Radio Telescope Research Articles

Comprehensive analysis of the Apertif fast radio burst sample. Similarities with young energetic neutron stars

Understanding the origin of energetic fast radio bursts (FRBs) has become the main science driver of recent dedicated FRB surveys powered by real-time instrumentation. Between July 2019 and February 2022, we carried out ALERT, an FRB survey at 1370\,MHz using the Apertif Radio Transient System (ARTS) installed at the Westerbork Synthesis Radio Telescope (WSRT). Here we report the detection of 18 new FRBs. We studied the properties of the entire 24-burst sample that were detected during the survey. For five bursts, we identified host galaxy candidates within their error regions with >50<!PCT!> probability association. We observed an average linear polarisation fraction of $ and an average circular polarisation fraction consistent with 0<!PCT!>. One-third of the FRBs display multiple components. These burst structures and the polarisation fractions are strikingly similar to those observed in young energetic pulsars and magnetars. The Apertif FRBs next reveal a population of highly scattered bursts. Given the observing frequency and time resolution, the scattering of most FRBs is likely to have been produced in the immediate circumburst environment. Furthermore, two FRBs show evidence of high rotation measure values which could reach RM in the source reference frames. This corroborates that some source environments are dominated by magneto-ionic effects. Together, the scattering and rotation measures that ALERT has found prove that a large fraction of FRBs are embedded in complex media such as star-forming regions or supernova remnants. Through the discovery of FRB\,20200719A, the third most dispersed FRB so far, we further show that one-off FRBs emit at frequencies in excess of 6\,GHz, the highest known to date. We compare this to the radio-bright high-frequency emission seen in magnetars. Finally, we determine an FRB all-sky rate of above a fluence limit of 4.1\ and a fluence cumulative distribution with a power-law index pm0.2 $, which is roughly consistent with the Euclidean Universe predictions. Through the high resolution in time, frequency, polarisation, and localisation that ALERT featured, we were able to determine the morphological complexity, polarisation, local scattering and magnetic environment, and high-frequency luminosity of FRBs. We find all of these parameters strongly resemble those seen in young, energetic, highly magnetised neutron stars.

Axions in Andromeda: Searching for minicluster-neutron star encounters with the Green Bank Telescope

The QCD axion and axionlike particles are compelling candidates for galactic dark matter. Theoretically, axions can convert into photons in the presence of a strong external magnetic field, which means it is possible to search for them experimentally. One approach is to use radio telescopes with high-resolution spectrometers to look for axion-photon conversion in the magnetospheres of neutron stars. In this paper, we describe the results obtained using a novel approach where we used the Green Bank Telescope (GBT) to search for radio transients produced by collisions between neutron stars and dark matter clumps known as axion miniclusters. We used the versatile GBT astronomical spectrometer and the X-band receiver (8–10 GHz) to observe the core of Andromeda. Our measurements are sensitive to axions with masses between 33 and 42 μeV with Δma=3.8×10−4 μeV. This paper gives a description of the search method we developed, including observation and analysis strategies. Given our analysis algorithm choices and the instrument sensitivity (∼2 mJy in each spectral channel), we did not find any candidate signals greater than 5σ. We are currently implementing this search method in other spectral bands. Published by the American Physical Society 2024

