B. C. Joshi

A double-pulsar system: A rare laboratory for relativistic gravity and plasma physics

The clocklike properties of pulsars moving in the gravitational fields of their unseen neutron-star companions have allowed unique tests of general relativity and provided evidence for gravitational radiation. We report here the detection of the 2.8-second pulsar J0737–3039B as the companion to the 23-millisecond pulsar J0737–3039A in a highly relativistic double neutron star system, allowing unprecedented tests of fundamental gravitational physics. We observed a short eclipse of J0737–3039A by J0737–3039B and orbital modulation of the flux density and the pulse shape of J0737–3039B, probably because of the influence of J0737–3039As energy flux on its magnetosphere. These effects will allow us to probe magneto-ionic properties of a pulsar magnetosphere.

The double pulsar system J0737-3039: Modulation of a by B at eclipse

We have investigated the eclipse of the 23 ms pulsar, PSR J0737-3039A, by its 2.8 s companion PSR J0737-3039B in the recently discovered double pulsar system using data taken with the Green Bank Telescope at 820 MHz. We find that the pulsed flux density at eclipse is strongly modulated with the periodicity of the 2.8 s pulsar. The eclipse occurs earlier and is deeper at those rotational phases of B when its magnetic axis is aligned with the line of sight than at phases when its magnetic axis is at right angles to the line of sight. This is consistent with the eclipse of A being due to synchrotron absorption by the shock-heated plasma surrounding B, the asymmetry arising from the higher plasma densities expected in the B magnetospheres polar cusps.

The Drifting Behavior of PSR B0031–07

The drifting behavior of PSR B0031-07 is studied using 40,205 periods of high-quality data obtained with the Ooty Radio Telescope, operating at 327 MHz. We confirm the three drift modes centered at slope α = -4.05, -7.78, and -11.46 ms period-1, in the proportion 15.6%, 81.8%, and 2.6%, respectively. Strictly, the three drift modes are not harmonically related. The average subpulse energy and the rms position of the subpulse about the mean slope are both higher in the dominant drift mode, but the average subpulse width is independent of α. The average subpulse profiles in the three drift modes are consistent with relativistic beaming. The average spacing P2 between two subpulses increases monotonically with | α | , contrary to the belief held so far that it is independent of | α | . The drift rate is enhanced at the edge of the integrated profile, which is apparently expected on the basis of the Ruderman & Sutherland model. The average pulse energy during a null is at least 844 times less than that during a burst. This is much higher than the factor of ≈ 100 that has been quoted so far. The integrated profiles in the three drift modes differ significantly from each other. These results (a) enhance the suspicion that the subpulse is the basic unit of radio emission in pulsars, (b) provide a possible model for mode changing in pulsars.

Long-term variations in the pulse emission from PSR J0737-3039B

Analysis of 20 months of observations at the Parkes radio telescope shows secular changes in the pulsed emission from J0737-3039B, the 2.77 s pulsar of the double-pulsar system. Pulse profiles are becoming single-peaked in both bright phases of the orbital modulation, although there is no clear variation in overall pulse width. The shape of the orbital modulation is also varying systematically, with both bright phases shrinking in longitude by ~7° yr-1. However, the combined span of the two bright phases is relatively constant, and together they are shifting to higher longitudes at a rate of ~3° yr-1. We discuss the possible contributions of geodetic precession and periastron advance to the observed variations.

The Mean Pulse Profile of PSR J0737–3039A

General relativity predicts that the spin axes of the pulsars in the double-pulsar system PSR J0737-3039A/B will precess rapidly, in general leading to a change in the observed pulse profiles. We have observed this system over a 1 yr interval using the Parkes 64 m radio telescope at three frequencies: 680, 1390, and 3030 MHz. These data, combined with the short survey observation made 2 years earlier, show no evidence for significant changes in the pulse profile of PSR J0737-3039A, the 22 ms pulsar. The limit on variations of the profile 10% width is about 050 yr-1. These results imply an angle δ between the pulsar spin axis and the orbit normal of 60°, consistent with recent evolutionary studies of the system. Although a wide range of system parameters remain consistent with the data, the model recently proposed by F. A. Jenet & S. M. Ransom can be ruled out. A nonzero ellipticity for the radiation beam gives slightly but not significantly improved fits to the data, so that a circular beam describes the data equally well within the uncertainties.

The Double Pulsar System J0737–3039: Modulation of the Radio Emission from B by Radiation from A

We have analyzed single pulses from PSR J0737-3039B, the 2.8 s pulsar in the recently discovered double pulsar system, using data taken with the Green Bank Telescope at 820 and 1400 MHz. We report the detection of features similar to drifting subpulses, detectable over only a fraction of the pulse window, with a fluctuation frequency of 0.196 cycles per period. This is exactly the beat frequency between the periods of the two pulsars. In addition, the drifting features have a separation within a given pulse of 23 ms, equal to the pulse period of A. These features are therefore due to the direct influence of J0737-3039As 44 Hz electromagnetic radiation on J0737-3039Bs magnetosphere. We only detect them over a small range of orbital phases, when the radiation from the recycled pulsar J0737-3039A meets our line of sight to J0737-3039B from the side.

Competing Drifting Radio Subpulses in PSR B0031–07

The pair of drifting subpulses of the radio pulsar PSR B0031-07 appear to be well separated from each other on average, overlapping at less than 1/30 of the peak energy. Strictly, the integrated profile of the pair (after removing the drift) does not show more than two subpulses; however, this result is likely to be modified with the availability of more data. On the other hand, rare instances of three simultaneous subpulses in a single period have been noticed. This is consistent with the Ruderman & Sutherland model of the drifting phenomenon in which several sparks, uniformly spaced on a circle, rotate around the polar cap. The third subpulse appears to show up strongly when subpulses belonging to the primary drift bands weaken. Although this conclusion is based mainly on two reliable examples, it suggests an anticorrelation of the subpulse energies. The normalized correlation coefficient between the energies of the two subpulses in a period is -0.16 ± 0.02, after accounting for a known selection effect. Simulations suggest that this result could not be an artifact. This suggests the idea of competing drifting subpulses which, if true, will have important ramifications for the growth and breakdown of the particle acceleration zones in pulsars.

SCATTER BROADENING MEASUREMENTS OF 124 PULSARS AT 327 MHZ

We present the measurements of scatter broadening time-scales (

The very soft X-ray spectrum of the Double Pulsar System J0737-3039

\tau_{sc}

Frequency independent quenching of pulsed emission

) for 124 pulsars at 327 MHz, using the upgraded Ooty Radio Telescope (ORT). These pulsars lie in the dispersion measure range of 37