Deep radio imaging of 47 Tuc identifies the peculiar X-ray source X9 as a new black hole candidate

ABSTRACT Using a 16.2-h radio observation by the Australia Telescope Compact Array and archival Chandra data, we found >5σ radio counterparts to four known and three new X-ray sources within the half-light radius (rh) of the Galactic globular cluster NGC 6397. The previously suggested millisecond pulsar (MSP) candidate, U18, is a steep-spectrum (Sν ∝ να; $\alpha =-2.0^{+0.4}_{-0.5}$) radio source with a 5.5-GHz flux density of 54.7 ± 4.3 $\mu \mathrm{ Jy}$. We argue that U18 is most likely a ‘hidden’ MSP that is continuously hidden by plasma shocked at the collision between the winds from the pulsar and companion star. The non-detection of radio pulsations so far is probably the result of enhanced scattering in this shocked wind. On the other hand, we observed the 5.5-GHz flux of the known MSP PSR J1740−5340 (U12) to decrease by a factor of >2.8 during epochs of 1.4-GHz eclipse, indicating that the radio flux is absorbed in its shocked wind. If U18 is indeed a pulsar whose pulsations are scattered, we note the contrast with U12’s flux decreases in eclipse, which argues for two different eclipse mechanisms at the same radio frequency. In addition to U12 and U18, we also found radio associations for five other Chandra X-ray sources, four of which are likely background galaxies. The last, U97, which shows strong H α variability, is mysterious; it may be either a quiescent black hole low-mass X-ray binary or something more unusual.

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Properties of Faint X-ray Activity of XTE J1908+094 in 2019

Galaxies ◽

10.3390/galaxies9020025 ◽

2021 ◽

Vol 9 (2) ◽

pp. 25

Author(s):

Debjit Chatterjee ◽

Arghajit Jana ◽

Kaushik Chatterjee ◽

Riya Bhowmick ◽

Sujoy Kumar Nath ◽

...

Keyword(s):

Black Hole ◽

Temporal Analysis ◽

Power Density Spectrum ◽

Periodic Oscillations ◽

Telescope Array ◽

Density Spectrum ◽

X Ray ◽

Black Hole Candidate ◽

Short Period ◽

Spectral State

We study the properties of the faint X-ray activity of Galactic transient black hole candidate XTE J1908+094 during its 2019 outburst. Here, we report the results of detailed spectral and temporal analysis during this outburst using observations from Nuclear Spectroscopic Telescope Array (NuSTAR). We have not observed any quasi-periodic-oscillations (QPOs) in the power density spectrum (PDS). The spectral study suggests that the source remained in the softer (more precisely, in the soft–intermediate) spectral state during this short period of X-ray activity. We notice a faint but broad Fe Kα emission line at around 6.5 keV. We also estimate the probable mass of the black hole to be 6.5−0.7+0.5M⊙, with 90% confidence.

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Slow decline and rise of the broad [O iii] emission line in globular cluster black hole candidate RZ2109

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2514 ◽

2019 ◽

Vol 489 (4) ◽

pp. 4783-4790 ◽

Cited By ~ 1

Author(s):

Kristen C Dage ◽

Stephen E Zepf ◽

Arash Bahramian ◽

Jay Strader ◽

Thomas J Maccarone ◽

...

Keyword(s):

Black Hole ◽

Emission Line ◽

Globular Clusters ◽

X Ray ◽

Hydrogen Emission ◽

Black Hole Candidate ◽

The Core ◽

Spectroscopic Monitoring ◽

Slow Decline ◽

Over Time

ABSTRACT RZ2109 is the first of several extragalactic globular clusters shown to host an ultraluminous X-ray source. RZ2109 is particularly notable because optical spectroscopy shows it has broad, luminous [O iii] λλ4959,5007 emission, while also having no detectable hydrogen emission. The X-ray and optical characteristics of the source in RZ2109 make it a good candidate for being a stellar mass black hole accreting from a white dwarf donor (i.e. an ultracompact black hole X-ray binary). In this paper we present optical spectroscopic monitoring of the [O iii]5007 emission line from 2007 to 2018. We find that the flux of the emission line is significantly lower in recent observations from 2016 to 2018 than it was in earlier observations in 2007–2011. We also explore the behaviour of the emission line shape over time. Both the core and the wings of the emission line decline over time, with some evidence that the core declines more rapidly than the wings. However, the most recent observations (in 2019) unexpectedly show the emission line core rebrightening

