Effelsberg Research Articles

On the Nature of the Radio Calibrator and Gamma-Ray Emitting NLS1 Galaxy 3C 286 and Its Multiwavelength Variability

The quasar 3C 286, a well-known calibrator source in radio astronomy, was found to exhibit exceptional multiwavelength properties. Its rich and complex optical emission-line spectrum revealed its narrow-line Seyfert 1 (NLS1) nature. Given its strong radio emission, this makes 3C 286 one of the radio-loudest NLS1 galaxies known to date. 3C 286 is also one of very few known compact steep-spectrum (CSS) sources detected in the gamma-ray regime. Observations in the X-ray regime, rarely carried out so far, revealed evidence for variability, raising the question whether it is driven by the accretion disk or jet. 3C 286 is also well known for its damped Lyman alpha system from an intervening absorber at z = 0.692, triggering a search for the corresponding X-ray absorption along the line-of-sight. Here, we present new observations in the radio, X-ray, optical, and UV bands. The nature of the X-ray variability is addressed. Spectral evidence suggests that it is primarily driven by the accretion disk (not the jet), and the X-ray spectrum is well fit by a powerlaw plus soft excess model. The radio flux density and polarization remain constant at the Effelsberg telescope resolution, reconfirming the use of 3C 286 as radio calibrator. The amount of reddening/absorption along the line-of-sight intrinsic to 3C 286 is rigorously assessed. None is found, validating the derivation of a high Eddington ratio (L/LEdd ∼ 1) and of the very high radio-loudness index of 3C 286. Based on the first deep Chandra image of 3C 286, tentative evidence for hard X-ray emission from the SW radio lobe is reported. A large variety of models for the gamma-ray emission of 3C 286 are briefly discussed.

Out-of-focus holography at the Effelsberg telescope

Context. Out-of-focus (OOF) holography can be used to determine the aperture deformations of radio telescopes that lead to errors in the phase of the complex aperture distribution. In contrast to traditional methods, OOF holography can be performed without a reference antenna, which has a number of practical advantages. Aims. The aim of this work is to develop a standard procedure for OOF holography at the Effelsberg telescope. This includes performing OOF holography observations and the development of dedicated software, the pyoof package, to compute aberrations of the telescope’s optical system. Methods. Based on the OOF holography method developed at the Green Bank telescope, we adapted the approach to the Effelsberg 100 m telescope in order to determine the aberrations of the aperture phase distribution (phase-error maps). Results. The developed OOF holography software is presented as well as the results from observations at Effelsberg. Early results reveal gravitation-related residual deformation not contained in the previously existing aperture and pointing model, and hence we propose changes to the model to counteract aberrations in the telescope’s surface. Conclusions. The OOF holography method (observations and pyoof package) works as expected at the Effelsberg 100 m telescope and is able to validate the good performance of the existing finite element model. Test measurements show that slight improvements of the aperture efficiency and gain elevation dependence are possible but limited in the current configuration.

A Candidate Period of 4.605 Days for FRB 20121102A and One Possible Implication of Its Origin

A firm establishment of the presence or the lack of periodicity in repeating fast radio bursts is crucial for determining their origins. Here, we compile 1145 radio bursts of FRB 20121102A with fluence larger than 0.15 Jy ms from observations using the Five-hundred-meter Aperture Spherical radio Telescope, the Arecibo Observatory, the Green Bank Telescope, the Effelsberg Telescope, the MeerKAT Telescope, the Lovell Telescope, the Deep Space Network 70 m radio telescopes, the Very Large Array, and the Westerbork Synthesis Radio Telescope, spanning the time interval of MJD 57175−58776. A quasi-period of 157.1−4.8+5.2 days and a candidate quasi-period of 4.605−0.010+0.003 days are found through the phase-folding probability binomial analysis. The former is consistent with previous findings and the latter is new. The 4.605 day periodicity is more obvious in high-energy bursts with fluence larger than 1 × 1038 erg. The presence of these (candidate) quasi-periods, together with the corresponding width of burst accumulation in the phase space, are consistent with the bursts originating from a binary degenerate star system with a close-by planet around the primary neutron star.

