Implications from Late-time X-Ray Detections of Optically Selected Tidal Disruption Events: State Changes, Unification, and Detection Rates

The Astrophysical Journal, vol. 889, pp. 166

Abstract

Abstract We present Chandra X-ray observations of four optically selected tidal disruption events (TDEs) obtained 4–9 yr after discovery. Three sources were detected with luminosities between 9 × 1040 and 3 × 1042 erg s−1. The spectrum of PTF09axc is consistent with a power law of index 2.5 ± 0.1, whereas the spectrum of PTF09ge is very soft. The power-law spectrum of PTF09axc and prior literature findings provide evidence that TDEs transition from an early-time soft state to a late-time hard state many years after disruption. We propose that the time to peak luminosity for optical and X-ray emission may differ substantially in TDEs, with X-rays being produced or becoming observable later. This delay helps explain the differences in observed properties such as L opt/L X of optically and X-ray-selected TDEs. We update TDE rate predictions for the eROSITA instrument: it ranges from 3 to 990 yr−1, depending sensitively on the distribution of black hole spins and the time delay between disruption and peak X-ray brightness. We further predict an asymmetry in the number of retrograde and prograde disks in samples of optically and X-ray-selected TDEs. The details of the observational biases can contribute to observed differences between optically and X-ray-selected TDEs (with optically selected TDEs being fainter in X-rays for retrograde TDE disks).

Authors 5

1. Peter Gustaaf Jonker corresponding Aachen Netherlands Institute for Space Research

   Radboud University Nijmegen · Space Research Organisation Netherlands

   Affiliation as printed

   Department of Astrophysics/IMAPP, Radboud University, P.O. Box 9010, 6500 GL, Nijmegen, The Netherlands

   SRON, Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA, Utrecht, The Netherlands; p.jonker@sron.nl

   SRON, Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA, Utrecht, The Netherlands

2. Nicholas Chamberlain Stone

   University of Maryland, College Park · Hebrew University of Jerusalem · Columbia University

   Affiliation as printed

   Department of Astronomy, University of Maryland, Stadium Drive, College Park, MD 20742-2421, USA

   Department of Physics, Department of Astronomy, and Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, USA

   Racah Institute of Physics, The Hebrew University, Jerusalem, 91904, Israel

3. Aleksey Generozov

   University of Colorado Boulder · Columbia University · National Institute of Standards and Technology · Joint Institute for Laboratory Astrophysics

   Affiliation as printed

   Department of Physics, Department of Astronomy, and Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, USA

   JILA, University of Colorado and National Institute of Standards and Technology, 440 UCB, Boulder, CO 80309-0440, USA

4. Sjoert van Velzen

   University of Maryland, College Park · New York University · Joint Space Science Institute

   Affiliation as printed

   Center for Cosmology and Particle Physics, New York University, New York, NY 10003, USA

   Joint Space-Science Institute, University of Maryland, College Park, MD 20742, USA

5. Brian D. Metzger

   Columbia University

   Affiliation as printed

   Department of Physics, Department of Astronomy, and Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, USA