- ID:
- ivo://CDS.VizieR/J/ApJ/807/150
- Title:
- 230GHz VLBI observations of M87
- Short Name:
- J/ApJ/807/150
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on 230GHz (1.3mm) very long baseline interferometry (VLBI) observations of M87 with the Event Horizon Telescope using antennas on Mauna Kea in Hawaii, Mt. Graham in Arizona, and Cedar Flat in California. For the first time, we have acquired 230GHz VLBI interferometric phase information on M87 through measurement of the closure phase on the triangle of long baselines. Most of the measured closure phases are consistent with 0{deg} as expected by physically motivated models for 230GHz structure such as jet models and accretion disk models. The brightness temperature of the event-horizon-scale structure is ~1x10^10^K derived from the compact flux density of ~1Jy and the angular size of ~40{mu}as~5.5R_s_, which is broadly consistent with the peak brightness of the radio cores at 1-86GHz located within ~10^2^R_s_. Our observations occurred in the middle of an enhancement in very-high-energy (VHE) {gamma}-ray flux, presumably originating in the vicinity of the central black hole. Our measurements, combined with results of multi-wavelength observations, favor a scenario in which the VHE region has an extended size of ~20-60R_s_.
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Search Results
- ID:
- ivo://CDS.VizieR/VIII/107
- Title:
- GLEAM sources ionospheric position shifts
- Short Name:
- VIII/107
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Nearly 200 hours of observing with the Murchison Widefield Array (MWA) radio telescope during the Galactic and Extra-galactic All-sky MWA (GLEAM) survey were used to assemble images of ionospheric structure. These images cover a nearly 50 degree-wide area on the sky at a cadence of 10 minutes over many 5-7 hours-long observing runs. They are generated by tracking the apparent motions of ~200-800 cosmic radio sources caused by changes in the transverse gradient of the ionospheric total electron content. Spectral analysis of these images revealed that the dataset was dominated by three distinct signatures. The first is consistent with field-aligned structures within the topside ionosphere/lower plasmasphere previously imaged with the MWA. The second are structures that are relatively large and aligned nearly east/west. Regional weather data implies that these are preferentially detected when there is a noticeable shear within the sub- tropical jet stream, which passes near the MWA. This suggests that this signature may be related to gravity waves launched by jet stream shear. The final signature is consistent with the properties of so-call electro-buoyancy waves that are known to occur at midlatitudes at night. Detections of these were more common when regional sporadic-E was present, supporting a proposed connection between these waves and polarization electric fields that may arise within sporadic-E. We discuss the implications for future observations with the Square Kilometer Array.
- ID:
- ivo://CDS.VizieR/J/A+A/622/A196
- Title:
- GMVA 86GHz Stokes IQU images of 3C84 jet
- Short Name:
- J/A+A/622/A196
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report results from a deep polarization imaging of the nearby radio galaxy 3C 84 (NGC 1275). The source was observed with the Global Millimeter VLBI Array (GMVA) at 86GHz at an ultrahigh angular resolution of 50{mu}as (corresponding to 200Rs). We also add complementary multiwavelength data from the Very Long Baseline Array (VLBA; 15 & 43GHz) and from the Atacama Large Millimeter/submillimeter Array (ALMA; 97.5, 233.0, and 343.5GHz). At 86GHz, we measured a fractional linear polarization of ~2% in the VLBI core region. The polarization morphology suggests that the emission is associated with an underlying limb-brightened jet. The fractional linear polarization is lower at 43 and 15GHz (~0.3-0.7% and <0.1%, respectively). This suggests an increasing linear polarization degree toward shorter wavelengths on VLBI scales. We also obtain a large rotation measure (RM) of ~10^5-6^rad/m^2^ in the core at >~43GHz. Moreover, the VLBA 43GHz observations show a variable RM in the VLBI core region during a small flare in 2015. Faraday depolarization and Faraday conversion in an inhomogeneous and mildly relativistic plasma could explain the observed linear polarization characteristics and the previously measured frequency dependence of the circular polarization. Our Faraday depolarization modeling suggests that the RM most likely originates from an external screen with a highly uniform RM distribution. To explain the large RM value, the uniform RM distribution, and the RM variability, we suggest that the Faraday rotation is caused by a boundary layer in a transversely stratified jet. Based on the RM and the synchrotron spectrum of the core, we provide an estimate for the magnetic field strength and the electron density of the jet plasma.
