skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Optical/UV-to-X-Ray Echoes from the Tidal Disruption Flare ASASSN-14li

Abstract

We carried out the first multi-wavelength (optical/UV and X-ray) photometric reverberation mapping of a tidal disruption flare (TDF) ASASSN-14li. We find that its X-ray variations are correlated with and lag the optical/UV fluctuations by 32 ± 4 days. Based on the direction and the magnitude of the X-ray time lag, we rule out X-ray reprocessing and direct emission from a standard circular thin disk as the dominant source of its optical/UV emission. The lag magnitude also rules out an AGN disk-driven instability as the origin of ASASSN-14li and thus strongly supports the tidal disruption picture for this event and similar objects. We suggest that the majority of the optical/UV emission likely originates from debris stream self-interactions. Perturbations at the self-interaction sites produce optical/UV variability and travel down to the black hole where they modulate the X-rays. The time lag between the optical/UV and the X-rays variations thus correspond to the time taken by these fluctuations to travel from the self-interaction site to close to the black hole. We further discuss these time lags within the context of the three variants of the self-interaction model. High-cadence monitoring observations of future TDFs will be sensitive enough to detect these echoes and wouldmore » allow us to establish the origin of optical/UV emission in TDFs in general.« less

Authors:
;  [1]; ;  [2];  [3];  [4];  [5]
  1. Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)
  2. NASA’s Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
  3. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)
  4. Columbia University, New York, NY 10027 (United States)
  5. The Johns Hopkins University, Baltimore, MD 21218 (United States)
Publication Date:
OSTI Identifier:
22654515
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 837; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; BLACK HOLES; DISTURBANCES; EMISSION; FLUCTUATIONS; INSTABILITY; INTERACTIONS; PERTURBATION THEORY; REPROCESSING; STREAMS; WAVELENGTHS; X RADIATION

