Wojciech Lewandowski

Pulsars with gigahertz-peaked spectra

Aims: We investigate a high frequency turn-over effect in radio spectra for pulsars with positive or flat spectral index. Methods. Using GMRT and Effelsberg observatory, we estimated the flux density to reconstruct pulsar spectra. Results. We find objects that have a maximum flux in their spectrum above 1 GHz, whose emitted energy decreases below 1 GHz and whose spectral indices are positive at lower frequencies. Some pulsars with a turn-over in their spectrum at high frequencies are found to exist in very interesting environments. We call these objects gigahertz-peaked spectra pulsars.

Pulse broadening analysis for several new pulsars and anomalous scattering

ABSTRACT We show the results of our analysis of the pulse broadening phenomenon in 25 pulsars at sev-eral frequencies using the data gathered with GMRT and Effelsberg radiotelescopes. Twentytwo of these pulsars were not studied in that regard before and our work has increased thetotal number of pulsars with multi-frequency scattering measurements to almost 50, basi-cally doubling the amount available so far. The majority of the pulsars we observed havehigh to very-high dispersion measures (DM > 200) and our results confirm the suggestion ofLo¨hmer et al. (2001, 2004) that the scatter time spectral indices for high-DM pulsars deviatefrom the value predicted by a single thin screen model with Kolmogorov’s distribution of thedensity fluctuations. In this paper we discuss the possible e xplanations for such deviations.Key words: stars: pulsars – general, pulsars – scattering 1 INTRODUCTIONThe existence of the ionized fraction of the Interstellar Medium(ISM) affects the incoming pulsar radiation in several ways. Thefirst order e ffect - the interstellar dispersion - is due to the amountof the free electrons along the line-of-sight, usually quantized bythe Dispersion Measure: DM =R

Observations of four glitches in the young pulsar J1833−1034 and study of its glitch activity

We present the results from timing observations with the GMRT of the young pulsar J1833 1034, in the galactic supernova remnant G21.5 0.9. We detect the presence of 4 glitches in this pulsar over a period of 5.5 years, making it o ne of a set of pulsars that show fairly frequent glitches. The glitch amplitudes, characte rized by the fractional change of the rotational frequency, range from 1 ×10 9 to 7 × 10 9 , with no evidence for any appreciable relaxation of the rotational frequency after the glitches. The fractional changes observed in the frequency derivative are of the order of 10 5 . We show conclusively that, in spite of having significant timing noise, the sudden irregularities lik e glitches detected in this pulsar can not be modeled as smooth timing noise. Our timing solution also provides a stable estimate of the second derivative of the pulsar spin-down model, and a plausible value for the braking index of 1.857, which, like the value for other such young pulsars, is much less than the canonical value of 3.0. PSR J1833 1034 appears to belong to a class of pulsars exhibiting fairly frequent occurrence of low amplitude glitches. This is further supported by an estimate of the glitch activity parameter, Ag = 1.53 × 10 15 s 2 , which is found to be significantly lower than the trend of glitch activity versus characterist ic age (or spin frequency derivative) that a majority of the glitching pulsars follow. We present evidence for a class of such young pulsars, including the Crab, where higher internal temperature of the neutron star could be responsible for the nature of the observed glitch activity.

The analysis of the largest sample of multifrequency pulsar scatter time estimates

We present our results of pulse broadening time estimates and the study of the frequency scaling of this quantity for 60 pulsars based on actual multi-frequency scattering estimates. This research was based on our own measurements, performed on the observational data and the profiles from various pulsar profile databases, as well as the scatter time measurements that were found in the literature. We were able to construct a database of over 60 pulsars with true multi-frequency

Flux-density spectral analysis for several pulsars and two newly identified gigahertz-peaked spectra pulsars

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THERMAL ABSORPTION AS THE CAUSE OF GIGAHERTZ-PEAKED SPECTRA IN PULSARS AND MAGNETARS

measurements, which allowed us to revise the previously proposed relations between the scatter time spectral slope and the dispersion measure (DM). We found that the deviations from theoretical predictions of the value of

Spectrum evolution in binary pulsar B1259−63/LS 2883 Be star and gigahertz‐peaked spectra

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Flux density measurements of gigahertz-peaked spectra candidate pulsars at 610 MHz using an interferometric imaging technique

appear for pulsars regardless of their DM, however the DM-averaged value of the scaling index is almost constant except for pulsars with very high DMs. Based on the obtained slopes we were also able to estimate the amount of scattering at the standard frequency of 1 GHz. We found that while the estimated standardized pulse broadening time increases with DM the relation seems to be much flatter than it was previously proposed, which suggests higher values of the scatter time for mid-DM pulsars, and lower values of expected pulse broadening for highly dispersed sources.

Time variation in the low-frequency spectrum of Vela-like pulsar B1800−21

In this paper, we present results from flux-density measurements for 21 pulsars over a wide frequency range, using the Giant Metrewave Radio Telescope (GMRT) and the Effelsberg telescope. Our sample was a set of mostly newly discovered pulsars from the selection of candidates for gigahertz-peaked spectra (GPS) pulsars. Using the results of our observations along with previously published data, we identify two new GPS pulsars. One of them, PSR J1740+1000, with dispersion measure (DM) of 24 pc cm

Gigahertz-peaked Spectra Pulsars and Thermal Absorption Model

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