PSR J1023+0038 is the first millisecond pulsar discovered to pulsate in the visible band; such a detection took place when the pulsar was surrounded by an accretion disk and also showed X-ray ...pulsations. We report on the first high time resolution observational campaign of this transitional pulsar in the disk state, using simultaneous observations in the optical (Telescopio Nazionale Galileo, Nordic Optical Telescope, Telescopi Joan Oró), X-ray (XMM-Newton, NuSTAR, NICER), infrared (Gran Telescopio Canarias), and UV (Swift) bands. Optical and X-ray pulsations were detected simultaneously in the X-ray high-intensity mode in which the source spends ∼70% of the time, and both disappeared in the low mode, indicating a common underlying physical mechanism. In addition, optical and X-ray pulses were emitted within a few kilometers and had similar pulse shapes and distributions of the pulsed flux density compatible with a power-law relation F ∝ −0.7 connecting the optical and the 0.3-45 keV X-ray band. Optical pulses were also detected during flares with a pulsed flux reduced by one-third with respect to the high mode; the lack of a simultaneous detection of X-ray pulses is compatible with the lower photon statistics. We show that magnetically channeled accretion of plasma onto the surface of the neutron star cannot account for the optical pulsed luminosity (∼1031 erg s−1). On the other hand, magnetospheric rotation-powered pulsar emission would require an extremely efficient conversion of spin-down power into pulsed optical and X-ray emission. We then propose that optical and X-ray pulses are instead produced by synchrotron emission from the intrabinary shock that forms where a striped pulsar wind meets the accretion disk, within a few light cylinder radii away, ∼100 km, from the pulsar.
Abstract
We present simultaneous optical and near-infrared (IR) photometry of the millisecond pulsar PSR J1023+0038 during its low-mass X-ray binary phase. The r΄- and Ks-band light curves show ...rectangular, flat-bottomed dips, similar to the X-ray mode-switching (active–passive state transitions) behaviour observed previously. The cross-correlation function (CCF) of the optical and near-IR data reveals a strong, broad negative anticorrelation at negative lags, a broad positive correlation at positive lags, with a strong, positive narrow correlation superimposed. The shape of the CCF resembles the CCF of black hole X-ray binaries but the time-scales are different. The features can be explained by reprocessing and a hot accretion flow close to the neutron star's magnetospheric radius. The optical emission is dominated by the reprocessed component, whereas the near-IR emission contains the emission from plasmoids in the hot accretion flow and a reprocessed component. The rapid active–passive state transition occurs when the hot accretion flow material is channelled on to the neutron star and is expelled from its magnetosphere. During the transition the optical reprocessing component decreases resulting in the removal of a blue spectral component. The accretion of clumpy material through the magnetic barrier of the neutron star produces the observed near-IR/optical CCF and variability. The dip at negative lags corresponds to the suppression of the near-IR synchrotron component in the hot flow, whereas the broad positive correlation at positive lags is driven by the increased synchrotron emission of the outflowing plasmoids. The narrow peak in the CCF is due to the delayed reprocessed component, enhanced by the increased X-ray emission.
We present a catalog of 9017 X-ray sources identified in Chandra observations of a 2°X 08 field around the Galactic center. This enlarges the number of known X-ray sources in the region by a factor ...of 2.5. The catalog incorporates all of the ACIS-I observations as of 2007 August, which total 2.25 Ms of exposure. At the distance to the Galactic center (8 kpc), we are sensitive to sources with luminosities of 4 X 1032 erg s-1 (0.5-8.0 keV; 90% confidence) over an area of 1 deg2, and up to an order of magnitude more sensitive in the deepest exposure (1.0 Ms) around Sgr A*. The positions of 60% of our sources are accurate to <1 '' (95% confidence), and 20% have positions accurate to <05. We search for variable sources, and find that 3% exhibit flux variations within an observation, and 10% exhibit variations from observation-to-observation. We also find one source, CXOUGC J174622.7 - 285218, with a periodic 1745 s signal (1.4% chance probability), which is probably a magnetically accreting cataclysmic variable. We compare the spatial distribution of X-ray sources to a model for the stellar distribution, and find 2.8s evidence for excesses in the numbers of X-ray sources in the region of recent star formation encompassed by the Arches, Quintuplet, and Galactic center star clusters. These excess sources are also seen in the luminosity distribution of the X-ray sources, which is flatter near the Arches and Quintuplet than elsewhere in the field. These excess point sources, along with a similar longitudinal asymmetry in the distribution of diffuse iron emission that has been reported by other authors, probably have their origin in the young stars that are prominent at l 01.
