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The rise of the black hole X-ray binary AT2019wey observed with TESS

Alyana Jusino, Kishalay De, Andrea Antoni

Abstract

Black hole X-ray binaries (BHXRBs) have traditionally been discovered by X-ray surveys with cadences of hours to days. However, large optical time-domain surveys now provide novel avenues for early detection and insights into their elusive outburst triggering mechanisms. We present early-time light curves of the BHXRB AT 2019wey serendipitously observed by the Transiting Exoplanet Survey Satellite (TESS). The TESS images are sampled at 30 minute cadence from $\approx2$ d prior to $\approx25$ d after outburst, providing the highest time resolution optical rising phase observations of any known BHXRB. We fit a piece-wise power law to the rising light curve, finding an outburst onset time of MJD $58817.86\pm0.09$ and power-law rise index $n=0.74\pm0.04$. The onset time precedes all ground-based optical detections, and suggests that the optical rise began after the start of the faint X-ray brightening in MAXI data. We search for periodic high frequency modulation and detect none exceeding amplitude $\approx0.48$ mJy at periods of $\gtrsim1$ h at 90% confidence.

The rise of the black hole X-ray binary AT2019wey observed with TESS

Abstract

Black hole X-ray binaries (BHXRBs) have traditionally been discovered by X-ray surveys with cadences of hours to days. However, large optical time-domain surveys now provide novel avenues for early detection and insights into their elusive outburst triggering mechanisms. We present early-time light curves of the BHXRB AT 2019wey serendipitously observed by the Transiting Exoplanet Survey Satellite (TESS). The TESS images are sampled at 30 minute cadence from d prior to d after outburst, providing the highest time resolution optical rising phase observations of any known BHXRB. We fit a piece-wise power law to the rising light curve, finding an outburst onset time of MJD and power-law rise index . The onset time precedes all ground-based optical detections, and suggests that the optical rise began after the start of the faint X-ray brightening in MAXI data. We search for periodic high frequency modulation and detect none exceeding amplitude mJy at periods of h at 90% confidence.

Paper Structure

This paper contains 4 sections, 1 equation, 1 figure.

Table of Contents

  1. INTRODUCTION
  2. OBSERVATIONS AND DATA ANALYSIS
  3. RESULTS AND CONCLUSION
  4. ACKNOWLEDGMENTS

Figures (1)

  • Figure 1: Optical rise of AT 2019wey observed by TESS overlaid with Yao_2020 model. ( Top panel) Reduced TESS light curve of the AT 2019wey outburst observed in Sector 19. Gray dots are individual measurements from difference imaging on the TESS full-frame images, with the red being the power-law rise model. The red line is the best-fit piecewise power-law function fit to the rising light curve. The green shaded region indicates the best-fit MAXI X-ray evolution found by Yao_2021. ( Bottom left panel) Residuals of the TESS data after subtracting the best-fit model (red dashed line centered at zero) for the light curve rise. The gray shaded region shows the $\pm 1\sigma$ standard deviation of the residuals. ( Bottom right) Lomb-Scargle periodogram of the residuals shown in the bottom left panel.