arXiv subjects

J. C. A. Miller-Jones

Publications and source records attributed to J. C. A. Miller-Jones.

At least 73 records · Page 4Linked to original sources

arXiv2021

Measuring fundamental jet properties with multi-wavelength fast timing of the black hole X-ray binary MAXI J1820+070

We present multi-wavelength fast timing observations of the black hole X-ray binary MAXI J1820+070 (ASASSN-18ey), taken with the Karl G. Jansky Very Large Array (VLA), Atacama Large Millimeter/Sub-Millimeter Array (ALMA), Very Large Telescope (VLT), New Technology Telescope (NTT), Neutron Star Interior Composition Explorer (NICER), and XMM-Newton. Our data set simultaneously samples ten different electromagnetic bands (radio - X-ray) over a 7-hour period during the hard state of the 2018-2019 outburst. The emission we observe is highly variable, displaying multiple rapid flaring episodes. To characterize the variability properties in our data, we implemented a combination of cross-correlation and Fourier analyses. We find that the emission is highly correlated between different bands, measuring time-lags ranging from hundreds of milliseconds between the X-ray/optical bands to minutes between the radio/sub-mm bands. Our Fourier analysis also revealed, for the first time in a black hole X-ray binary, an evolving power spectral shape with electromagnetic frequency. Through modelling these variability properties, we find that MAXI J1820+070 launches a highly relativistic ($Γ=6.81^{+1.06}_{-1.15}$) and confined ($ϕ=0.45^{+0.13}_{-0.11}$ deg) jet, which is carrying a significant amount of power away from the system (equivalent to $\sim0.6 \, L_{1-100{\rm keV}}$). We additionally place constraints on the jet composition and magnetic field strength in the innermost jet base region. Overall, this work demonstrates that time-domain analysis is a powerful diagnostic tool for probing jet physics, where we can accurately measure jet properties with time-domain measurements alone.

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arXiv2021

The black hole transient MAXI J1348-630: evolution of the compact and transient jets during its 2019/2020 outburst

We present the radio and X-ray monitoring campaign of the 2019/2020 outburst of MAXI J1348-630, a new black hole X-ray binary (XRB) discovered in 2019 January. We observed MAXI J1348-630 for $\sim$14 months in the radio band with MeerKAT and the Australia Telescope Compact Array (ATCA), and in the X-rays with MAXI and Swift/XRT. Throughout the outburst we detected and tracked the evolution of the compact and transient jets. Following the main outburst, the system underwent at least 4 hard-state-only re-flares, during which compact jets were again detected. For the major outburst, we observed the rise, quenching, and re-activation of the compact jets, as well as two single-sided discrete ejecta, launched $\sim$2 months apart and travelling away from the black hole. These ejecta displayed the highest proper motion ($\gtrsim$100 mas day$^{-1}$) ever measured for an accreting black hole binary. From the jet motion, we constrain the ejecta inclination and speed to be $\leq$46$^{\circ}$ and $\geq$0.69 $c$, and the opening angle and transverse expansion speed of the first component to be $\leq$6$^{\circ}$ and $\leq$0.05 $c$. We also infer that the first ejection happened at the hard-to-soft state transition, before a strong radio flare, while the second ejection was launched during a short excursion from the soft to the intermediate state. After traveling with constant speed, the first component underwent a strong deceleration, which was covered with unprecedented detail and suggested that MAXI J1348-630 could be located inside a low-density cavity in the interstellar medium, as already proposed for XTE J1550-564 and H1743-322.

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arXiv2021

Rapid-response radio observations of short GRB 181123B with the Australia Telescope Compact Array

