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

2019 ◽  
Vol 488 (4) ◽  
pp. 4816-4830 ◽  
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.

scholarly journals Discovery and follow-up of the unusual nuclear transient OGLE17aaj

2019 ◽  
Vol 622 ◽  
pp. L2 ◽  
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.

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

2020 ◽  
Vol 497 (2) ◽  
pp. 1925-1934 ◽  
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).

scholarly journals 2.13. Optical and X-ray variability in NGC 4395

1998 ◽  
Vol 184 ◽  
pp. 83-84 ◽  
Author(s):  
P. Lira ◽  
A. Lawrence
Keyword(s):  
Emission Lines ◽  
X Ray ◽  
High Ionization ◽  
Ngc 4395 ◽  
Narrow Emission

The spectrum of the dwarf Seyfert 1 nucleus in NGC 4395 was first reported about a decade ago (Filippenko & Sargent 1989), showing high ionization narrow emission lines and broad permitted lines. The later detection of radio and X-ray compact nuclear sources and of a featureless UV continuum gave support to the idea that NGC 4395 is a genuine low luminosity AGN (Sramek 1992; Filippenko, Ho & Sargent 1993). However, it has been claimed that, unlike classic Seyferts, NGC 4395 does not vary at all (Shields & Filippenko 1992).

scholarly journals V2282 Sgr Revisited

2014 ◽  
Vol 1 (1) ◽  
pp. 118-122
Author(s):  
Roberto Nesci ◽  
Corinne Rossi ◽  
Antonio Frasca ◽  
Ettore Marilli ◽  
Paolo Persi ◽  
...  
Keyword(s):  
Light Curve ◽  
Accretion Disk ◽  
Main Sequence ◽  
Optical Spectra ◽  
Emission Lines ◽  
Main Sequence Star ◽  
Strong Emission ◽  
X Ray ◽  
Type Spectrum

The nature of V2282 Sgr is examined on the basis of several multiband observations: a 20 years long I-band light curve of V2282 Sgr obtained from archive photographic plates of the Asiago and Catania Observatories; a CCD R-band light curve obtained at Cornero Observatory; JHK photometry from 2MASS and UKDISS; <em>Spitzer</em> IRAC and MIPS images; optical spectra from Loiano Observatory; X-ray flux from <em>CHANDRA</em>. The star has a K-type spectrum with strong emission lines and is irregularly variable at all wavebands. The overall evidences suggest that V2282 Sgr is a Pre Main Sequence star with an accretion disk.

scholarly journals Optical and X-ray studies of three polars: RX J0859.1+0537, RX J0749.1–0549, and RX J0649.8–0737

2019 ◽  
Vol 491 (1) ◽  
pp. 201-214 ◽  
Author(s):  
Arti Joshi ◽  
J C Pandey ◽  
Ashish Raj ◽  
K P Singh ◽  
G C Anupama ◽  
...  
Keyword(s):  
White Dwarf ◽  
Optical Spectra ◽  
Emission Lines ◽  
X Ray ◽  
Long Period ◽  
Photometric And Spectroscopic Observations ◽  
High Ionization ◽  
Orbital Periods ◽  
Actual Size ◽  
Balmer Decrement

ABSTRACT We present optical photometric and spectroscopic observations, and an analysis of archival X-ray data of three polars: RX J0859.1+0537, RX J0749.1–0549, and RX J0649.8–0737. Optical light curves of these three polars reveal eclipse-like features that are deep, total, and variable in shape. The optical and X-ray modulations of RX J0859.1+0537, RX J0749.1–0549, and RX J0649.8–0737 are both found to occur at the orbital periods of 2.393 ± 0.003 h, 3.672 ± 0.001 h, and 4.347 ± 0.001 h, respectively. RX J0859.1+0537 is found to be a polar that lies in the region of the period gap, whereas RX J0749.1–0549 and RX J0649.8–0737 are found to be long-period polars above the period gap. The eclipse length is found to be 61 min for RX J0749.1–0549 in the Rband, which is the highest among the long-period eclipsing polars. The radius of the eclipsed light source is found to be more than the actual size of the white dwarf for these three systems, indicating that the eclipsed component is not only the white dwarf but also appears to include the presence of an extended accretion region. Optical spectra of these systems show the presence of high-ionization emission lines along with the strong Balmer emission lines with an inverted Balmer decrement. Cyclotron harmonics are also detected in the optical spectra from which we infer magnetic field strength of the surface of the white dwarf to be 49 ± 2 MG, 43.5 ± 1.4 MG, and 44 ± 1 MG for RX J0859.1+0537, RX J0749.1–0549, and RX J0649.8–0737, respectively.

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

2020 ◽  
Vol 639 ◽  
pp. A100 ◽  
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.

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

2020 ◽  
Vol 499 (1) ◽  
pp. 482-504 ◽  
Author(s):  
M Nicholl ◽  
T Wevers ◽  
S R Oates ◽  
K D Alexander ◽  
G Leloudas ◽  
...  
Keyword(s):  
Light Curve ◽  
Optical Emission ◽  
Companion Paper ◽  
Host Galaxy ◽  
X Rays ◽  
Tidal Disruption ◽  
X Ray ◽  
Maximum Light ◽  
Sudden Transition ◽  
Disruption Event

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.

scholarly journals Possible X-Ray Quasi-periodic Eruptions in a Tidal Disruption Event Candidate

2021 ◽  
Vol 921 (2) ◽  
pp. L40
Author(s):  
Joheen Chakraborty ◽  
Erin Kara ◽  
Megan Masterson ◽  
Margherita Giustini ◽  
Giovanni Miniutti ◽  
...  
Keyword(s):  
Tidal Disruption ◽  
X Ray ◽  
Disruption Event

scholarly journals Long-term radio and X-ray evolution of the tidal disruption event ASASSN-14li

2018 ◽  
Vol 475 (3) ◽  
pp. 4011-4019 ◽  
Author(s):  
J S Bright ◽  
R P Fender ◽  
S E Motta ◽  
K Mooley ◽  
Y C Perrott ◽  
...  
Keyword(s):  
Tidal Disruption ◽  
X Ray ◽  
Disruption Event
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