An outflow powers the optical rise of the nearby, fast-evolving tidal disruption event AT2019qiz

ABSTRACT At 66 Mpc, AT2019qiz is the closest optical tidal disruption event (TDE) to date, with a luminosity intermediate between the bulk of the population and the faint-and-fast event iPTF16fnl. Its proximity allowed a very early detection and triggering of multiwavelength and spectroscopic follow-up well before maximum light. The velocity dispersion of the host galaxy and fits to the TDE light curve indicate a black hole mass ≈106 M⊙, disrupting a star of ≈1 M⊙. By analysing our comprehensive UV, optical, and X-ray data, we show that the early optical emission is dominated by an outflow, with a luminosity evolution L ∝ t2, consistent with a photosphere expanding at constant velocity (≳2000 km s−1), and a line-forming region producing initially blueshifted H and He ii profiles with v = 3000–10 000 km s−1. The fastest optical ejecta approach the velocity inferred from radio detections (modelled in a forthcoming companion paper from K. D. Alexander et al.), thus the same outflow may be responsible for both the fast optical rise and the radio emission – the first time this connection has been observed in a TDE. The light-curve rise begins 29 ± 2 d before maximum light, peaking when the photosphere reaches the radius where optical photons can escape. The photosphere then undergoes a sudden transition, first cooling at constant radius then contracting at constant temperature. At the same time, the blueshifts disappear from the spectrum and Bowen fluorescence lines (N iii) become prominent, implying a source of far-UV photons, while the X-ray light curve peaks at ≈1041 erg s−1. Assuming that these X-rays are from prompt accretion, the size and mass of the outflow are consistent with the reprocessing layer needed to explain the large optical to X-ray ratio in this and other optical TDEs, possibly favouring accretion-powered over collision-powered outflow models.

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The Tidal Disruption Event AT 2018hyz II: Light-curve modelling of a partially disrupted star

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2099 ◽

2020 ◽

Vol 497 (2) ◽

pp. 1925-1934 ◽

Cited By ~ 5

Author(s):

Sebastian Gomez ◽

Matt Nicholl ◽

Philip Short ◽

Raffaella Margutti ◽

Kate D Alexander ◽

...

Keyword(s):

Light Curve ◽

Uv Light ◽

Companion Paper ◽

Tidal Disruption ◽

X Ray ◽

Inverse Compton Scattering ◽

Radiated Energy ◽

Photon Index ◽

Best Fit ◽

Disruption Event

ABSTRACT AT 2018hyz (= ASASSN-18zj) is a tidal disruption event (TDE) located in the nucleus of a quiescent E+A galaxy at a redshift of z = 0.04573, first detected by the All-Sky Automated Survey for Supernovae (ASAS-SN). We present optical+UV photometry of the transient, as well as an X-ray spectrum and radio upper limits. The bolometric light curve of AT 2018hyz is comparable to other known TDEs and declines at a rate consistent with a t−5/3 at early times, emitting a total radiated energy of E = 9 × 1050 erg. An excess bump appears in the UV light curve about 50 d after bolometric peak, followed by a flattening beyond 250 d. We detect a constant X-ray source present for at least 86 d. The X-ray spectrum shows a total unabsorbed flux of ∼4 × 10−14 erg cm−2 s−1 and is best fit by a blackbody plus power-law model with a photon index of Γ = 0.8. A thermal X-ray model is unable to account for photons >1 keV, while a radio non-detection favours inverse-Compton scattering rather than a jet for the non-thermal component. We model the optical and UV light curves using the Modular Open-Source Fitter for Transients (MOSFiT) and find a best fit for a black hole of 5.2 × 106 M⊙ disrupting a 0.1 M⊙ star; the model suggests the star was likely only partially disrupted, based on the derived impact parameter of β = 0.6. The low optical depth implied by the small debris mass may explain how we are able to see hydrogen emission with disc-like line profiles in the spectra of AT 2018hyz (see our companion paper).

