The curious DM events of J1713+0747 Fang Xi Lin w/ Michael Lam, - PowerPoint PPT Presentation

The curious DM events of J1713+0747 Fang Xi Lin w/ Michael Lam, Hsiu-Hsien Lin, Jing Luo, Ue-Li Pen, Dana Simard CITA, University of Toronto Data from NANOGrav Collab.

Intro to corrugated sheets Pen & Levin 2014 Simard & Pen 2018

Intro to corrugated sheets Simard & Pen 2018

NANOGrav 12.5y DM timeseries of J1713+0747

NANOGrav 12.5y DM timeseries of J1713+0747

NANOGrav 12.5y DM timeseries of J1713+0747

NANOGrav 12.5y DM timeseries of J1713+0747

Fitting a thin, underdone crest 1st event χ 2 reduced = 1.81

Fitting a thin, underdone crest 1st event 2nd event χ 2 χ 2 reduced = 1.81 reduced = 0.99

Underdense crest predictions • 2 images before crossing the crest: line-of-sight & lensed image • � up to 40% of � μ lensed μ LoS • 1 image after crossing the crest

Underdense crest predictions • If you time-resolve the images, you should see an echo. • If you don’t, they could interfere.

Underdense crest predictions • For an observation ~ 1 month before the 1st event, • For � , we expect an d lens = d psr /2 interference frequency width of � few ∼ hundred kHz, below NANOGrav’s 1.5MHz frequency resolution. • A closer screen would have a larger frequency width, that Michael Lam & NANOGrav collaborators would have detected. • A farther screen would lead to a dimmer lensed image, but larger delay � profile change (pre-crossing) ⇒

SVD Analysis • “Eigendecomposition” of data matrix. • Tailor-made to analyze whether there are profile variations from observation to observation. • We SVD 11.5 years of profiles (separately for each telescope at each observing band), and project out the first two modes.

Greenbank, 1.5GHz MJD MJD Pulse phase Pulse phase Pulse phase Pulse phase

+ Greenbank, 820MHz MJD MJD Pulse phase Pulse phase Pulse phase Pulse phase

+ Arecibo, 1.4GHz MJD MJD Pulse phase Pulse phase Pulse phase Pulse phase

+ Arecibo, 2.0GHz MJD MJD Pulse phase Pulse phase Pulse phase Pulse phase

+ Greenbank, 1.5GHz MJD MJD Pulse phase Pulse phase Pulse phase Pulse phase

+ Greenbank, 820MHz MJD MJD Pulse phase Pulse phase Pulse phase Pulse phase

+ Arecibo, 2.0GHz MJD MJD Pulse phase Pulse phase Pulse phase Pulse phase

+ Arecibo, 1.4GHz MJD MJD Pulse phase Pulse phase Pulse phase Pulse phase

Unlikely to be instrumental effect! MJD MJD Pulse phase Pulse phase Pulse phase Pulse phase

Profile zoom at Arecibo 2.0GHz of the second event Normalized profiles & SVD residuals, pre-dip

Profile zoom at Arecibo 2.0GHz of the second event Normalized profiles & SVD residuals, post-dip

What else can it be?

What else could it be? • Dedispersed to the wrong DM after the the dips. • There’s an echo, but after the dips. • There’s some extra scattering after the dips. • Extra RM and/or leakage to Stokes I

Wrong DM?

Echo?

Extra scattering?

Polarization?

Summary • J1713+0747 crosses 2 events that looks like underdense crests of a corrugated sheet in 12.5 years. • We do not see evidence for a predicted second image pre-crossing, but perhaps we can with better data. • We do see profile shape change post-crossing, which is unexpected, and maybe unexplained by an underdense crest.