We introduce the Australia Telescope Compact Array (ATCA) rapid-response mode by presenting the first successful trigger on the short-duration gamma-ray burst (GRB) 181123B. Early-time radio observations of short GRBs may provide vital insights into the radio afterglow properties of Advanced LIGO- and Virgo-detected gravitational wave events, which will in turn inform follow-up strategies to search for counterparts within their large positional uncertainties. The ATCA was on target within 12.6 hr post-burst, when the source had risen above the horizon. While no radio afterglow was detected during the 8.3 hr observation, we obtained force-fitted flux densities of $7 \pm 12$ and $15 \pm 11~μ$Jy at 5.5 and 9 GHz, respectively. Afterglow modelling of GRB 181123B showed that the addition of the ATCA force-fitted radio flux densities to the Swift X-ray Telescope detections provided more stringent constraints on the fraction of thermal energy in the electrons (log$ε_e = -0.75^{+0.39}_{-0.40}$ rather than log$ε_e = -1.13^{+0.82}_{-1.2}$ derived without the inclusion of the ATCA values), which is consistent with the range of typical $ε_e$ derived from GRB afterglow modelling. This allowed us to predict that the forward shock may have peaked in the radio band $\sim10$ days post-burst, producing detectable radio emission $\gtrsim3-4$ days post-burst. Overall, we demonstrate the potential for extremely rapid radio follow-up of transients and the importance of triggered radio observations for constraining GRB blast wave properties, regardless of whether there is a detection, via the inclusion of force-fitted radio flux densities in afterglow modelling efforts.

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arXiv2021

Toward a Larger Sample of Radio Jets from Quiescent Black Hole X-ray Binaries

Quiescent black hole X-ray binaries (X-ray luminosities <1e34 erg/s) are believed to be fed by hot accretion flows that launch compact, relativistic jets. However, due to their low luminosities, quiescent jets have been detected in the radio waveband from only five systems so far. Here, we present radio observations of two quiescent black hole X-ray binaries with the Australia Telescope Compact Array. One system, GS 1124-684, was not detected. The other system, BW Cir, was detected over two different epochs in 2018 and 2020, for which we also obtained quasi-simultaneous X-ray detections with Chandra and Swift. BW Cir is now the sixth quiescent X-ray binary with a confirmed radio jet. However, the distance to BW Cir is uncertain, and we find that BW Cir shows different behaviour in the radio/X-ray luminosity plane depending on the correct distance. Estimates based on its G-type subgiant donor star place BW Cir at >25 kpc, while initial optical astrometric measurements from Gaia Data Release 2 suggested likely distances of just a few kpc. Here, we use the most recent measurements from Gaia Early Data Release 3 and find a distance d=7.1(+4.8/-3.9) kpc and a potential kick velocity PKV=165(+81/-17) km/s, with distances up to ~20 kpc possible based on its parallax and proper motion. Even though there is now less tension between the parallax and donor-star based distance measurements, it remains an unresolved matter, and we conclude with suggestions on how to reconcile the two measurements.

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arXiv2021

Radio and optical observations of the possible AE Aqr twin, LAMOST J024048.51+195226.9

Thorstensen (2020) recently argued that the cataclysmic variable (CV) LAMOST J024048.51+195226.9 may be a twin to the unique magnetic propeller system AE Aqr. If this is the case, two predictions are that it should display a short period white dwarf spin modulation, and that it should be a bright radio source. We obtained follow-up optical and radio observations of this CV, in order to see if this holds true. Our optical high-speed photometry does not reveal a white dwarf spin signal, but lacks the sensitivity to detect a modulation similar to the 33-s spin signal seen in AE Aqr. We detect the source in the radio, and measure a radio luminosity similar to that of AE Aqr and close to the highest so far reported for a CV. We also find good evidence for radio variability on a time scale of tens of minutes. Optical polarimetric observations produce no detection of linear or circular polarization. While we are not able to provide compelling evidence, our observations are all consistent with this object being a propeller system.

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arXiv2021

AT 2019avd: A novel addition to the diverse population of nuclear transients

We report on SRG/eROSITA, ZTF, ASAS-SN, Las Cumbres, NEOWISE-R, and Swift XRT/UVOT observations of the unique ongoing event AT 2019avd, located in the nucleus of a previously inactive galaxy at $z=0.029$. eROSITA first observed AT 2019avd on 2020-04-28 during its first all sky survey, when it was detected as an ultra-soft X-ray source ($kT\sim 85$ eV) that was $\gtrsim 90$ times brighter in the $0.2-2$ keV band than a previous 3$σ$ upper flux detection limit (with no archival X-ray detection at this position). The ZTF optical light curve in the $\sim 450$ days preceding the eROSITA detection is double peaked, and the eROSITA detection coincides with the rise of the second peak. Follow-up optical spectroscopy shows the emergence of a Bowen fluorescence feature and high-ionisation coronal lines ([\ion{Fe}{X}] 6375 Å, [\ion{Fe}{XIV}] 5303 Å), along with persistent broad Balmer emission lines (FWHM$\sim 1400$ km s$^{-1}$). Whilst the X-ray properties make AT 2019avd a promising tidal disruption event (TDE) candidate, the optical properties are atypical for optically selected TDEs. We discuss potential alternative origins that could explain the observed properties of AT 2019avd, such as a stellar binary TDE candidate, or a TDE involving a super massive black hole binary.

