Descattering pulsar emission UNIVERSITY OF with giant pulses - - PowerPoint PPT Presentation

Descattering pulsar emission with giant pulses

NIKHIL MAHA JAN

UNIVERSITY OF TORONTO

ADVISOR: MARTEN VAN KERKWIJK

Scattering from the ISM

ISM introduces scattering and scintillation effects. Stronger at low frequencies. Scattering smears away fine structure in pulsar emission.

Fig 1.11 from Handbook of Pulsar Astronomy, by Lorimer and Kramer (2005)

Effects of the ISM

Assume the ISM is a linear and time-invariant filter.

(Over sufficiently short timescales)

𝒊(𝒖) is the impulse response function of the ISM. 𝒚(𝒖) 𝒊(𝒖) 𝒊 𝒖 ∗ 𝒚 𝒖 = 𝒜(𝒖)

Giant Pulses are impulses

An observed giant pulse is a noisy, but direct measurement of the impulse response function at that instant. Signal from a giant pulse prior to scattering. Τ 𝑻 𝑶 = 𝟐𝟏𝟏𝟏 The same giant pulse after scattering.

PSR B1937+21

Brightest millisecond pulsar in the North, also has giant pulses!

PSR B1937+21 for just 2 minutes of observation (275 – 375 MHz at Arecibo)

Let’s descatter!

Here’s 10 seconds of data from PSR B1937+21 (at ~343 MHz)

Let’s descatter!

Here’s 10 seconds of data from PSR B1937+21 (at ~343 MHz)

Giant pulse!

Let’s descatter!

Here’s 10 seconds of data from PSR B1937+21 (at ~343 MHz)

Complex baseband signal

• f the giant pulse

Let’s descatter!

Here’s 10 seconds of data from PSR B1937+21 (at ~343 MHz)

Let’s use this … … To descatter this!

Let’s descatter!

Here’s 10 seconds of data from PSR B1937+21 (at ~343 MHz)

Let’s descatter!

Here’s 10 seconds of data from PSR B1937+21 (at ~343 MHz)

Let’s descatter!

Here’s 10 seconds of data from PSR B1937+21 (at ~343 MHz)

Original giant pulse

Found 8 - 10 giant pulses that weren’t obviously visible before.

Let’s descatter!

Here’s 10 seconds of data from PSR B1937+21 (at ~343 MHz)

Giant pulse has been descattered entirely into a single sample! (< 320 ns)

Can we keep descattering?

Giant pulse!

Can we keep descattering?

Can we keep descattering?

Oh no! It’s the scintillation timescale! A single giant pulse can only take you so far.

Approximating ℎ(𝑢)

One giant pulse Many giant pulses

We can do this recursively!

Use GPs to descatter more nearby GPs and repeat recursively.

Giant pulse!

We can do this recursively!

Use GPs to descatter more nearby GPs and repeat recursively.

We can do this recursively!

Use GPs to descatter more nearby GPs and repeat recursively.

We can do this recursively!

Use GPs to descatter more nearby GPs and repeat recursively.

We can do this recursively!

Use GPs to descatter more nearby GPs and repeat recursively.

We can do this recursively!

Use GPs to descatter more nearby GPs and repeat recursively.

We can do this recursively!

Use GPs to descatter more nearby GPs and repeat recursively.

Now, we have 𝒊(𝒖)

Every GP is a measurement of ℎ(𝑢) at that instant. With many of these, we can model and interpolate ℎ 𝑢 across

• ur entire observation!

“True” Pulse Profile

Fold the descattered signal to get the intrinsic pulse profile.

Modelling the IRF

Taking the Fourier Transform of all giant pulse signals over time, we get a model

• f the impulse response function.

We can infer the IRF at any point in time, with less noise than simply using nearby giant pulses. The model also tells us more about scattering screens in the ISM.

What can we do with this?

Perhaps better pulsar timing? Study pulsar emission phenomena at low 𝜉. Study the interstellar scattering screen. Use with VLBI to extract more information? Downside: Only works on pulsars with giant pulses.