Constraining Annihilating Dark Matter Using the Multifrequency Radio Flux Profiles of the M33 Galaxy

Radio data can give stringent constraints for annihilating dark matter. In general, radio observations can detect very accurate radio flux density with high resolution and different frequencies for nearby galaxies. We are able to obtain the radio flux density as a function of distance from the galactic center and frequencies S(r, ν). In this article, we demonstrate a comprehensive radio analysis of the M33 galaxy, combining the radio flux density profile S(r) and the frequency spectrum S(ν) to get the constraints of dark matter annihilation parameters. By analyzing the archival radio data obtained from the Effelsberg telescope, we show that the dark matter annihilation contributing to the radio flux density might be insignificant in the disk region of the M33 galaxy. Moreover, by including the baryonic radio contribution, we constrain the 2σ conservative upper limits of the annihilation cross section, which can be complementary to the existing constraints based on neutrino, cosmic-ray, and gamma-ray observations. Our results indicate that analyzing the galactic multifrequency radio flux profiles can give useful and authentic constraints on dark matter for the leptophilic annihilation channels.

Disentangling Magnetic Fields in NGC 6946 with Wide-band Polarimetry

We present λ13 cm polarization observations of the nearby spiral galaxy NGC 6946 with the Westerbork Synthesis Radio Telescope (WSRT) to examine the nearside halo magnetic fields. Despite λ13 cm exhibiting similar two-dimensional morphology as observed at longer (λ18–22 cm) or shorter (λ3 and λ6 cm) wavelengths, more complete frequency coverage will be required to explain the gap in polarization in the southwest quadrant of the galaxy. We fit models of the turbulent and coherent line-of-sight magnetic fields to the fractional degree of linearly polarized emission at λ3, λ6, λ13, λ18, and λ22 cm from observations taken with the WSRT, Karl G. Jansky Very Large Array, and Effelsberg telescopes. The results favor a multilayer turbulent magneto-ionized medium consistent with current observations of edge-on galaxies. We constrain the physical properties of the synchrotron-emitting thin and thick disks (scale heights of 300 pc and 1.4 kpc, respectively) along with the thermal thick disk and halo (scale heights of 1 and 5 kpc, respectively). Our preferred model indicates a clumpy and highly turbulent medium within 1 kpc of the midplane, and a diffuse extraplanar layer with a substantially lower degree of Faraday depolarization. In the halo, we estimate a regular magnetic field strength of 0.4–2.2 μG and that turbulence and a total magnetic field strength of ∼6 μG result in a Faraday dispersion of σ RM = 4–48 rad m−2. This work is an example of how the advanced capabilities of modern radio telescopes are opening a new frontier for the study of cosmic magnetism.

Variations of the HCO+, HCN, HNC, N2H+, and NH3 deuterium fractionation in high-mass star-forming regions

ABSTRACT We use spectra and maps of the J = 1 − 0 and J = 2 − 1 DCO+, DCN, DNC, $\rm N_2D^+$ lines, and 111−101 ortho- and para-NH2D lines, obtained with the Institut de Radioastronomie Millimétrique (IRAM)-30 m telescope, as well as observations of their hydrogenated isotopologues to study deuteration processes in five high-mass star-forming regions. The temperature was estimated from CH 3CCH lines, also observed with the IRAM-30 m telescope, and from NH 3 lines, observed with the 100 m radio telescope in Effelsberg, as well as using the integrated intensity ratios of the J = 1 − 0 H13CN and HN13C lines and their main isotopologues. Applying a non-local thermodynamic equilibrium radiative transfer model with radex, the gas density and the molecular column densities were estimated. D/H ratios are 0.001–0.05 for DCO+, 0.001–0.02 for DCN, 0.001–0.05 for DNC, and 0.02–0.4 for NH2D. The D/H ratios decrease with increasing temperature in the range of 20–40 K and slightly vary at densities $n(\rm H_2) \sim 10^4\!-\!10^6$ cm−3. The deuterium fraction of $\rm N_2H^{+}$ is 0.008–0.1 at temperatures in the range of 20–25 K and at a density of ∼105 cm−3. We also estimate relative abundances and find ∼10−11–10−9 for DCO+ and DNC, ∼10−11–10−10 for $\rm N_2D^+$, and ∼10−10–10−8 for NH2D. The relative abundances of these species decrease with increasing temperature. However, the DCN/H2 ratio is almost constant (∼10−10). The observational results agree with the predictions of chemical models (although in some cases there are significant differences).