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arXiv2020

Disk-jet coupling changes as a possible indicator for outbursts from GX 339-4 remaining within the X-ray hard state

We present quasi-simultaneous radio, (sub-)millimetre, and X-ray observations of the Galactic black hole X-ray binary GX 339-4, taken during its 2017--2018 outburst, where the source remained in the hard X-ray spectral state. During this outburst, GX 339-4 showed no atypical X-ray behaviour that may act as a indicator for an outburst remaining within the hard state. However, quasi-simultaneous radio and X-ray observations showed a flatter than expected coupling between the radio and X-ray luminosities (with a best fit relation of $L_{\rm radio} \propto L_{\rm X}^{0.39 \pm 0.06}$), when compared to successful outbursts from this system ($L_{\rm radio} \propto L_{\rm X}^{0.62 \pm 0.02}$). While our 2017--2018 outburst data only span a limited radio and X-ray luminosity range ($\sim$1 order of magnitude in both, where more than 2-orders of magnitude in $L_{\rm X}$ is desired), including data from other hard-only outbursts from GX 339-4 extends the luminosity range to $\sim$1.2 and $\sim$2.8 orders of magnitude, respectively, and also results in a flatter correlation (where $L_{\rm radio} \propto L_{\rm X}^{0.46 \pm 0.04}$). This result is suggestive that for GX 339-4 a flatter radio -- X-ray correlation, implying a more inefficient coupling between the jet and accretion flow, could act as an indicator for a hard-only outburst. However, further monitoring of both successful and hard-only outbursts over larger luminosity ranges with strictly simultaneous radio and X-ray observations is required from different, single sources, to explore if this applies generally to the population of black hole X-ray binaries, or even GX 339-4 at higher hard-state luminosities.

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arXiv2020

Observations of the Disk/Jet Coupling of MAXI J1820+070 During its Descent to Quiescence

Black hole X-ray binaries in the quiescent state (Eddington ratios typically $\lesssim$10$^{-5}$) display softer X-ray spectra (photon indices $Γ\sim2$) compared to higher-luminosity black hole X-ray binaries in the hard state ($Γ\sim1.7$). However, the cause of this softening, and its implications for the underlying accretion flow, are still uncertain. Here, we present quasi-simultaneous X-ray and radio spectral monitoring of the black hole X-ray binary MAXI J1820$+$070 during the decay of its 2018 outburst and of a subsequent re-flare in 2019, providing an opportunity to monitor a black hole X-ray binary as it actively transitions into quiescence. We probe 1-10 keV X-ray luminosities as low as $L_{\rm X}\sim4\times10^{32}$ erg s$^{-1}$, equivalent to Eddington fractions of $\sim4\times10^{-7}$. During its decay towards quiescence, the X-ray spectrum of MAXI J1820$+$070 softens from $Γ\sim1.7$ to $Γ\sim2$, with the softening taking $\sim30$d, and completing at $L_{\rm X}\approx10^{34}$ erg s$^{-1}$ ($\approx10^{-5} L_{\rm Edd}$). While the X-ray spectrum softens, the radio spectrum generally remains flat/inverted throughout the decay. We also find that MAXI J1820$+$070 follows a radio ($L_{\rm R}$) -- X-ray luminosity correlation of the form $L_{\rm R} \propto L_{\rm X}^{0.52\pm0.07}$, making it the fourth black hole system to follow the so-called `standard track' unbroken over several (in this case, four) decades in $L_{\rm X}$. Comparing the radio/X-ray spectral evolution(s) with the $L_{\rm R}$ -- $L_{\rm X}$ plane, we find that the X-ray softening is consistent with X-rays produced by Comptonization processes in a radiatively inefficient accretion flow. We generally disfavor X-ray emission originating solely from within the jet, with the possible exception of X-rays produced via synchrotron self-Compton processes.

