The face-on disc of MAXI J1836−194 Russell, T. D; Soria, R; Motch, C ...
Monthly notices of the Royal Astronomical Society,
04/2014, Letnik:
439, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We present Very Large Telescope optical spectra of the black hole candidate X-ray binary MAXI J1836−194 at the onset of its 2011 outburst. Although the spectrum was taken at the beginning of the ...outburst and contains a significant contribution from the optically thin synchrotron emission that originates in the radio jet, we find that the accretion disc was already large and bright. Single-peaked, narrow Hα and He ii λ4686 lines imply the most face-on accretion disc observed in a black hole low-mass X-ray binary to date, with an inclination angle between 4° and 15°, assuming a black hole mass of between 5 and 12 M, for distances of between 4 and 10 kpc. We use New Technology Telescope observations of the system in quiescence to place strong upper limits on the mass and radius of the donor star and the orbital period. The donor is a main-sequence star with a mass <0.65 M and a radius <0.59 R with an orbital period of <4.9 h. From those values and Roche lobe geometry constraints we find that the compact object must be >1.9 M if the system is located 4 kpc away and >7.0 M at 10 kpc.
Aims.
The modelling of spectroscopic observations of tidal disruption events (TDEs) to date suggests that the newly formed accretion disks are mostly quasi-circular. In this work we study the ...transient event AT 2020zso, hosted by an active galactic nucleus (AGN; as inferred from narrow emission line diagnostics), with the aim of characterising the properties of its newly formed accretion flow.
Methods.
We classify AT 2020zso as a TDE based on the blackbody evolution inferred from UV/optical photometric observations and spectral line content and evolution. We identify transient, double-peaked Bowen (N
III
), He
I
, He
II,
and H
α
emission lines. We model medium-resolution optical spectroscopy of the He
II
(after careful de-blending of the N
III
contribution) and H
α
lines during the rise, peak, and early decline of the light curve using relativistic, elliptical accretion disk models.
Results.
We find that the spectral evolution before the peak can be explained by optical depth effects consistent with an outflowing, optically thick Eddington envelope. Around the peak, the envelope reaches its maximum extent (approximately 10
15
cm, or ∼3000–6000 gravitational radii for an inferred black hole mass of 5−10 × 10
5
M
⊙
) and becomes optically thin. The H
α
and He
II
emission lines at and after the peak can be reproduced with a highly inclined (
i
= 85 ± 5 degrees), highly elliptical (
e
= 0.97 ± 0.01), and relatively compact (
R
in
= several 100
R
g
and
R
out
= several 1000
R
g
) accretion disk.
Conclusions.
Overall, the line profiles suggest a highly elliptical geometry for the new accretion flow, consistent with theoretical expectations of newly formed TDE disks. We quantitatively confirm, for the first time, the high inclination nature of a Bowen (and X-ray dim) TDE, consistent with the unification picture of TDEs, where the inclination largely determines the observational appearance. Rapid line profile variations rule out the binary supermassive black hole hypothesis as the origin of the eccentricity; these results thus provide a direct link between a TDE in an AGN and the eccentric accretion disk. We illustrate for the first time how optical spectroscopy can be used to constrain the black hole spin, through (the lack of) disk precession signatures (changes in inferred inclination). We constrain the disk alignment timescale to > 15 days in AT2020zso, which rules out high black hole spin values (
a
< 0.8) for
M
BH
∼ 10
6
M
⊙
and disk viscosity
α
≳ 0.1.
Using high-precision astrometric optical observations from the Walter Baade Magellan Telescope in conjunction with high-resolution very long baseline interferometric (VLBI) radio imaging with the ...Very Long Baseline Array (VLBA), we have located the core of the X-ray binary system XTE J1752−223. Compact radio emission from the core was detected following the state transition from the soft to the hard X-ray state. Its position to the south-east of all previously detected jet components mandated a re-analysis of the existing VLBI data. Our analysis suggests that the outburst comprised at least two ejection events prior to 2010 February 26. No radio-emitting components were detected to the south-east of the core at any epoch, suggesting that the receding jets were Doppler-deboosted below our sensitivity limit. From the ratio of the brightness of the detected components to the measured upper limits for the receding ejecta, we constrain the jet speed β > 0.66 and the inclination angle to the line of sight θ < 49°. Assuming that the initial ejection event occurred at the transition from the hard intermediate state to the soft intermediate state, an initial period of ballistic motion followed by a Sedov phase (i.e. self-similar adiabatic expansion) appears to fit the motion of the ejecta better than a uniform deceleration model. The accurate core location can provide a long time baseline for a future proper motion determination should the system show a second outburst, providing insights into the formation mechanism of the compact object.