The SOFIA Massive (SOMA) Star Formation Q-band follow-up

Context. Evidence that the chemical characteristics around low- and high-mass protostars are similar has been found: notably, a variety of carbon-chain species and complex organic molecules (COMs) form around both types. On the other hand, the chemical compositions around intermediate-mass (IM) protostars (2 M⊙ < m* < 8 M⊙) have not been studied with large samples. In particular, it is unclear the extent to which carbon-chain species form around them. Aims. We aim to obtain the chemical compositions of a sample of IM protostars, focusing particularly on carbon-chain species. We also aim to derive the rotational temperatures of HC5N to confirm whether carbon-chain species are formed in the warm gas around these stars. Methods. We conducted Q-band (31.5–50 GHz) line survey observations toward 11 mainly IM protostars with the Yebes 40 m radio telescope. The target protostars were selected from a subsample of the source list of the SOFIA Massive Star Formation project. Assuming local thermodynamic equilibrium, we derived the column densities of the detected molecules and the rotational temperatures of HC5N and CH3 OH. Results. Nine carbon-chain species (HC3N, HC5N, C3H, C4H linear-H2CCC, cyclic-C3H2, CCS, C3S, and CH3CCH), three COMs (CH3OH, CH3CHO, and CH3CN), H2CCO, HNCO, and four simple sulfur-bearing species (13CS, C34S, HCS+, and H2CS) are detected. The rotational temperatures of HC5N are derived to be ~20–30 K in three IM protostars (Cepheus E, HH288, and IRAS 20293+3952). The rotational temperatures of CH3OH are derived in five IM sources and found to be similar to those of HC5N. Conclusions. The rotational temperatures of HC5N around the three IM protostars are very similar to those around low- and high-mass protostars. These results indicate that carbon-chain molecules are formed in lukewarm gas (~20–30 K) around IM protostars via the warm carbon-chain chemistry process. Thus, carbon-chain formation occurs ubiquitously in the warm gas around protostars across a wide range of stellar masses. Carbon-chain molecules and COMs coexist around most of the target IM protostars, which is similar to the situation for low- and high-mass protostars. In summary, the chemical characteristics around protostars are the same in the low-, intermediate- and high-mass regimes.

ALMA and GMRT Studies of Dust Continuum Emission and Spectral Lines Toward Oort Cloud Comet C/2022 E3 (ZTF)

The atomic and molecular compounds of cometary ices serve as valuable knowledge into the chemical and physical properties of the outer solar nebula, where comets are formed. From the cometary atmospheres, the atoms and gas-phase molecules arise mainly in three ways: (i) the outgassing from the nucleus, (ii) the photochemical process, and (iii) the sublimation of icy grains from the nucleus. In this paper, we present the radio and millimeter wavelength observation results of Oort cloud non-periodic comet C/2022 E3 (ZTF) using the Giant Metrewave Radio Telescope (GMRT) band L and the Atacama Large Millimeter/submillimeter Array (ALMA) band 6. We do not detect continuum emissions and an emission line of atomic hydrogen (H I) at rest frequency 1420 MHz from this comet using the GMRT. Based on ALMA observations, we detect the dust continuum emission and rotational emission lines of methanol (CH3OH) from comet C/2022 E3 (ZTF). From the dust continuum emission, the dust production (Afρ) activity of comet ZTF is 2280 ± 50 cm. Based on LTE spectral modeling, the column density and excitation temperature of CH3OH toward C/2022 E3 (ZTF) are (4.50 ± 0.25) × 1014 cm−2 and 70 ± 3 K respectively. The integrated emission maps show that CH3OH was emitted from the coma region of the comet. The production rate of CH3OH toward C/2022 E3 (ZTF) is (7.32 ± 0.64) × 1026 molecules s−1. The fractional abundance of CH3OH with respect to H2O in the coma of the comet is 1.52%. We also compare our derived abundance of CH3OH with the existence modeled value, and we see the observed and modeled values are quite similar. We claim that CH3OH is formed via the subsequential hydrogenation of formaldehyde (H2CO) on the grain surface of comet C/2022 E3 (ZTF).

FAST H i 21 cm Study of Blueberry Galaxies

Green Peas (GPs) and blueberry galaxies (BBs) are thought to be local analogs (z < 0.1) of high redshift Lyα emitters. H i study of these can help us understand the star formation in the primordial Universe. In this Letter, we present the results of H i 21 cm study of 28 high specific star formation rate (sSFR ≳ 10−8yr −1) BBs at z ≲ 0.05 with the Five-hundred-meter Aperture Spherical radio Telescope. We report significant H i detection towards two BBs, namely J1026+0426 and J1132+0809, and discuss possible H i contribution from neighboring galaxies. The median 3σ upper limit of ∼2.0 × 108 M ⊙ was obtained on H i mass for galaxies with nondetections. We find BBs tend to have lower H i-to-stellar-mass ratio or gas fraction (f H i ) than expected from f H i –sSFR and f H i –M * relations for main-sequence galaxies. The BBs also have a median 3σ upper limit on H i gas depletion timescale (τ H i ) ∼ 0.5 Gyr, about 1 order of magnitude lower than τ H i for local main-sequence galaxies. We find a significantly low H i detection rate of 2/28 (7.1 −4.6+9.4 %) towards these galaxies, which is similar to previous H i studies of low redshift GPs of high ionization parameter indicator, O32 ≡ O[iii]λ5007/O[ii]λ3727 ratios ≳10.

