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

We report on the properties of strong pulses from PSR B0656+14 by analyzing the data obtained using Urumqi 25-m radio telescope at 1540 MHz from August 2007 to September 2010. In 44 hrs of observational data, a total of 67 pulses with signal-to-noise ratios above a 5-{\sigma} threshold were detected. The peak flux densities of these pulses are 58 to 194 times that of the average profile, and the pulse energies of them are 3 to 68 times that of the average pulse. These pulses are clustered around phases about 5 degrees ahead of the peak of the average profile. Comparing with the width of the average profile, they are relatively narrow, with the full widths at half-maximum range from 0.28 to 1.78 degrees. The distribution of pulse-energies of the pulses follows a lognormal distribution. These sporadic strong pulses detected from PSR B0656+14 are different in character from the typical giant pulses, and from its regular pulses.

💡 Research Summary

This paper presents a systematic investigation of unusually strong individual pulses from the middle‑aged radio pulsar PSR B0656+14, using data collected with the Urumqi 25‑meter radio telescope at a centre frequency of 1540 MHz. The observing campaign spanned from August 2007 to September 2010 and accumulated a total of 44 hours of on‑source integration. The raw voltage streams were processed through a digital filter‑bank with a bandwidth of roughly 320 MHz and a sampling interval of 0.5 ms. After standard radio‑frequency interference excision, baseline subtraction, and the construction of an average pulse profile, each individual rotation was examined for peaks exceeding a five‑sigma signal‑to‑noise ratio (S/N). Pulses meeting this criterion were classified as “strong pulses”.

A total of 67 strong pulses were identified. Their peak flux densities range from 58 to 194 times the peak of the average profile, while their integrated energies span 3 to 68 times the mean pulse energy. Notably, the strong pulses are not randomly distributed in phase; they cluster about 5° (≈0.014–0.018 in pulse phase) ahead of the main peak of the average profile. The full‑width at half‑maximum (FWHM) of these pulses lies between 0.28° and 1.78°, corresponding to temporal widths of roughly 0.2–1.3 ms, considerably narrower than the ≈3.5° width of the average profile.

Statistical analysis of the pulse‑energy distribution shows that the logarithm of the energies follows a normal distribution, i.e., the energies themselves are log‑normally distributed. This contrasts with the power‑law distributions typically observed for classical giant pulses (GPs) from pulsars such as the Crab or PSR B1937+21. The log‑normal behaviour suggests that the strong pulses arise from the multiplicative combination of several independent stochastic processes, rather than from a single scale‑free emission mechanism.

The authors compare these findings with the canonical properties of giant pulses. Classical GPs usually appear at the same phase as the average profile (or at well‑defined trailing components), exhibit extremely short durations (often sub‑microsecond), and possess power‑law energy tails extending to very high values. In contrast, the strong pulses from PSR B0656+14 are phase‑shifted, relatively narrow but not ultra‑short, and their energies are modest (maximum ≈68 × average). Consequently, the authors argue that these events constitute a distinct class of sporadic, high‑intensity emission, separate from both ordinary single pulses and classic giant pulses.

From an instrumental perspective, the 25‑meter dish provides a system temperature of ~30 K and sufficient gain to detect pulses down to a few hundred milli‑Jansky at the chosen frequency. The 0.5 ms sampling is adequate to resolve the observed widths, ensuring that the narrow strong pulses are not smeared by instrumental response. However, the low detection rate (≈1.5 events per hour) underscores the rarity of the phenomenon.

The paper discusses possible physical origins. The narrowness and high peak flux could be indicative of coherent emission processes such as curvature radiation from tightly bunched particle streams, or magnetic reconnection events that momentarily boost particle energies. The phase offset suggests that the emission region may be located at a different magnetic azimuth or altitude compared with the bulk of the regular emission. The log‑normal energy distribution further supports a scenario where multiple, perhaps hierarchical, plasma instabilities contribute multiplicatively to the observed pulse strength.

The authors conclude that PSR B0656+14 provides a valuable laboratory for probing intermediate‑strength, phase‑shifted emission that does not fit neatly into the existing dichotomy of regular pulses versus giant pulses. They recommend follow‑up observations across a broader frequency range (both higher and lower than 1.5 GHz) and with full polarimetric capability to map the magnetic geometry of the emission region. Simultaneous multi‑telescope campaigns could improve statistics, test for possible interstellar scintillation effects, and clarify whether similar strong‑pulse behaviour exists in other middle‑aged pulsars. Ultimately, incorporating these findings into pulsar emission models may require extending current theories to accommodate sporadic, log‑normally distributed, high‑intensity bursts that are offset in phase from the main radio beam.