1.4 GHz on the Fundamental Plane of Black Hole Activity

The fundamental plane of black hole activity is an empirical relationship between the OIII/X-ray luminosity depicting the accretion power, the radio luminosity as a probe of the instantaneous jet power and the mass of the black hole. For the first time, we use the 1.4 GHz FIRST radio luminosities on the optical fundamental plane, to investigate whether or not FIRST fluxes can trace nuclear activity. We use a SDSS-FIRST cross-correlated sample of 10149 active galaxies and analyse their positioning on the optical fundamental plane. We focus on various reasons that can cause the discrepancy between the observed FIRST radio fluxes and the theoretically expected core radio fluxes, and show that that FIRST fluxes are heavily contaminated by non-nuclear, extended components and other environmental factors. We show that the subsample of 'compact sources', which should have negligible lobe contribution, statistically follow the fundamental plane when corrected for relativistic beaming, while all the other sources lie above the plane. The sample of LINERs, which should have negligible lobe and beaming contribution, also follow the fundamental plane. A combined fit of the low-luminosity AGN and the X-ray binaries, with the LINERs, results in the relation log L$_R$ = 0.77 log L$_{OIII}$ + 0.69 log M. Assuming that the original fundamental plane relation is correct, we conclude that 1.4 GHz FIRST fluxes do not trace the pure 'core' jet and instantaneous nuclear activity in the AGN, and one needs to be careful while using it on the fundamental plane of black hole activity.Comment: 10 pages, 5 figures, accepted for publication by MNRA

Clockwise evolution in the hardness-intensity diagram of the black hole X-ray binary Swift J1910.2-0546

We present a detailed study of optical data from the 2012 outburst of the candidate black hole X-ray binary Swift J1910.2-0546 using the Faulkes Telescope and Las Cumbres Observatory (LCO). We analyse the peculiar spectral state changes of Swift J1910.2-0546 in different energy bands, and characterise how the optical and UV emission correlates with the unusual spectral state evolution. Using various diagnostic tools like the optical/X-ray correlation and spectral energy distributions, we disentangle the different emission processes contributing towards the optical flux of the system. When Swift J1910.2-0546 transitions to the pure hard state, we find significant optical brightening of the source along with a dramatic change in the optical colour due to the onset of a jet during the spectral state transition. For the rest of the spectral states, the optical/UV emission is mostly dominated by an X-ray irradiated disk. From our high cadence optical study, we have discovered a putative modulation. Assuming that this modulation arises from a superhump, we suggest Swift J1910.2-0546 to have an orbital period of 2.25-2.47 hr, which would make it the shortest orbital period black hole X-ray binary known to date. Finally, from the state transition luminosity of the source, we find that the distance to the source is likely to be ~4.5-20.8 kpc, which is also supported by the comparative position of the source in the global optical/X-ray correlation of a large sample of black hole and neutron star X-ray binaries.Comment: Published at MNRAS, 12 page

Seven reflares, a mini-outburst and an outburst : High amplitude optical variations in the black hole X-ray binary Swift J1910.2-0546

We present long-term (2012-2022) optical monitoring of the candidate black hole X-ray binary Swift J1910.2-0546 with the Faulkes Telescopes and Las Cumbres Observatory (LCO) network. Following its initial bright 2012 outburst, we find that the source displayed a series of at least 7 quasi-periodic, high amplitude (~3 mags) optical reflares in 2013, with a recurrence time increasing from ~42 days to ~49 days. In 2014, the source experienced a mini-outburst with two peaks in the optical. We also study the recent 2022 outburst of the source at optical wavelengths, and perform a comparative analysis with the earlier rebrightenings. A single X-ray detection and only two radio detections were obtained during the 2013 reflaring period, and only optical detections were acquired in 2014. During the reflaring in both 2013 and 2014, the source showed bluer-when-brighter behavior, having optical colors consistent with a blackbody heating and cooling between 4500 and 9500 K, i.e. the temperature range in which hydrogen starts to ionize. Finally, we compare the flaring behavior of the source to re-brightening events in other X-ray binaries. We show that the repeated reflarings of Swift J1910.2-0546 are highly unusual, and propose that they arise from a sequence of repetitive heating and cooling front reflections travelling through the accretion disk.Comment: Accepted for publication in ApJ, appendix will appear at the published version of the pape

A multiwavelength study of the hard and soft states of MAXI J1820+070 during its 2018 outburst