Fine Structure of the Solar Corona in High-Frequency Resolution Radio Observations

Fine Structure of the Solar Corona in High-Frequency Resolution Radio Observations

A Repeating Fast Radio Burst Source in a Low-luminosity Dwarf Galaxy

We present the localization and host galaxy of FRB 20190208A, a repeating source of fast radio bursts (FRBs) discovered using CHIME/FRB. As part of the Pinpointing REpeating ChIme Sources with EVN dishes repeater localization program on the European VLBI Network (EVN), we monitored FRB 20190208A for 65.6 hr at ∼1.4 GHz and detected a single burst, which led to its very long baseline interferometry localization with 260 mas uncertainty (2σ). Follow-up optical observations with the MMT Observatory (i ≳ 25.7 mag (AB)) found no visible host at the FRB position. Subsequent deeper observations with the Gran Telescopio Canarias, however, revealed an extremely faint galaxy (r = 27.32 ± 0.16 mag), very likely (99.95%) associated with FRB 20190208A. Given the dispersion measure of the FRB (∼580 pc cm−3), even the most conservative redshift estimate ( zmax∼0.83 ) implies that this is the lowest-luminosity FRB host to date (≲108 L ⊙), even less luminous than the dwarf host of FRB 20121102A. We investigate how localization precision and the depth of optical imaging affect host association and discuss the implications of such a low-luminosity dwarf galaxy. Unlike the other repeaters with low-luminosity hosts, FRB 20190208A has a modest Faraday rotation measure of a few tens of rad m−2, and EVN plus Very Large Array observations reveal no associated compact persistent radio source. We also monitored FRB 20190208A for 40.4 hr over 2 yr as part of the Extragalactic Coherent Light from Astrophysical Transients repeating FRB monitoring campaign on the Nançay Radio Telescope and detected one burst. Our results demonstrate that, in some cases, the robust association of an FRB with a host galaxy will require both high localization precision and deep optical follow-up.

An Extreme Radio Fluctuation of Pulsar B1929+10

We report the detection of an extreme flux decrease accompanied by clear dispersion measure (DM) and rotation measure (RM) variations for pulsar B1929+10 during the 110 minute radio observation with the Five-hundred-meter Aperture Spherical radio Telescope. The radio flux decreases by 2–3 orders of magnitude within a rapid timescale of about 20 minutes. Meanwhile, the variations of DM and RM are approximately 0.05 pc cm−3 and 0.7 rad m−2, respectively. Frequency-dependent analysis of DM indicates an extremely weak chromatic DM feature, which does not notably affect the radiative behavior detected. Moreover, the pulsar timing analysis shows an additional time delay from 100 μs to 400 μs in the event. These results are speculated to be due to the eclipse and bend for the radio emission of pulsar B1929+10 by a highly dense outflow from the pulsar. This not only impacts the intrinsic radio emission feature but also affects the pulsar timing behavior. Nevertheless, a plasma lens effect lasting around 20 minutes could also be responsible for the event.