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Discovery and follow-up of ASASSN-19dj: an X-ray and UV luminous TDE in an extreme post-starburst galaxy

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3170 ◽

2020 ◽

Vol 500 (2) ◽

pp. 1673-1696 ◽

Cited By ~ 3

Author(s):

Jason T Hinkle ◽

T W-S Holoien ◽

K Auchettl ◽

B J Shappee ◽

J M M Neustadt ◽

...

Keyword(s):

Optical Emission ◽

Starburst Galaxy ◽

Late Time ◽

X Rays ◽

Tidal Disruption ◽

X Ray ◽

Bolometric Luminosity ◽

Order Of Magnitude ◽

High Cadence

ABSTRACT We present observations of ASASSN-19dj, a nearby tidal disruption event (TDE) discovered in the post-starburst galaxy KUG 0810+227 by the All-Sky Automated Survey for Supernovae (ASAS-SN) at a distance of d ≃ 98 Mpc. We observed ASASSN-19dj from −21 to 392 d relative to peak ultraviolet (UV)/optical emission using high-cadence, multiwavelength spectroscopy and photometry. From the ASAS-SN g-band data, we determine that the TDE began to brighten on 2019 February 6.8 and for the first 16 d the rise was consistent with a flux ∝t2 power law. ASASSN-19dj peaked in the UV/optical on 2019 March 6.5 (MJD = 58548.5) at a bolometric luminosity of L = (6.2 ± 0.2) × 1044 erg s−1. Initially remaining roughly constant in X-rays and slowly fading in the UV/optical, the X-ray flux increased by over an order of magnitude ∼225 d after peak, resulting from the expansion of the X-ray emitting region. The late-time X-ray emission is well fitted by a blackbody with an effective radius of ∼1 × 1012 cm and a temperature of ∼6 × 105 K. The X-ray hardness ratio becomes softer after brightening and then returns to a harder state as the X-rays fade. Analysis of Catalina Real-Time Transient Survey images reveals a nuclear outburst roughly 14.5 yr earlier with a smooth decline and a luminosity of LV ≥ 1.4 × 1043 erg s−1, although the nature of the flare is unknown. ASASSN-19dj occurred in the most extreme post-starburst galaxy yet to host a TDE, with Lick HδA = 7.67 ± 0.17 Å.

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SEARCHING FOR EVIDENCE OF TIDAL DISRUPTION EVENT IN LONG-TERM X-RAY LIGHT CURVE OF SEYFERT GALAXY MCG-2-58-22

Current High-Energy Emission Around Black Holes ◽

10.1142/9789812777959_0004 ◽

2002 ◽

Author(s):

CHUL-SUNG CHOI ◽

TADAYASU DOTANI ◽

HEON-YOUNG CHANG ◽

INSU YI

Keyword(s):

Light Curve ◽

Seyfert Galaxy ◽

Tidal Disruption ◽

X Ray ◽

Disruption Event

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Evidence for rapid disc formation and reprocessing in the X-ray bright tidal disruption event candidate AT 2018fyk

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1976 ◽

2019 ◽

Vol 488 (4) ◽

pp. 4816-4830 ◽

Cited By ~ 30

Author(s):

T Wevers ◽

D R Pasham ◽

S van Velzen ◽

G Leloudas ◽

S Schulze ◽

...

Keyword(s):

