The reproducible radio outbursts of SS Cygni Russell, T. D; Miller-Jones, J. C. A; Sivakoff, G. R ...
Monthly notices of the Royal Astronomical Society,
08/2016, Letnik:
460, Številka:
4
Journal Article
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We present the results of our intensive radio observing campaign of the dwarf nova SS Cyg during its 2010 April outburst. We argue that the observed radio emission was produced by synchrotron ...emission from a transient radio jet. Comparing the radio light curves from previous and subsequent outbursts of this system (including high-resolution observations from outbursts in 2011 and 2012) shows that the typical long and short outbursts of this system exhibit reproducible radio outbursts that do not vary significantly between outbursts, which is consistent with the similarity of the observed optical, ultraviolet and X-ray light curves. Contemporaneous optical and X-ray observations show that the radio emission appears to have been triggered at the same time as the initial X-ray flare, which occurs as disc material first reaches the boundary layer. This raises the possibility that the boundary region may be involved in jet production in accreting white dwarf systems. Our high spatial resolution monitoring shows that the compact jet remained active throughout the outburst with no radio quenching.
We present the discovery of a low-frequency 5.7 Hz quasi-periodic oscillation (QPO) feature in observations of the black hole X-ray binary MAXI J1535-571 in its soft-intermediate state, obtained in ...2017 September-October by the Neutron Star Interior Composition Explorer. The feature is relatively broad (compared to other low-frequency QPOs; quality factor Q 2) and weak (1.9% rms in 3-10 keV), and is accompanied by a weak harmonic and low-amplitude broadband noise. These characteristics identify it as a weak Type A/B QPO, similar to ones previously identified in the soft-intermediate state of the transient black hole X-ray binary XTE J1550-564. The lag-energy spectrum of the QPO shows increasing soft lags toward lower energies, approaching 50 ms at 1 keV (with respect to a 3-10 keV continuum). This large phase shift has similar amplitude but opposite sign to that seen in Rossi X-Ray Timing Explorer data for a Type B QPO from the transient black hole X-ray binary GX 339-4. Previous phase-resolved spectroscopy analysis of the Type B QPO in GX 339-4 pointed toward a precessing jet-like corona illuminating the accretion disk as the origin of the QPO signal. We suggest that this QPO in MAXI J1535-571 may have the same origin, with the different lag sign depending on the scale height of the emitting region and the observer inclination angle.
ABSTRACT We present two different search methods for electromagnetic counterparts to gravitational-wave (GW) events from ground-based detectors using archival NASA high-energy data from the Fermi ...Gamma-ray Burst Monitor (GBM) and RXTE All-sky Monitor (ASM) instruments. To demonstrate the methods, we use a limited number of representative GW background noise events produced by a search for binary neutron star coalescence over the last two months of the LIGO-Virgo S6/VSR3 joint science run. Time and sky location provided by the GW data trigger a targeted search in the high-energy photon data. We use two custom pipelines: one to search for prompt gamma-ray counterparts in GBM, and the other to search for a variety of X-ray afterglow model signals in ASM. We measure the efficiency of the joint pipelines to weak gamma-ray burst counterparts, and a family of model X-ray afterglows. By requiring a detectable signal in either electromagnetic instrument coincident with a GW event, we are able to reject a large majority of GW candidates. This reduces the signal-to-noise ratio of the loudest surviving GW background event by around 15-20%.
MAXI J1836−194 is a Galactic black hole candidate X-ray binary that was discovered in 2011 when it went into outburst. In this paper, we present the full radio monitoring of this system during its ...‘failed’ outburst, in which the source did not complete a full set of state changes, only transitioning as far as the hard intermediate state. Observations with the Karl G. Jansky Very Large Array (VLA) and Australia Telescope Compact Array (ATCA) show that the jet properties changed significantly during the outburst. The VLA observations detected linearly polarized emission at a level of ∼1 per cent early in the outburst, increasing to ∼3 per cent as the outburst peaked. High-resolution images with the Very Long Baseline Array (VLBA) show an ∼15 mas jet along the position angle −21 ± 2°, in agreement with the electric vector position angle found from our polarization results (−21 ± 4°), implying that the magnetic field is perpendicular to the jet. Astrometric observations suggest that the system required an asymmetric natal kick to explain its observed space velocity. Comparing quasi-simultaneous X-ray monitoring with the 5 GHz VLA observations from the 2011 outburst shows an unusually steep hard-state radio/X-ray correlation of
$L_{\rm R} \propto L_{\rm X}^{1.8\pm 0.2}$
, where L
R and L
X denote the radio and X-ray luminosities, respectively. With ATCA and Swift monitoring of the source during a period of re-brightening in 2012, we show that the system lay on the same steep correlation. Due to the low inclination of this system, we then investigate the possibility that the observed correlation may have been steepened by variable Doppler boosting.