Observations of the galaxy cluster CL 0217+70 and its surrounding region at 1.4 GHz with the Sardinia Radio Telescope

Abstract We present the results of observations performed with the Sardinia Radio Telescope (SRT) at 1.3–1.8 GHz of the galaxy cluster CL 0217+70 and a 3○ × 3○ region around it. We combine the SRT data with archival Very Large Array (VLA) data to obtain images having the VLA angular resolution, but sensitive up to largest scales. The SRT+VLA combination allows us to derive a cluster radio halo flux density higher by $\sim 14{{\%}}$ compared to the VLA-only data, although consistent within 1σ. We derive a spectral index map between 140 MHz and 1.4 GHz, finding an extended region with spectral index α ∼ 0.6 on the external part of the south-eastern candidate relic, questioning the real nature of this relic. Moreover, we detect an extended emission outside the cluster in the south-eastern area, having an angular extension of ∼50 arcmin on the longer side, which would correspond to ∼10 Mpc at the cluster distance; the emissivity that this region would have if located at the cluster distance is in line with the one estimated in candidate filaments of the cosmic web; however, the peculiar orientation of this region, not pointed towards the cluster, and the low Galactic latitude of this cluster suggest that its origin can be due to a foreground emission originating in our Galaxy.

An Optimization Method for Design Solutions to Active Reflective Surface Control Systems Based on Axiomatic Design and Multi-Criteria Decision Making

The design of an Active Reflective Surface Control System (ARCS) is a complex engineering task involving multidimensional and multi-criteria constraints. This paper proposes a novel methodological approach for ARCS design and optimization by integrating Axiomatic Design (AD) and Multi-Criteria Decision Making (MCDM) techniques. Initially, a structured design plan is formulated within the axiomatic design framework. Subsequently, four MCDM methods—Technique for Order Preference by Similarity to Ideal Solution (TOPSIS), Entropy Weight Method (EWM), Multi-Criteria Optimization and Compromise Solution (VIKOR), and the integrated TOPSIS–Grey Relational Analysis (GRA) approach—are used to evaluate and compare the alternative solutions. Additionally, fuzzy information axioms are used to calculate the total information content for each alternative to identify the optimal design. A case study is conducted, selecting the optimal actuator for a 5 m diameter scaled model of the Five-hundred-meter Aperture Spherical radio Telescope (FAST), followed by digital control experiments on the chosen actuator. Based on the optimal design scheme, an ARCS prototype is constructed, which accelerates project completion and substantially reduces trial-and-error costs.

Radio Continuum Halos of Seven Nearby Large Galaxies Using uGMRT

We present the results of deep radio observations of seven nearby large galaxies observed using the upgraded Giant Metrewave Radio Telescope (uGMRT) 0.3–0.5 GHz receivers with an angular resolution of ∼10″. The achieved sensitivities of these observations range from ≈15 to 50 μJy beam−1, which is a factor of ≈3–4 lower than the previous observations at these frequencies. For two galaxies (NGC 3344 and NGC 3627) with moderate inclination angles, significant diffuse emissions are seen for the first time. The detected radio halos in the vertical direction are significantly larger in our 0.4 GHz maps compared to the observations at ∼1.5 GHz for four nearly edge-on galaxies—NGC 3623, NGC 4096, NGC 4594, and NGC 4631. For these four galaxies, significantly larger halos are also detected along the galaxy disk. For NGC 3623 and NGC 4594, we could detect elongated radio disks that were not seen before. We also present new uGMRT images of NGC 3344 and NGC 3623 at 1.3 GHz and a new VLA image of NGC 3627 at 1.5 GHz. We fitted an exponential function to the flux densities along different cross-cuts and found a significantly wider distribution at the 0.4 GHz uGMRT images compared to the high-frequency images at ∼1.5 GHz. Using maps at 0.144, 0.4, and ∼1.5 GHz, we made spectral index maps of the seven sample galaxies and found a steepening of the spectrum up to a value of ∼−1.5 in the halo regions of the galaxies.