High frequency study of FRB 20180916B using the 100-m Effelsberg radio telescope

ABSTRACT FRB 20180916B is a repeating fast radio burst (FRB) with an activity period of 16.33 d. In previous observations ranging from ∼150−1400 MHz, the activity window was found to be frequency dependent, with lower frequency bursts occurring later. In this work, we present the highest frequency detections of bursts from this FRB, using the 100-m Effelsberg radio telescope at 4−8 GHz. We present the results from two observing campaigns. We performed the first campaign over an entire activity period which resulted in no detections. The second campaign was done in an active window at 4−8 GHz which we predicted from our modelling of chromaticity, resulting in eight burst detections. The bursts were detected in a window of 1.35 d, 3.6 d preceding the activity peak seen by Canadian hydrogen intensity mapping experiment, suggesting the chromaticity extends to higher frequency. The detected bursts have narrower temporal widths and larger spectral widths compared to lower frequencies. All of them have flat polarization position angle sweeps and high polarization fractions. The bursts also exhibit diffractive scintillation due to the Milky Way, following a f3.90 ± 0.05 scaling, and vary significantly over time. We find that burst rate across frequency scales as f−2.6 ± 0.2. Lastly, we examine implications of the frequency dependency on the source models.

The Effelsberg survey of FU Orionis and EX Lupi objects

Context. FU Orionis (FUor) and EX Lupi (EXor) type objects are two groups of peculiar and rare pre-main sequence low-mass stars that are undergoing powerful accretion outbursts during their early stellar evolution. Although water masers are widespread in star-forming regions and serve as powerful probes of mass accretion and ejection on small scales, little is known about the prevalence of water masers toward FUors and EXors. Aims. We aim to perform the first systematic search for the 22.2 GHz water maser line in FUors and EXors in order to determine its overall incidence in these eruptive variables and to facilitate high angular-resolution follow-up observations. Methods. We used the Effelsberg 100-m radio telescope to observe the H2O (616 – 523) transition at 22.2GHz toward a sample of 51 eruptive young stellar objects. Results. We detected a total of five water masers in our survey; three are associated with eruptive stars, equivalent to a detection rate of ~6% for our sample of eruptive sources. These detections include one EXor, V512 Per (also known as SVS 13 or SVS 13A), and two FUors, Z CMa, and HH 354 IRS. This is the first reported detection of water maser emission towards HH 354 IRS. We also detected water maser emission in our pointing towards the FUor binary RNO 1B/1C, which most likely originates from the nearby deeply embedded source IRAS 00338+6312 (~4″ from RNO 1B/1C). Emission was also detected from H2O(B), (also known as SVS 13C), a Class 0 source ~30″ from the EXor V512 Per. The peak flux density of H2O(B) in our observations, 498.7 Jy, is the highest observed to date, indicating that we have serendipitously detected a water maser flare in this source. In addition to the two non-eruptive Class 0 sources (IRAS 00338+6312 and H2O(B)/SVS 13C), we detected maser emission towards one Class 0/I (HH 354 IRS) and two Class I (V512 Per/SVS 13A and Z CMa) eruptive stars. Conclusions. Despite the low detection rate, we demonstrate the presence of 22.2 GHz water maser emission in both FUor and EXor systems, paving the way to radio interferometric observations to study the environments of these eruptive stars on small scales. Comparisons of our data with historical observations spanning several decades suggest that multiple water maser flares have occurred in both V512 Per and H2O(B).

The Effelsberg survey of FU Orionis and EX Lupi objects

Context. FU Orionis (FUor) and EX Lupi (EXor) type objects represent two small but rather spectacular groups of low-mass, young, eruptive stars. In both cases, outbursts of several magnitudes are observed, which are attributed to enhanced mass accretion from the circumstellar disc onto the central protostar. Although these objects are well studied at optical and near-infrared wavelengths, their host molecular environments are poorly explored because of the scarcity of systematic molecular line observations. Aims. We aim to carry out the first dedicated survey of the molecular environments of a large sample of FUors and EXors, observing a total of 51 sources, including some Gaia alerts, to study the ammonia (NH3) emission in their host environments. Methods. We observed the ammonia (J, K) = (1,1), (2,2), and (3,3) inversion transitions at ~23.7 GHz in position-switching mode using the Effelsberg 100-m radio telescope. For 19 of the 51 sources in our sample, we derived H2 column densities and dust temperatures using archival Herschel/SPIRE data at 250 µm, 300 µm, and 500 µm. Results. We detected the NH3 (1,1) transition toward 28 sources and the (2,2) transition toward 12 sources, while the (3,3) transition was detected towards only two sources in our sample. We find kinetic temperatures between ~12 K and 21 K, ammonia column densities from 5.2 × 1013 cm−2 to 3.2 × 1015 cm−2, and fractional ammonia abundances with respect to H2 from 4.7 × 10−9 to 1.5 × 10−7. These results are comparable to those found in infrared dark clouds (IRDCs). Our kinematic analysis suggests that most of the eruptive stars in our sample reside in rather quiescent (sonic or transonic) host environments. Conclusions. Our NH3 observations and analysis of the SPIRE dust-based H2 column density maps confirm the presence of dense material towards seven sources in our sample; additional sources might also harbour dense gas based on their NH2 (2,2) detections, potentially indicating an earlier phase than originally classified. Based on our results, we suggest that observations targeting additional molecular lines would help to refine the evolutionary classification of eruptive stars.

