Ali Esamdin

Timing observations of Rotating Radio Transient J1819-1458 at Urumqi observatory

We report the timing-analysis results obtained for Rotating Radio Transient (RRAT) J1819−1458 from regular timing observations at 1.54 GHz using the Urumqi 25-m radio telescope between 2007 April and 2008 March. RRAT J1819−1458 is a relatively young and highly magnetized neutron star discovered by its sporadic short bursts in the Parkes Multibeam Pulsar Survey data. In 94 h of observation data, we detected a total of 162 dispersed bursts of RRAT J1819−1458 with the signal-to-noise ratios (S/Ns) above 5 σ threshold. Among them, five bursts clearly show two-component structure. The S/N of the strongest burst is 13.3. The source’s DM measured through our data is 196.0 ± 0.4 pc cm −3 . The timing position, frequency and its first derivative were determined using standard pulsar timing techniques on the arrival times of these individual bursts. The accuracy of the solved rotating parameters is improved comparing with that in previous publication. Our timing position with 2σ error is consistent with the position of its X-ray counterpart CXOU J181934.1−145804. The effect of timing noise and the phase fluctuation of the individual short bursts on the timing residuals is briefly discussed. The distribution of the timing residuals is bimodal, which cannot be explained readily by timing irregularity.

PSR B0826-34: SOMETIMES A ROTATING RADIO TRANSIENT

We report on the detection of sporadic, strong single pulses coexisting with a periodic weak emission in the duration of weak mode of PSR B0826-34. The intensities and durations of these pulses are comparable with those of the subpulses in the strong mode, and these pulses are distributed within the phase ranges of the main-pulse and interpulse of the strong-mode average profile. These results suggest that there is very possibly sporadic, very short timescale turn-on of strong-mode emission during the weak-mode state of the pulsar. The emission features of the bursts of strong pulses of PSR B0826-34 during its weak-mode state are similar to those of the rotating radio transients (RRATs). PSR B0826-34 is the second known pulsar, which oscillates between pulsar-like and RRAT-like modes.

Radiation properties of extreme nulling pulsar J1502-5653

We report on radiation properties of extreme nulling pulsar J1502 5653, by analyzing the data acquired from the Parkes 64-m telescope at 1374 MHz. The radio emission from this pulsar exhibits sequences of several tens to several hundreds consecutive burst pulses, separated by null pulses, and the appearance of the emission seems quasi-periodic. The null fraction from the data is estimated to be 93.6%. No emission is detected in the integrated profile of all null pulses. Systematic modulations of pulse intensity and phase are found at the beginning of burst-pulse sequences just after null. The intensity usually rises to a maximum for the first few pulses, then declines exponentially afterwards, and becomes stable after few tens of pulse periods. The peak phase appears at later longitudes for the first pulse, then drifts to earlier longitudes rapidly, and then systematic drifting gradually vanishes while the intensity becomes stable. In this pulsar, the intensity variation and phase modulation of pulses are correlated in a short duration after the emission starts following a null. Observed properties of the pulsar are compared with other nulling pulsars published previously, and the possible explanation for phase modulation is discussed.

A study of the long-term flux density variation of PSRs B0329+54 and B1508+55

We have observed the flux densities of PSRs B0329+54 and B1508+55 for 460 days at 327 MHz using the 25 m telescope of NAOC Urumqi Observatory. The flux density time series and the corresponding structure functions are presented. Our observational results at 327 MHz and other observations at 74 MHz and 610 MHz are compared with the predictions of the refractive scintillation theory. The frequency dependence of the refractive scintillation parameters for PSR B0329+54 has been investigated. The results show that the long-term flux density modulations of PSR B0329+54 at the three frequencies are best described by a Kolmogorov spectrum for electron density inhomogeneities. For PSR B 1508+55, we suggest that the spectrum of the electron density fluctuation has a power exponent beta<4.

Two-component model for the interstellar scattering in direction to the Vela pulsar

This paper discusses a rigorous treatment of the refractive scintillation of pulsar PSR B0833-45 caused by a two-component interstellar scattering medium. It is assumed that the interstellar scattering medium is composed of a thin screen ISM and an extended interstellar medium. We consider that the scattering of the thin screen concentrates in a thin layer presented by a delta function distribution and that the scattering density of the extended irregular medium satisfies the Gaussian distribution. We investigate and develop equations for the flux density structure function corresponding to this two-component ISM geometry in the scattering density distribution and compare our result with that of the Vela pulsar observations. We conclude that the refractive scintillation caused by this two-component ISM scattering gives a more satisfactory explanation for the observed flux density variation of the Vela pulsar than does the single extended medium model. The level of refractive scintillation is strongly sensitive to the distribution of scattering material along the line of sight. The logarithmic slope of the structure function is sensitive to thin screen location and is relatively insensitive to the scattering strength of the thin screen medium. Therefore, the proposed model can be applied to interpret the structure function of flux density observed in pulsar PSR B0833-45. The result suggests that the medium consists of a discontinuous distribution of plasma turbulence embedded in the Vela supernova remnant. Thus our work provides some insight into the distribution of the scattering along the line of sight to the Vela pulsar.

