arXiv subjects

B. C. Joshi

Publications and source records attributed to B. C. Joshi.

43 records · Page 3Linked to original sources

arXiv2003

An increased estimate of the merger rate of double neutron stars from observations of a highly relativistic system

The merger of close binary systems containing two neutron stars should produce a burst of gravitational waves, as predicted by the theory of general relativity. A reliable estimate of the double-neutron-star merger rate in the Galaxy is crucial in order to predict whether current gravity wave detectors will be successful in detecting such bursts. Present estimates of this rate are rather low, because we know of only a few double-neutron-star binaries with merger times less than the age of the Universe. Here we report the discovery of a 22-ms pulsar, PSR J0737-3039, which is a member of a highly relativistic double-neutron-star binary with an orbital period of 2.4 hours. This system will merge in about 85 Myr, a time much shorter than for any other known neutron-star binary. Together with the relatively low radio luminosity of PSR J0737-3039, this timescale implies an order-of-magnitude increase in the predicted merger rate for double-neutron-star systems in our Galaxy (and in the rest of the Universe).

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arXiv2003

Giant pulses in Millisecond Pulsars

Giant pulses (GPs), occasional individual pulses with an intensity 100 times the average intensity, have been detected in four pulsars todate. Their origin is not well understood, but studies suggest a connection between the strength of magnetic field at the light cylinder B_lc and the existence of GPs. Here, we report on detection of significant Large Amplitude Pulses (LAPs) in two more pulsars with high values of B_lc, PSRs J0218+4232 and B1957+20, observed using Giant Meterwave Radio Telescope (GMRT).

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arXiv2003

The Parkes multibeam pulsar survey: III. Young pulsars & the discovery and timing of 200 pulsars

The Parkes multibeam pulsar survey has unlocked vast areas of the Galactic plane which were previously invisible to earlier low-frequency and less-sensitive surveys. The survey has discovered more than 600 new pulsars so far, including many that are young and exotic. In this paper we report the discovery of 200 pulsars for which we present positional and spin-down parameters, dispersion measures, flux densities and pulse profiles. A large number of these new pulsars are young and energetic, and we review possible associations of $γ$-ray sources with the sample of about 1300 pulsars for which timing solutions are known. Based on a statistical analysis, we estimate that about $19\pm6$ associations are genuine. The survey has also discovered 12 pulsars with spin properties similar to those of the Vela pulsar, nearly doubling the known population of such neutron stars. Studying the properties of all known `Vela-like' pulsars, we find their radio luminosities to be similar to normal pulsars, implying that they are very inefficient radio sources. Finally, we review the use of the newly discovered pulsars as Galactic probes and discuss the implications of the new NE2001 Galactic electron density model for the determination of pulsar distances and luminosities.

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arXiv2003

Observations of fourteen pulsar glitches

About 76 glitches in 25 pulsars have been reported to date. Most glitches are `giant', with fractional increases of frequency dnu_0/nu_0 ~ 10^{-6}. 25 glitches were analysed and presented by Shemar & Lyne (1996) who detected them mainly at Jodrell Bank during the monitoring of a sample of 279 pulsars in a regular timing programme up to MJD 49500. This paper is a continuation of their work up to MJD 50500. We present the detection and analysis of a further 14 glitches in 9 pulsars, 6 of which have glitched for the first time since monitoring had started. Eleven of these glitches are small (dnu_0/nu_0 ~ 10^{-9}) and below the completeness threshold of Shemar and Lyne(1996). We report a giant glitch in PSR B1930+22, the second largest reported hitherto, with a dnu_0/nu_0 = 4.5 x 10^{-6}. We also report four recent glitches in PSR B1737$-$30 which continues to exhibit frequent glitches. Few of these pulsars show any recovery after the glitch.

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arXiv2002

A Very Large Glitch in PSR J1806-2125

PSR J1806-2125 is a pulsar discovered in the Parkes multibeam pulsar survey with a rotational period of 0.4s and a characteristic age of 65kyr. Between MJDs 51462 and 51894 this pulsar underwent an increase in rotational frequency of $Δν/ν\approx 16 \times 10^{-6}$. The magnitude of this glitch is approximately 2.5 times greater than any previously observed in any pulsar and 16 times greater than the mean glitch size. This letter gives the parameters of the glitch and compares its properties to previously observed events. The existence of such large and rare glitches offers new hope for attempts to observe thermal X-ray emission from the internal heat released following a glitch, and suggests that pulsars which previously have not been observed to glitch may do so on long timescales.

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arXiv2001

Young Pulsars from the Parkes Multibeam Pulsar Survey and their Associations

The Parkes multibeam pulsar survey is covering a 10deg-wide strip of the southern Galactic plane from l=260deg to l=50deg. It utilizes a 13-beam receiver operating in the 20-cm band on the Parkes 64-m radio telescope and is much more sensitive than any previous large-scale survey. Most of the 608 pulsars discovered so far are relatively distant and many are young, with 37 having a characteristic age of less than 10^5 years. At least one of these is associated with a supernova remnant and four other probable associations are suggested. Several multibeam pulsars have high values of the parameter Edot/d^2 and are within the position error contours of unidentified EGRET gamma-ray sources. These possible associations will be tested with the advent of new gamma-ray telescopes.

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arXiv1998

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 the average, overlapping at less than one thirtieth 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 and 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 anti correlation of the subpulse energies. The normalised 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 artefact. 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.

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