- ID:
- ivo://CDS.VizieR/J/A+A/593/A49
- Title:
- G35.20-0.74N VLA continuum images
- Short Name:
- J/A+A/593/A49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Atacama Large Millimeter/submillimeter Array (ALMA) observations of the high-mass star-forming region G35.20-0.74N have revealed the presence of a Keplerian disk in core B rotating about a massive object of 18M_{sun}_, as computed from the velocity field. The luminosity of such a massive star would be comparable to (or higher than) the luminosity of the whole star-forming region. To solve this problem it has been proposed that core B could harbor a binary system. This could also explain the possible precession of the radio jet associated with this core, which has been suggested by its S-shaped morphology. We establish the origin of the free-free emission from core B and investigate the existence of a binary system at the center of this massive core and the possible precession of the radio jet. We carried out VLA continuum observations of G35.20-0.74N at 2cm in the B configuration and at 1.3cm and 7mm in the A and B configurations. The bandwidth at 7mm covers the CH3OH maser line at 44.069GHz. Continuum images at 6 and 3.6cm in the A configuration were obtained from the VLA archive. We also carried out VERA observations of the H_2_O maser line at 22.235GHz.
- ID:
- ivo://CDS.VizieR/J/ApJ/818/116
- Title:
- Gould's Belt VLA survey. V. Perseus region
- Short Name:
- J/ApJ/818/116
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present multiepoch, large-scale (~2000 arcmin^2^), fairly deep (~16 {mu}Jy), high-resolution (~1") radio observations of the Perseus star-forming complex obtained with the Karl G. Jansky Very Large Array at frequencies of 4.5 and 7.5 GHz. These observations were mainly focused on the clouds NGC 1333 and IC 348, although we also observed several fields in other parts of the Perseus complex. We detect a total of 206 sources, 42 of which are associated with young stellar objects (YSOs). The radio properties of about 60% of the YSOs are compatible with a nonthermal radio emission origin. Based on our sample, we find a fairly clear relation between the prevalence of nonthermal radio emission and evolutionary status of the YSOs. By comparing our results with previously reported X-ray observations, we show that YSOs in Perseus follow a Gudel-Benz relation with {kappa}=0.03, consistent with other regions of star formation. We argue that most of the sources detected in our observations but not associated with known YSOs are extragalactic, but provide a list of 20 unidentified radio sources whose radio properties are consistent with being YSO candidates. Finally, we also detect five sources with extended emission features that can clearly be associated with radio galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/715/1438
- Title:
- Gravitational-wave bursts with GRBs
- Short Name:
- J/ApJ/715/1438
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a search for gravitational-wave bursts (GWBs) associated with 137 gamma-ray bursts (GRBs) that were detected by satellite-based gamma-ray experiments during the fifth LIGO science run and first Virgo science run. The data used in this analysis were collected from 2005 November 4 to 2007 October 1, and most of the GRB triggers were from the Swift satellite. The search uses a coherent network analysis method that takes into account the different locations and orientations of the interferometers at the three LIGO-Virgo sites. We find no evidence for GWB signals associated with this sample of GRBs. Using simulated short-duration (<1s) waveforms, we set upper limits on the amplitude of gravitational waves associated with each GRB. We also place lower bounds on the distance to each GRB under the assumption of a fixed energy emission in gravitational waves, with a median limit of D~12Mpc(E^iso^_GW_/0.01M_{sun}_c^2^)^1/2^ for emission at frequencies around 150Hz, where the LIGO-Virgo detector network has best sensitivity.
- ID:
- ivo://CDS.VizieR/J/ApJ/814/159
- Title:
- H{alpha} interferometric visibilities of o Aqr
- Short Name:
- J/ApJ/814/159
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Omicron Aquarii is a late-type, Be shell star with a stable and nearly symmetric H{alpha} emission line. We combine H{alpha} interferometric observations obtained with the Navy Precision Optical Interferometer covering 2007 through 2014 with H{alpha} spectroscopic observations over the same period and a 2008 observation of the system's near-infrared spectral energy distribution to constrain the properties of o Aqr's circumstellar disk. All observations are consistent with a circumstellar disk seen at an inclination of 75{deg}+/-3{deg} with a position angle on the sky of 110{deg}+/-8{deg} measured East from North. From the best-fit disk density model, we find that 90% of the H{alpha} emission arises from within 9.5 stellar radii, and the mass associated with this H{alpha} disk is ~1.8x10^-10^ of the stellar mass, and that the associated angular momentum, assuming Keplerian rotation for the disk, is ~1.6x10^-8^ of the total stellar angular momentum. The occurrence of a central quasi-emission feature in Mg II {lambda}4481 is also predicted by this best-fit disk model and the computed profile compares successfully with observations from 1999. To obtain consistency between the H{alpha} line profile modeling and the other constraints, it was necessary in the profile fitting to weight the line core (emission peaks and central depression) more heavily than the line wings, which were not well reproduced by our models. This may reflect the limitation of assuming a single power law for the disk's variation in equatorial density. The best-fit disk density model for o Aqr predicts that H{alpha} is near its maximum strength as a function of disk density, and hence the H{alpha} equivalent width and line profile change only weakly in response to large (factor of ~5) changes in the disk density. This may in part explain the remarkable observed stability of o Aqr's H{alpha} emission line profile.
