A Giant Sample of Giant Pulses From the Crab Pulsar

Abstract

We observed the Crab pulsar with the 43 m telescope in Green Bank, WV over a timespan of 15 months. In total we obtained 100 hr of data at 1.2 GHz and seven hours at 330 MHz, resulting in a sample of about 95,000 giant pulses (GPs). This is the largest sample, to date, of GPs from the Crab pulsar taken with the same telescope and backend and analyzed as one data set. We calculated power-law fits to amplitude distributions for main pulse (MP) and interpulse (IP) GPs, resulting in indices in the range of 2.1-3.1 for MP GPs at 1.2 GHz and in the range of 2.5-3.0 and 2.4-3.1 for MP and IP GPs at 330 MHz. We also correlated the GPs at 1.2 GHz with GPs from the Robert C. Byrd Green Bank Telescope (GBT), which were obtained simultaneously at a higher frequency (8.9 GHz) over a span of 26 hr. In total, 7933 GPs from the 43 m telescope at 1.2 GHz and 39,900 GPs from the GBT were recorded during these contemporaneous observations. At 1.2 GHz, 236 (3%) MP GPs and 23 (5%) IP GPs were detected at 8.9 GHz, both with zero chance probability. Another 15 (4%) low-frequency IP GPs were detected within one spin period of high-frequency IP GPs, with a chance probability of 9%. This indicates that the emission processes at high and low radio frequencies are related, despite significant pulse profile shape differences. The 43 m GPs were also correlated with Fermi γ -ray photons to see if increased pair production in the magnetosphere is the mechanism responsible for GP emission. A total of 92,022 GPs and 393 γ -ray photons were used in this correlation analysis. No significant correlations were found between GPs and γ -ray photons. This indicates that increased pair production in the magnetosphere is likely not the dominant cause of GPs. Possible methods of GP production may be increased coherence of synchrotron emission or changes in beaming direction.

Spectral Flattening at Low Frequencies in Crab Giant Pulses

“…Our results in terms ofβ for the two Parkes subbands are within the range of those reported by Mickaliger et al (2012) between 330 and 1200 MHz (β MP ∼ 2.1-3.1, β IP ∼ 2.4-3.1), but steeper than reported by Bhat et al (2008) between 1300 and 1470 MHz (β = 2.33 ± 0.15, where the MP and IP are combined), except in the case of our 3100 MHz Parkes IP exponent. For the MWA subbands, results are typically steeper than the estimated value at 325 MHz (β MP = 2.61±0.14,β IP = 2.7±0.7) reported by Mikami et al (2016), and are also steeper than the slopes calculated by Karuppusamy et al (2010) between 110-180 MHz (β MP ∼ 1.5-2.4,β IP ∼ 0.7-2.7, with errors typically around ±0.1 for main pulses and ±0.5 for interpulses).…”

Transient Events in Archival Very Large Array Observations of the Galactic Center

“…These pulses are incredibly bright, with observed peak flux densities as high as 2.2 MJy in less than 0.9 ns (Hankins & Eilek 2007). Much work has been done characterizing the Crab giant pulses, which seem to follow a power-law distribution in amplitude (Lundgren et al 1995;Bhat et al 2008;Majid et al 2011;Mickaliger et al 2012). Most studies report the index for the differential power-law amplitude distribution, n(S) ∝ S −γ , which gives the number of pulses within some amplitude bin.…”

“…Most studies report the index for the differential power-law amplitude distribution, n(S) ∝ S −γ , which gives the number of pulses within some amplitude bin. Measurements of the index range from 2 γ 4 for observing frequencies from ν obs = 0.1 − 4 GHz (Mickaliger et al 2012, and reference therein). Since the intrinsic widths of Crab giant pulses can be smaller than the instrumental resolution, the observed peak flux density is often less than the intrinsic value.…”

The Galactic Millisecond Pulsar Population

“…The z distribution was motivated by my earlier results (Lorimer 1995) based on the low-frequency surveys. † Data analysis by the Einstein@Home team has so far discovered 23 sources including one highly dispersed millisecond pulsar, while Mickaliger et al (2012) have recently announced the discovery of five further millisecond pulsars. Mean of log-normal reduced to -1.2 -2.1 1.3 36,000 C Uniform surface density over the disk -7.1 2.8 2,670 D Cordes & Chernoff (1998) spin period distribution -12.8…”

“…In addition, multiple analyses of the data often result in additional discoveries (e.g. Keith et al 2009;Eatough et al 2010;Mickaliger et al 2012).…”