We present a comprehensive multiwavelength spectral analysis of the black hole (BH) X-ray binary MAXI J1820+070 during its 2018 outburst, utilizing AstroSat far-UV, soft X-ray, and hard X-ray data, along with (quasi-)simultaneous optical and X-ray data from the Las Cumbres Observatory and NICER, respectively. In the soft state, we detect soft X-ray and UV/optical excess components over and above the intrinsic accretion disk emission (kT in ∼ 0.58 keV) and a steep X-ray power-law component. The soft X-ray excess is consistent with a high-temperature blackbody (kT ∼ 0.79 keV), while the UV/optical excess is described by UV emission lines and two low-temperature blackbody components (kT ∼ 3.87 and ∼0.75 eV). Employing continuum spectral fitting, we determine the BH spin parameter (a = 0.77 ± 0.21), using the jet inclination angle of 64° ± 5° and a mass spanning 5–10 M ☉. In the hard state (HS), we observe a significantly enhanced optical/UV excess component, indicating a stronger reprocessed emission in the outer disk. Broadband X-ray spectroscopy in the HS reveals a two-component corona, each associated with its reflection component, in addition to the disk emission (kT in ∼ 0.19 keV). The softer coronal component dominates the bolometric X-ray luminosity and produces broader relativistic reflection features, while the harder component gets reflected far from the inner disk, yielding narrow reflection features. Furthermore, our analysis in the HS suggests a substantial truncation of the inner disk (≳51 gravitational radii) and a high disk density (∼1020 cm−3)

A Multiwavelength Study of GRS 1716-249 in Outburst: Constraints on Its System Parameters

We present a detailed study of the evolution of the Galactic black hole transient GRS 1716-249 during its 2016-2017 outburst at optical (Las Cumbres Observatory), mid-infrared (Very Large Telescope), near-infrared (Rapid Eye Mount telescope), and ultraviolet (the Neil Gehrels Swift Observatory Ultraviolet/Optical Telescope) wavelengths, along with archival radio and X-ray data. We show that the optical/near-infrared and UV emission of the source mainly originates from a multi-temperature accretion disk, while the mid-infrared and radio emission are dominated by synchrotron emission from a compact jet. The optical/UV flux density is correlated with the X-ray emission when the source is in the hard state, consistent with an X-ray irradiated accretion disk with an additional contribution from the viscous disk during the outburst fade. We find evidence for a weak, but highly variable jet component at mid-infrared wavelengths. We also report the long-term optical light curve of the source and find that the quiescent i'-band magnitude is 21.39 +/- 0.15 mag. Furthermore, we discuss how previous estimates of the system parameters of the source are based on various incorrect assumptions, and so are likely to be inaccurate. By comparing our GRS 1716-249 data set to those of other outbursting black hole X-ray binaries, we find that while GRS 1716-249 shows similar X-ray behavior, it is noticeably optically fainter, if the literature distance of 2.4 kpc is adopted. Using several lines of reasoning, we argue that the source distance is further than previously assumed in the literature, likely within 4-17 kpc, with a most likely range of similar to 4-8 kpc

Chasing the break: tracing the full evolution of a black hole X-ray binary jet with multiwavelength spectral modeling

Black hole (BH) X-ray binaries (XRBs) are ideal targets to study the connection between accretion inflow and jet outflow. Here we present quasi-simultaneous, multiwavelength observations of the Galactic BH system MAXI J1820+070, throughout its 2018–2019 outburst. Our data set includes coverage from the radio through X-ray bands from 17 different instruments/telescopes, and encompasses 19 epochs over a 7 month period, resulting in one of the most well-sampled multiwavelength data sets of a BH XRB outburst to date. With our data, we compile and model the broadband spectra of this source using a phenomenological model that includes emission from the jet, a companion star, and an accretion flow. This modeling allows us to track the evolution of the spectral break in the jet spectrum, a key observable that samples the jet launching region. We find that the spectral break location changes over at least ≈3 orders of magnitude in electromagnetic frequency over this period. Using these spectral break measurements, we link the full cycle of jet behavior, including the rising, quenching, and reignition, to the changing accretion flow properties as the source evolves through its different accretion states. Our analysis shows consistent jet behavior with other sources in similar phases of their outbursts, reinforcing the idea that jet quenching and recovery may be a global feature of BH XRB systems in outburst. Our results also provide valuable evidence supporting a close connection between the geometry of the inner accretion flow and the base of the jet

