Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userPulse Fluctuation Properties at 35 MHz
50
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
High time-resolution observations of pulsars were carried out at 35 MHz, using the Gauribidanur Radio Telescope (India), to study the spectra of intrinsic pulse-to-pulse fluctuations. Our sample consists of a few bright pulsars, each of which was observed for $sim$1000~seconds so as to obtain long sequences of single-pulse data. The results, in terms of fluctuation features apparent at this radio frequency, are presented and compared with similar measurements at higher frequencies. We show that the picture of a circulating system of sub-beams emerges naturally from the behaviour apparent even at these long wavelengths.
rate research
Read More
We report preliminary results of our study of linear polarization in the pulsar emission at 35 & 327 MHz. We have exploited for this purpose the spectral modulation resulting from the differential Faraday rotation across the observed band. We discuss the results on a few bright pulsars by comparing them with the existing measurements at higher radio frequencies.
We present 154 MHz Murchison Widefield Array imaging observations and variability information for a sample of pulsars. Over the declination range $-80^{circ} < {delta} < 10^{circ}$ we detect 17 known pulsars with mean flux density greater than 0.3 Jy. We explore the variability properties of this sample on timescales of minutes to years. For three of these pulsars, PSR J0953+0755, PSR J0437-4715 and PSR J0630-2834 we observe interstellar scintillation and variability on timescales of greater than 2 minutes. One further pulsar, PSR J0034-0721, showed significant variability, the physical origins of which are difficult to determine. The dynamic spectra for PSR J0953+0755 and PSR J0437-4715 show discrete time and frequency structure consistent with diffractive interstellar scintillation and we present the scintillation bandwidth and timescales from these observations. The remaining pulsars within our sample were statistically non-variable. We also explore the spectral properties of this sample and find spectral curvature in pulsars PSR J0835-4510, PSR J1752-2806 and PSR J0437-4715.
Over the past years, ultrafast lasers with average powers in the 100 W range have become a mature technology, with a multitude of applications in science and technology. Nonlinear temporal compression of these lasers to few- or even single-cycle duration is often essential, yet still hard to achieve, in particular at high repetition rates. Here we report a two-stage system for compressing pulses from a 1030 nm ytterbium fiber laser to single-cycle durations with 5 ${mu}$J output pulse energy at 9.6 MHz repetition rate. In the first stage, the laser pulses are compressed from 340 to 25 fs by spectral broadening in a krypton-filled single-ring photonic crystal fiber (SR-PCF), subsequent phase compensation being achieved with chirped mirrors. In the second stage, the pulses are further compressed to single-cycle duration by soliton-effect self-compression in a neon-filled SR-PCF. We estimate a pulse duration of ~3.4 fs at the fiber output by numerically back-propagating the measured pulses. Finally, we directly measured a pulse duration of 3.8 fs (1.25 optical cycles) after compensating (using chirped mirrors) the dispersion introduced by the optical elements after the fiber, more than 50% of the total pulse energy being in the main peak. The system can produce compressed pulses with peak powers >0.6 GW and a total transmission exceeding 70%.
We present radio observations of the Moon between $35$ and $80$ MHz to demonstrate a novel technique of interferometrically measuring large-scale diffuse emission extending far beyond the primary beam (global signal) for the first time. In particular, we show that (i) the Moon appears as a negative-flux source at frequencies $35< u<80$ MHz since it is `colder than the diffuse Galactic background it occults, (ii) using the (negative) flux of the lunar disc, we can reconstruct the spectrum of the diffuse Galactic emission with the lunar thermal emission as a reference, and (iii) that reflected RFI (radio-frequency interference) is concentrated at the center of the lunar disc due to specular nature of reflection, and can be independently measured. Our RFI measurements show that (i) Moon-based Cosmic Dawn experiments must design for an Earth-isolation of better than $80$ dB to achieve an RFI temperature $<1$ mK, (ii) Moon-reflected RFI contributes to a dipole temperature less than $20$ mK for Earth-based Cosmic Dawn experiments, (iii) man-made satellite-reflected RFI temperature exceeds $20$ mK if the aggregate cross section of visible satellites exceeds $80$ m$^2$ at $800$ km height, or $5$ m$^2$ at $400$ km height. Currently, our diffuse background spectrum is limited by sidelobe confusion on short baselines (10-15% level). Further refinement of our technique may yield constraints on the redshifted global $21$-cm signal from Cosmic Dawn ($40>z>12$) and the Epoch of Reionization ($12>z>5$).
Recent results regarding subpulse-drift in pulsar B0943+10 have led to the identification of a stable system of sub-beams circulating around the magnetic axis of the star. Here, we present single-pulse analysis of pulsar B0834+06 at 35 MHz, using observations from the Gauribidanur Radio Telescope. Certain signatures in the fluctuation spectra and correlations allow estimation of the circulation time and drift direction of the underlying emission pattern responsible for the observed modulation. We use the `cartographic transform mapping technique to study the properties of the polar emission pattern. These properties are compared with those for the other known case of B0943+10, and the implications are discussed.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
