Long-term X-ray variability of Swift J1644+57

Saxton, C. J.; Soria, Roberto; Wu, Kinwah; Kuin, N. P. M.

doi:10.1111/j.1365-2966.2012.20739.x

Cited by 59 publications

(85 citation statements)

References 79 publications

(117 reference statements)

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“…Transient radio, X-ray and γ-ray components could be the result of collimated jets erupting through the opaque surface: briefly, persistently, or with instabilities and pre-cession effects depending on idiosyncrasies of each system (e.g. Gezari et al 2009;van Velzen, Körding & Falcke 2011;Bloom et al 2011;Levan et al 2011;van Velzen et al 2013;Saxton et al 2012;Cenko et al 2012b;Bower et al 2013;van Velzen et al 2016a;Alexander et al 2016). In events where jets ceased after an initial burst, their emissions might ionize distant clouds, like the early hot photosphere's 'flash' in our light-echo models.…”

Section: Subluminous Agn Flaring Scenariomentioning

confidence: 99%

Spectral features of tidal disruption candidates and alternative origins for such transient flares

Saxton

Perets

Baskin

2017

Monthly Notices of the Royal Astronomical Society

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UV and optically selected candidates for stellar tidal disruption events (TDE) often exhibit broad spectral features (He ii emission, Hα emission, or absorption lines) on a blackbody-like continuum (10 4 K T 10 5 K). The lines presumably emit from TDE debris or circumnuclear clouds photoionized by the flare. Line velocities however are much lower than expected from a stellar disruption by supermassive black hole (SMBH), and are somewhat faster than expected for the broad line region (BLR) clouds of a persistently active galactic nucleus (AGN). The distinctive spectral states are not strongly related to observed luminosity and velocity, nor to SMBH mass estimates. We use exhaustive photoionization modelling to map the domain of fluxes and cloud properties that yield (e.g.) a He-overbright state where a large He II(4686Å )/Hα line-ratio creates an illusion of helium enrichment. Although observed line ratios occur in a plausible minority of cases, AGN-like illumination can not reproduce the observed equivalent widths. We therefore propose to explain these properties by a light-echo photoionization model: the initial flash of a hot blackbody (detonation) excites BLR clouds, which are then seen superimposed on continuum from a later, expanded, cooled stage of the luminous source. The implied cloud mass is substellar, which may be inconsistent with a TDE. Given these and other inconsistencies with TDE models (e.g. host-galaxies distribution) we suggest to also consider alternative origins for these nuclear flares, which we briefly discuss (e.g. nuclear supernovae and starved/subluminous AGNs).

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Section: Subluminous Agn Flaring Scenariomentioning

confidence: 99%

Spectral features of tidal disruption candidates and alternative origins for such transient flares

Saxton

Perets

Baskin

2017

Monthly Notices of the Royal Astronomical Society

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“…This may be indicative of dipping as seen in Swift J1644+57 (Levan et al 2011;Bloom et al 2011;Saxton et al 2012) at similar times, or perhaps of a longer term cessation of activity as identified in Swift J1644+57 at much later epochs of ∼1.5 years (Sbarufatti et al 2012;Levan & Tanvir 2012;Berger et al 2012) and similarly in Swift J2058+05 (Pasham et al 2015). In any case, the final epoch of observations results in a limit which is significantly below the extrapolation of the early emission, requiring either a steepening of the decay or a rapid drop.…”

Section: Relativistic Tidal Disruption Flaresmentioning

confidence: 99%

Swift J1112.2−8238: a candidate relativistic tidal disruption flare

Brown

Levan

Stanway

et al. 2015

Mon. Not. R. Astron. Soc.

137

134

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We present observations of Swift J1112.2-8238, and identify it as a candidate relativistic tidal disruption flare (rTDF). The outburst was first detected by Swift/BAT in June 2011 as an unknown, long-lived (order of days) γ-ray transient source. We show that its position is consistent with the nucleus of a faint galaxy for which we establish a likely redshift of z = 0.89 based on a single emission line that we interpret as the blended [Oii]λ3727 doublet. At this redshift, the peak X/γ-ray luminosity exceeded 10 47 ergs s −1 , while a spatially coincident optical transient source had i ∼22 (M g ∼ − 21.4 at z = 0.89) during early observations, ∼20 days after the Swift trigger. These properties place Swift J1112.2-8238 in a very similar region of parameter space to the two previously identified members of this class, Swift J1644+57 and Swift J2058+0516. As with those events the high-energy emission shows evidence for variability over the first few days, while late time observations, almost 3 years postoutburst, demonstrate that it has now switched off. Swift J1112.2-8238 brings the total number of such events observed by Swift to three, interestingly all detected by Swift over a ∼3 month period (< 3% of its total lifetime as of March 2015). While this suggests the possibility that further examples may be uncovered by detailed searches of the BAT archives, the lack of any prime candidates in the years since 2011 means these events are undoubtedly rare.

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“…In any case, the observed luminosity would be periodically modulated by the precession. It will be interesting to investigate the disk precession and look for the signature in TDEs, especially for the well-observed jetted TDE candidate Sw J1644 + 57 which show numerous dips in the X-ray light curves and from which quasi-periodicity is claimed [17]. A few studies have investigated the possibility that the dips in the Sw J1644 X-ray light curve might be due to the disk precession [18,19], but they did not consider the evolution of the disk and thus of the precession period.…”

Section: Disk Precession and Its Evolutionmentioning

confidence: 99%

Evolution and precession of accretion disk in tidal disruption events

Shen

Matzner

2012

EPJ Web of Conferences

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Abstract. In a supermassive black hole (BH) tidal disruption event (TDE), the tidally disrupted star feeds the BH via an accretion disk. Most often it is assumed that the accretion rate history, hence the emission light curve, tracks the rate at which new debris mass falls back onto the disk, notably the t −5/3 power law. But this is not the case when the disk evolution due to viscous spreading -the driving force for accretion -is carefully considered. We construct a simple analytical model that comprehensively describes the accretion rate history across 4 different phases of the disk evolution, in the presence of mass fallback and disk wind loss. Accretion rate evolves differently in those phases which are governed by how the disk heat energy is carried away, early on by advection and later by radiation. The accretion rate can decline as steeply as t −5/3 only if copious disk wind loss is present during the early advection-cooled phase. Later, the accretion rate history is t −8/7 or shallower. These have great implications on the TDE flare light curve. A TDE accretion disk is most likely misaligned with the equatorial plane of the spinning BH. Moreover, in the TDE the accretion rate is super-or near-Eddington thus the disk is geometrically thick, for which case the BH's frame dragging effect may cause the disk precess as a solid body, which may manifest itself as quasi-periodic signal in the TDE light curve. Our disk evolution model predicts the disk precession period increases with time, typically as ∝ t. The results are applied to the recently jetted TDE flare Swift transient J1644 + 57 which shows numerous, quasi-periodic dips in its long-term X-ray light curve. As the current TDE sample increases, the identification of the disk precession signature provides a unique way of measuring BH spin and studying BH accretion physics.

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Long-term X-ray variability of Swift J1644+57

Cited by 59 publications

References 79 publications

Spectral features of tidal disruption candidates and alternative origins for such transient flares

Spectral features of tidal disruption candidates and alternative origins for such transient flares

Swift J1112.2−8238: a candidate relativistic tidal disruption flare

Evolution and precession of accretion disk in tidal disruption events

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