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arXiv2020

Delimiting the black hole mass in the X-ray transient MAXI J1659-152 with H$α$ spectroscopy

MAXI J1659-152 is a 2.4 h orbital period X-ray dipping transient black hole candidate. We present spectroscopy of its $I\approx23$ quiescent counterpart where we detect H$α$ emission with full-width at half-maximum (FWHM) of $3200 \pm 300$ km s$^{-1}$. Applying the correlation between the H$α$ FWHM and radial velocity semi-amplitude of the donor star for quiescent X-ray transients, we derive $K_2 = 750 \pm 80$ km s$^{-1}$. The orbital period and $K_2$ lead to a mass function of $4.4\pm1.4~M{_\odot}$ (1$σ$). The donor to compact object mass ratio and binary inclination are likely in the range $q={M_2}/{M_1} = 0.02-0.07$ and $i=70{^\circ}-80{^\circ}$. These constraints imply a 68% confidence level interval for the compact object mass of $3.3 \lesssim M_1(M_\odot) \lesssim 7.5$, confirming its black hole nature. These quasi-dynamical limits are compared to mass estimates from modelling of X-ray data and any discrepancies are discussed. We review the properties of optical spectroscopy and time-series photometry collected during the 2010-2011 outburst. We interpret the apparent modulations found soon after the onset of high-accretion activity and during the 2011 rebrightening event as originating in the accretion disc. These have signatures consistent with superhumps, with the 2011 modulation having a fractional period excess $< 0.6\%$ (3$σ$). We propose that direct irradiation of the donor by the central X-ray source was not possible due to its occultation by the disc outer regions. We argue that disc shielding significantly weakens the donor star contribution to the optical variability in systems with $q\lesssim0.07$, including neutron star ultra-compact X-ray binaries.

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arXiv2020

Measuring the distance to the black hole candidate X-ray binary MAXI J1348-630 using HI absorption

We present HI absorption spectra of the black hole candidate X-ray binary (XRB) MAXI J1348-630 using the Australian Square Kilometre Array Pathfinder (ASKAP) and MeerKAT. The ASKAP HI spectrum shows a maximum negative radial velocity (with respect to the local standard of rest) of $-31\pm4$ km s$^{-1}$ for MAXI J1348-630, as compared to $-50\pm4$ km s$^{-1}$ for a stacked spectrum of several nearby extragalactic sources. This implies a most probable distance of $2.2^{+0.5}_{-0.6}$ kpc for MAXI J1348-630, and a strong upper limit of the tangent point distance at $5.3\pm0.1$ kpc. Our preferred distance implies that MAXI J1348-630 reached $17\pm10$ % of the Eddington luminosity at the peak of its outburst, and that the source transited from the soft to the hard X-ray spectral state at $2.5\pm1.5$ % of the Eddington luminosity. The MeerKAT HI spectrum of MAXI J1348-630 (obtained from the older, low-resolution 4k mode) is consistent with the re-binned ASKAP spectrum, highlighting the potential of the eventual capabilities of MeerKAT for XRB spectral line studies.

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arXiv2020

A new lepto-hadronic model applied to the first simultaneous multiwavelength data set for Cygnus X--1

Cygnus X--1 is the first Galactic source confirmed to host an accreting black hole. It has been detected across the entire electromagnetic spectrum from radio to GeV $γ$-rays. The source's radio through mid-infrared radiation is thought to originate from the relativistic jets. The observed high degree of linear polarisation in the MeV X-rays suggests that the relativistic jets dominate in this regime as well, whereas a hot accretion flow dominates the soft X-ray band. The origin of the GeV non-thermal emission is still debated, with both leptonic and hadronic scenarios deemed to be viable. In this work, we present results from a new semi-analytical, multi-zone jet model applied to the broad-band spectral energy distribution of Cygnus X--1 for both leptonic and hadronic scenarios. We try to break this degeneracy by fitting the first-ever high-quality, simultaneous multiwavelength data set obtained from the CHOCBOX campaign (Cygnus X--1 Hard state Observations of a Complete Binary Orbit in X-rays). Our model parameterises dynamical properties, such as the jet velocity profile, the magnetic field, and the energy density. Moreover, the model combines these dynamical properties with a self-consistent radiative transfer calculation including secondary cascades, both of leptonic and hadronic origin. We conclude that sensitive TeV $γ$-ray telescopes like Cherenkov Telescope Array (CTA) will definitively answer the question of whether hadronic processes occur inside the relativistic jets of Cygnus X--1.