We studied the outburst evolution and timing properties of the recently discovered X-ray transient MAXI J1348−630 as observed with NICER. We produced the fundamental diagrams commonly used to trace ...the spectral evolution, and power density spectra to study the fast X-ray variability. The main outburst evolution of MAXI J1348−630 is similar to that commonly observed in blackhole transients. The source evolved from the hard state (HS), through hard- and soft-intermediate states, into the soft state in the outburst rise, and back to the HS in reverse during the outburst decay. At the end of the outburst, MAXI J1348−630 underwent two reflares with peak fluxes approximately one and two orders of magnitude fainter than the main outburst, respectively. During the reflares, the source remained in the HS only, without undergoing any state transitions, which is similar to the so-called ‘failed outbursts’. Different types of quasi-periodic oscillations (QPOs) are observed at different phases of the outburst. Based on our spectral-timing results, we conclude that MAXI J1348−630 is a black hole candidate.
ABSTRACT
We present the results of a large multiwavelength follow-up campaign of the tidal disruption event (TDE) AT 2019dsg, focusing on low to high resolution optical spectroscopy, X-ray, and radio ...observations. The galaxy hosts a super massive black hole of mass $\rm (5.4\pm 3.2)\times 10^6\, M_\odot$ and careful analysis finds no evidence for the presence of an active galactic nucleus, instead the TDE host galaxy shows narrow optical emission lines that likely arise from star formation activity. The transient is luminous in the X-rays, radio, UV, and optical. The X-ray emission becomes undetected after ∼100 d, and the radio luminosity density starts to decay at frequencies above 5.4 GHz by ∼160 d. Optical emission line signatures of the TDE are present up to ∼200 d after the light-curve peak. The medium to high resolution spectra show traces of absorption lines that we propose originate in the self-gravitating debris streams. At late times, after ∼200 d, narrow Fe lines appear in the spectra. The TDE was previously classified as N-strong, but after careful subtraction of the host galaxy’s stellar contribution, we find no evidence for these N lines in the TDE spectrum, even though O Bowen lines are detected. The observed properties of the X-ray emission are fully consistent with the detection of the inner regions of a cooling accretion disc. The optical and radio properties are consistent with this central engine seen at a low inclination (i.e. seen from the poles).
ABSTRACT
We present a systematic spectral-timing analysis of a fast appearance/disappearance of a type-B quasi-periodic oscillation (QPO), observed in four Neutron Star Interior Composition Explorer ...(NICER) observations of MAXI J1348−630. By comparing the spectra of the period with and without the type-B QPO, we found that the main difference appears at energy bands above ∼2 keV, suggesting that the QPO emission is dominated by the hard Comptonized component. During the transition, a change in the relative contribution of the disc and Comptonized emission was observed. The disc flux decreased while the Comptonized flux increased from non-QPO to type-B QPO. However, the total flux did not change too much in the NICER band. Our results reveal that the type-B QPO is associated with a redistribution of accretion power between the disc and Comptonized emission. When the type-B QPO appears, more accretion power is dissipated into the Comptonized region than in the disc. Our spectral fits give a hint that the increased Comptonized emission may come from an additional component that is related to the base of the jet.