SDSS-FIRST-selected interacting galaxies

Context. In the hierarchical model of evolution of the Universe, galaxy mergers play an important role, especially at high redshifts. Interactions among galaxies appear to be associated with incidences of radio-loudness in quasars and it is of interest to study the galaxies that are in the process of interacting with each other, where there is at least one nucleus that is active in the radio regime. Aims. In order to understand the various processes taking place within colliding galaxies, it is important to study the radio and optical properties of these sources, as well as any possible correlations that might exist. Methods. To this end, we present optical long-slit spectroscopy data for ten pairs of interacting galaxies selected from SDSS-FIRST at redshifts of ∼0.05, observed using the multi-object double spectrographs at the Large Binocular Telescope. Results. We used line fluxes extracted from the spectra of the nuclear regions of galaxies to plot optical diagnostic diagrams and estimate the masses of the central supermassive black holes, as well as their Eddington ratios. Additionally, we used previously published Effelsberg radio telescope data at 4.85 GHz and FIRST survey data at 1.4 GHz to estimate radio spectral slopes and the radio-loudness parameters for all of the radio-detected sources. We also used WISE data to plot a mid-infrared colour-colour diagram. Conclusions. We see that while the sample of galaxies covers all of the classes on the optical diagnostic diagrams, the sources that are radio-detected fall in the composite or transition region of the diagram. Additionally, we notice a trend of the highest radio-loudness parameter in a pair of interacting galaxies being associated with the galaxy that hosts the more massive central supermassive black hole. We do not see any obvious trends with respect to the radio spectral slope, radio-loudness parameter, and Eddington ratio. With respect to the mid-infrared data of the galaxies detected by WISE, we see that most of them have some type of contribution from star formation, however, two of them seem to have a significant contribution from an AGN as well.

A burst storm from the repeating FRB 20200120E in an M81 globular cluster

ABSTRACT The repeating fast radio burst (FRB) source FRB 20200120E is exceptional because of its proximity and association with a globular cluster. Here we report 60 bursts detected with the Effelsberg telescope at 1.4 GHz. We observe large variations in the burst rate, and report the first FRB 20200120E ‘burst storm’, where the source suddenly became active and 53 bursts (fluence ≥0.04 Jy ms) occurred within only 40 min. We find no strict periodicity in the burst arrival times, nor any evidence for periodicity in the source’s activity between observations. The burst storm shows a steep energy distribution (power-law index α = 2.39 ± 0.12) and a bimodal wait-time distribution, with log-normal means of 0.94$^{+0.07}_{-0.06}$ s and 23.61$^{+3.06}_{-2.71}$ s. We attribute these wait-time distribution peaks to a characteristic event time-scale and pseudo-Poisson burst rate, respectively. The secondary wait-time peak at ∼1 s is ∼50 × longer than the ∼24 ms time-scale seen for both FRB 20121102A and FRB 20201124A – potentially indicating a larger emission region, or slower burst propagation. FRB 20200120E shows order-of-magnitude lower burst durations and luminosities compared with FRB 20121102A and FRB 20201124A. Lastly, in contrast to FRB 20121102A, which has observed dispersion measure (DM) variations of ΔDM > 1 pc cm−3 on month-to-year time-scales, we determine that FRB 20200120E’s DM has remained stable (ΔDM < 0.15 pc cm−3) over >10 months. Overall, the observational characteristics of FRB 20200120E deviate quantitatively from other active repeaters, but it is unclear whether it is qualitatively a different type of source.

