We have studied the timing and spectral properties of the BeXB 4U 1901+03 during the 2019 outburst using
NuSTAR
,
Swift
, and
NICER
observations. Flares are in all observations and were of tens to ...hundreds of seconds duration. Pulse profiles were changing significantly with time and the luminosity of the source. An increase in the height of the peak of the pulse profiles was observed with energy. The pulse fraction increases with energy and at the end of the outburst. The variation of the pulse profile with time indicates the transition of the pulsar in different accretion regimes. The absorption like feature at 10 keV shows a positive correlation with the luminosity and along with other spectral parameters this feature was also pulse phase dependent. As the distance to the source is not precisely known we cannot confirm this feature to be CSRF and also cannot ignore other possible explanations of the feature. Another absorption like feature about 30 keV was observed in the spectra of the last two
NuSTAR
observations and has line energy of about 30.37 ± 0.55 and 30.23 ± 0.62 keV, respectively. We have also studied the variation of the line energy, width, and optical depth of this feature with pulse phase. The softening of the spectrum along with the increase in pulse fraction at the end of the outburst and absence of pulsation after 58665.09 MJD suggest that the pulsar has entered a propeller phase, also an abrupt decrease in
Swift
-XRT flux supports the fact.
Key Clinical Message
Dengue fever can also have various neurological complications but involvement of the spinal cord is often unusual. This is a case where the patient had transverse myelitis as a ...complication of dengue fever.
Dengue fever can have various neurological complications but involvement of the spinal cord is often unusual. We report a case of a 49‐year‐old female, a known case of dengue fever, who presented with urine retention, inability to stand and walk with tingling sensation of bilateral lower limbs. Her vibration and joint position sensation was reduced below T2 level along with altered reflexes but MRI could not explain the examination findings. She was diagnosed clinically as transverse myelitis (TM) in the background of dengue fever. She showed drastic improvement with treatment of steroids. As TM as a complication in a patient with dengue fever is rare, and due to the paucity of similar case reports in Nepal, this case report is of value for the scientific community.
MRI spine showing mild disc bulge at L4/L5.
ABSTRACT
We present here the timing and spectral analysis of the accreting millisecond pulsar (AMXP) SwiftJ1756.9−2508 during its recent outburst in 2018 using Swift and NUSTAR observations. The ...simultaneous fitting of the Swift and NUSTAR spectra indicates that the source was in the hard state with a cut-off energy of about 74.58 keV. We also study in detail the pulse profile of the AMXP and its dependence on energy. The colour–colour diagram of the source is different from those previously reported. We performed phase- and time-resolved spectral analysis using NUSTAR data. Pulse phase-resolved spectra were fitted with a power-law model and significant changes in the spectral parameters with pulse phase were observed. The orbital phase and time-resolved spectra were fitted with a cut-off power-law model. The column density and photon index obtained from orbital phase spectral analysis were found to show some anticorrelation with the flux. Through time-resolved spectral analysis, we observed that the spectral parameters show positive correlation with each other and with the flux. We do not observe a softening of the spectrum with time. No emission lines or Compton bump were observed in the spectrum of the AMXP.
ABSTRACT
We report X-ray observations of the high mass X-ray binary (HMXB) pulsar 4U 1907+09. Spectral and timing analysis of the source has been performed using Nuclear Spectroscopic Telescope Array ...(NuSTAR) observation. Timing analysis of the photon events revealed the coherent X-ray pulsation of the source with a pulse period of 442.92 ± 0.03 s. It is observed that the source is spinning down at a rate of 0.1971(4) s yr−1. The pulse profile is characterized by a decaying amplitude of the secondary peak and relative growth in the amplitude of the primary peak with an increase in energy. The broad-band spectral coverage of NuSTAR has been used to observe multiple absorption features in the X-ray continuum of the source. We confirm the presence of two prominent cyclotron absorption features at ∼17 and ∼38 keV, respectively. In addition, we have detected an absorption-line feature at ∼8 keV, with an equivalent width of ∼1.3 keV. The variation of the spectral parameters with pulse phase has been observed using phase-resolved spectroscopy and the relevant variabilities of the parameters have been discussed with the underlying physical implications. The continuum evolution and variations in spectral parameters have also been studied by time-resolved spectroscopy.
ABSTRACT
We present the timing and spectral analysis of the high-mass X-ray binary source 4U 1538−522 using Nuclear Spectroscopic Telescope Array (NuSTAR) observations. One of the observations ...partially covers the X-ray eclipse of the source along with eclipse ingress. The source is found to spin down at the rate of 0.163 ± 0.002 s yr−1 between ∼54973 and 58603 MJD. It is evident that at time ∼58620 MJD, a torque reversal occurred; thereafter, the source exhibited a spin-up trend at the rate −(0.305 ± 0.018) s yr−1 until 59275 MJD. A recent NuSTAR observation finds the pulse period of the source: (526.2341 ± 0.0041) s. The pulse profile exhibits a transition from double-peaked to single-peaked nature above ∼30 keV. We analysed the overall trend of the temporal evolution of fundamental cyclotron resonance scattering feature, Ecyc, incorporating recent NuSTAR measurements. Initially, during the time span ∼50452.16–55270.8 MJD, the cyclotron line energy is found to increase at a rate of 0.11 ± 0.03 keV yr−1, which is further followed by a decrease at a rate −0.14 ± 0.01 keV yr−1 between 55270.8 and 59267 MJD. The combined measurements in the time span 50452.16–59267 MJD reveal that the cyclotron line energy is increasing linearly at a rate of 0.08 ± 0.02 keV yr−1.
The ongoing spin-down episode of 4U 1626-67 Tobrej, Mohammed; Tamang, Ruchi; Rai, Binay ...
