An Extreme Scattering Event Toward PSR J2313+4253

TL;DR

The paper addresses how extreme scattering events reveal AU-scale ionized ISM structures by analyzing a high-cadence ESE toward PSR J2313+4253. It combines dynamic spectra, secondary spectra, and scintillation-arc analysis to measure scintillation bandwidths and timescales, estimate screen distances, and detect a detached feature suggesting double-lensing. A Gaussian plasma lens model provides strong statistical support (Bayes factor ≈ $197$) over a pure-noise description, with an inferred lens distance of $1.04$ kpc and a transverse size of about $15.6$ AU over a $220$-day event, including evidence for a second lens. These results demonstrate how ESEs constrain small-scale ISM structures, velocities, and densities, and highlight potential implications for pulsar timing arrays due to scattering-induced timing noise. High-cadence, multi-epoch pulsar scintillation studies therefore offer a powerful probe of the ISM and its impact on precision pulsar timing.

Abstract

We present evidence of an extreme scattering event (ESE) toward PSR J2313+4253 using high-cadence observations taken with the Green Bank Observatory 20m telescope. The high density of observations in time allow for detailed tracking of the event. We observe a pair of caustic spikes along with the characteristic drop in scintillation bandwidth that is expected during an ESE. This pattern implies that the structures predominantly responsible for scattering occur at different distances than those from previous and subsequent epochs. A secondary spectrum processed during the event shows a detached feature similar to those found in double lensing events from previously observed ESEs. We measure this event as originating from a scattering region with a distance of 1.04(1) kpc, a transverse size of 15 AU, and a duration of approximately 220 days. We model the event using a Gaussian plasma lens, which, when compared to a pure-noise model, is 197 times more probable. These rare events provide opportunities to study the properties of small-scale structures in the ISM.

Figures (10)

• Figure 1: A sample dynamic spectrum from MJD 60539 (top), the corresponding 2D ACF (second from top), and the 1D ACFs and fits in frequency (second from bottom) and time (bottom).
• Figure 2: A scintillation arc and its corresponding fit (red) from an observation on MJD 60539. This epoch is after the ESE's conclusion. The color bar represents the logarithmic power in units of dB.
• Figure 3: A time-series of the measured scintillation bandwidths $\Delta \nu_{\rm{d}}$ (top) and timescales $\Delta t_{\rm{d}}$ (bottom). The shaded regions indicate the duration over which the ESE takes place.
• Figure 4: A time-series of the calculated scattering screen distance. $D_{V_{\rm ISS}}$ is calculated using the Lorentzian values for scintillation bandwidth and timescale. $D_{\rm \eta}$ is calculated using the scintillation arc curvature. The ESE takes place in the region shaded in blue.
• Figure 5: A secondary spectrum corresponding to an observation before (top), during (middle), and after (bottom) the ESE. In the observation taken during the event, there is a detached feature from the main arc corresponding to a delay value of 0.6$\mu s$ which is not present in the secondary spectra processed before or after the event. This detached feature resembles those seen in other double lensing events.