H13CN–HN13C Intensity Ratio as a Temperature Indicator of Interstellar Clouds

With the 30-m IRAM radio telescope, we observed several massive star forming regions at wavelengths of 3–4 and 2 mm. The temperature of the gas in the sources was estimated from the lines of CH3CCH and from the transitions of the NH3 molecule obtained during observations at the 100-m radio telescope in Effelsberg. As a result, a correlation between the integrated intensity ratios of the J = 1−0 transitions of H13CN–HN13C and the kinetic temperature has been obtained. The obtained results allow us to propose the use of the intensity ratio H13CN–HN13C as a possible temperature indicator of interstellar clouds. We also compared the obtained estimates of the kinetic temperature with the dust temperature $${{T}_{{{\text{dust}}}}}$$ . As a result, no significant correlation was found.

Local Volume dwarf KK242: radial velocity, SF region and metallicity

Abstract KK242 is a LV dwarf of transition type residing in the void environment. Koda et al. present clear indications on its connection with Scd galaxy NGC6503. This implies the distance to KK242 of ∼6.3 Mpc and its MB=–10.5 mag. Its radial velocity, known from the Effelsberg radio telescope H i observations, reveals, however, the difference with that of NGC6503, ΔV∼400 km s−1. If real, this fact implies the substantial constraints on its origin. To clear-up the issue of KK242 radial velocity, we obtained with the SAO 6-m telescope spectra of its faint star-forming (SF) complex. Hα and Hβ emission is detected in two adjacent compact regions, the southern and northern, separated by ∼2 arcsec (∼60 pc). Their mean radial velocity is Vhel=–66 km s−1, ∼100 km s−1 lower than that of NGC6503. We use the HST Legacy Archive images and photometry of individual stars from the Extragalactic Distance Database, available for KK242, to identify in the SF complex the exciting hot stars, the probable BHeB and RHeB stars and a supernova remnant. We address, based on the possible range of its gas metallicity, the probable evolutionary paths of KK242. Using package Cloudy and parameters of the exciting B0V stars, we conclude that the observed flux ratio of the [S ii] doublet to Hα is consistent with the value of 12+log (O/H) ∼7.35 ±0.18 dex, expected for a stripped void dIrr galaxy.

And then they were two: Detection of non-thermal radio emission from the bow shocks of two runaway stars

Context. In recent years, winds from massive stars have been considered promising sites for investigating relativistic particle acceleration. In particular, the resulting bow-shaped shocks from the interaction of the supersonic winds of runaway stars with interstellar matter have been intensively observed at many different wavelengths, from radio to γ-rays. Aims. In this study we investigate the O4If star, BD+43° 3654, the bow shock of which is, so far, the only one proven to radiate both thermal and non-thermal emission at radio frequencies. In addition, we consider NGC 7635, the Bubble Nebula, as a bow shock candidate and examine its apex for indications of thermal and non-thermal radio emission. Methods. We observed both bow shocks in radio frequencies with the Very Large Array (VLA) in the C and X bands (4–8 GHz and 8–12 GHz) and with the Effelsberg telescope at 4–8 GHz. We analysed single-dish and interferometric results individually, in addition to their combined emission, obtained spectral index maps for each source, and calculated their spectral energy distributions. Results. We find that both sources emit non-thermal emission in the radio regime, with the clearest evidence for NGC 7635, whose radio emission has a strongly negative spectral index along the northern rim of the bubble. We present the first high-resolution maps of radio emission from NGC 7635, finding that the morphology closely follows the optical nebular emission. Our results are less conclusive for the bow shock of BD+43° 3654, as its emission becomes weaker and faint at higher frequencies in VLA data. Effelsberg data show a much larger emitting region (albeit a region of thermal emission) than is detected with the VLA for this source. Conclusions. Our results extend the previous radio results from the BD+43° 3654 bow shock to higher frequencies, and with our NGC 7635 results we double the number of bow shocks around O stars with detected non-thermal emission, from one to two. Modelling of the multi-wavelength data for both sources shows that accelerated electrons at the wind termination shock are a plausible source for the non-thermal radio emission, but energetics arguments suggest that any non-thermal X-ray and γ-ray emission could be significantly below existing upper limits. Enhanced synchrotron emission from compressed galactic cosmic rays in the radiative bow shock could also explain the radio emission from the BD+43° 3654 bow shock, but not from NGC 7635. The non-detection of point-like radio emission from BD+43° 3654 puts an upper limit on the mass-loss rate of the star that is lower than values quoted in the literature.