Periodic Gamma-Ray Modulation of the Blazar PG 1553+113 Confirmed by Fermi-LAT and Multiwavelength Observations

A 2.1 yr periodic oscillation of the gamma-ray flux from the blazar PG 1553+113 has previously been tentatively identified in ∼7 yr of data from the Fermi Large Area Telescope. After 15 yr of Fermi sky-survey observations, doubling the total time range, we report >7 cycle gamma-ray modulation with an estimated significance of 4σ against stochastic red noise. Independent determinations of oscillation period and phase in the earlier and the new data are in close agreement (chance probability <0.01). Pulse timing over the full light curve is also consistent with a coherent periodicity. Multiwavelength new data from Swift X-Ray Telescope, Burst Alert Telescope, and UVOT, and from KAIT, Catalina Sky Survey, All-Sky Automated Survey for Supernovae, and Owens Valley Radio Observatory ground-based observatories as well as archival Rossi X-Ray Timing Explorer satellite-All Sky Monitor data, published optical data of Tuorla, and optical historical Harvard plates data are included in our work. Optical and radio light curves show clear correlations with the gamma-ray modulation, possibly with a nonconstant time lag for the radio flux. We interpret the gamma-ray periodicity as possibly arising from a pulsational accretion flow in a sub-parsec binary supermassive black hole system of elevated mass ratio, with orbital modulation of the supplied material and energy in the jet. Other astrophysical scenarios introduced include instabilities, disk and jet precession, rotation or nutation, and perturbations by massive stars or intermediate-mass black holes in polar orbit.

Simulating the LOcal Web (SLOW) III. Synchrotron emission from the local cosmic web

Detecting diffuse synchrotron emission from the cosmic web is still a challenge for current radio telescopes. We aim to make predictions about the detectability of cosmic web filaments from simulations. We present the first cosmological magnetohydrodynamic simulation of a 500 $h^ c$Mpc volume with an on-the-fly spectral cosmic ray (CR) model. This allows us to follow the evolution of populations of CR electrons and protons within every resolution element of the simulation. We modeled CR injection at shocks, while accounting for adiabatic changes to the CR population and high-energy-loss processes of electrons. The synchrotron emission was then calculated from the aged electron population, using the simulated magnetic field, as well as different models for the origin and amplification of magnetic fields. We used constrained initial conditions, which closely resemble the local Universe, and compared the results of the cosmological volume to a zoom-in simulation of the Coma cluster, to study the impact of resolution and turbulent reacceleration of CRs on the results. We find a consistent injection of CRs at accretion shocks onto cosmic web filaments and galaxy clusters. This leads to diffuse emission from filaments of the order $S_ $ for a potential LOFAR observation at 144 MHz, when assuming the most optimistic magnetic field model. The flux can be increased by up to two orders of magnitude for different choices of CR injection parameters. This can bring the flux within a factor of ten of the current limits for direct detection. We find a spectral index of the simulated synchrotron emission from filaments of $ -1.0 -- -1.5 in the LOFAR band.

The Impact of Partial Solar Eclipse on the Observation of Neutral Hydrogen Emission Line

The research involves examining the influence of partial solar eclipse on the strength of neutral hydrogen from the Sun. Baghdad University Radio Telescope (BURT) was used to monitor the partial solar eclipse on the 25th of October, 2022. Radio observations from the Sun were recorded from 11:30 AM to 03:36 PM. This means that the HI emission from the Sun was recorded before, during and after the event. It was noticed, that at the moment of maximum eclipse, ~ 46% of the Sun’s disk was covered by the Moon. For the purpose of this research, the solar radio wave intensity was monitored and the solar flux density was determined at different times, i.e. before, during and after the partial solar eclipse. The obtained results showed that both of the solar flux and power spectrum decrease with the progress of the eclipse until the moment of maximum eclipse, i.e. the moment at which the minimum values of solar flux density and antenna temperature were recorded (7 × 104 Jy and ~ 80 K). Then, at the last moments of the partial eclipse, it was noticed that both parameters started to increase again due to the decrease in the area of the Sun’s disk until both reached their normal values. In Conclusion, the partial solar eclipse affects the strength of neutral hydrogen from the Sun because the Moon blocks the neutral hydrogen from the Sun during the solar eclipse.

