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Discovery of a 36-minute long-period transient ASKAP J142431.2-612611

Joshua Pritchard, Tara Murphy, Dougal Dobie, Emil Lenc, Akash Anumarlapudi, Manisha Caleb, Sophia Grainger, Natasha Hurley-Walker, David L. Kaplan, Samuel J. McSweeney, Jackson Mitchell-Bolton, Kovi Rose, Rahul Sengar, Ziteng Wang, Jayde Willingham, Andrew Zic

Abstract

We report the discovery of a new long-period radio transient, ASKAP J142431.2-612611, with a 36 minute period, identified in the Australian SKA Pathfinder Evolutionary Map of the Universe survey. We detected pulsed emission from ASKAP J142431.2-612611 over a period of eight days during follow-up observations with the Australia Telescope Compact Array, after which the source appears to have switched off. No optical or near-infrared counterpart is detected in archival surveys or in targeted Gemini South FLAMINGOS-2 observations. During its active state, the source exhibits a stable pulse profile with fractional polarisation consistent with 100%, evolving from elliptically to linearly polarised and tracing a well-defined great-circle trajectory on the Poincaré sphere. We show that this behaviour is consistent with fully linearly polarised intrinsic emission modified by propagation through a linearly polarised birefringent medium. This discovery expands the known population of long-period transients and highlights the intermittent nature of their activity. We discuss the implications for proposed models of long-period transients and outline future observations needed to constrain the origin of their intermittency and polarisation properties.

Discovery of a 36-minute long-period transient ASKAP J142431.2-612611

Abstract

We report the discovery of a new long-period radio transient, ASKAP J142431.2-612611, with a 36 minute period, identified in the Australian SKA Pathfinder Evolutionary Map of the Universe survey. We detected pulsed emission from ASKAP J142431.2-612611 over a period of eight days during follow-up observations with the Australia Telescope Compact Array, after which the source appears to have switched off. No optical or near-infrared counterpart is detected in archival surveys or in targeted Gemini South FLAMINGOS-2 observations. During its active state, the source exhibits a stable pulse profile with fractional polarisation consistent with 100%, evolving from elliptically to linearly polarised and tracing a well-defined great-circle trajectory on the Poincaré sphere. We show that this behaviour is consistent with fully linearly polarised intrinsic emission modified by propagation through a linearly polarised birefringent medium. This discovery expands the known population of long-period transients and highlights the intermittent nature of their activity. We discuss the implications for proposed models of long-period transients and outline future observations needed to constrain the origin of their intermittency and polarisation properties.
Paper Structure (14 sections, 2 equations, 4 figures, 1 table)

This paper contains 14 sections, 2 equations, 4 figures, 1 table.

Table of Contents

  1. Introduction
  2. Observations and Data Analysis
  3. Detection and radio follow-up
  4. Infrared photometric follow-up
  5. Time-domain analysis
  6. Polarisation properties
  7. Discussion and Conclusions
  8. Radio followup observations
  9. Archival multi-wavelength data
  10. Dispersion modelling
  11. Polarisation modelling on the Poincaré sphere
  12. Poincaré sphere representation
  13. Propagation through a linear birefringent medium
  14. Great circle fitting

Figures (4)

  • Figure 1: $K_s$-band Gemini observation with Stokes $I$ radio contours from ATCA C3363 observation overlaid. The green ellipse indicates the 5$\sigma$ astrometric uncertainty of $0\hbox{$^{\prime\prime}$}9-1\hbox{$^{\prime\prime}$}9$. The positions of catalogued VVV sources are indicated with red markers.
  • Figure 2: Folded pulse profile of 17 pulses detected in ASKAP observation SB70271. Lightcurves are formed from frequency-averaged dynamic spectra binned to $2000$ pulse phase bins, folded at a period of 2147.27s. From bottom to top, panels show full polarisation folded pulse profiles, polarisation position angle, and fractional polarisation. Points in the top two panels are masked below a signal-to-noise ratio (SNR) of $S_I/\sigma_{S_I} < 5$.
  • Figure 3: Time evolution of polarisation state in the ASKAP SB70271 folded pulse profile. Points show a Gnomonic projection of Poincaré sphere normalised by total polarisation $P = \sqrt{Q^2 + U^2 + V^2}$. The red line shows the best linear fit to the projected data, corresponding to a great circle of inclination $31.5 \pm 0.6\deg$ crossing the equator at $64.0 \pm 0.4\deg$ longitude.
  • Figure 4: Lightcurves from all ASKAP, ATCA, and MeerKAT radio observations phase-folded to the radio period of 2147.27s. Green shading indicates the range of uncertainty in predicted pulse time around the expected pulse phase of 0.5. Pulses are only detected in the ASKAP and ATCA observations between 2025-01-09 and 2025-01-17.