Stringent limits on 28SiO maser emission from the recurrent nova T Coronae Borealis

ABSTRACT There are indications that the third-known eruption of the recurrent nova T CrB is imminent, and multiwavelength observations prior to the eruption are important to characterize the system before it erupts. T CrB is known to display the SiO fundamental vibrational feature at 8 $\, \mu$m. When the anticipated eruption occurs, it is possible that the shock produced when the ejected material runs into the wind of the red giant in the system may be traced using SiO maser emission. We have used the 100 m Effelsberg Radio Telescope to search for 28SiO emission in the υ = 1, υ = 2, J = 1 → 0 transitions, at 43.122 GHz and 42.820 GHz, respectively, while the system is in quiescence. We find no evidence for such emission. We set stringent 3σ upper limits of 1.66 mJy on emission in the υ = 1, J = 1 → 0 transition, and 1.72 mJy in the υ = 2, J = 1 → 0 transition, respectively, for a noise bandwidth of 250 kHz. The corresponding limits for a 31.25 kHz bandwidth are 4.69 and 4.86 mJy, respectively. These upper limits improve on previous upper limits for this system by more than two orders of magnitude.

Observations of multiple NH3 transitions in W33

At a distance of 2.4 kpc, W33 is an outstanding massive and luminous 10 pc-sized star forming complex containing quiescent infrared dark clouds as well as highly active infrared bright cloud cores heated by young massive stars. We report measurements of ammonia (NH3) inversion lines in the frequency range 18–26 GHz obtained with the 40′′ resolution of the 100 m Effelsberg telescope. We detect the (J, K) = (1,1), (2,2), (3,3), (4,4), (5,5), (6,6), (2,1), and (3,2) transitions. There is a maser line in the (3,3) transition towards W33 Main. Brightness temperature and line shape indicate no significant variation during the last ~36 yr. We determined kinetic temperatures, column densities, and other physical properties of NH3 and the molecular clouds in W33. For the total-NH3 column density inside 40′′ (0.5 pc) regions, we find 6.0 (±2.1) × 1014, 3.5 (±0.1) × 1015, 3.4 (±0.2) × 1015, 3.1 (±0.2) × 1015, 2.8 (±0.2) × 1015, and 2.0 (±0.2) × 1015 cm−2 at the peak positions of W33 Main, W33 A, W33 B, W33 Main1, W33 A1, and W33 B1, respectively. W33 Main has a total-NH3 fractional abundance of 1.3 (±0.1) × 10−9 at the peak position. High values of 1.4 (±0.3) × 10−8, 1.6 (±0.3) × 10−8, 3.4 (±0.5) × 10−8, 1.6 (±0.5) × 10−8, and 4.0 (±1.2) × 10−8 are obtained at the central positions of W33 A, W33 B, W33 Main1, W33 A1, and W33 B1. From this, we confirm the previously proposed variation in the evolutionary stages of the six W33 clumps and find that there is no hot core in the region approaching the extreme conditions encountered in W51-IRS2 or Sgr B2. The ortho-to-para-NH3 abundance ratios suggest that ammonia should have been formed in the gas phase or on dust grain mantles at kinetic temperatures of ≳20 K. We determine kinetic temperatures only using NH3 (1,1) and (2,2), and from this we provide gas volume densities for the six main sources in the W33 region. With our new Tkin values, we find that our volume densities are similar to those estimated by Immer et al. (2014, A&A, 572, A63), suggesting that ammonia beam-filling factors are close to unity.

