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Register a new userEvolution of the X-ray Profile of the Crab Pulsar
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Using the archive data from the Rossi X-ray Timing Explorer ({sl RXTE}), we have studied the evolution of the X-ray profile of the Crab pulsar in a time span of 11 years. The X-ray profiles, as characterized by a few parameters, changed slightly but significantly in these years: the separation of the two peaks increased with a rate $0.88pm0.20,textordmasculine$,per century, the flux ratio of the second pulse to the first pulse decreased with $(3.64pm0.86)times10^{-2}$,per century, and the pulse widths of the two pulses descended with $1.44pm0.15,textordmasculine$, and $1.09pm0.73,textordmasculine$,per century, respectively. The evolutionary trends of the above parameters are similar to the radio results, but the values are different. We briefly discussed the constraints of these X-ray properties on the geometry of the emission region of this pulsar.
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Pulsars are highly-magnetised rotating neutron stars and are well-known for the stability of their signature pulse shapes, allowing high-precision studies of their rotation. However, during the past 22 years, the radio pulse profile of the Crab pulsar has shown a steady increase in the separation of the main pulse and interpulse components at 0.62$^{rm o}pm$0.03$^{rm o}$ per century. There are also secular changes in the relative strengths of several components of the profile. The changing component separation indicates that the axis of the dipolar magnetic field, embedded in the neutron star, is moving towards the stellar equator. This evolution of the magnetic field could explain why the pulsar does not spin down as expected from simple braking by a rotating dipolar magnetic field.
To search for giant X-ray pulses correlated with the giant radio pulses (GRPs) from the Crab pulsar, we performed a simultaneous observation of the Crab pulsar with the X-ray satellite Hitomi in the 2 -- 300 keV band and the Kashima NICT radio observatory in the 1.4 -- 1.7 GHz band with a net exposure of about 2 ks on 25 March 2016, just before the loss of the Hitomi mission.The timing performance of the Hitomi instruments was confirmed to meet the timing requirement and about 1,000 and 100 GRPs were simultaneously observed at the main and inter-pulse phases, respectively, and we found no apparent correlation between the giant radio pulses and the X-ray emission in either the main or inter-pulse phases.All variations are within the 2 sigma fluctuations of the X-ray fluxes at the pulse peaks, and the 3 sigma upper limits of variations of main- or inter- pulse GRPs are 22% or 80% of the peak flux in a 0.20 phase width, respectively, in the 2 -- 300 keV band.The values become 25% or 110% for main or inter-pulse GRPs, respectively, when the phase width is restricted into the 0.03 phase.Among the upper limits from the Hitomi satellite, those in the 4.5-10 keV and the 70-300 keV are obtained for the first time, and those in other bands are consistent with previous reports.Numerically, the upper limits of main- and inter-pulse GRPs in the 0.20 phase width are about (2.4 and 9.3) $times 10^{-11}$ erg cm$^{-2}$, respectively. No significant variability in pulse profiles implies that the GRPs originated from a local place within the magnetosphere and the number of photon-emitting particles temporally increases.However, the results do not statistically rule out variations correlated with the GRPs, because the possible X-ray enhancement may appear due to a $>0.02$% brightening of the pulse-peak flux under such conditions.
During the search for counterparts of very-high-energy gamma-ray sources, we serendipitously discovered large, extended, low surface brightness emission from PWNe around pulsars with the ages up to ~100 kyrs, a discovery made possible by the low and stable background of the Suzaku X-ray satellite. A systematic study of a sample of 8 of these PWNe, together with Chandra datasets, has revealed us that the nebulae keep expanding up to for ~100 kyrs, although time scale of the synchrotron X-ray emission is only ~60 yr for typical magnetic fields of 100 microG. Our result suggests that the accelerated electrons up to ~80 TeV can escape from the PWNe without losing most energies. Moreover, in order to explain the observed correlation between the X-ray size and the pulsar spindwon age, the magnetic field strength in the PWNe must decrease with time.
We present broadband (3 -- 78 keV) NuSTAR X-ray imaging and spectroscopy of the Crab nebula and pulsar. We show that while the phase-averaged and spatially integrated nebula + pulsar spectrum is a power-law in this energy band, spatially resolved spectroscopy of the nebula finds a break at $sim$9 keV in the spectral photon index of the torus structure with a steepening characterized by $DeltaGammasim0.25$. We also confirm a previously reported steepening in the pulsed spectrum, and quantify it with a broken power-law with break energy at $sim$12 keV and $DeltaGammasim0.27$. We present spectral maps of the inner 100as of the remnant and measure the size of the nebula as a function of energy in seven bands. These results find that the rate of shrinkage with energy of the torus size can be fitted by a power-law with an index of $gamma = 0.094pm 0.018$, consistent with the predictions of Kennel and Coroniti (1984). The change in size is more rapid in the NW direction, coinciding with the counter-jet where we find the index to be a factor of two larger. NuSTAR observed the Crab during the latter part of a $gamma$-ray flare, but found no increase in flux in the 3 - 78 keV energy band.
Giant radio pulses (GRPs) are sporadic bursts emitted by some pulsars, lasting a few microseconds. GRPs are hundreds to thousands of times brighter than regular pulses from these sources. The only GRP-associated emission outside radio wavelengths is from the Crab Pulsar, where optical emission is enhanced by a few percent during GRPs. We observed the Crab Pulsar simultaneously at X-ray and radio wavelengths, finding enhancement of the X-ray emission by $3.8pm0.7%$ (a 5.4$sigma$ detection) coinciding with GRPs. This implies that the total emitted energy from GRPs is tens to hundreds of times higher than previously known. We discuss the implications for the pulsar emission mechanism and extragalactic fast radio bursts.
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