We report the discovery of PSR J2251−3711, a radio pulsar with a spin period of 12.1 s, the second longest currently known. Its timing parameters imply a characteristic age of 15 Myr, a surface ...magnetic field of 1.3 × 10^(13) G, and a spin-down luminosity of 2.9 × 10^(29) erg/s. Its dispersion measure of 12.12(1) pc/cu. cm leads to distance estimates of 0.5 and 1.3 kpc according to the NE2001 and YMW16 Galactic free electron density models, respectively. Some of its single pulses show an uninterrupted 180-deg sweep of the phase-resolved polarization position angle, with an S-shape reminiscent of the rotating vector model prediction. However, the fact that this sweep occurs at different phases from one pulse to another is remarkable and without straightforward explanation. Although PSR J2251−3711 lies in the region of the P − P˙ parameter space occupied by the X-ray isolated neutron stars (XINS), there is no evidence for an X-ray counterpart in our Swift XRT observation; this places a 99 per cent-confidence upper bound on its unabsorbed bolometric thermal luminosity of 1.1 × 10^(31) (d/1 kpc)^2 erg/s for an assumed temperature of 85 eV, where d is the distance to the pulsar. Further observations are needed to determine whether it is a rotation-powered pulsar with a true age of at least several Myr, or a much younger object such as an XINS or a recently cooled magnetar. Extreme specimens like PSR J2251−3711 help bridge populations in the so-called neutron star zoo in an attempt to understand their origins and evolution.
We present results of recent Neutron Star Interior Composition Explorer (NICER) observations of the accreting millisecond X-ray pulsar (AMXP) IGR J17062−6143 that show that it resides in a circular, ...ultracompact binary with a 38-minute orbital period. NICER observed the source for 26 ks over a 5.3-day span in 2017 August, and again for 14 and 11 ks in 2017 October and November, respectively. A power spectral analysis of the August exposure confirms the previous detection of pulsations at 163.656 Hz in Rossi X-ray Timing Explorer (RXTE) data, and reveals phase modulation due to orbital motion of the neutron star. A coherent search for the orbital solution using the Z2 method finds a best-fitting circular orbit with a period of 2278.21 s (37.97 minutes), a projected semimajor axis of 0.00390 lt-s, and a barycentric pulsar frequency of 163.6561105 Hz. This is currently the shortest known orbital period for an AMXP. The mass function is 9.12 × 10−8 M , presently the smallest known for a stellar binary. The minimum donor mass ranges from 0.005 to 0.007 M for a neutron star mass from 1.2 to 2 M . Assuming mass transfer is driven by gravitational radiation, we find donor mass and binary inclination bounds of 0.0175-0.0155 M and 19° < i < 27 5, where the lower and upper bounds correspond to 1.4 and 2 M neutron stars, respectively. Folding the data accounting for the orbital modulation reveals a sinusoidal profile with fractional amplitude 2.04 0.11% (0.3-3.2 keV).
Following the detection of strong TeV gamma-ray flares from the BL Lac object 1ES 1959+650 with the Whipple 10 m Cerenkov telescope on 2002 May 16 and 17, we performed intensive target of opportunity ...radio, optical, X-ray, and TeV gamma-ray observations from 2002 May 18 to August 14. Observations with the X- ray telescope Rossi X-Ray Timing Explorer and the Whipple and HEGRA gamma- ray telescopes revealed several strong flares, enabling us to sensitively test the X-ray-gamma-ray flux correlation properties. Although the X-ray and gamma- ray fluxes seemed to be correlated in general, we found an "orphan" gamma-ray flare that was not accompanied by an X-ray flare. While we detected optical flux variability with the Boltwood and Abastumani observatories, the data did not give evidence for a correlation of the optical flux variability with the observed X-ray and gamma-ray flares. Within statistical errors of about 0.03 Jy at 14.5 GHz and 0.05 Jy at 4.8 GHz, the radio fluxes measured with the University of Michigan Radio Astronomy Observatory stayed constant throughout the campaign; the mean values agreed well with the values measured on 2002 May 7 and June 7 at 4.9 and 15 GHz with the Very Large Array and at 4.8 GHz with archival flux measurements. After describing in detail the radio, optical, X-ray and gamma-ray light curves, and spectral energy distributions (SEDs), we present initial modeling of the SED with a simple synchrotron self-Compton model. With the addition of another TeV blazar with good broadband data, we consider the set of all TeV blazars, to begin to look for a connection of the jet properties to the properties of the central accreting black hole thought to drive the jet. Remarkably, the temporal and spectral X-ray and gamma-ray emission characteristics of TeV blazars are very similar, even though the mass estimates of their central black holes differ by up to 1 order of magnitude.
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