ABSTRACT
Tidal disruption events (TDEs) occur when a star gets torn apart by a supermassive black hole as it crosses its tidal radius. We present late-time optical and X-ray observations of the ...nuclear transient AT2019qiz, which showed the typical signs of an optical-UV transient class commonly believed to be TDEs. Optical spectra were obtained 428, 481, and 828 rest-frame days after optical light-curve peak, and a UV/X-ray observation coincided with the later spectrum. The optical spectra show strong coronal emission lines, including Fe vii, Fe x, Fe xi, and Fe xiv. The Fe lines rise and then fall, except Fe xiv that appears late and rises. We observe increasing flux of narrow H α and H β and a decrease in broad H α flux. The coronal lines have full width at half-maximum ranging from ∼150−300 km s−1, suggesting they originate from a region between the broad- and narrow-line emitting gas. Between the optical flare and late-time observation, the X-ray spectrum softens dramatically. The 0.3–1 keV X-ray flux increases by a factor of ∼50, while the hard X-ray flux decreases by a factor of ∼6. Wide-field Infrared Survey Explorer fluxes also rose over the same period, indicating the presence of an infrared echo. With AT2017gge, AT2019qiz is one of two examples of a spectroscopically confirmed optical-UV TDE showing delayed coronal line emission, supporting speculations that Extreme Coronal Line Emitters in quiescent galaxies can be echos of unobserved past TDEs. We argue that the coronal lines, narrow lines, and infrared emission arise from the illumination of pre-existing material likely related to either a previous TDE or active galactic nucleus activity.
ABSTRACT
We present a dynamical study of the intermediate polar and dwarf nova cataclysmic variable GK Persei (Nova Persei 1901) based on a multisite optical spectroscopy and R-band photometry ...campaign. The radial velocity curve of the evolved donor star has a semi-amplitude $K_2=126.4 \pm 0.9 \, \mathrm{km}\, \mathrm{s}^{-1}$ and an orbital period $P=1.996872 \pm 0.000009 \, \mathrm{d}$. We refine the projected rotational velocity of the donor star to $v_\mathrm{rot} \sin i = 52 \pm 2 \, \mathrm{km}\, \mathrm{s}^{-1}$ that, together with K2, provides a donor star to white dwarf mass ratio q = M2/M1 = 0.38 ± 0.03. We also determine the orbital inclination of the system by modelling the phase-folded ellipsoidal light curve and obtain i = 67° ± 5°. The resulting dynamical masses are $M_{1}=1.03^{+0.16}_{-0.11} \, \mathrm{M}_{\odot }$ and $M_2 = 0.39^{+0.07}_{-0.06} \, \mathrm{M}_{\odot }$ at 68 per cent confidence level. The white dwarf dynamical mass is compared with estimates obtained by modelling the decline light curve of the 1901 nova event and X-ray spectroscopy. The best matching mass estimates come from the nova light curve models and an X-ray data analysis that uses the ratio between the Alfvén radius in quiescence and during dwarf nova outburst.
The optical/near-infrared (OIR) region of the spectra of low-mass X-ray binaries (XBs) appears to lie at the intersection of a variety of different emission processes. In this paper we present ...quasi-simultaneous OIR–X-ray observations of 33 XBs in an attempt to estimate the contributions of various emission processes in these sources, as a function of X-ray state and luminosity. A global correlation is found between OIR and X-ray luminosity for low-mass black hole candidate XBs (BHXBs) in the hard X-ray state, of the form LOIR∝L0.6X. This correlation holds over eight orders of magnitude in LX and includes data from BHXBs in quiescence and at large distances Large Magellanic Cloud (LMC) and M31. A similar correlation is found in low-mass neutron star XBs (NSXBs) in the hard state. For BHXBs in the soft state, all the near-infrared (NIR) and some of the optical emissions are suppressed below the correlation, a behaviour indicative of the jet switching off/on in transition to/from the soft state. We compare these relations to theoretical models of a number of emission processes. We find that X-ray reprocessing in the disc and emission from the jets both predict a slope close to 0.6 for BHXBs, and both contribute to the OIR in BHXBs in the hard state, the jets producing ∼90 per cent of the NIR emission at high luminosities. X-ray reprocessing dominates the OIR in NSXBs in the hard state, with possible contributions from the jets (only at high luminosity) and the viscously heated disc. We also show that the optically thick jet spectrum of BHXBs extends to near the K band. OIR spectral energy distributions of 15 BHXBs help us to confirm these interpretations. We present a prediction of the LOIR–LX behaviour of a BHXB outburst that enters the soft state, where the peak LOIR in the hard state rise is greater than in the hard state decline (the well-known hysteretical behaviour). In addition, it is possible to estimate the X-ray, OIR and radio luminosity and the mass accretion rate in the hard state quasi-simultaneously, from observations of just one of these wavebands, since they are all linked through correlations. Finally, we have discovered that the nature of the compact object, the mass of the companion and the distance/reddening can be constrained by quasi-simultaneous OIR and X-ray luminosities.
