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Title: THE WISE DETECTION OF AN INFRARED ECHO IN TIDAL DISRUPTION EVENT ASASSN-14li

Abstract

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 is 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.

Authors:
; ; ; ;  [1];  [2]
  1. Key laboratory for Research in Galaxies and Cosmology, Department of Astronomy, The University of Science and Technology of China, Chinese Academy of Sciences, Hefei, Anhui 230026 (China)
  2. Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)
Publication Date:
OSTI Identifier:
22654231
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 828; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BLACK HOLES; BOLOMETERS; COMPARATIVE EVALUATIONS; DETECTION; DUSTS; EMISSION; EQUILIBRIUM; GALAXIES; GALAXY NUCLEI; INFRARED SURVEYS; LUMINOSITY; REGENERATION; SUBLIMATION

Citation Formats

Jiang, Ning, Dou, Liming, Wang, Tinggui, Yang, Chenwei, Zhou, Hongyan, and Lyu, Jianwei, E-mail: jnac@ustc.edu.cn. THE WISE DETECTION OF AN INFRARED ECHO IN TIDAL DISRUPTION EVENT ASASSN-14li. United States: N. p., 2016. Web. doi:10.3847/2041-8205/828/1/L14.
Jiang, Ning, Dou, Liming, Wang, Tinggui, Yang, Chenwei, Zhou, Hongyan, & Lyu, Jianwei, E-mail: jnac@ustc.edu.cn. THE WISE DETECTION OF AN INFRARED ECHO IN TIDAL DISRUPTION EVENT ASASSN-14li. United States. doi:10.3847/2041-8205/828/1/L14.
Jiang, Ning, Dou, Liming, Wang, Tinggui, Yang, Chenwei, Zhou, Hongyan, and Lyu, Jianwei, E-mail: jnac@ustc.edu.cn. 2016. "THE WISE DETECTION OF AN INFRARED ECHO IN TIDAL DISRUPTION EVENT ASASSN-14li". United States. doi:10.3847/2041-8205/828/1/L14.
@article{osti_22654231,
title = {THE WISE DETECTION OF AN INFRARED ECHO IN TIDAL DISRUPTION EVENT ASASSN-14li},
author = {Jiang, Ning and Dou, Liming and Wang, Tinggui and Yang, Chenwei and Zhou, Hongyan and Lyu, Jianwei, E-mail: jnac@ustc.edu.cn},
abstractNote = {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 is 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.},
doi = {10.3847/2041-8205/828/1/L14},
journal = {Astrophysical Journal Letters},
number = 1,
volume = 828,
place = {United States},
year = 2016,
month = 9
}
  • 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 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 similarmore » 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.« less
  • We report European Very Long Baseline Interferometry Network (EVN) radio continuum observations of ASASSN-14li, one of the best studied tidal disruption events (TDEs) to date. At 1.7 GHz with ≃12 × 6 mas resolution, the emission is unresolved. At 5.0 GHz with ≃3 × 2 mas resolution, the radio emission shows an extended structure that can be modeled with two components: a core-like component and a fainter, possibly elongated source 4.3 mas (∼2 pc) away. Our observations are not conclusive as to the nature of the components, but three scenarios are discussed. One possibility is a core-jet/outflow morphology, thus makingmore » of ASASSN-14li the first TDE jet/outflow directly imaged. For this case, the projected separation between the two components can only be explained by superluminal motion, rather than the lower velocities inferred from low-resolution radio observations. However, typical fast moving jets have brightness temperatures ∼5 orders of magnitude higher than we find, thus making this scenario less likely. The second possibility is that we are imaging a non-relativistic jet from past AGN/TDE activity. In this case a past TDE is preferred given that the spatial extension and radio luminosity of the elongated component are consistent with the theoretical predictions for a TDE outflow. Alternatively, the two sources could indicate the presence of a binary black hole, which would then naturally explain the enhanced TDE rates of post-starburst galaxies. Future EVN observations will help us to distinguish between these scenarios.« less
