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Register a new userThe two emission states of PSR B1534+12
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We have observed PSR~B1534+12 (J1537+1155), a pulsar with a neutron star companion, using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). We found that this pulsar shows two distinct emission states: a weak state with a wide pulse profile and a burst state with a narrow pulse profile. The weak state is always present. We cannot, with our current data, determine whether the pulse energy of the weak state follows a normal or a log-normal distribution. The burst state energy distribution follows a power-law. The amplitude of the single pulse emission in the burst state varies significantly; the peak flux intensity of the brightest pulse is 334 times stronger than that of the average pulse. We also examined the timing precision achievable using only bright pulses, which showed no demonstrable improvement because of pulse jitter and therefore quantified the jitter noise level for this pulsar.
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We have recently measured the angle between the spin and orbital angular momenta of PSR B1534+12 to be either 25+/-4 deg or 155+/-4 deg. This misalignment was almost certainly caused by an asymmetry in the supernova explosion that formed its companion neutron star. Here we combine the misalignment measurement with measurements of the pulsar and companion masses, the orbital elements, proper motion, and interstellar scintillation. We show that the orbit of the binary in the Galaxy is inconsistent with a velocity kick large enough to produce a nearly antialigned spin axis, so the true misalignment must be ~25 deg. Similar arguments lead to bounds on the mass of the companion star immediately before its supernova: 3+/-1 Msun. The result is a coherent scenario for the formation of the observed binary. After the first supernova explosion, the neutron star that would eventually become the observed pulsar was in a Be/X-ray type binary system with a companion of at least 10--12 Msun. During hydrogen (or possibly helium) shell burning, mass transfer occurred in a common envelope phase, leaving the neutron star in a roughly half-day orbit with a helium star with mass above ~3.3 Msun. A second phase of mass transfer was then initiated by Roche lobe overflow during shell helium burning, further reducing both the helium star mass and orbital period before the second supernova. Scenarios that avoid Roche lobe overflow by the helium star require larger helium star masses and predict space velocities inconsistent with our measurements. The companion neutron star experienced a velocity kick of 230+/-60 km/s at birth, leading to a systemic kick to the binary of 180+/-60 km/s.
The emission from PSR J1107-5907 is erratic. Sometimes the radio pulse is undetectable, at other times the pulsed emission is weak, and for short durations the emission can be very bright. In order to improve our understanding of these state changes, we have identified archival data sets from the Parkes radio telescope in which the bright emission is present, and find that the emission never switches from the bright state to the weak state, but instead always transitions to the off state. Previous work had suggested the identification of the off state as an extreme manifestation of the weak state. However, the connection between the off and bright emission reported here suggests that the emission can be interpreted as undergoing only two emission states: a bursting state consisting of both bright pulses and nulls as well as the weak-emission state.
We present analysis of the timing noise in PSR J1733-3716, which combines data from Parkes 64-m radio telescope and nearly 15 years of timing data obtained from the Nanshan 25-m radio telescope. The variations in the spin frequency and frequency derivative are determined. The fluctuation in the spin frequency is obvious with an amplitude of 1.94(7)*10 -9 Hz. Variations of the integrated profile at 1369 MHz are detected with the changes occur in the relative peak intensity from the right profile component. From analysis of the single pulse data at 1382 MHz, we detect weak emission states that account for 63% of the whole data, and its duration distribution can be fitted with a power law. The pulsar also exhibits strong emission states, during which the emission shows multiple modes. This includes the normal mode, left mode and the right mode, with the time scales spanning between one and seventeen pulse periods. Such short term variability in pulses contributes to the variation of the integrated profile. Examination of the correlations between the spin parameters and the integrated profiles shows likelihood of a random distribution, which reveals that there is probably no obvious relationship between spin-down rate variations and changes of emission in this pulsar.
We present a hard X-ray NuSTAR observation of PSR J0437-4715, the nearest millisecond pulsar. The known pulsations at the apparent pulse period ~5.76 ms are detected at energies up to 20 keV. We measure a photon index $Gamma= 1.65pm0.24$ (90% confidence) for the power law fit to the non-thermal emission. It had been shown that spectral models with two or three thermal components fit the XMM-Newton spectrum of PSR J0437-4715, depending on the slope of the power-law component, and the amount of absorption of soft X-rays. The new constraint on the high-energy emission provided by NuSTAR removes ambiguities regarding the thermal components of the emission below 3 keV. We performed a simultaneous spectral analysis of the XMM-Newton and NuSTAR data to confirm that three thermal components and a power law are required to fit the 0.3-20 keV emission of PSR J0437-4715. Adding a ROSAT-PSPC spectrum further confirmed this result and allowed us to better constrain the temperatures of the three thermal components. A phase-resolved analysis of the NuSTAR data revealed no significant change in the photon index of the high-energy emission. This NuSTAR observation provides further impetus for future observations with the NICER mission (Neutron Star Interior Composition Explorer) whose sensitivity will provide much stricter constraints on the equation of state of nuclear matter by combining model fits to the pulsars phase-folded lightcurve with the pulsars well-defined mass and distance from radio timing observations.
We analyzed a deep {it XMM-Newton} observation of the radio-quiet $gamma$-ray PSR J2055+2539. The spectrum of the X-ray counterpart is non-thermal, with a photon index of $Gamma$=2.36$pm$0.14 (1$sigma$ confidence). We detected X-ray pulsations with a pulsed fraction of (25$pm$3)% and a sinusoidal shape. Taking into account considerations on the $gamma$-ray efficiency of the pulsar and on its X-ray spectrum, we can infer a pulsar distance ranging from 450 pc to 750 pc. We found two different nebular features associated to PSR J2055+2539 and protruding from it. The angle between the two nebular main axes is $sim$ (162.8$pm$0.7)$^{circ}$. The main, brighter feature is 12 long and $<$20 thick, characterized by an asymmetry with respect to the main axis that evolves with the distance from the pulsar, possibly forming a helical pattern. The secondary feature is 250 $times$ 30. Both nebulae present an almost flat brightness profile with a sudden decrease at the end. The nebulae can be fitted either by a power-law model or a thermal bremsstrahlung model. A plausible interpretation of the brighter nebula is in terms of a collimated ballistic jet. The secondary nebula is most likely a classical synchrotron-emitting tail.
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