UGMRT Survey of EXoplanets Around M-dwarfs (GS-EXAM): Radio Observations of GJ 1151

Coherent radio emission with properties similar to planetary auroral signals has been reported from GJ 1151, a quiescent, slow-rotating mid-M star, by the LOFAR Two-meter (120–170 MHz) Sky Survey. The observed LOFAR emission is fairly bright at 0.89 mJy with 64% circular polarization, and the emission characteristics are consistent with the interaction between an Earth-sized planet with an orbital period of 1–5 days and the magnetic field of the host star. However, no short-period planet has been detected around GJ 1151. To confirm the reported radio emission caused by the putative planet around GJ 1151 and to investigate the nature of this emission, we carried out upgraded Giant Metrewave Radio Telescope observations of GJ 1151 at 150, 218, and 400 MHz over 33 hr across ten epochs. No emission was detected at any frequency. While at 150 and 218 MHz, nondetection could be due to the low sensitivity of our observations, at 400 MHz, the rms sensitivities achieved were sufficient to detect the emission observed with LOFAR at ∼20σ level. Our findings suggest that the radio emission is highly time variable, likely influenced by the star-planet system’s phase and the host star’s magnetic field. Additional observations below 170 MHz, at more frequent epochs (as the periodicity of the emission is unknown), especially during periods of high stellar magnetic field strength, are needed to confirm the emission.

Radio-AGN activity across the galaxy population: dependence on stellar mass, star-formation rate, and redshift

Abstract We characterise the co-evolution of radio-loud AGN and their galaxies by mapping the dependence of radio-loud AGN activity on stellar mass and star-formation rate (SFR) across cosmic time (out to z ∼ 1.5). Deep LOFAR radio observations are combined with large galaxy samples to study the incidence of radio-loud AGN across the galaxy population; the AGN are further split into low-excitation radio galaxies (LERGs) and high-excitation radio galaxies (HERGs). We find that LERG activity occurs over a wide range of SFRs, whereas HERGs are typically found in galaxies with ongoing star formation. The LERGs are then split based on their SFRs relative to the main sequence, across redshift. Within quiescent galaxies, LERG activity shows a steep stellar mass dependence with the same normalisation across the past ∼ 10 Gyr; this indicates that hot gas fuels LERGs in quiescent galaxies across cosmic time. In massive galaxies ($\log _{10}(M/\rm {{\rm M}_{\odot }}) \gtrsim 11$), the incidence of LERGs is roughly constant across the galaxy population, suggesting that LERGs in massive galaxies may be fuelled by hot gas regardless of the star-formation activity. At lower masses, however, LERG activity is significantly more enhanced (by a factor of up to 10) in star-forming galaxies compared to quiescent galaxies; this suggests that an additional fuelling mechanism, likely associated with cold gas, may fuel the LERGs in galaxies with higher SFRs. We find that HERGs typically accrete above 1percnt of the Eddington-scaled accretion rate, and the LERGs typically accrete below this level.

Multisegment Overlap–Save Method for Coherent Dedispersion

Dispersion occurs due to the interstellar medium, which functions as a prism and causes different time delays in radio waves of varying frequencies. The coherent dedispersion technique is often used in pulsar and fast radio burst observations to mitigate this phenomenon. The widely recognized Overlap–Save approach enables this dedispersion algorithm to efficiently perform long linear convolution. However, with the present implementation, the necessary filter length for dedispersion can reach 100 million points or more. The corresponding fast Fourier transform (FFT) points should be larger than this value and a GPU cluster can be used to tackle this demanding process. This study presents the Multisegment Overlap–Save Method (MS-OSM) to effectively address this problem. Our algorithm divides signal bands into separate short segments based on frequency component delays during dedispersion. By using the short segments shuffling technique with the Overlap-Save structure, MS-OSM can greatly reduce the FFT and inverse FFT points required down to fewer than 65,536 points. To evaluate the performance of MS-OSM, a synthetic pulsar signal is created and verified using standard software tools like DSPSR and PRESTO. The results show that MS-OSM maintains the same resolution while reducing execution time and resource usage. The validation of MS-OSM is taken by processing real pulsar observation data.

