Publications associated with Four Pi Sky


Bow-shocks, nova shells, disc winds and tilted discs: the Nova-Like V341 Ara Has It All

Monthly Notices of the Royal Astronomical Society Oxford University Press 501 (2021) 1951-1969

N Castro Segura, C Knigge, JA Acosta-Pulido, R Fender, A Ponomareva, D Williams

V341 Ara was recently recognized as one of the closest (d ≃ 150 pc) and brightest (V ≃ 10) nova-like cataclysmic variables. This unique system is surrounded by a bright emission nebula, likely to be the remnant of a recent nova eruption. Embedded within this nebula is a prominent bow shock, where the system’s accretion disc wind runs into its own nova shell. In order to establish its fundamental properties, we present the first comprehensive multiwavelength study of the system. Long-term photometry reveals quasi-periodic, super-orbital variations with a characteristic time-scale of 10–16 d and typical amplitude of ≃1 mag. High-cadence photometry from theTransiting Exoplanet Survey Satellite (TESS) reveals for the first time both the orbital period and a ‘negative superhump’ period. The latter is usually interpreted as the signature of a tilted accretion disc. We propose a recently developed disc instability model as a plausible explanation for the photometric behaviour. In our spectroscopic data, we clearly detect antiphased absorption and emission-line components. Their radial velocities suggest a high mass ratio, which in turn implies an unusually low white-dwarf mass. We also constrain the wind mass-loss rate of the system from the spatially resolved [O III] emission produced in the bow shock; this can be used to test and calibrate accretion disc wind models. We suggest a possible association between V341 Ara and a ‘guest star’ mentioned in Chinese historical records in AD 1240. If this marks the date of the system’s nova eruption, V341 Ara would be the oldest recovered nova of its class and an excellent laboratory for testing nova theory.


MKT J170456.2–482100: the first transient discovered by MeerKAT

Monthly Notices of the Royal Astronomical Society Oxford University Press 491 (2019) 560-575

LN Driessen, I McDonald, DAH Buckley, M Caleb, EJ Kotze, SB Potter, KM Rajwade, A Rowlinson, BW Stappers, E Tremou, PA Woudt, RP Fender, R Armstrong, P Groot, I Heywood, A Horesh, A van der Horst, E Koerding, VA McBride, JCA Miller-Jones, KP Mooley, RAMJ Wijers

We report the discovery of the first transient with MeerKAT, MKT J170456.2–482100, discovered in ThunderKAT images of the low-mass X-ray binary GX339–4. MKT J170456.2–482100 is variable in the radio, reaching a maximum flux density of 0.71±0.11mJy on 2019 October 12, and is undetected in 15 out of 48 ThunderKAT epochs. MKT J170456.2–482100 is coincident with the chromospherically active K-type sub-giant TYC 8332-2529-1, and ∼18yr of archival optical photometry of the star shows that it varies with a period of 21.25±0.04d⁠. The shape and phase of the optical light curve changes over time, and we detect both X-ray and UV emission at the position of MKT J170456.2–482100, which may indicate that TYC 8332-2529-1 has large star spots. Spectroscopic analysis shows that TYC 8332-2529-1 is in a binary, and has a line-of-sight radial velocity amplitude of 43kms−1⁠. We also observe a spectral feature in antiphase with the K-type sub-giant, with a line-of-sight radial velocity amplitude of ∼12±10kms−1⁠, whose origins cannot currently be explained. Further observations and investigation are required to determine the nature of the MKT J170456.2–482100 system.


Observation of inverse Compton emission from a long γ-ray burst

Nature Nature Research 575 (2019) 459-463

P Veres, P Bhat, M Briggs, W Cleveland, R Hamburg, C Hui, B Mailyan, R Preece, O Roberts, A von Kienlin, C Wilson-Hodge, D Kocevski, M Arimoto, K Asano, M Axelsson, G Barbiellini, E Bissaldi, FF Dirirsa, J Granot, J McEnery, N Omodei, J Racusin, D Thompson, M Bernardini, MAGIC Collaboration

