X-Ray Properties of TDEs Saxton, R.; Komossa, S.; Auchettl, K. ...
Space science reviews,
08/2020, Letnik:
216, Številka:
5
Journal Article
Recenzirano
Observational astronomy of tidal disruption events (TDEs) began with the detection of X-ray flares from quiescent galaxies during the ROSAT all-sky survey of 1990–1991. The flares complied with ...theoretical expectations, having high peak luminosities (
L
x
up to
≥
4
×
10
44
erg/s
), a thermal spectrum with
k
T
∼
few
×
10
5
K
, and a decline on timescales of months to years, consistent with a diminishing return of stellar debris to a black hole of mass
10
6
–
8
M
⊙
. These measurements gave solid proof that the nuclei of quiescent galaxies are habitually populated by a super-massive black hole. Beginning in 2000, XMM-
Newton
, Chandra and
Swift
have discovered further TDEs which have been monitored closely at multiple wavelengths. A general picture has emerged of, initially near-Eddington accretion, powering outflows of highly-ionised material, giving way to a calmer sub-Eddington phase, where the flux decays monotonically, and finally a low accretion rate phase with a harder X-ray spectrum indicative of the formation of a disk corona. There are exceptions to this rule though which at the moment are not well understood. A few bright X-ray TDEs have been discovered in optical surveys but in general X-ray TDEs show little excess emission in the optical band, at least at times coincident with the X-ray flare. X-ray TDEs are powerful new probes of accretion physics down to the last stable orbit, revealing the conditions necessary for launching jets and winds. Finally we see that evidence is mounting for nuclear and non-nuclear intermediate mass black holes based on TDE flares which are relatively hot and/or fast.
Stellar binaries that survive supernovae Kochanek, C S; Auchettl, K; Belczynski, K
Monthly notices of the Royal Astronomical Society,
06/2019, Letnik:
485, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Abstract
The number of binaries containing black holes (BH) or neutron stars (NS) depends critically on the fraction of binaries that survive supernova (SN) explosions. We searched for surviving star ...plus remnant binaries in a sample of 49 supernova remnants (SNR) containing 23 previously identified compact remnants and three high-mass X-ray binaries (HMXB), finding no new interacting or non-interacting binaries. The upper limits on any main-sequence stellar companion are typically $\lesssim 0.2\, \mathrm{M}_\odot$ and are at worst $\lesssim 3\, \mathrm{M}_\odot$. This implies that f < 0.1 of core-collapse SNRs contain a non-interacting binary, and f = 0.083 (0.032 < f < 0.17) contain an interacting binary at 90 per cent confidence. We also find that the transverse velocities of HMXBs are low, with a median of only 12 km s−1 for field HMXBs, so surviving binaries will generally be found very close to the explosion centre. We compare the results to a ‘standard’ StarTrack binary population synthesis (BPS) model, finding reasonable agreement with the observations. In particular, the BPS models predict that 6 per cent of initial binaries leave a star plus remnant binary, or 5 per cent of SNRs assuming an 84 per cent binary fraction.
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.
We present the discovery of ASASSN-18ey (MAXI J1820+070), a new black hole low-mass X-ray binary (LMXB) discovered by the All-Sky Automated Survey for SuperNovae (ASAS-SN). A week after ASAS-SN ...discovered ASASSN-18ey as an optical transient, it was detected as an X-ray transient by MAXI/GCS. Here, we analyze ASAS-SN and Asteroid Terrestrial-impact Last Alert System pre-outburst optical light curves, finding evidence of intrinsic variability for several years prior to the outburst. While there was no long-term rise leading to the outburst, as has been seen in several other systems, the start of the outburst in the optical preceded that in the X-rays by 7.20 0.97 days. We analyze the spectroscopic evolution of ASASSN-18ey from pre-maximum to >100 days post-maximum. The spectra of ASASSN-18ey exhibit broad, asymmetric, double-peaked H emission. The Bowen blend (λ 4650 ) in the post-maximum spectra shows highly variable double-peaked profiles, likely arising from irradiation of the companion by the accretion disk, typical of low-mass X-ray binaries. The optical and X-ray luminosities of ASASSN-18ey are consistent with black hole low-mass X-ray binaries, both in outburst and quiescence.
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.
Abstract
We present panchromatic observations and modeling of supernova (SN) 2020tlf, the first normal Type II-P/L SN with confirmed precursor emission, as detected by the Young Supernova Experiment ...transient survey. Pre-SN activity was detected in
riz
-bands at −130 days and persisted at relatively constant flux until first light. Soon after discovery, “flash” spectroscopy of SN 2020tlf revealed narrow, symmetric emission lines that resulted from the photoionization of circumstellar material (CSM) shed in progenitor mass-loss episodes before explosion. Surprisingly, this novel display of pre-SN emission and associated mass loss occurred in a red supergiant (RSG) progenitor with zero-age main-sequence mass of only 10–12
M
⊙
, as inferred from nebular spectra. Modeling of the light curve and multi-epoch spectra with the non-LTE radiative-transfer code CMFGEN and radiation-hydrodynamical code HERACLES suggests a dense CSM limited to
r
≈ 10
15
cm, and mass-loss rate of 10
−2
M
⊙
yr
−1
. The luminous light-curve plateau and persistent blue excess indicates an extended progenitor, compatible with an RSG model with
R
⋆
= 1100
R
⊙
. Limits on the shock-powered X-ray and radio luminosity are consistent with model conclusions and suggest a CSM density of
ρ
< 2 × 10
−16
g cm
−3
for distances from the progenitor star of
r
≈ 5 × 10
15
cm, as well as a mass-loss rate of
M
̇
<
1.3
×
10
−
5
M
☉
yr
−
1
at larger distances. A promising power source for the observed precursor emission is the ejection of stellar material following energy disposition into the stellar envelope as a result of gravity waves emitted during either neon/oxygen burning or a nuclear flash from silicon combustion.
