post-transcriptionally regulating gene expression. This study investigated the function of novel sRNA FenSr3 by constructing fenSr3 deficient strain and complementary strains in B. amyloliquefaciens LPB-18 , which were named LPN-18N and LPB-18P, respectively. The result showed significant differences in fengycin yield between strain LPB -18N and LPB-18P. The production of fengycin was significantly enhanced in B. amyloliquefaciens LPB-18N, compared with that of the strain LPB-18 from 190.908 mg/L to 327.598 mg/L. Moreover, the production of fengycin decreased from 190.464 mg/L to 38.6 mg/L in B . amyloliquefaciens LPB-18P. A comparative transcriptome sequencing was carried out to better understand the complex regulatory mechanism. Transcription analysis revealed that 1037 genes were differentially expressed between B. amyloliquefaciens LPB-18 and B. amyloliquefaciens LPB-18N, including the key regulatory genes in fatty acid, amino acid biosynthesis, and central carbon metabolism, which could provide sufficient quantities of building precursors for fengycin biosynthesis. The biofilm formation and sporulation was also enhanced in the strain LPB-18N, which indicates that FenSr3 could play a vital role in stress resistance and promotes survival in B. amyloliquefaciens. Some sRNAs involved in stress response have been identified in the literature, but their regulatory roles in fengycin production remain unclear. The study will contribute a novel perspective to the regulation mechanism of biosynthesis and the optimization of key metabolites of B. amyloliquefaciens