We report the observation of gravitational waves from a binary-black-hole coalescence during the first two weeks of LIGO’s and Virgo’s third observing run. The signal was recorded on April 12, 2019 ...at05∶30∶44 UTC with a network signal-to-noise ratio of 19. The binary is different from observations during the first two observing runs most notably due to its asymmetric masses: a∼30M⊙black hole merged with a ∼8M⊙black hole companion. The more massive black hole rotated with a dimensionless spin magnitude between 0.22 and 0.60 (90% probability). Asymmetric systems are predicted to emit gravitational waves with stronger contributions from higher multipoles, and indeed we find strong evidence for gravitational radiation beyond the leading quadrupolar order in the observed signal. A suite of tests performed onGW190412 indicates consistency with Einstein’s general theory of relativity. While the mass ratio of this system differs from all previous detections, we show that it is consistent with the population model of stellar binary black holes inferred from the first two observing runs.
NuSTAR reveals the hidden nature of SS433 Middleton, M J; Walton, D J; Alston, W ...
Monthly notices of the Royal Astronomical Society,
09/2021, Letnik:
506, Številka:
1
Journal Article
Recenzirano
Odprti dostop
SS433 is the only Galactic binary system known to persistently accrete at highly super-critical (or hyper-critical) rates, similar to those in tidal disruption events, and likely needed to explain ...the rapid growth of those very high redshift quasars containing massive SMBHs. Probing the inner regions of SS433 in the X-rays is crucial to understanding this system, and super-critical accretion in general, but is highly challenging due to obscuration by the surrounding wind, driven from the accretion flow. NuSTAR observed SS433 in the hard X-ray band across multiple
phases of its 162 day super-orbital precession period. Spectral-timing tools allow us to infer that the hard X-ray emission from the inner regions is likely being scattered towards us by the walls of the wind-cone. By comparing to numerical models, we determine an intrinsic X-ray luminosity of >= 2 x 10^37 erg/s and that, if viewed face on, we would infer an apparent luminosity of > 1 x 10^39 erg/s, confirming SS433’s long-suspected nature as an ultraluminous X-ray source (ULX). We present the discovery of a narrow, ~ 100 s lag due to atomic processes occurring in outflowing material travelling at least 0.14-0.29c, which matches absorption lines seen in ULXs and – in the future – will allow us to map a super-critical outflow for the first time.
ABSTRACT
Recently, a novel idea has been proposed to use a spacecraft orbiting closely around the L4 or L5 Lagrangian points of the Earth–Moon system as a vantage location for astronomical ...observations under unique and advantageous conditions, e.g. to investigate the Solar corona or Kordylewski clouds. In this paper, we explore the scientific advantages of this configuration to observe lunar occultations. By using simulations based on actual orbital parameters and detector performance, we find that even a telescope as small as 10 cm in a L4 orbit would enable better light-curve sampling and higher angular resolution than from ground, and open up at the same time new spectral windows such as e.g. in the UV. We focus in particular on angular diameter measurements, which we find would be possible at the 100 $\mu$as level even at magnitudes normally considered faint in the context of ground-based LOs. Considerable benefits would also be afforded in the area of small separation binary objects, not just in terms of angular resolution but also by the capability of L4-based observations to repeat an LO scan of a source at multiple different position angles. Additional science cases would be made possible by the high time resolution intrinsic to the LO technique and the access to UV wavelengths. On-board data pipeline codes already exist, greatly simplifying the automatic pre-processing and the data transfer requirements.