Long-duration γ-ray bursts (GRBs) originate from ultra-relativistic jets launched from the collapsing cores of dying massive stars. They are characterized by an initial phase of bright and highly variable radiation in the kiloelectronvolt-to-megaelectronvolt band, which is probably produced within the jet and lasts from milliseconds to minutes, known as the prompt emission1,2. Subsequently, the interaction of the jet with the surrounding medium generates shock waves that are responsible for the afterglow emission, which lasts from days to months and occurs over a broad energy range from the radio to the gigaelectronvolt bands1-6. The afterglow emission is generally well explained as synchrotron radiation emitted by electrons accelerated by the external shock7-9. Recently, intense long-lasting emission between 0.2 and 1 teraelectronvolts was observed from GRB 190114C10,11. Here we report multi-frequency observations of GRB 190114C, and study the evolution in time of the GRB emission across 17 orders of magnitude in energy, from 5 × 10-6 to 1012 electronvolts. We find that the broadband spectral energy distribution is double-peaked, with the teraelectronvolt emission constituting a distinct spectral component with power comparable to the synchrotron component. This component is associated with the afterglow and is satisfactorily explained by inverse Compton up-scattering of synchrotron photons by high-energy electrons. We find that the conditions required to account for the observed teraelectronvolt component are typical for GRBs, supporting the possibility that inverse Compton emission is commonly produced in GRBs.


Late-outburst radio flaring in SS Cyg and evidence for a powerful kinetic output channel in cataclysmic variables

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 490 (2019) L76-L80

R Fender, J Bright, K Mooley, J Miller-Jones


Synchrotron self-absorption and the minimum energy of optically thick radio flares from stellar mass black holes

Monthly Notices of the Royal Astronomical Society Oxford University Press 489 (2019) 4836-4846

R Fender, J Bright

We consider the case of radio flares from black hole X-ray binaries in which the flare spectrum evolves from optically thick to optically thin, under the assumption that this is due to decreasing optical depth to synchrotron self-absorption. We are able to place upper and lower limits on the size of the emitting region associated with a radio flare, and determine the synchrotron source magnetic field and energy as a function of size. The energy has a clear minimum which occurs close to the condition that the magnetic field derived from synchrotron self-absorption equals that calculated from equipartition. This minimum energy estimate is independent of the rise time of the event, and so may be applied to any event for which the peak flux is measured and there is evidence for self-absorption. This is a much more accurate approach to minimum energy estimation than assuming expansion at close to the speed of light. We apply this method to four examples of optically thick radio flares and find that in each case either the filling factor of the synchrotron source is considerably less than unity, or the expansion speed is considerably less than the speed of light. The combination of unity filling factor and expansion speeds close to the speed of light is completely ruled out on energetic grounds for three of the four events we consider. The inferred slowed expansion is consistent with detailed modelling of such events, which has been recently reported in the literature. The minimum power requirements associated with the flares are found to be ∼1036 erg s−1, which are easily accommodated in the context of stellar mass black hole accretion at near-Eddington levels, when these flares typically occur. However, the true jet power could still be orders of magnitude higher.


Disk-Jet Coupling in the 2017/2018 Outburst of the Galactic Black Hole Candidate X-Ray Binary MAXI J1535-571

Astrophysical Journal American Astronomical Society 883 (2019) 198

T Russell, A Tetarenko, J Miller-Jones, G Sivakoff, A Parikh, S Rapisarda, R Wijnands, S Corbel, E Tremou, D Altamirano, M Baglio, C Ceccobello, N Degenaar, J Eijnden, R Fender, I Heywood, H Krimm, M Lucchini, S Markoff, D Russell, R Soria, P Woudt

MAXI J1535-571 is a Galactic black hole candidate X-ray binary that was discovered going into outburst in 2017 September. In this paper, we present comprehensive radio monitoring of this system using the Australia Telescope Compact Array, as well as the MeerKAT radio observatory, showing the evolution of the radio jet during its outburst. Our radio observations show the early rise and subsequent quenching of the compact jet as the outburst brightened and then evolved toward the soft state. We constrain the compact jet quenching factor to be more than 3.5 orders of magnitude. We also detected and tracked (for 303 days) a discrete, relativistically moving jet knot that was launched from the system. From the motion of the apparently superluminal knot, we constrain the jet inclination (at the time of ejection) and speed to ≤45° and ≥0.69 c, respectively. Extrapolating its motion back in time, our results suggest that the jet knot was ejected close in time to the transition from the hard intermediate state to soft intermediate state. The launching event also occurred contemporaneously with a short increase in X-ray count rate, a rapid drop in the strength of the X-ray variability, and a change in the type-C quasi-periodic oscillation (QPO) frequency that occurs >2.5 days before the first appearance of a possible type-B QPO.