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arXiv2020

Rapid compact jet quenching in the Galactic black hole candidate X-ray binary MAXI J1535-571

We present results from six epochs of quasi-simultaneous radio, (sub-)millimetre, infrared, optical, and X-ray observations of the black hole X-ray binary MAXI~J1535$-$571. These observations show that as the source transitioned through the hard-intermediate X-ray state towards the soft intermediate X-ray state, the jet underwent dramatic and rapid changes. We observed the frequency of the jet spectral break, which corresponds to the most compact region in the jet where particle acceleration begins (higher frequencies indicate closer to the black hole), evolve from the IR band into the radio band (decreasing by $\approx$3 orders of magnitude) in less than a day. During one observational epoch, we found evidence of the jet spectral break evolving in frequency through the radio band. Estimating the magnetic field and size of the particle acceleration region shows that the rapid fading of the high-energy jet emission was not consistent with radiative cooling; instead the particle acceleration region seems to be moving away from the black hole on approximately dynamical timescales. This result suggests that the compact jet quenching is not caused by local changes to the particle acceleration, rather we are observing the acceleration region of the jet travelling away from the black hole with the jet flow. Spectral analysis of the X-ray emission show a gradual softening in the few days before the dramatic jet changes, followed by a more rapid softening $\sim$1--2\,days after the onset of the jet quenching.

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arXiv2020

A MeerKAT Survey of Nearby Novalike Cataclysmic Variables

We present the results of MeerKAT radio observations of eleven nearby novalike cataclysmic variables. We have detected radio emission from IM Eri, RW Sex, V3885 Sgr and V603 Aql. While RW Sex, V3885 Sgr and V603 Aql had been previously detected, this is the first reported radio detection of IM Eri. Our observations have doubled the sample of non-magnetic CVs with sensitive radio data. We observe that at our radio detection limits, a specific optical luminosity $\gtrsim 2.2\times 10^{18}$ erg/s/Hz (corresponding to $M_V \lesssim 6.0$) is required to produce a radio detection. We also observe that the X-ray and radio luminosities of our detected novalikes are on an extension of the $L_{X} \propto L_{R}^{\sim 0.7}$ power law originally proposed for non-pulsating neutron star low-mass X-ray binaries. We find no other correlations between the radio emission and emission in other wavebands or any other system parameters for the existing sample of radio-detected non-magnetic CVs. We measure in-band (0.9-1.7 GHz) radio spectral indices that are consistent with reports from earlier work. Finally, we constructed broad spectral energy distributions for our sample from published multi-wavelength data, and use them to place constraints on the mass transfer rates of these systems.

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arXiv2020

The variable radio counterpart of Swift J1858.6-0814

Swift J1858.6-0814 is a transient neutron star X-ray binary discovered in October 2018. Multi-wavelength follow-up observations across the electromagnetic spectrum revealed many interesting properties, such as erratic flaring on minute timescales and evidence for wind outflows at both X-ray and optical wavelengths, strong and variable local absorption, and an anomalously hard X-ray spectrum. Here, we report on a detailed radio observing campaign consisting of one observation at 5.5/9 GHz with the Australia Telescope Compact Array, and nine observations at 4.5/7.5 GHz with the Karl G. Jansky Very Large Array. A radio counterpart with a flat to inverted radio spectrum is detected in all observations, consistent with a compact jet being launched from the system. Swift J1858.6-0814 is highly variable at radio wavelengths in most observations, showing significant variability when imaged on 3-to-5-minute timescales and changing up to factors of 8 within 20 minutes. The periods of brightest radio emission are not associated with steep radio spectra, implying they do not originate from the launching of discrete ejecta. We find that the radio variability is similarly unlikely to have a geometric origin, be due to scintillation, or be causally related to the observed X-ray flaring. Instead, we find that it is consistent with being driven by variations in the accretion flow propagating down the compact jet. We compare the radio properties of Swift J1858.6-0814 with those of Eddington-limited X-ray binaries with similar X-ray and optical characteristics, but fail to find a match in radio variability, spectrum, and luminosity.