Citation Formats

Pasham, Dheeraj R., Sadowski, Aleksander, Cenko, S. Bradley, Cannizzo, John K., Guillochon, James, Stone, Nicholas C., and Velzen, Sjoert van. Optical/UV-to-X-Ray Echoes from the Tidal Disruption Flare ASASSN-14li. United States: N. p., 2017. Web. doi:10.3847/2041-8213/AA6003.
Pasham, Dheeraj R., Sadowski, Aleksander, Cenko, S. Bradley, Cannizzo, John K., Guillochon, James, Stone, Nicholas C., & Velzen, Sjoert van. Optical/UV-to-X-Ray Echoes from the Tidal Disruption Flare ASASSN-14li. United States. doi:10.3847/2041-8213/AA6003.
Pasham, Dheeraj R., Sadowski, Aleksander, Cenko, S. Bradley, Cannizzo, John K., Guillochon, James, Stone, Nicholas C., and Velzen, Sjoert van. Fri . "Optical/UV-to-X-Ray Echoes from the Tidal Disruption Flare ASASSN-14li". United States. doi:10.3847/2041-8213/AA6003.
@article{osti_22654515,
title = {Optical/UV-to-X-Ray Echoes from the Tidal Disruption Flare ASASSN-14li},
author = {Pasham, Dheeraj R. and Sadowski, Aleksander and Cenko, S. Bradley and Cannizzo, John K. and Guillochon, James and Stone, Nicholas C. and Velzen, Sjoert van},
abstractNote = {We carried out the first multi-wavelength (optical/UV and X-ray) photometric reverberation mapping of a tidal disruption flare (TDF) ASASSN-14li. We find that its X-ray variations are correlated with and lag the optical/UV fluctuations by 32 ± 4 days. Based on the direction and the magnitude of the X-ray time lag, we rule out X-ray reprocessing and direct emission from a standard circular thin disk as the dominant source of its optical/UV emission. The lag magnitude also rules out an AGN disk-driven instability as the origin of ASASSN-14li and thus strongly supports the tidal disruption picture for this event and similar objects. We suggest that the majority of the optical/UV emission likely originates from debris stream self-interactions. Perturbations at the self-interaction sites produce optical/UV variability and travel down to the black hole where they modulate the X-rays. The time lag between the optical/UV and the X-rays variations thus correspond to the time taken by these fluctuations to travel from the self-interaction site to close to the black hole. We further discuss these time lags within the context of the three variants of the self-interaction model. High-cadence monitoring observations of future TDFs will be sensitive enough to detect these echoes and would allow us to establish the origin of optical/UV emission in TDFs in general.},
doi = {10.3847/2041-8213/AA6003},
journal = {Astrophysical Journal Letters},
number = 2,
volume = 837,
place = {United States},
year = {Fri Mar 10 00:00:00 EST 2017},
month = {Fri Mar 10 00:00:00 EST 2017}
}
  • In this paper, we present ground-based and Swift photometric and spectroscopic observations of the candidate tidal disruption event (TDE) ASASSN-14li, found at the centre of PGC 043234 (d ≃ 90 Mpc) by the All-Sky Automated Survey for SuperNovae (ASAS-SN). The source had a peak bolometric luminosity of L ≃ 10 44 erg s -1 and a total integrated energy of E ≃ 7 × 10 50 erg radiated over the ~6 months of observations presented. The UV/optical emission of the source is well fitted by a blackbody with roughly constant temperature of T ~ 35 000 K, while the luminositymore » declines by roughly a factor of 16 over this time. The optical/UV luminosity decline is broadly consistent with an exponential decline, L∝e -t/t0, with t 0 ≃ 60 d. ASASSN-14li also exhibits soft X-ray emission comparable in luminosity to the optical and UV emission but declining at a slower rate, and the X-ray emission now dominates. Spectra of the source show broad Balmer and helium lines in emission as well as strong blue continuum emission at all epochs. Finally, we use the discoveries of ASASSN-14li and ASASSN-14ae to estimate the TDE rate implied by ASAS-SN, finding an average rate of r ≃ 4.1 × 10 -5 yr -1 per galaxy with a 90 per cent confidence interval of (2.2–17.0) × 10 -5 yr -1 per galaxy. ASAS-SN found roughly 1 TDE for every 70 Type Ia supernovae in 2014, a rate that is much higher than that of other surveys.« less
  • We report the detection of a significant infrared variability of the nearest tidal disruption event (TDE) ASASSN-14li using Wide-field Infrared Survey Explorer and newly released Near-Earth Object WISE Reactivation data. In comparison with the quiescent state, the infrared flux is brightened by 0.12 and 0.16 mag in the W1 (3.4 μ m) and W2 (4.6 μ m) bands at 36 days after the optical discovery (or ∼110 days after the peak disruption date). The flux excess is still detectable ∼170 days later. Assuming that the flare-like infrared emission is from the dust around the black hole, its blackbody temperature ismore » estimated to be ∼2.1 × 10{sup 3} K, slightly higher than the dust sublimation temperature, indicating that the dust is likely located close to the dust sublimation radius. The equilibrium between the heating and radiation of the dust claims a bolometric luminosity of ∼10{sup 43}–10{sup 45} erg s{sup −1}, comparable with the observed peak luminosity. This result has for the first time confirmed the detection of infrared emission from the dust echoes of TDEs.« less
  • Theory suggests that a star making a close passage by a supermassive black hole at the center of a galaxy can under most circumstances be expected to emit a giant flare of radiation as it is disrupted and a portion of the resulting stream of shock-heated stellar debris falls back onto the black hole itself. We examine the first results of an ongoing archival survey of galaxy clusters using Chandra and XMM-Newton-selected data and report a likely tidal disruption flare from SDSS J131122.15-012345.6 in A1689. The flare is observed to vary by a factor of {approx}>30 over at least twomore » years to have maximum L{sub X} (0.3-3.0 keV) {approx}> 5 x 10{sup 42} erg s{sup -1} and to emit as a blackbody with kT {approx} 0.12 keV. From the galaxy population as determined by existing studies of the cluster, we estimate a tidal disruption rate of 1.2 x 10{sup -4} galaxy{sup -1} yr{sup -1} if we assume a contribution to the observable rate from galaxies whose range of luminosities corresponds to a central black hole mass (M{sub .}) between 10{sup 6} and 10{sup 8} M{sub sun}.« less
  • We report on the discovery of an ultrasoft X-ray transient source, 3XMM J152130.7+074916. It was serendipitously detected in an XMM-Newton observation on 2000 August 23, and its location is consistent with the center of the galaxy SDSS J152130.72+074916.5 (z = 0.17901 and d{sub L} = 866 Mpc). The high-quality X-ray spectrum can be fitted with a thermal disk with an apparent inner disk temperature of 0.17 keV and a rest-frame 0.24–11.8 keV unabsorbed luminosity of ∼5 × 10{sup 43} erg s{sup −1}, subject to a fast-moving warm absorber. Short-term variability was also clearly observed, with the spectrum being softer atmore » lower flux. The source was covered but not detected in a Chandra observation on 2000 April 3, a Swift observation on 2005 September 10, and a second XMM-Newton observation on 2014 January 19, implying a large variability (>260) of the X-ray flux. The optical spectrum of the candidate host galaxy, taken ∼11 years after the XMM-Newton detection, shows no sign of nuclear activity. This, combined with its transient and ultrasoft properties, leads us to explain the source as tidal disruption of a star by the supermassive black hole in the galactic center. We attribute the fast-moving warm absorber detected in the first XMM-Newton observation to the super-Eddington outflow associated with the event and the short-term variability to a disk instability that caused fast change of the inner disk radius at a constant mass accretion rate.« less
  • We study the emission from tidal disruption events (TDEs) produced as radiation from black hole accretion propagates through an extended, optically thick envelope formed from stellar debris. We analytically describe key physics controlling spectrum formation, and present detailed radiative transfer calculations that model the spectral energy distribution and optical line strengths of TDEs near peak brightness. The steady-state transfer is coupled to a solver for the excitation and ionization states of hydrogen, helium, and oxygen (as a representative metal), without assuming local thermodynamic equilibrium. Our calculations show how an extended envelope can reprocess a fraction of soft X-rays and producemore » the observed optical fluxes of the order of 10{sup 43} erg s{sup −1}, with an optical/UV continuum that is not described by a single blackbody. Variations in the mass or size of the envelope may help explain how the optical flux changes over time with roughly constant color. For high enough accretion luminosities, X-rays can escape to be observed simultaneously with the optical flux. Due to optical depth effects, hydrogen Balmer line emission is often strongly suppressed relative to helium line emission (with He ii-to-H line ratios of at least 5:1 in some cases) even in the disruption of a solar-composition star. We discuss the implications of our results to understanding the type of stars destroyed in TDEs and the physical processes responsible for producing the observed flares.« less