Discovery of a radio transient in M81

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 489 (2019) 1181-1196

GE Anderson, JCA Miller-Jones, MJ Middleton, R Soria, DA Swartz, R Urquhart, N Hurley-Walker, PJ Hancock, RP Fender, P Gandhi, S Markoff, TP Roberts


Disk-Jet Coupling in the 2017/2018 Outburst of the Galactic Black Hole Candidate X-Ray Binary MAXI J1535-571

ASTROPHYSICAL JOURNAL 883 (2019) ARTN 198

T Russell, A Tetarenko, J Miller-Jones, G Sivakoff, A Parikh, S Rapisarda, R Wijnands, S Corbel, E Tremou, D Altamirano, M Baglio, C Ceccobello, N Degenaar, J van den Eijnden, R Fender, I Heywood, H Krimm, M Lucchini, S Markoff, D Russell, R Soria, P Woudt


Nine-hour X-ray quasi-periodic eruptions from a low-mass black hole galactic nucleus

Nature Nature Research 573 (2019) 381-384

G Miniutti, R Saxton, M Giustini, K Alexander, R Fender, I Heywood, I Monageng, M Coriat, A Tzioumis, A Read, C Knigge, P Gandhi, M Pretorius, B Agís-González

In the past two decades, high-amplitude electromagnetic outbursts have been detected from dormant galaxies and often attributed to the tidal disruption of a star by the central black hole1,2. X-ray emission from the Seyfert 2 galaxy GSN 069 (2MASX J01190869-3411305) at a redshift of z = 0.018 was first detected in July 2010 and implies an X-ray brightening by a factor of more than 240 over ROSAT observations performed 16 years earlier3,4. The emission has smoothly decayed over time since 2010, possibly indicating a long-lived tidal disruption event5. The X-ray spectrum is ultra-soft and can be described by accretion disk emission with luminosity proportional to the fourth power of the disk temperature during long-term evolution. Here we report observations of quasi-periodic X-ray eruptions from the nucleus of GSN 069 over the course of 54 days, from December 2018 onwards. During these eruptions, the X-ray count rate increases by up to two orders of magnitude with an event duration of just over an hour and a recurrence time of about nine hours. These eruptions are associated with fast spectral transitions between a cold and a warm phase in the accretion flow around a low-mass black hole (of approximately 4 × 105 solar masses) with peak X-ray luminosity of about 5 × 1042 erg per second. The warm phase has kT (where T is the temperature and k is the Boltzmann constant) of about 120 electronvolts, reminiscent of the typical soft-X-ray excess, an almost universal thermal-like feature in the X-ray spectra of luminous active nuclei6,7,8. If the observed properties are not unique to GSN 069, and assuming standard scaling of timescales with black hole mass and accretion properties, typical active galactic nuclei with higher-mass black holes can be expected to exhibit high-amplitude optical to X-ray variability on timescales as short as months or years9.


Accretion and outflow in V404 Cyg

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 488 (2019) 1356-1365

J Casares, T Munoz-Darias, DM Sanchez, PA Charles, MAP Torres, M Armas Padilla, RP Fender, J Garcia-Rojas


ALMA observations of A0620-00: fresh clues on the nature of quiescent black hole X-ray binary jets

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 488 (2019) 191-197

E Gallo, R Teague, RM Plotkin, JCA Miller-Jones, DM Russell, T Dincer, C Bailyn, TJ Maccarone, S Markoff, RP Fender


Hard-state Accretion Disk Winds from Black Holes: The Revealing Case of MAXI J1820+070

ASTROPHYSICAL JOURNAL LETTERS 879 (2019) ARTN L4

T Munoz-Darias, F Jimenez-Ibarra, G Panizo-Espinar, J Casares, DM Sanchez, G Ponti, RP Fender, DAH Buckley, P Garnavich, MAP Torres, M Armas Padilla, PA Charles, JM Corral-Santana, JJE Kajava, EJ Kotze, C Littlefield, J Sanchez-Sierras, D Steeghs, J Thomas


Mass and spin measurements for the neutron star 4U1608-52 through the relativistic precession model

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 486 (2019) 4485-4497

L du Buisson, S Motta, R Fender


A detailed radio study of the energetic, nearby, and puzzling GRB 171010A

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 486 (2019) 2721-2729

JS Bright, A Horesh, AJ van der Horst, R Fender, GE Anderson, SE Motta, SB Cenko, DA Green, Y Perrott, D Titterington


A rapidly changing jet orientation in the stellar-mass black-hole system V404 Cygni

Nature Nature Research 569 (2019) 374-377

JCA Miller-Jones, AJ Tetarenko, GR Sivakoff, MJ Middleton, D Altamirano, GE Anderson, TM Belloni, RP Fender, PG Jonker, EG Körding, HA Krimm, D Maitra, S Markoff, S Migliari, KP Mooley, MP Rupen, DM Russell, TD Russell, CL Sarazin, R Soria, V Tudose