Gravitational waves enable tests of general relativity in the highly dynamical and strong-field regime. Using events detected by LIGO-Virgo up to 1 October 2019, we evaluate the consistency of the ...data with predictions from the theory. We first establish that residuals from the best-fit waveform are consistent with detector noise, and that the low- and high-frequency parts of the signals are in agreement. We then consider parametrized modifications to the waveform by varying post-Newtonian and phenomenological coefficients, improving past constraints by factors of ∼2; we also find consistency with Kerr black holes when we specifically target signatures of the spin-induced quadrupole moment. Looking for gravitational-wave dispersion, we tighten constraints on Lorentz-violating coefficients by a factor of ∼2.6 and bound the mass of the graviton to m(g)≤1.76 x 10^(-23) eV/sq. c with 90% credibility. We also analyze the properties of the merger remnants by measuring ringdown frequencies and damping times, constraining fractional deviations away from the Kerr frequency to δ{\hat {f}}(220)=0.03(+0.38,-0.35) for the fundamental quadrupolar mode, and δ{\hat {f}}(221)=0.04(+0.27,-0.32) for the first overtone; additionally, we find no evidence for postmerger echoes. Finally, we determine that our data are consistent with tensorial polarizations through a template-independent method. When possible, we assess the validity of general relativity based on collections of events analyzed jointly. We find no evidence for new physics beyond general relativity, for black hole mimickers, or for any unaccounted systematics.
ABSTRACT
This paper provides a catalogue of stars, quasars, and galaxies for the Southern Photometric Local Universe Survey Data Release 2 (S-PLUS DR2) in the Stripe 82 region. We show that a 12-band ...filter system (5 Sloan-like and 7 narrow bands) allows better performance for object classification than the usual analysis based solely on broad bands (regardless of infrared information). Moreover, we show that our classification is robust against missing values. Using spectroscopically confirmed sources retrieved from the Sloan Digital Sky Survey DR16 and DR14Q, we train a random forest classifier with the 12 S-PLUS magnitudes + 4 morphological features. A second random forest classifier is trained with the addition of the W1 (3.4 $\mu\mathrm{m} $) and W2 (4.6 $\mu\mathrm{m} $) magnitudes from the Wide-field Infrared Survey Explorer (WISE). Forty-four per cent of our catalogue have WISE counterparts and are provided with classification from both models. We achieve 95.76 per cent (52.47 per cent) of quasar purity, 95.88 per cent (92.24 per cent) of quasar completeness, 99.44 per cent (98.17 per cent) of star purity, 98.22 per cent (78.56 per cent) of star completeness, 98.04 per cent (81.39 per cent) of galaxy purity, and 98.8 per cent (85.37 per cent) of galaxy completeness for the first (second) classifier, for which the metrics were calculated on objects with (without) WISE counterpart. A total of 2926 787 objects that are not in our spectroscopic sample were labelled, obtaining 335 956 quasars, 1347 340 stars, and 1243 391 galaxies. From those, 7.4 per cent, 76.0 per cent, and 58.4 per cent were classified with probabilities above 80 per cent. The catalogue with classification and probabilities for Stripe 82 S-PLUS DR2 is available for download.
The detection of gravitational waves by Advanced LIGO and Advanced Virgo provides an opportunity to test general relativity in a regime that is inaccessible to traditional astronomical observations ...and laboratory tests. We present four tests of the consistency of the data with binary black hole gravitational waveforms predicted by general relativity. One test subtracts the best-fit waveform from the data and checks the consistency of the residual with detector noise. The second test checks the consistency of the low- and high-frequency parts of the observed signals. The third test checks that phenomenological deviations introduced in the waveform model (including in the post-Newtonian coefficients) are consistent with 0. The fourth test constrains modifications to the propagation of gravitational waves due to a modified dispersion relation, including that from a massive graviton. We present results both for individual events and also results obtained by combining together particularly strong events from the first and second observing runs of Advanced LIGO and Advanced Virgo, as collected in the catalog GWTC-1. We do not find any inconsistency of the data with the predictions of general relativity and improve our previously presented combined constraints by factors of 1.1 to 2.5. In particular, we bound the mass of the graviton to be mg≤4.7×10−23 eV/c2 (90% credible level), an improvement of a factor of 1.6 over our previously presented results. Additionally, we check that the four gravitational-wave events published for the first time in GWTC-1 do not lead to stronger constraints on alternative polarizations than those published previously.
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