Seven Reflares, a Mini Outburst, and an Outburst: High-amplitude Optical Variations in the Black Hole X-Ray Binary Swift J1910.2–0546

We present long-term (2012–2022) optical monitoring of the candidate black hole X-ray binary Swift J1910.2–0546 with the Faulkes Telescopes and Las Cumbres Observatory network. Following its initial bright 2012 outburst, we find that the source displayed a series of at least seven quasi-periodic, high-amplitude (~3 mag) optical reflares in 2013, with a recurrence time increasing from ∼42 to ∼49 days. In 2014, the source experienced a mini outburst with two peaks in the optical. We also study the recent 2022 outburst of the source at optical wavelengths, and perform a comparative analysis with the earlier rebrightenings. A single X-ray detection and only two radio detections were obtained during the 2013 reflaring period, and only optical detections were acquired in 2014. During the reflaring in both 2013 and 2014, the source showed bluer-when-brighter behavior, having optical colors consistent with blackbody heating and cooling between 4500 and 9500 K, i.e., the temperature range in which hydrogen starts to ionize. Finally, we compare the flaring behavior of the source to rebrightening events in other X-ray binaries. We show that the repeated reflarings of Swift J1910.2–0546 are highly unusual, and propose that they arise from a sequence of repetitive heating and cooling front reflections traveling through the accretion disk

15-GHz radio emission from nearby low-luminosity active galactic nuclei

We present a sub-arcsec resolution radio imaging survey of a sample of 76 low-luminosity active galactic nuclei (LLAGN) that were previously not detected with the Very Large Array at 15 GHz. Compact, parsec-scale radio emission has been detected above a flux density of 40 μ Jy in 60% (45 of 76) of the LLAGN sample. We detect 20 out of 31 (64%) low-ionization nuclear emission-line region (LINER) nuclei, ten out of 14 (71%) low-luminosity Seyfert galaxies, and 15 out of 31 (48%) transition objects. We use this sample to explore correlations between different emission lines and the radio luminosity. We also populate the X-ray and the optical fundamental plane of black hole activity and further refine its parameters. We obtain a fundamental plane relation of log LR = 0.48 (±0.04) log LX + 0.79 (±0.03) log M and an optical fundamental plane relation of log LR = 0.63 (±0.05) log L[O III] + 0.67 (±0.03) log M after including all the LLAGN detected at high resolution at 15 GHz, and the best-studied hard-state X-ray binaries (luminosities are given in erg s-1 while the masses are in units of solar mass). Finally, we find conclusive evidence that the nuclear 15 GHz radio luminosity function (RLF) of all the detected Palomar Sample LLAGN has a turnover at the low-luminosity end, and is best-fitted with a broken power law. The break in the power law occurs at a critical mass accretion rate of 1.2 × 10-3 M⊙ yr-1, which translates to an Eddington ratio of mEdd ∼ 5.1 × 10-5, assuming a black hole mass of 109 M⊙. The local group stands closer to the extrapolation of the higher-luminosity sources, and the classical Seyferts agree with the nuclear RLF of the LLAGN in the local universe.</p

Clockwise evolution in the hardness-intensity diagram of the black hole X-ray binary Swift J1910.2-0546

We present a detailed study of optical data from the 2012 outburst of the candidate black hole X-ray binary Swift J1910.2-0546 using the Faulkes Telescope and Las Cumbres Observatory (LCO). We analyse the peculiar spectral state changes of Swift J1910.2-0546 in different energy bands, and characterise how the optical and UV emission correlates with the unusual spectral state evolution. Using various diagnostic tools like the optical/X-ray correlation and spectral energy distributions, we disentangle the different emission processes contributing towards the optical flux of the system. When Swift J1910.2-0546 transitions to the pure hard state, we find significant optical brightening of the source along with a dramatic change in the optical colour due to the onset of a jet during the spectral state transition. For the rest of the spectral states, the optical/UV emission is mostly dominated by an X-ray irradiated disk. From our high cadence optical study, we have discovered a putative modulation. Assuming that this modulation arises from a superhump, we suggest Swift J1910.2-0546 to have an orbital period of 2.25-2.47 hr, which would make it the shortest orbital period black hole X-ray binary known to date. Finally, from the state transition luminosity of the source, we find that the distance to the source is likely to be ~4.5-20.8 kpc, which is also supported by the comparative position of the source in the global optical/X-ray correlation of a large sample of black hole and neutron star X-ray binaries