Optical follow-up of the tidal disruption event iPTF16fnl: new insights from X-shooter observations

ABSTRACT We present the results from Nordic Optical Telescope and X-shooter follow-up campaigns of the tidal disruption event (TDE) iPTF16fnl, covering the first ∼100 d after the transient discovery. We followed the source photometrically until the TDE emission was no longer detected above the host galaxy light. The bolometric luminosity evolution of the TDE is consistent with an exponential decay with e-folding constant t0 = 17.6 ± 0.2 d. The early-time spectra of the transient are dominated by broad He ii λ4686, H $\beta$, H $\alpha$, and N iii λ4100 emission lines. The latter is known to be produced together with the N iii λ4640 in the Bowen fluorescence mechanism. Due to the medium-resolution X-shooter spectra we have been able to separate the Bowen blend contribution from the broad He ii emission line. The detection of the Bowen fluorescence lines in iPTF16fnl place this transient among the N-rich TDE subset. In the late-time X-shooter spectra, narrow emission lines of [O iii] and [N ii] originating from the host galaxy are detected, suggesting that the host galaxy harbours a weak active galactic nucleus in its core. The properties of all broad emission lines evolve with time. The equivalent widths follow an exponential decay compatible with the bolometric luminosity evolution. The full width at half-maximum of the broad lines decline with time and the line profiles develop a narrow core at later epochs. Overall, the optical emission of iPTF16fnl can be explained by being produced in an optically thick region in which high densities favour the Bowen fluorescence mechanism and where multiple electron scatterings are responsible for the line broadening.

Download Full-text

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.

Download Full-text

The tidal disruption event AT 2018hyz – I. Double-peaked emission lines and a flat Balmer decrement

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2065 ◽

2020 ◽

Vol 498 (3) ◽

pp. 4119-4133 ◽

Cited By ~ 6

Author(s):

P Short ◽

M Nicholl ◽

A Lawrence ◽

S Gomez ◽

I Arcavi ◽

...

Keyword(s):

Cataclysmic Variables ◽

Absolute Magnitude ◽

Emission Lines ◽

Late Time ◽

Tidal Disruption ◽

Broad Emission ◽

Balmer Lines ◽

High Cadence ◽

Balmer Decrement

ABSTRACT We present results from spectroscopic observations of AT 2018hyz, a transient discovered by the All-Sky Automated Survey for Supernova survey at an absolute magnitude of MV ∼ −20.2 mag, in the nucleus of a quiescent galaxy with strong Balmer absorption lines. AT 2018hyz shows a blue spectral continuum and broad emission lines, consistent with previous TDE candidates. High cadence follow-up spectra show broad Balmer lines and He i in early spectra, with He ii making an appearance after ∼70–100 d. The Balmer lines evolve from a smooth broad profile, through a boxy, asymmetric double-peaked phase consistent with accretion disc emission, and back to smooth at late times. The Balmer lines are unlike typical active galactic nucleus in that they show a flat Balmer decrement (Hα/Hβ ∼ 1.5), suggesting the lines are collisionally excited rather than being produced via photoionization. The flat Balmer decrement together with the complex profiles suggests that the emission lines originate in a disc chromosphere, analogous to those seen in cataclysmic variables. The low optical depth of material due to a possible partial disruption may be what allows us to observe these double-peaked, collisionally excited lines. The late appearance of He ii may be due to an expanding photosphere or outflow, or late-time shocks in debris collisions.

Download Full-text

The tidal disruption event AT2017eqx: spectroscopic evolution from hydrogen rich to poor suggests an atmosphere and outflow

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1837 ◽

2019 ◽

Vol 488 (2) ◽

pp. 1878-1893 ◽

Cited By ~ 12

Author(s):

M Nicholl ◽

P K Blanchard ◽

E Berger ◽

S Gomez ◽

R Margutti ◽

...

Keyword(s):

Host Galaxy ◽

Mass Star ◽

Late Time ◽

Solar Mass ◽

Tidal Disruption ◽

Relativistic Jet ◽

Proposed Model ◽

Complete Disruption ◽

Disruption Event ◽

Rule Out

ABSTRACT We present and analyse a new tidal disruption event (TDE), AT2017eqx at redshift z = 0.1089, discovered by Pan-STARRS and ATLAS. The position of the transient is consistent with the nucleus of its host galaxy; the spectrum shows a persistent blackbody temperature T ≳ 20 000 K with broad H i and He ii emission; and it peaks at a blackbody luminosity of L ≈ 1044 erg s−1. The lines are initially centred at zero velocity, but by 100 d, the H i lines disappear while the He ii develops a blueshift of ≳ 5000 km s−1. Both the early- and late-time morphologies have been seen in other TDEs, but the complete transition between them is unprecedented. The evolution can be explained by combining an extended atmosphere, undergoing slow contraction, with a wind in the polar direction becoming visible at late times. Our observations confirm that a lack of hydrogen a TDE spectrum does not indicate a stripped star, while the proposed model implies that much of the diversity in TDEs may be due to the observer viewing angle. Modelling the light curve suggests AT2017eqx resulted from the complete disruption of a solar-mass star by a black hole of ∼106.3 M⊙. The host is another Balmer-strong absorption galaxy, though fainter and less centrally concentrated than most TDE hosts. Radio limits rule out a relativistic jet, while X-ray limits at 500 d are among the deepest for a TDE at this phase.

Download Full-text

The evolution of luminous red nova AT 2017jfs in NGC 4470

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935511 ◽

2019 ◽

Vol 625 ◽

pp. L8 ◽

Cited By ~ 9

Author(s):

A. Pastorello ◽

T.-W. Chen ◽

Y.-Z. Cai ◽

A. Morales-Garoffolo ◽

Z. Cano ◽

...