Powerful relativistic jets are one of the main ways in which accreting black holes provide kinetic feedback to their surroundings. Jets launched from or redirected by the accretion flow that powers them are expected to be affected by the dynamics of the flow, which for accreting stellar-mass black holes has shown evidence for precession1 due to frame-dragging effects that occur when the black-hole spin axis is misaligned with the orbital plane of its companion star2. Recently, theoretical simulations have suggested that the jets can exert an additional torque on the accretion flow3, although the interplay between the dynamics of the accretion flow and the launching of the jets is not yet understood. Here we report a rapidly changing jet orientation—on a time scale of minutes to hours—in the black-hole X-ray binary V404 Cygni, detected with very-long-baseline interferometry during the peak of its 2015 outburst. We show that this changing jet orientation can be modelled as the Lense–Thirring precession of a vertically extended slim disk that arises from the super-Eddington accretion rate4. Our findings suggest that the dynamics of the precessing inner accretion disk could play a role in either directly launching or redirecting the jets within the inner few hundred gravitational radii. Similar dynamics should be expected in any strongly accreting black hole whose spin is misaligned with the inflowing gas, both affecting the observational characteristics of the jets and distributing the black-hole feedback more uniformly over the surrounding environment5,6.


The twisted jets of Circinus X-1

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 484 (2019) 1672-1686

M Coriat, RP Fender, C Tasse, O Smirnov, AK Tzioumis, JW Broderick


Identifying transient and variable sources in radio images

ASTRONOMY AND COMPUTING 27 (2019) 111-129

A Rowlinson, AJ Stewart, JW Broderick, JD Swinbank, RAMJ Wijers, D Carbone, Y Cendes, R Fender, A van der Horst, G Molenaar, B Scheers, T Staley, S Farrell, J-M Griessmeier, M Bell, J Eisloeffel, CJ Law, J van Leeuwen, P Zarka


A connection between accretion states and the formation of ultrarelativistic outflows in a neutron star X-ray binary

Monthly Notices of the Royal Astronomical Society Oxford University Press 483 (2018) 3686-3699

S Motta, RP Fender

The nearby accreting neutron star binary Sco X-1 is the closest example of ongoing relativistic jet production at high Eddington ratios. Previous radio studies have revealed that alongside mildly relativistic, radio-emitting ejecta, there is at times a much faster transfer of energy from the region of the accretion flow along the jet. The nature of this ultrarelativistic flow remains unclear and while there is some evidence for a similar phenomenon in other systems that might contain neutron stars, it has never been observed in a confirmed black hole system. We have compared these previous radio observations with a new analysis of simultaneous X-ray observations that were performed with the RXTE mission. We find that the ejection of the ultrarelativistic flow seems to be associated with the simultaneous appearance of two particular types of quasi-periodic oscillations in the X-ray power spectrum. In contrast, the mildly relativistic, radio-emitting outflows may be associated with flat-topped broad-band noise in the X-ray power spectrum. This is the first time a link, albeit tentative, has been found between these mysterious unseen flows and the accretion flow from which they are launched.


The First Tidal Disruption Flare in ZTF: From Photometric Selection to Multi-wavelength Characterization

ASTROPHYSICAL JOURNAL 872 (2019) ARTN 198

S van Velzen, S Gezaril, SB Cenko, E Karal, JCA Miller-Jones, T Hung, J Bright, N Roth, N Blagorodnova, D Huppenkothen, L Yan, E Ofek, J Sollerman, S Frederic, H Ward, MJ Grahan, R Fender, MM Kasliwal, C Canella, R Stein, M Giomi, V Brinnel, J van Santen, J Nordin, EC Bellm, R Dekany, C Fremling, VZ Golkhou, T Kupfer, SR Kulkarni, RR Laher, A Mahabal, FJ Masci, AA Miller, JD Neill, R Riddle, M Rigault, B Rusholme, MT Soumagnac, Y Tachiba


Tracking the variable jets of V404 Cygni during its 2015 outburst

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 482 (2019) 2950-2972

AJ Tetarenko, GR Sivakoff, JCA Miller-Jones, M Bremer, KP Mooley, RP Fender, C Rumsey, A Bahramian, D Altamirano, S Heinz, D Maitra, SB Markoff, S Migliari, MP Rupen, DM Russell, TD Russell, CL Sarazin

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