- ID:
- ivo://CDS.VizieR/J/ApJ/843/24
- Title:
- H{alpha} interferometry obs. of the Be star 48 Per
- Short Name:
- J/ApJ/843/24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We utilize a multi-step modeling process to produce synthetic interferometric and spectroscopic observables, which are then compared to their observed counterparts. Our extensive set of interferometric observations of the Be star 48 Per, totaling 291 data points, were obtained at the Navy Precision Optical Interferometer from 2006 November 07 to 23. Our models were further constrained by comparison with contemporaneous H{alpha} line spectroscopy obtained at the John S. Hall Telescope at the Lowell Observatory on 2006 November 1. Theoretical spectral energy distributions, SEDs, for 48 Per were confirmed by comparison with observations over a wavelength regime of 0.4-60 {mu}m from Touhami+ (2010PASP..122..379T) and Vieira+ (2017MNRAS.464.3071V). Our best-fitting combined model from H{alpha} spectroscopy, H{alpha} interferometry, and SED fitting has a power-law density fall off, n, of 2.3 and an initial density at the stellar surface of {rho}_0_=1.0x10^-11^g/cm^-3^ with an inclination constrained by H{alpha} spectroscopy and interferometry of 45+/-5{deg}. The position angle for the system, measured east from north, is 114+/-18{deg}. Our best-fit model shows that the disk emission originates in a moderately large disk with a radius of 25 R*, which is consistent with a disk mass of approximately 5x10^24^g or 3x10^-10^M*. Finally, we compare our results with previous studies of 48 Per by Quirrenbach+ (1997ApJ...479..477Q) and find agreement, whereas our disk size does not agree with Delaa+ (2011A&A...529A..87D), based on a much smaller visibility set.
- ID:
- ivo://CDS.VizieR/J/A+A/617/A31
- Title:
- HCO+, CN, and 13CO maps of R Mon
- Short Name:
- J/A+A/617/A31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To our knowledge, R Mon is the only B0 star in which a gaseous Keplerian disk has been detected. However, there is some controversy about the spectral type of R Mon. Some authors propose that it could be a later B8e star, where disks are more common. Our goal is to re-evaluate the R Mon spectral type and characterize its protoplanetary disk. The spectral type of R Mon has been re-evaluated using the available continuum data and UVES emission lines. We used a power-law disk model to fit previous ^12^CO 1-0 and 2-1 interferometric observations and the PACS CO data to investigate the disk structure. Interferometric detections of ^13^CO J=1-0, HCO^+^ 1-0, and CN 1-0 lines using the IRAM Plateau de Bure Interferometer (PdBI) are presented. The HCN 1-0 line was not detected. Our analysis confirms that R Mon is a B0 star. The disk model compatible with the ^12^CO 1-0 and 2-1 interferometric observations falls short of predicting the observed fluxes of the 14<Ju<31 PACS lines; this is consistent with the scenario in which some contribution to these lines is coming from a warm envelope and/or UV-illuminated outflow walls. More interestingly, the upper limits to the fluxes of the Ju>31 CO lines suggest the existence of a region empty of CO at R<=20au in the proto-planetary disk. The intense emission of the HCO^+^ and CN lines shows the strong influence of UV photons on gas chemistry. The observations gathered in this paper are consistent with the presence of a transition disk with a cavity of Rin>=20 au around R Mon. This size is similar to the photoevaporation radius that supports the interpretation that UV photoevaporation is main disk dispersal mechanism in massive stars
- ID:
- ivo://CDS.VizieR/J/A+A/597/A137
- Title:
- HD 123999 and Alpha Cen A and B OIFITS files
- Short Name:
- J/A+A/597/A137
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The photospheric radius is one of the fundamental parameters governing the radiative equilibrium of a star. We report new observations of the nearest solar-type stars Alpha Centauri A (G2V) and B (K1V) with the VLTI/PIONIER optical interferometer. The combination of four configurations of the VLTI enable us to measure simultaneously the limb darkened angular diameter thetaLD and the limb darkening parameters of the two solar-type stars in the near-infrared H band (lambda=1.65um). We obtain photospheric angular diameters of {theta}_LD(A)_=8.502+/-0.038mas (0.43%) and {theta}_LD(B)_=5.999+/-0.025mas (0.42%), through the adjustment of a power law limb darkening model. We find H band power law exponents of {alpha}_(A)_=0.1404+/-0.0050 (3.6%) and {alpha}_(B)_=0.1545+/-0.0044 (2.8%), which closely bracket the observed solar value (alpha_{sun}_=0.15027). Combined with the parallax pi=747.17+/-0.61mas determined by Kervella et al. (2016), we derive linear radii of R_A_=1.2234+/-0.0053R_{sun}_ (0.43%) and R_B_=0.8632+/-0.0037R_{sun}_ (0.43%). The power law exponents that we derive for the two stars indicate a significantly weaker limb darkening than predicted by both 1D and 3D stellar atmosphere models. As this discrepancy is also observed on the near-infrared limb darkening profile of the Sun, an improvement of the calibration of stellar atmosphere models is clearly needed. The reported PIONIER visibility measurements of Alpha Cen A and B provide a robust basis to validate the future evolutions of these models.
