Long-term study of extreme giant pulses from PSR B0950+08 with AARTFAAC

Abstract

We report on the detection of extreme giant pulses (GPs) from one of the oldest-known pulsars, the highly variable PSR B0950+08, with the Amsterdam-ASTRON Radio Transient Facility And Analysis Centre (AARTFAAC), a parallel transient detection instrument operating as a subsystem of the LOw Frequency ARray (LOFAR). During processing of our Northern Hemisphere survey for low-frequency radio transients, a sample of 275 pulses with fluences ranging from 42 to 177 kJy ms were detected in one-second snapshot images. The brightest pulses are an order of magnitude brighter than those previously reported at 42 and 74 MHz, on par with the levels observed in a previous long-term study at 103 MHz. Both their rate and fluence distribution differ between and within the various studies done to date. The GP rate is highly variable, from 0 to 30 per hour, with only two three-hour observations accounting for nearly half of the pulses detected in the 96 h surveyed. It does not vary significantly within a few-hour observation, but can vary strongly one from day to the next. The spectra appear strongly and variably structured, with emission sometimes confined to a single 195.3 kHz subband, and the pulse spectra changing on a timescale of order 10 min.

A Southern-Hemisphere all-sky radio transient monitor for SKA-Low prototype stations

“…This value of corresponds to approximately 360 average pulses (APs) assuming mean flux of 2.37 Jy at 150 MHz (Lorimer et al 1995) and pulsar period s according to the ATNF pulsar catalogue (Manchester et al 2005). This is very similar to the distributions of GP fluences previously reported by Kuiack et al (2020c) and shown in Figure 6 in their paper, where their fitted power law indexes were and at frequency 58.3 MHz and and at 61.8 MHz. In their work, the ‘break fluence’ values were 45 AP fluences at 58.3 MHz and 88 AP fluences at 61.8 MHz.…”

“…The relative rarity of occurrence (3 nights out 24 spread over nearly 6 months) further supports such a conjecture. A similar possibility was also suggested by the recent work of Kuiack et al (2020c).…”

“…The most interesting detections of astrophysical phenomena were extremely bright pulses from the pulsar PSR B0950+08. Similar activity was reported by the AARTFAAC experiment and claimed them to be due to giant pulses similar to those produced by the Crab pulsar (Kuiack et al 2020c). The highest activity of the pulsar was observed during 3 h of the night 2020 April 10/11 when pulses as bright as 150 Jy beam –1 (fluence 300 Jy s beam –1 ) were detected in 2 s images with over 208 and 278 pulses exceeding 5 thresholds of 21 and 18 Jy beam –1 for AAVS2 and EDA2, respectively.…”

“…Interestingly, they were initially discovered in the ‘blind’ search performed on the 2020 April 10/11 dataset. A very similar ‘blind’ detection of extremely bright pulses from PSR B0950+08 was also obtained by the AARTFAAC experiment (Kuiack et al 2020c), where the authors concluded that these are micro-second giant pulses (GPs) similar to those observed in the Crab pulsar (PSR B0531+21 or J0534+2200; Staelin & Reifenstein 1968).…”

“…The extreme brightness of these events, steep slope (fitted power law index ) of the cumulative fluence distribution of the brighter population of transients (fluence 220 Jy s), and rare occurrence (only 3 out of 24 nights spread over nearly 6 months) makes it unlikely to be entirely due to diffractive scintillation and indicates another mechanisms, such as combination of diffractive and refractive scintillation or intrinsic emission mechanisms (e.g. giant pulses as suggested by earlier study by Kuiack et al 2020c). However, we leave further analysis and conclusions to the future publications.…”