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Register a new userThe beam topology and dynamic emission properties of pulsar B0943+10 -- VI. Discovery of a Q-mode precursor and comparison with pulsar B1822-09
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This paper reports new observations of pulsars B0943+10 and B1822--09 carried out with the Arecibo Observatory (AO) and the Giant Metrewave Radio Telescope (GMRT), respectively. Both stars exhibit two stable emission modes. We report the discovery in B0943+10 of a highly linearly polarized precursor component that occurs primarily in only one mode. This emission feature closely resembles B1822-09s precursor which also occurs brightly in only one mode. B0943+10s other mode is well known for its highly regular drifting subpulses that are apparently produced by a rotating carousel system of 20 beamlets. Similary, B1822-09 exhibits subpulse-modulation behavior only in the mode where its precursor is absent. We survey our 18 hours of B0943+10 observations and find that the sideband-modulation features, from which the carousel-rotation time can be directly determined, occur rarely--less than 5% of the time--but always indicating 20 beamlets. We present an analysis of B1822-09s modal modulation characteristics at 325-MHz and compare them in detail with B0943+10. The pulsar never seems to null, and we find a 43-rotation-period feature in the stars Q mode that modulates the interpulse as well as the conal features in the main pulse. We conclude that B1822-09 must have a nearly orthogonal geometry and that its carousel circulation time is long compared to the modal sub-sequences available in our observations, and the mainpulse/interpulse separation is almost exactly 180 degrees. We conclude the precursors for both stars are incompatible with core-cone emission. We assess the interesting suggestion by Dyks et al. that downward-going radiation produces B1822-09s precursor emission.
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The research presented here examines an 8-hour observation of pulsar B1822-09,taken by the Giant Metrewave Radio Telescope. B1822-09 has been known to exhibit two stable emission modes, the B-mode, where the precursor (PC) `turns-on, and the Q-mode, which is defined by interpulse (IP) emission. The results of our analysis, of this extremely long observation, have shown that B1822-09 exhibits at least three other emission behaviors that have not been seen before in other similar pulsars or in other observations of B1822-09. These three behaviors can be described as: Q-mode emission with PC emission, B-mode emission with IP emission, and instances where both the PC and IP are `on when transitioning from one mode to the other. The pulse structure has been found to be more complex than previously thought. The MP has an inner cone/core triple (T) configuration together with a central sightline traverse. The IP is a 15/degr-wide region, that along with the MP originate from an open dipolar field. The PC emission comes from a still unknown source. We argue that the PC emission arises within the same region as the MP, but likely comes from higher in the magnetosphere. Overall, our analyses strongly suggest that mode changes allow information transfer between the two magnetic polar regions and contribute to global magnetospheric changes.
We report analysis of an 8 hr observation of PSR B0943+10 at 325 MHz performed at the Giant Metrewave Radio Telescope (GMRT) in India. B0943+10 is well known for displaying regular sub-pulse drifting and two emission modes. We investigate the modal behavior of B0943+10. By reconstructing an entire B mode from two consecutive B modes, we estimate that the pulsar spends roughly 7.5 hrs in the B mode and about 2.2 hrs in the Q mode, on average. Although the pulsar can switch modes within one pulse, the sub-pulse drift rate changes with a characteristic time of 1.2 hrs over the course of a B mode. Under the subbeam carousel model we find the drift-rate changes are produced by a 10% increase in the average number of subbeams and a 16% increase in the carousel circulation time. We speculate that under the partially screened gap model the increase in circulation time should be related to a small increase in the neutron star surface temperature.
We report on simultaneous X-ray and radio observations of the radio-mode-switching pulsar PSR B1822-09 with ESAs XMM-Newton and the WSRT, GMRT and Lovell radio telescopes. PSR B1822-09 switches between a radio-bright and radio-quiet mode, and we discovered a relationship between the durations of its modes and a known underlying radio-modulation timescale within the modes. We discovered X-ray (energies 0.2-1.4 keV) pulsations with a broad sinusoidal pulse, slightly lagging the radio main pulse in phase by 0.094 +/- 0.017, with an energy-dependent pulsed fraction varying from ~0.15 at 0.3 keV to ~0.6 at 1 keV. No evidence is found for simultaneous X-ray and radio mode switching. The total X-ray spectrum consists of a cool component (T ~ 0.96 x 10^6 K, hot-spot radius R ~ 2.0 km) and a hot component (T ~ 2.2 x 10^6 K, R ~ 100 m). The hot component can be ascribed to the pulsed emission and the cool component to the unpulsed emission. The high-energy characteristics of PSR B1822-09 resemble those of middle-aged pulsars such as PSR B0656+14, PSR B1055-52 and Geminga, including an indication for pulsed high-energy gamma-ray emission in Fermi LAT data. Explanations for the high pulsed fraction seem to require different temperatures at the two poles of this orthogonal rotator, or magnetic anisotropic beaming effects in its strong magnetic field. In the X-ray skymap we found a harder source at only (5.1+/- 0.5 )arcsec from PSR B1822-09, which might be a pulsar wind nebula.
Observations obtained in the last years challenged the widespread notion that rotation-powered neutron stars are steady X-ray emitters. Besides a few allegedly rotation-powered neutron stars that showed magnetar-like variability, a particularly interesting case is that of PSR B0943+10. Recent observations have shown that this pulsar, well studied in the radio band where it alternates between a bright and a quiescent mode, displays significant X-ray variations, anticorrelated in flux with the radio emission. The study of such synchronous radio/X-ray mode switching opens a new window to investigate the processes responsible for the pulsar radio and high-energy emission. Here we review the main X-ray properties of PSR B0943+10 derived from recent coordinated X-ray and radio observations.
PSR J1825$-$0935 (PSR B1822$-$09) switches between radio-quiet (Q-mode) and radio-bright (B-mode) modes. The Q-mode is known to have a periodic fluctuation that modulates both the interpulse and the main pulse with the same period. Earlier investigators argued that the periodic Q-mode modulation is associated with drifting subpulses. We report on single-pulse observations of PSR J1825$-$0935 that were made using the Parkes 64-m radio telescope with a central frequency of 1369 MHz. The high-sensitivity observations revealed that the periodic Q-mode modulation is in fact a periodic longitude-stationary intensity modulation occurring in the interpulse and the main pulse. The fluctuation spectral analysis showed that the modulation period is about $43 P_1$, where $P_1$ is the rotation period of the pulsar. Furthermore, we confirm that the modulation patterns in the interpulse and the main pulse are phase-locked. Specifically, the intensities of the interpulse and the immediately following main pulse are more highly correlated than for the main pulse and interpulse at any other lag. Polarization properties of the strong and weak Q-mode states are different, even for the trailing part of the main pulse which does not show the periodic intensity modulation.
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