Light Curve ◽

Optical Spectra ◽

Emission Lines ◽

Tidal Disruption ◽

X Ray ◽

Physical Conditions ◽

High Ionization ◽

Optical Light Curve ◽

Narrow Emission ◽

Disruption Event

ABSTRACT We present optical spectroscopic and Swift UVOT/XRT observations of the X-ray and UV/optical bright tidal disruption event (TDE) candidate AT 2018fyk/ASASSN–18ul discovered by ASAS–SN. The Swift light curve is atypical for a TDE, entering a plateau after ∼40 d of decline from peak. After 80 d the UV/optical light curve breaks again to decline further, while the X-ray emission becomes brighter and harder. In addition to broad H, He, and potentially O/Fe lines, narrow emission lines emerge in the optical spectra during the plateau phase. We identify both high-ionization (O iii) and low-ionization (Fe ii) lines, which are visible for ∼45 d. We similarly identify Fe ii lines in optical spectra of ASASSN–15oi 330 d after discovery, indicating that a class of Fe-rich TDEs exists. The spectral similarity between AT 2018fyk, narrow-line Seyfert 1 galaxies, and some extreme coronal line emitters suggests that TDEs are capable of creating similar physical conditions in the nuclei of galaxies. The Fe ii lines can be associated with the formation of a compact accretion disc, as the emergence of low-ionization emission lines requires optically thick, high-density gas. Taken together with the plateau in X-ray and UV/optical luminosity this indicates that emission from the central source is efficiently reprocessed into UV/optical wavelengths. Such a two-component light curve is very similar to that seen in the TDE candidate ASASSN–15lh, and is a natural consequence of a relativistic orbital pericentre.

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Rapid late-time X-ray brightening of the tidal disruption event OGLE16aaa

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038165 ◽

2020 ◽

Vol 639 ◽

pp. A100 ◽

Cited By ~ 2

Author(s):

Jari J. E. Kajava ◽

Margherita Giustini ◽

Richard D. Saxton ◽

Giovanni Miniutti

Keyword(s):

Black Hole ◽

Host Galaxy ◽

Late Time ◽

Tidal Disruption ◽

Massive Black Hole ◽

X Ray ◽

Tidal Forces ◽

Upper Limits ◽

Optical Light Curve ◽

Disruption Event

Stars that pass too close to a super-massive black hole may be disrupted by strong tidal forces. OGLE16aaa is one such tidal disruption event (TDE) which rapidly brightened and peaked in the optical/UV bands in early 2016 and subsequently decayed over the rest of the year. OGLE16aaa was detected in an XMM-Newton X-ray observation on June 9, 2016 with a flux slightly below the Swift/XRT upper limits obtained during the optical light curve peak. Between June 16–21, 2016, Swift/XRT also detected OGLE16aaa and based on the stacked spectrum, we could infer that the X-ray luminosity had jumped up by more than a factor of ten in just one week. No brightening signal was seen in the simultaneous optical/UV data to cause the X-ray luminosity to exceed the optical/UV one. A further XMM-Newton observation on November 30, 2016 showed that almost a year after the optical/UV peak, the X-ray emission was still at an elevated level, while the optical/UV flux decay had already leveled off to values comparable to those of the host galaxy. In all X-ray observations, the spectra were nicely modeled with a 50–70 eV thermal component with no intrinsic absorption, with a weak X-ray tail seen only in the November 30 XMM-Newton observation. The late-time X-ray behavior of OGLE16aaa strongly resembles the tidal disruption events ASASSN-15oi and AT2019azh. We were able to pinpoint the time delay between the initial optical TDE onset and the X-ray brightening to 182 ± 5 days, which may possibly represent the timescale between the initial circularization of the disrupted star around the super-massive black hole and the subsequent delayed accretion. Alternatively, the delayed X-ray brightening could be related to a rapid clearing of a thick envelope that covers the central X-ray engine during the first six months.

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XMMSL2 J144605.0+685735: a slow tidal disruption event

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935650 ◽

2019 ◽

Vol 630 ◽

pp. A98 ◽

Cited By ~ 8

Author(s):

R. D. Saxton ◽

A. M. Read ◽

S. Komossa ◽

P. Lira ◽

K. D. Alexander ◽

...

Keyword(s):