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Tracing Black Hole Signatures in Several Black Hole Candidates Based on Their X-Ray Spectral Evolution

EPJ Web of Conferences ◽

10.1051/epjconf/202024004001 ◽

2020 ◽

Vol 240 ◽

pp. 04001

Author(s):

Fahmi Iman Alfarizki ◽

Kiki Vierdayanti

Keyword(s):

Black Hole ◽

Compact Object ◽

Spectral Evolution ◽

Thermal Component ◽

X Ray ◽

Black Hole Candidate ◽

Spectral Fitting ◽

Transient Nature ◽

Transient System ◽

Black Hole Candidates

Investigation of spectral evolution of four black hole candidates was carried out by using color-color diagram as well as spectral fitting on Swift/XRT data. Newly found candidates, which are classified as low-mass X-ray binary system based on their transient nature, are the focus of our work. We compare their spectral evolutions to that of XTE J1752-223, a transient system and a more convincing black hole candidate whose mass has been determined from spectral-timing correlation scaling. In addition, comparison to Cygnus X-1, a well-known stellar-mass black hole, was done despite its persistent nature. The spectral fitting, by using a combination of thermal disk and non-thermal component model, results in the innermost temperature values in the range of the typical innermost temperature of black hole binary which is 0.7 – 1.5 keV. The spectral evolutions of the candidates bear a resemblance to both Cygnus X-1 and XTE J1752-223. We note that during Swift/XRT observations, the spectra of Cygnus X-1 and IGR J17451-3022 are mostly dominated by the non- thermal component. We conclude that the compact object of MAXI J1535- 571 and MAXI J1828-249 is highly likely to be a black hole. However, the lack of data rendered conclusive result impossible for IGR J17454-2919.

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TTM Observations of X1755-338

International Astronomical Union Colloquium ◽

10.1017/s0252921100035314 ◽

1995 ◽

Vol 151 ◽

pp. 334-335

Author(s):

H.C. Pan ◽

G.K. Skinner ◽

R.A. Sunyaev ◽

K.N. Borozdin

Keyword(s):

Black Hole ◽

Energy Resolution ◽

Space Station ◽

Galactic Centre ◽

Imaging Spectrometer ◽

X Ray ◽

Black Hole Candidate ◽

Coded Mask

X1755-338 is an X-ray binary source which displays X-ray dips with a 4.4 hour period (White et al. 1984). It was previously noted as an unusually soft X-ray source by Jones (1977) and was suggested later as a black-hole candidate (BHC) by White & Marshall (1984), and White et al. (1984), based on the similarity of its location in an X-ray colour-colour diagram to that of a group of BHCs.The TTM is a coded-mask imaging spectrometer on board the KVANT module of the MIR space station. It is capable of producing images in the 2 – 30 keV band with an energy resolution of about 18% at 6 keV. The instrumental details are given in Brinkman et al. (1985).We observed X1755-338 in 1989 March-September during the period of the TTM Galactic Centre Survey.

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Discovery of a New X-ray Transient in Scorpius GRO J1655-40 ≡ X-ray Nova Scorpii 1994

Symposium - International Astronomical Union ◽

10.1017/s0074180900055820 ◽

1996 ◽

Vol 165 ◽

pp. 363-367

Author(s):

W.S. Paciesas ◽

S.N. Zhang ◽

B.C. Rubin ◽

B.A. Harmon ◽

C.A. Wilson ◽

...

Keyword(s):

Black Hole ◽

High Resolution ◽

Power Law ◽

Radio Observations ◽

X Ray ◽

Black Hole Candidate ◽

Radio Jets ◽

Transient Source ◽

Galactic Source ◽

Photon Index

A bright transient X-ray source, GRO J1655-40 (X-ray Nova Scorpii 1994) was discovered with BATSE (the Burst and Transient Source Experiment) in late July 1994. More recently, the source also became a strong radio emitter, its rise in the radio being approximately anti-correlated with a decline in the hard X-ray intensity. High-resolution radio observations subsequent to this symposium showed evidence for superluminally expanding jets. Since the hard X-ray emission extends to at least 200 keV and we find no evidence of pulsations, we tentatively classify the source as a black-hole candidate. However, its hard X-ray spectrum is unusually steep (power-law photon index α ≃ −3) relative to most other black-hole candidates. In this regard, it resembles GRS 1915+105, the first galactic source to show superluminal radio jets.

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