# How are pulsars detected from Earth?

This paper on Arxiv indicates that the signal period of known pulsars is 1 ms-15 s (0.07-1,000 Hz since F=1/T). I have an EE background and it's a long story how I ended up here, but suffice it to say I'm weak on astronomy.

This chart on Wikipedia implies that the entire range of pulsar frequencies should be absorbed by the atmosphere, but this guide and even this budget RF telescope writeup clearly state that pulsars can be detected from Earth's surface.

My questions is: how are pulsars detected from Earth--what am I missing here? Are RF telescopes simply that receptive? Any insights appreciated.

the signal period of known pulsars is 1 ms-15 s (0.07-1,000 Hz since F=1/T).

That's the frequency of how often the signals occur, not the frequency of the waves they emit. Just compare it to a lighthouse, which has a signal period of a few seconds but a wave frequency of $$10^{15}$$ Hz.

The first known pulsars, for example "Little Green Man" or PSR B1919+21, were radio pulsars; your graph shows those waves are detectable from Earth's surface. I stumbled upon this article which lists the frequency of some of the pulsars:

After the discovery of pulsars at 81.5 MHz (Hewish et al. 1968), the first pulsar detected at 40 MHz was PSR B1133+16 (Arecibo Observatory, 1968, unpublished). In 1969–1970 the pulsars PSR B1133+16 and B0809+74 were detected at 25 MHz (Bruck 1970).

Below is the full detection range for the telescopes:

Therefore joint observations (simultaneous or not) will be highly beneficial, providing a continuous frequency coverage from 8–240 MHz.

which is roughly equivalent to wavelengths of 40m to 1m.

X-ray pulsars like Centaurus X-3 were discovered later, and not by telescopes on the surface:

Centaurus X-3 was first observed during experiments of cosmic X-ray sources made on May 18, 1967. These initial X-ray spectrum and location measurements were performed using a sounding rocket.

• This 100% answers my question. Thanks Glorfindel. – pulsardork May 25 at 17:34
• An additional consideration for radio pulsars: the dispersion delay and broadening of the pulse (and therefore the timing precision) caused by the interstellar plasma scales with frequency^{-2}. This makes higher frequencies better for precise timing and a frequency range is used to estimate the dispersion. See this figure of pulse shapes at different frequencies (from this course which also shows the discovery chart recordings of the pulses from "LGM1" or PSR B1919+21) – astrosnapper May 26 at 4:07