Abstract
Fomalhaut b is a directly imaged object in the debris disc of the star Fomalhaut. It has been hypothesized to be a planet; however, there are issues with the observed colours of the object ...that do not fit planetary models. An alternative hypothesis is that the object is a neutron star in the near fore- or background of Fomalhaut's disc. We test if Fomalhaut b could be a neutron star using X-ray observations with Chandra's HRC-I instrument in the energy range of 0.08–10 keV. We do not detect X-ray emission from either Fomalhaut b or the star Fomalhaut itself. Our non-detection corresponds to an upper limit on the X-ray flux of Fomalhaut b of F
X < 1.3 × 10−14 erg cm−2 s−1 in the energy range 0.08–10 keV. For the A-type central star Fomalhaut, we derive an X-ray upper limit of L
X < 2.0 × 1025 erg s−1 in the energy range 0.08–10 keV. Fomalhaut b's X-ray non-detection constrains the parameter space for a possible neutron star significantly, implying surface temperatures lower than 91 000 K and distances closer than 13.3 pc to the Solar system. In addition, we find that reflected starlight from the central star fits the available optical detections of Fomalhaut b; a smaller planet with a large ring system might explain such a scenario.
On 2018 February 4.41, the All-Sky Automated Survey for SuperNovae (ASAS-SN) discovered ASASSN-18bt in the K2 Campaign 16 field. With a redshift of z = 0.01098 and a peak apparent magnitude of Bmax = ...14.31, ASASSN-18bt is the nearest and brightest SNe Ia yet observed by the Kepler spacecraft. Here we present the discovery of ASASSN-18bt, the K2 light curve, and prediscovery data from ASAS-SN and the Asteroid Terrestrial-impact Last Alert System. The K2 early-time light curve has an unprecedented 30-minute cadence and photometric precision for an SN Ia light curve, and it unambiguously shows a ∼4 day nearly linear phase followed by a steeper rise. Thus, ASASSN-18bt joins a growing list of SNe Ia whose early light curves are not well described by a single power law. We show that a double-power-law model fits the data reasonably well, hinting that two physical processes must be responsible for the observed rise. However, we find that current models of the interaction with a nondegenerate companion predict an abrupt rise and cannot adequately explain the initial, slower linear phase. Instead, we find that existing published models with shallow 56Ni are able to span the observed behavior and, with tuning, may be able to reproduce the ASASSN-18bt light curve. Regardless, more theoretical work is needed to satisfactorily model this and other early-time SNe Ia light curves. Finally, we use Swift X-ray nondetections to constrain the presence of circumstellar material (CSM) at much larger distances and lower densities than possible with the optical light curve. For a constant-density CSM, these nondetections constrain < 4.5 × 105 cm−3 at a radius of 4 × 1015 cm from the progenitor star. Assuming a wind-like environment, we place mass loss limits of for vw = 100 km s−1, ruling out some symbiotic progenitor systems. This work highlights the power of well-sampled early-time data and the need for immediate multiband, high-cadence follow-up for progress in understanding SNe Ia.
Abstract
We present extensive multifrequency Karl G. Jansky Very Large Array (VLA) and Very Long Baseline Array (VLBA) observations of the radio-bright supernova (SN) IIb SN 2004C that span ∼40–2793 ...days post-explosion. We interpret the temporal evolution of the radio spectral energy distribution in the context of synchrotron self-absorbed emission from the explosion’s forward shock as it expands in the circumstellar medium (CSM) previously sculpted by the mass-loss history of the stellar progenitor. VLBA observations and modeling of the VLA data point to a blastwave with average velocity ∼0.06
c
that carries an energy of ≈10
49
erg. Our modeling further reveals a flat CSM density profile
ρ
CSM
∝
R
−0.03±0.22
up to a break radius
R
br
≈ (1.96 ± 0.10) × 10
16
cm, with a steep density gradient following
ρ
CSM
∝
R
−2.3±0.5
at larger radii. We infer that the flat part of the density profile corresponds to a CSM shell with mass ∼0.021
M
☉
, and that the progenitor’s effective mass-loss rate varied with time over the range (50–500) × 10
−5
M
☉
yr
−1
for an adopted wind velocity
v
w
= 1000 km s
−1
and shock microphysical parameters
ϵ
e
= 0.1,
ϵ
B
= 0.01. These results add to the mounting observational evidence for departures from the traditional single-wind mass-loss scenarios in evolved, massive stars in the centuries leading up to core collapse. Potentially viable scenarios include mass loss powered by gravity waves and/or interaction with a binary companion.
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