Refractive Interstellar Scintillation for Flux Density Variations of Two Pulsars

The flux density structure functions of PSRs B0525+21 and B2111+46 are calculated with the refractive interstellar scintillation (RISS) theory. The theoretical curves are in good agreement with observations [Astrophys. J. 539 (2000) 300] (hereafter S2000). The spectra of the electron density fluctuations both are of Kolmogorov spectra. We suggest that the flux density variations observed for these two pulsars are attributed to refractive interstellar scintillation, not to intrinsic variability.

A study of variable stars in the open cluster NGC 1582 and its surrounding field

This paper presents the Charge-Coupled Device time-series photometric observations of the open cluster NGC 1582 and its surrounding field with Johnson B, V and R filters by using Nanshan 1m telescope of Xinjiang Astronomical Observatory. 19 variable stars and 3 variable candidates were detected in a 45 {\times} 48.75 field around the cluster. 12 of the variable stars are newly-discovered variable objects. The physical properties, classifications, and membership of the 22 objects are studied through their light curves, their positions on the color-magnitude diagram, and with the archival data from the Naval Observatory Merged Astrometric Dataset. Among these objects, 5 are eclipsing binary systems, 6 are pulsating variable stars including one known Delta Scuti star and one newly-discovered RR Lyrae star. The distance of the RR Lyrae star is estimated to be 7.9 {\pm} 0.3 kpc, indicates that the star locates far behind the cluster. 4 variable stars are probable members of the cluster, and 13 of the 22 objects are confirmed to be field stars.

Strong pulses detected from rotating radio transient J1819 − 1458

Aims. We analyze individual pulses detected from RRAT J1819-1458. Methods. From April 2007 to April 2010, we carried out observations using the Nanshan 25-m radio telescope of Urumqi Observatory at a central frequency of 1541.25 MHz. Results. We obtain a dispersion measure DM = 195.7 +/- 0.3 pc cm(-3) by analyzing all the 423 detected bursts. The tri-band pattern of arrival time residuals is confirmed by a single pulse timing analysis. Twenty-seven bimodal bursts located in the middle residual band are detected, and, profiles of two typical bimodal bursts and two individual single-peak pulses are presented. We determine the statistical properties of SNR and W-50 of bursts in different residual bands. The W50 variation with SNR shows that the shapes of bursts are quite different from each other. The cumulative probability distribution of intensity for a possible power law with index alpha = 1.6 +/- 0.2 is inferred from the number of those bursts with SNR >= 6 and high intensities.

A study of the strong pulses detected from PSR B0656+14 using the Urumqi 25-m radio telescope at 1540 MHz

We report on the properties of strong pulses from PSR B0656+14 by an- alyzing the data obtained using the Urumqi 25-m radio telescope at 1540 MHz from August 2007 to September 2010. In 44 h of observational data, a total of 67 pulses with signal-to-noise ratios above a 5ae threshold were detected. The peak flux den- sities of these pulses are 58 to 194 times that of the average profile, and their pulse energies are 3 to 68 times that of the average pulse. These pulses are clustered around phases about 5 - ahead of the peak of the average profile. Compared with the width of the average profile, they are relatively narrow, with the full widths at half-maximum ranging from 0.28 - to 1.78 - . The distribution of pulse-energies follows a lognormal distribution. These sporadic strong pulses detected from PSR B0656+14 have different characteristics from both typical giant pulses and its regular pulses.

Recovering the pulse profiles and polarization position angles of some pulsars from interstellar scattering

Interstellar scattering causes broadening and distortion in the mean pulse profiles and polarization position angle (PPA) curves of pul sars, especially pulse pro- files observed at lower frequencies. This paper implements a method to recover the pulse profiles and PPA curves of five pulsars which have obviou s scattered pulse pro- files at lower frequency. It reports a simulation to show the s cattering and descatter- ing of pulse profiles and PPA curves, and as a practical applic ation the lower fre- quency profiles and PPA curves of PSR 1356 −60, PSR 1831−03, PSR 1838+04, PSR 1859+03 and PSR 1946+35 are obtained. It is found that the original pulse profiles and PPA curves can be recovered.