  • The galaxy SDSSJ095209.56+214313.3 (SDSSJ0952+2143 hereafter) showed remarkable emission-line and continuum properties and strong emission-line variability first reported in 2008 (Paper I). The spectral properties and low-energy variability are the consequence of a powerful high-energy flare which was itself not observed directly. Here we report follow-up optical, near-infrared (NIR), mid-infrared (MIR), and X-ray observations of SDSSJ0952+2143. We discuss outburst scenarios in terms of stellar tidal disruption by a supermassive black hole, peculiar variability of an active galactic nucleus (AGN), and a supernova (SN) explosion, and possible links between these scenarios and mechanisms. The optical spectrum of SDSSJ0952+2143 exhibits several peculiarities: anmore » exceptionally high ratio of [Fe VII] transitions over [O III], a dramatic decrease by a factor of 10 of the highest-ionization coronal lines, a very unusual and variable Balmer line profile including a triple-peaked narrow component with two unresolved horns, and a large Balmer decrement. The MIR emission measured with the Spitzer IRS in the narrow 10-20 {mu}m band is extraordinarily luminous and amounts to L {sub 10-20{mu}}{sub m} = 3.5 x 10{sup 43} erg s{sup -1}. The IRS spectrum shows a bump around {approx}11 {mu}m and an increase toward longer wavelengths, reminiscent of silicate emission. The strong MIR excess over the NIR implies the dominance of relatively cold dust. The pre- and post-flare NIR host galaxy colors indicate a nonactive galaxy. The X-ray luminosity of L {sub x,0.1-10keV} = 10{sup 41} erg s{sup -1} measured with Chandra is below that typically observed in AGNs. Similarities of SDSSJ0952+2143 with some extreme SNe suggest the explosion of a SN of Type IIn. However, an extreme accretion event in a low-luminosity AGN or inactive galaxy, especially stellar tidal disruption, remain possibilities, which could potentially produce a very similar emission-line response. If indeed a SN, SDSSJ0952+2143 is one of the most distant X-ray- and MIR-detected SNe known so far, the most MIR luminous, and one of the most X-ray luminous. It is also by far the most luminous (>10{sup 40} erg s{sup -1}) in high-ionization coronal lines, exceeding previous SNe by at least a factor of 100.« less
  • We have discovered an ultrasoft X-ray transient source, 2XMMi J184725.1-631724, which was detected serendipitously in two XMM-Newton observations in the direction of the center of the galaxy IC 4765-f01-1504 at a redshift of 0.0353. These two observations were separated by 211 days, with the 0.2-10 keV absorbed flux increasing by a factor of about nine. Their spectra are best described by a model dominated by a thermal disk or a single-temperature blackbody component (contributing {approx}>80% of the flux) plus a weak power-law component. The thermal emission has a temperature of a few tens of eV, and the weak power-law componentmore » has a photon index of {approx}3.5. Similar to the black hole X-ray binaries in the thermal state, our source exhibits an accretion disk whose luminosity appears to follow the L{proportional_to}T {sup 4} relation. This would indicate that the black hole mass is about 10{sup 5}-10{sup 6} M{sub sun} using the best-fitting inner disk radius. Both XMM-Newton observations show variability of about 21% on timescales of hours, which can be explained as due to fast variations in the mass accretion rate. The source was not detected by ROSAT in an observation in 1992, indicating a variability factor of {approx}>64 over longer timescales. The source was not detected again in X-rays in a Swift observation in 2011 February, implying a flux decrease by a factor of {approx}>12 since the last XMM-Newton observation. The transient nature, in addition to the extreme softness of the X-ray spectra and the inactivity of the galaxy implied by the lack of strong optical emission lines, makes it a candidate tidal disruption event. If this is the case, the first XMM-Newton observation would have been in the rising phase and the second one in the decay phase.« less