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arXiv2020

On the nature of the soft gamma-ray emission in the hard state of the black hole transient GRS 1716-249

The black hole transient GRS 1716-249 was monitored from the radio to the gamma-ray band during its 2016-2017 outburst. This paper focuses on the Spectral Energy Distribution (SED) obtained in 2017 February-March, when GRS 1716-249 was in a bright hard spectral state. The soft gamma-ray data collected with the INTEGRAL/SPI telescope show the presence of a spectral component which is in excess of the thermal Comptonisation emission. This component is usually interpreted as inverse Compton emission from a tiny fraction of non-thermal electrons in the X-ray corona. We find that hybrid thermal/non-thermal Comptonisation models provide a good fit to the X/gamma-ray spectrum of GRS 1716-249. The best-fit parameters are typical of the bright hard state spectra observed in other black hole X-ray binaries. Moreover, the magnetised hybrid Comptonisation model BELM provides an upper limit on the intensity of the coronal magnetic field of about 1E+06 G. Alternatively, this soft gamma-ray emission could originate from synchrotron emission in the radio jet. In order to test this hypothesis, we fit the SED with the irradiated disc plus Comptonisation model combined with the jet internal shock emission model ISHEM. We found that a jet with an electron distribution of p~2.1 can reproduce the soft gamma-ray emission of GRS 1716-249. However, if we introduce the expected cooling break around 10 keV, the jet model can no longer explain the observed soft gamma-ray emission, unless the index of the electron energy distribution is significantly harder (p<2).

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arXiv2020

An extremely powerful long-lived superluminal ejection from the black hole MAXI J1820+070

Black holes in binary systems execute patterns of outburst activity where two characteristic X-ray states are associated with different behaviours observed at radio wavelengths. The hard state is associated with radio emission indicative of a continuously replenished, collimated, relativistic jet, whereas the soft state is rarely associated with radio emission, and never continuously, implying the absence of a quasi-steady jet. Here we report radio observations of the black hole transient MAXI J1820$+$070 during its 2018 outburst. As the black hole transitioned from the hard to soft state we observed an isolated radio flare, which, using high angular resolution radio observations, we connect with the launch of bi-polar relativistic ejecta. This flare occurs as the radio emission of the core jet is suppressed by a factor of over 800. We monitor the evolution of the ejecta over 200 days and to a maximum separation of 10$''$, during which period it remains detectable due to in-situ particle acceleration. Using simultaneous radio observations sensitive to different angular scales we calculate an accurate estimate of energy content of the approaching ejection. This energy estimate is far larger than that derived from state transition radio flare, suggesting a systematic underestimate of jet energetics.

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arXiv2020

A radio parallax to the black hole X-ray binary MAXI J1820+070

Using the Very Long Baseline Array and the European Very Long Baseline Interferometry Network we have made a precise measurement of the radio parallax of the black hole X-ray binary MAXI\,J1820+070, providing a model-independent distance to the source. Our parallax measurement of ($0.348\pm0.033$) mas for MAXI J1820+070 translates to a distance of ($2.96\pm0.33$) kpc. This distance implies that the source reached ($15\pm3)\%$ of the Eddington luminosity at the peak of its outburst. Further, we use this distance to refine previous estimates of the jet inclination angle, jet velocity and the mass of the black hole in MAXI J1820+070 to be ($63\pm3)^{\circ}$, ($0.89\pm0.09)c$ and ($9.2\pm1.3) M_{\odot}$, respectively.

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arXiv2020

Radio & X-ray detections of GX 339--4 in quiescence using MeerKAT and Swift

The radio:X-ray correlation that characterises accreting black holes at all mass scales - from stellar mass black holes in binary systems to super-massive black holes powering Active Galactic Nuclei - is one of the most important pieces of observational evidence supporting the existence of a connection between the accretion process and the generation of collimated outflows - or jets - in accreting systems. Although recent studies suggest that the correlation extends down to low luminosities, only a handful of stellar mass black holes have been clearly detected, and in general only upper limits (especially at radio wavelengths) can be obtained during quiescence. We recently obtained detections of the black hole X-ray binary GX 339--4 in quiescence using the MeerKAT radio telescope and Swift X-ray Telescope instrument onboard the Neil Gehrels Swift Observatory, probing the lower end of the radio:X-ray correlation. We present the properties of accretion and of the connected generation of jets in the poorly studied low-accretion rate regime for this canonical black hole XRB system.

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