Keyword(s):

Near Infrared ◽

Absolute Magnitude ◽

Emission Lines ◽

Late Time ◽

Absorption Bands ◽

Common Envelope ◽

Bolometric Luminosity ◽

Link Type ◽

Second Peak

We present the results of our photometric and spectroscopic follow-up of the intermediate-luminosity optical transient AT 2017jfs. At peak, the object reaches an absolute magnitude of Mg = −15.46 ± 0.15 mag and a bolometric luminosity of 5.5 × 1041 erg s−1. Its light curve has the double-peak shape typical of luminous red novae (LRNe), with a narrow first peak bright in the blue bands, while the second peak is longer-lasting and more luminous in the red and near-infrared (NIR) bands. During the first peak, the spectrum shows a blue continuum with narrow emission lines of H and Fe II. During the second peak, the spectrum becomes cooler, resembling that of a K-type star, and the emission lines are replaced by a forest of narrow lines in absorption. About 5 months later, while the optical light curves are characterized by a fast linear decline, the NIR ones show a moderate rebrightening, observed until the transient disappears in solar conjunction. At these late epochs, the spectrum becomes reminiscent of that of M-type stars, with prominent molecular absorption bands. The late-time properties suggest the formation of some dust in the expanding common envelope or an IR echo from foreground pre-existing dust. We propose that the object is a common-envelope transient, possibly the outcome of a merging event in a massive binary, similar to NGC 4490−2011OT1.

Download Full-text

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.

Download Full-text

The evolution of Kerr discs and late-time tidal disruption event light curves

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/sty2467 ◽

2018 ◽

Vol 481 (3) ◽

pp. 3348-3356 ◽

Cited By ~ 11

Author(s):

Steven A Balbus ◽

Andrew Mummery

Keyword(s):

Light Curves ◽

Late Time ◽

Tidal Disruption ◽

Event Light ◽

Disruption Event

Download Full-text

Radio Monitoring of the Tidal Disruption Event Swift J164449.3+573451. III. Late-time Jet Energetics and a Deviation from Equipartition

The Astrophysical Journal ◽

10.3847/1538-4357/aaa8e0 ◽

2018 ◽

Vol 854 (2) ◽

pp. 86 ◽

Cited By ~ 17

Author(s):

T. Eftekhari ◽

E. Berger ◽

B. A. Zauderer ◽

R. Margutti ◽

K. D. Alexander

Keyword(s):

Late Time ◽

Tidal Disruption ◽

Radio Monitoring ◽

Disruption Event

Download Full-text

Relativistic accretion disc in tidal disruption events

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1604 ◽

2020 ◽

Vol 496 (2) ◽

pp. 1784-1802

Author(s):

T Mageshwaran ◽

Sudip Bhattacharyya

Keyword(s):

Surface Density ◽

Accretion Disc ◽

Time Parameter ◽

Light Curves ◽

Initial Time ◽

Late Time ◽

Tidal Disruption ◽

Bolometric Luminosity ◽

Spectral Bands ◽

Accretion Model

ABSTRACT We construct a time-dependent relativistic accretion model for tidal disruption events (TDEs) with an α-viscosity and the pressure dominated by gas pressure. We also include the mass fallback rate $\dot{M}_\mathrm{ f}$ for both full and partial disruption TDEs, and assume that the infalling debris forms a seed disc in time tc, which evolves due to the mass addition from the infalling debris and the mass-loss via accretion on to the black hole. Besides, we derive an explicit form for the disc height that depends on the angular momentum parameter in the disc. We show that the surface density of the disc increases at an initial time due to mass addition, and then decreases as the mass fallback rate decreases, which results in a decrease in the disc mass Md with a late-time evolution of Md ∝ t−1.05 and t−1.38 for full and partial disruption TDEs, respectively, where t is the time parameter. The bolometric luminosity L shows a rise and decline that follows a power law at late times given by L ∝ t−1.8 and t−2.3 for full and partial disruption TDEs, respectively. Our obtained luminosity declines faster than the luminosity inferred using $L \propto \dot{M}_\mathrm{ f}$. We also compute the light curves in various spectral bands.

Download Full-text

Discovery and follow-up of the unusual nuclear transient OGLE17aaj

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833682 ◽

2019 ◽

Vol 622 ◽

pp. L2 ◽

Cited By ~ 7

Author(s):

M. Gromadzki ◽

A. Hamanowicz ◽

L. Wyrzykowski ◽

K. V. Sokolovsky ◽

M. Fraser ◽

...

Keyword(s):

Light Curve ◽

Black Body ◽

Emission Lines ◽

First Year ◽

Tidal Disruption ◽

Massive Black Holes ◽

X Ray ◽

New Type ◽

Narrow Emission

Aims. We report on the discovery and follow-up of a peculiar transient, OGLE17aaj, which occurred in the nucleus of a weakly active galaxy. We investigate whether it can be interpreted as a new candidate for a tidal disruption event (TDE). Methods. We present the OGLE-IV light curve that covers the slow 60-day-long rise to maximum along with photometric, spectroscopic, and X-ray follow-up during the first year. Results. OGLE17aaj is a nuclear transient exhibiting some properties similar to previously found TDEs, including a long rise time, lack of colour-temperature evolution, and high black-body temperature. On the other hand, its narrow emission lines and slow post-peak evolution are different from previously observed TDEs. Its spectrum and light-curve evolution is similar to F01004-2237 and AT 2017bgt. Signatures of historical low-level nuclear variability suggest that OGLE17aaj may instead be related to a new type of accretion event in active super-massive black holes.

Download Full-text