Abstract Fast X-ray Transients (FXTs) are extragalactic bursts of soft X-rays first identified ≳10 yr ago. Since then, nearly 40 events have been discovered, although almost all of these have been ...recovered from archival Chandra and XMM-Newton data. To date, optical sky surveys and follow-up searches have not revealed any multiwavelength counterparts. The Einstein Probe, launched in 2024 January, has started surveying the sky in the soft X-ray regime (0.5–4 keV) and will rapidly increase the sample of FXTs discovered in real time. Here we report the first discovery of both an optical and radio counterpart to a distant FXT, the fourth source publicly released by the Einstein Probe. We discovered a fast-fading optical transient within the 3′ localization radius of EP 240315a with the all-sky optical survey ATLAS, and our follow-up Gemini spectrum provides a redshift, z = 4.859 ± 0.002. Furthermore, we uncovered a radio counterpart in the S band (3.0 GHz) with the MeerKAT radio interferometer. The optical (rest-frame UV) and radio luminosities indicate that the FXT most likely originates from either a long gamma-ray burst or a relativistic tidal disruption event. This may be a fortuitous early mission detection by the Einstein Probe or may signpost a mode of discovery for high-redshift, high-energy transients through soft X-ray surveys, combined with locating multiwavelength counterparts.
Context.
Extragalactic fast X-ray transients (FXTs) are short flashes of X-ray photons of unknown origin that last a few minutes to hours.
Aims.
We extend the previous search for extragalactic FXTs ...(based on sources in the
Chandra
Source Catalog 2.0, CSC2) to further
Chandra
archival data between 2014 and 2022.
Methods.
We extracted X-ray data using a method similar to that employed by CSC2 and applied identical search criteria as in previous work.
Results.
We report the detection of eight FXT candidates, with peak 0.3–10 keV fluxes between 1 × 10
−13
to 1 × 10
−11
erg cm
−2
s
−1
and
T
90
values from 0.3 to 12.1 ks. This sample of FXTs likely has redshifts between 0.7 and 1.8. Three FXT candidates exhibit light curves with a plateau (≈1−3 ks duration) followed by a power-law decay and X-ray spectral softening, similar to what was observed for a few before-reported FXTs. In light of the new, expanded source lists (eight FXTs with known redshifts from a previous paper and this work), we have updated the event sky rates derived previously, finding 36.9
−8.3
+9.7
deg
−2
yr
−1
for the extragalactic samples for a limiting flux of ≳1 × 10
−13
erg cm
−2
s
−1
, calculated the first FXT X-ray luminosity function, and compared the volumetric density rate between FXTs and other transient classes.
Conclusions.
Our latest
Chandra
-detected extragalactic FXT candidates boost the total
Chandra
sample by ∼50%, and appear to have a similar diversity of possible progenitors.
We report on the discovery of an apparent triple radio structure hidden inside the radio bubble of the ultraluminous X-ray source Holmberg II X-1. The morphology is consistent with a collimated jet ...structure, which is observed to emit optically thin synchrotron radiation. The central component has a steep radio spectrum and is brighter than the outer components indicating a renewed radio activity. We estimate a minimum time-averaged jet power of ∼2 × 1039 erg s−1 that is associated with a time-averaged isotropic X-ray luminosity of at least 4 × 1039 erg s−1. Our results suggest that Holmberg II X-1 is powered by a black hole of M
BH ≥ 25 M, that is inferred to be accreting at a high Eddington rate with intermittent radio activity.
Abstract
We present the results of a photometric and spectroscopic analysis of the Galactic Bulge Survey X-ray source CXOGBS J174954.5−294335 (hereafter, referred to as CX19). CX19 is a long period, ...eclipsing intermediate polar-type cataclysmic variable with broad, single-peaked Balmer and Paschen emission lines along with He ii λ4686 and Bowen blend emission features. With coverage of one full and two partial eclipses and archival photometry, we determine the ephemeris for CX19 to be HJD(eclipse) = 2455691.8581(5) + 0.358704(2) × N. We also recovered the white dwarf spin period of P
spin = 503.32(3) s that gives a P
spin/P
orb = 0.016(6), comparable to several confirmed, long-period intermediate polars. CX19 also shows a clear X-ray eclipse in the 0.3–8.0 keV range observed with Chandra. Two optical outbursts were observed lasting between 6 and 8 h (lower limits) reaching ∼1.3 mag in amplitude. The outbursts, both in duration and magnitude, the accretion disc-dominated spectra and hard X-ray emission are reminiscent of the intermediate polar V1223 Sgr sharing many of the same characteristics. If we assume a main-sequence companion, we estimate the donor to be an early G-type star and find a minimum distance of d ≈ 2.1 kpc and a 0.5–10.0 keV X-ray luminosity upper limit of 2.0 × 1033 erg s−1. Such an X-ray luminosity is consistent with a white dwarf accretor in a magnetic cataclysmic variable system. To date, CX19 is only the second deeply eclipsing intermediate polar with X-ray eclipses and the first that is optically accessible.
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