Stellar Population ◽

X Rays ◽

Time Data ◽

Tidal Disruption ◽

X Ray ◽

Bolometric Luminosity ◽

Uv Emission ◽

The Galaxy ◽

Multi Wavelength ◽

Disruption Event

Aims. We investigate the evolution of X-ray selected tidal disruption events. Methods. New events are found in near real-time data from XMM-Newton slews, and are monitored by multi-wavelength facilities. Results. In August 2016, X-ray emission was detected from the galaxy XMMSL2 J144605.0+685735 (also known as 2MASX 14460522+6857311), that was 20 times higher than an upper limit from 25 years earlier. The X-ray flux was flat for ∼100 days and then fell by a factor of 100 over the following 500 days. The UV flux was stable for the first 400 days before fading by a magnitude, while the optical (U,B,V) bands were roughly constant for 850 days. Optically, the galaxy appears to be quiescent, at a distance of 127 ± 4 Mpc (z = 0.029 ± 0.001) with a spectrum consisting of a young stellar population of 1–5 Gyr in age, an older population, and a total stellar mass of ∼6 × 109 M⊙. The bolometric luminosity peaked at Lbol ∼ 1043 ergs s−1 with an X-ray spectrum that may be modelled by a power law of Γ ∼ 2.6 or Comptonisation of a low-temperature thermal component by thermal electrons. We consider a tidal disruption event to be the most likely cause of the flare. Radio emission was absent in this event down to < 10 μJy, which limits the total energy of a hypothetical off-axis jet to E < 5 × 1050 ergs. The independent behaviour of the optical, UV, and X-ray light curves challenges models where the UV emission is produced by reprocessing of thermal nuclear emission or by stream-stream collisions. We suggest that the observed UV emission may have been produced from a truncated accretion disc and the X-rays from Compton upscattering of these disc photons.

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Limits on mass outflow from optical tidal disruption events

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab240 ◽

2021 ◽

Vol 502 (3) ◽

pp. 3385-3393

Author(s):

Tatsuya Matsumoto ◽

Tsvi Piran

Keyword(s):

Energy Band ◽

New Method ◽

Hydrodynamic Modelling ◽

X Rays ◽

Will Emit ◽

Tidal Disruption ◽

X Ray ◽

Mass Outflow ◽

Current Sample ◽

Stellar Masses

ABSTRACT The discovery of optical/UV (ultraviolet) tidal disruption events (TDEs) was surprising. The expectation was that, upon returning to the pericentre, the stellar-debris stream will form a compact disc that will emit soft X-rays. Indeed, the first TDEs were discovered in this energy band. A common explanation for the optical/UV events is that surrounding optically thick matter reprocesses the disc’s X-ray emission and emits it from a large photosphere. If accretion follows the super-Eddington mass infall rate, it would inevitably result in an energetic outflow, providing naturally the reprocessing matter. We describe here a new method to estimate, using the observed luminosity and temperature, the mass and energy of outflows from optical transients. When applying this method to a sample of supernovae, our estimates are consistent with a more detailed hydrodynamic modelling. For the current sample of a few dozen optical TDEs, the observed luminosity and temperature imply outflows that are significantly more massive than typical stellar masses, posing a problem to this common reprocessing picture.

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Constraining Soft and Hard X-Ray Irradiation in Ultraluminous X-Ray Sources

The Astrophysical Journal ◽

10.3847/1538-4357/ac3569 ◽

2021 ◽

Vol 922 (2) ◽

pp. 91

Author(s):

Yanli Qiu ◽

Hua Feng

Keyword(s):

Optical Emission ◽

Current Data ◽

Compact Objects ◽

X Rays ◽

Optical Counterpart ◽

X Ray ◽

Outer Disk ◽

Stringent Constraint ◽

Supercritical Accretion ◽

Key Questions

Abstract Most ultraluminous X-ray sources (ULXs) are argued to be powered by supercritical accretion onto compact objects. One of the key questions regarding these objects is whether or not the hard X-rays are geometrically beamed toward the symmetric axis. We propose testing the scenario using disk irradiation to see how much the outer accretion disk sees the central hard X-rays. We collect a sample of 11 bright ULXs with an identification of a unique optical counterpart, and model their optical fluxes considering two irradiating sources: soft X-rays from the photosphere of the optically thick wind driven by supercritical accretion, and if needed in addition, hard X-rays from the Comptonization component. Our results indicate that the soft X-ray irradiation can account for the optical emission in the majority of ULXs, and the fraction of hard X-rays reprocessed on the outer disk is constrained to be no more than ∼10−2 in general. Such an upper limit is well consistent with the irradiation fraction expected in the case of no beaming. Therefore, no stringent constraint on the beaming effect can be placed according to the current data quality.

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