Monthly Notices of the Royal Astronomical Society,
01/2024, Letnik:
528, Številka:
2
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
We report the X-ray characteristics of the persistent X-ray pulsar 4U 1626-67 using simultaneous NuSTAR and NICER observations. The X-ray pulsar 4U 1626-67 has just encountered a torque ...reversal in 2023 and is presently in the spin-down state. We have examined the temporal and spectral characteristics of the source during its ongoing spin-down episode. The pulse profiles of the source are characterized by multiple substructures at lower energies and a wide asymmetric single-peaked structure at higher energies. The pulse fraction follows an overall increasing trend with energy. We confirm the existence of mHz quasi-periodic oscillation (QPO) exclusively during the current spin-down phase in all the observations. The source is spinning down at 0.00045(4) s yr−1. The broad-band spectrum during this phase is described by empirical NPEX model and a soft blackbody component with kT ∼ 0.25 keV. In addition to the iron emission line, we also confirm the presence of cyclotron line at ∼36 keV. The source flux continues to decrease during the current spin-down phase, and the corresponding luminosity ∼(3.3–4.9) × 1036 erg s−1 lies in the intermediate range of accreting X-ray pulsars that may be associated with a hybrid accretion geometry. The magnetic field strengths estimated using the cyclotron line measurements and QPO frequency are consistent. The evolution of the spectral parameters relative to the pulsed phase is examined using phase-resolved spectroscopy.
NuSTAR observation of X-ray pulsar 1E 1145.1−6141 Ghising, Manoj; Tobrej, Mohammed; Rai, Binay ...
Monthly notices of the Royal Astronomical Society,
11/2022, Letnik:
517, Številka:
3
Journal Article
Recenzirano
ABSTRACT
In this work, we report on hard X-ray observations of the X-ray pulsar 1E 1145.1−6141 performed with the Nuclear Spectroscopic Telescope Array mission (NuSTAR). Coherent pulsation of the ...source with a period of $\sim \! 296.653\, \pm \, 0.021\, \mathrm{ s}$ is detected. The source may be in the equilibrium phase, according to the most recent measurements of its pulse period. The pulse profile reveals a mild energy dependence and generally hints at a pencil-beam pattern. The pulse profile has evolved with time. The pulse fraction is found to depend on energy, with a fall in value at $\sim \! 32\, \mathrm{ keV}$. The NuSTAR spectra can be approximated by a composite model with two continuum components, blackbody emission, a cut-off power law, and a discrete component in the form of a Gaussian to account for the emission line of iron. The estimated absorbed flux of the source is $\sim \! 6\times 10^{-10}\, \mathrm{ erg}\, \mathrm{ cm}^{-2}\, \mathrm{ s}^{-1}$, which corresponds to a luminosity of $\sim \! 5\times 10^{36}\, \mathrm{ erg}\, \mathrm{ s}^{-1}$. Pulse phase-resolved spectroscopy was performed to understand the evolution of the spectral parameters with pulse phase. The estimated blackbody radius is found to be consistent with the size of the theoretical prediction.
ABSTRACT
We present X-ray observations of the recent outburst of 2022 from the neutron star low-mass X-ray binary source 1A 1744−361. Spectral properties of the source have been analysed using joint ...Nuclear Spectroscopic Telescope Array and Neutron Star Interior Composition Explorer observations. During our observations, the source happens to be in the banana state (soft state) of the hardness–intensity diagram. In addition to a power law with a high-energy cut-off, the spectrum is found to exhibit broad iron Kα emission along with distinct absorption features. A prominent absorption feature observed at 6.92 keV may be interpreted as Kα absorption line from hydrogen-like iron. The absorption feature observed at 7.98 keV may be interpreted as a blend of Fe xxv and Ni xxvii transitions. We have summarized the evidence of variability of the spectral features observed in the X-ray continuum by time-resolved spectroscopy.
ABSTRACT
We report the X-ray spectral and timing analysis of the high mass X-ray binary EXO 2030+375 during the 2021 type II outburst. We have incorporated NuSTAR, NICER, Swift/BAT, and Fermi/GBM ...observations to carry out a comprehensive analysis of the source. Pulse profiles in different energy ranges and time intervals have been generated and analysed. We have performed a brief comparison of the observations amidst the peak outburst condition and also during the decaying state of the outburst. Pulse profiles are found to evolve with time and energy. An iron emission line at (6–7) keV is observed in the X-ray continuum. Distinct absorption features were observed in the spectra corresponding to the peak outburst state while such features were not detected during the later decaying phase of the outburst. We have estimated the characteristic spin-up time-scale to be ∽ 60 yr. The continuum flux of the system and the varying luminosities covering the entire outburst period have been used to interpret the characteristics of the source. We have summarized the variability of various parameters along with their underlying physical implications.
ABSTRACT
We study the recently discovered Be/X-ray pulsar MAXI J0655-013 using the 2022 NuSTAR observations. This paper is the first detailed study of the timing and spectral properties of the ...source. The pulse profiles of the pulsar vary with energy. The pulsed fraction is found to increase monotonically with energy. In between the two NuSTAR observations, a large spin-up rate of ∼−1.23 s d−1 is observed, which can be due to large spin-up torque acting on the pulsar during an outburst. Such a large spin-up rate is observed for the first time in an X-ray pulsar during an outburst. The variation of the spin period with time can be employed to obtain the orbital parameters of the binary system, and we found the orbital period to be ∼27.9 d. The second NuSTAR observation is done in a low-luminosity state (LX ∼ 3.9 × 1034 $\text{erg}\, \text{s}^{-1}\,$). We have detected the pulsation of the pulsar in such a low-luminosity state. In such a low-luminosity state, the pulsar MAXI J0655-013 might be accreting from the cold disc.
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