Late-time non-thermal emission from mildly relativistic tidal ejecta of compact objects merger

Abstract Mergers of compact objects (binary neutron stars, BNS, or neutron star-black hole, NSBH) with a substantial mass ratio (q &amp;gt; 1.5) are expected to produce a mildly relativistic ejecta within ∼20○ from the equatorial plane. We present a semi-analytic approach to calculate the expected synchrotron emission observed from various viewing angles, along with the corresponding radio maps, that are produced by a collisionless shock driven by such ejecta into the interstellar medium. This method reproduces well (up to $\sim 30\%$ deviations) the observed emission produced by 2D numerical calculations of the full relativistic hydrodynamics. We consider a toroidal ejecta with an opening angle of 15○ ≤ θopen ≤ 30○ and broken power-law mass distribution, M( &amp;gt; γβ)∝(γβ)−s with s = sKN at γβ &amp;lt; γ0β0 and s = sft at γβ &amp;gt; γ0β0 (where γ is the Lorentz factor). The parameter values are chosen to characterize merger calculation results- a ”shallow” mass distribution, 1 &amp;lt; sKN &amp;lt; 3, for the bulk of the ejecta (at γβ ≈ 0.2), and a steep, sft &amp;gt; 5, ”fast tail” mass distribution. While the peak flux is dimmer by a factor of ∼2-3, and the peak time remains roughly the same (within $20\%$), for various viewing angles compared to isotropic equivalent ejecta (θopen = 90○) considered in preceding papers, the radio maps are significantly different from the spherical case. The semi-analytic method can provide information on the ejecta geometry and viewing angle from future radio map observations and, consequently, constrain the ejection mechanism. For NSBH mergers with a significant mass ejection (∼0.1M⊙), this late non-thermal signal can be observed to distances of ≲ 200Mpc for typical parameter values.

Structure of the Baryon Halo Around a Supermassive Primordial Black Hole

According to some theoretical models, primordial black holes with masses of more than 108 solar masses could be born in the early universe, and their possible observational manifestations have been investigated in a number of works. Dense dark matter and baryon halos could form around such primordial black holes even at the pre-galactic stage (in the cosmological Dark Ages epoch). In this paper, the distribution and physical state of the gas in the halo are calculated, taking into account the radiation transfer from the central accreting primordial black hole. This made it possible to find the ionization radius, outside of which there are regions of neutral hydrogen absorption in the 21 cm line. The detection of annular absorption regions at high redshifts in combination with a central bright source may provide evidence of the existence of supermassive primordial black holes. We also point out the fundamental possibility of observing absorption rings with strong gravitational lensing on galaxy clusters, which weakens the requirements for the angular resolution of radio telescopes.

Long-term Simultaneous Monitoring Observations of SiO and H2O Masers toward the Mira Variable WX Serpentis

We present the results from long-term simultaneous monitoring observations of SiO and H2O masers toward the Mira variable star WX Serpentis. This study has been conducted with 21 m single-dish radio telescopes of the Korean VLBI Network from 2009 June to 2021 June. Five maser lines were considered: SiO v = 1, 2, J = 1−0; SiO v = 1, J = 2−1, 3−2; and H2O 61,6–52,3 transitions, with the SiO maser lines distributed near the stellar velocity and the H2O maser exhibiting an asymmetric line profile with five to six peaked components. Intense H2O maser emissions suddenly appeared in 2019 September, indicating flaring. The intensity variations of SiO and H2O masers are strongly correlated with the optical light curve (OLC) of the central star, with individual phase lags; the phase lag of the H2O maser relative to the OLC is larger than that of the SiO masers. The consequent phase difference between the SiO masers and the H2O maser likely indicates that their formation regions and main driving mechanisms are different from each other. The SiO masers in WX Ser exhibit a dominant single-peak velocity distribution, similar to other Mira variable stars. However, the H2O maser displays distinct morphological features, showing a radial acceleration and preferential intensity dominance at blueshifted velocities. This suggests that the H2O maser clouds of WX Ser are moving outward, thereby developing an asymmetric outflow owing to nonuniform material ejection from the stellar atmosphere. The findings confirm that an initial asymmetric outflow structure emerged during the thermally pulsing asymptotic giant branch phase, specifically in the Mira variable star stage.