Scintillation time-scale measurement of the highly active FRB20201124A

ABSTRACT Scintillation of compact radio sources results from the interference between images caused by multipath propagation, and probes the intervening scattering plasma and the velocities of the emitting source and scattering screen. In FRB20201124A, a repeating fast radio burst (FRB) that entered a period of extreme activity, we obtained many burst detections in observations at the upgraded Giant Metrewave Radio Telescope (uGMRT) and the Effelsberg 100-m Radio Telescope. Bursts nearby in time show similar scintillation patterns, and we measure a scintillation time-scale of 14.3 ± 1.2 and 7 ± 2 min at Effelsberg (1370 MHz) and uGMRT (650 MHz), respectively, by correlating burst pair spectra. The scintillation bandwidth scaled to 1 GHz is 0.5 ± 0.1 MHz, and the inferred scintillation velocity at Effelsberg is $V_{\mathrm{ISS}}\approx (59\pm 7) \sqrt{d_{\mathrm{ l}}/2\, \rm {kpc}}~{\rm km~s}^{-1}$, higher than Earth’s velocity for any screen beyond a lens distance of $d_{\mathrm{ l}} \gtrsim 400\,$ pc. From the measured scintillation bandwidth, FRB20201124A has comparatively lower scattering than nearby pulsars, and is underscattered by a factor of ∼30 or ∼1200 compared to the NE2001 and YMW16 model predictions, respectively. This underscattering together with the measured scintillation velocity is consistent with a scattering screen more nearby the Earth at $d_{\mathrm{ l}} \sim 400\,$ pc, rather than at 2 kpc spiral arm that NE2001 predicts to be the dominant source of scattering. With future measurements, the distance, geometry, and velocity of the scattering screen could be obtained through modelling of the annual variation in VISS, or through interstation time delays or interferometric observations. Scintillation/scattering measurements of FRBs could help improve Galactic electron density models, particularly in the Galactic halo or at high Galactic latitudes.

Radio and X-ray observations of giant pulses from XTE J1810 − 197

ABSTRACT We present the results of two years of radio and X-ray monitoring of the magnetar XTE J1810 − 197 since the radio re-activation in late 2018. Single pulse analysis of radio observations from the Lovell and MkII telescopes at 1564 MHz and the Effelsberg telescope at 6 GHz has resulted in the detection of a total of 91 giant pulses (GPs) between MJDs 58858 and 59117. These GPs appear to be confined to two specific phase ranges (0.473 ≤ ϕ ≤ 0.502 and 0.541 ≤ ϕ ≤ 0.567). We also observe that the first detection of GP emission corresponds to a minimum in the spin-down rate. Simultaneous radio and X-ray observations were performed on MJDs 59009 and 59096. The 0.5–10 keV X-ray spectrum from NICER is well characterized by a two-component blackbody model that can be interpreted as two hot spots on the polar cap of the neutron star. The blackbody temperature decreases with time, consistent with the previous outburst, while the change in the pulsed fraction does not follow the same trend as was seen in the previous outburst. The radio and X-ray flux of XTE J1810 − 197 are correlated during the initial phase of the outburst (MJD 58450 – MJD 58550) and an increase in the radio flux is observed later that may be correlated to the onset of GPs. We argue that the disparity in the evolution of the current outburst compared to the previous one can be attributed to a change in geometry of the neutron star.

Polarization properties of FRB 20201124A from detections with the Effelsberg 100-m radio telescope

ABSTRACT The repeating fast radio burst (FRB) source, FRB 20201124A, was found to be highly active in 2021 March and April. We observed the source with the Effelsberg 100-m radio telescope at 1.36 GHz on 2021 April 9 and detected 20 bursts. A downward drift in frequency over time is clearly seen from the majority of bursts in our sample. A structure-maximizing dispersion measure (DM) search on the multicomponent bursts in our sample yields a DM of 411.6 ± 0.6 pc cm−3. We find that the rotation measure (RM) of the bursts varies around their weighted mean value of −601 rad m−2 with a standard deviation of 11.1 rad m−2. This RM magnitude is 10 times larger than the expected Galactic contribution along this line of sight (LoS). We estimate an LoS magnetic field strength of 4–6 µG, assuming that the entire host galaxy DM contributes to the RM. Further polarization measurements will help determine FRB 20201124A’s RM stability. The bursts are highly linearly polarized, with some showing signs of circular polarization, the first for a repeating FRB. Their polarization position angles (PAs) are flat across the burst envelopes and vary between bursts. We argue that the varying polarization fractions and PAs of FRB 20201124A are similar to known magnetospheric emission from pulsars, while the observed circular polarization, combined with the RM variability, is hard to explain with Faraday conversion. The high linear polarization fractions, flat PAs, and downward drift from FRB 20201124A bursts are similar to previous repeating sources, while the observed circular polarization is a newly seen behaviour among repeaters.

FAST early pulsar discoveries: Effelsberg follow-up

ABSTRACT We report the follow-up of 10 pulsars discovered by the Five-hundred-metre Aperture Spherical radio-Telescope (FAST) during its commissioning. The pulsars were discovered at a frequency of 500-MHz using the ultrawide-band (UWB) receiver in drift-scan mode, as part of the Commensal Radio Astronomy FAST Survey (CRAFTS). We carried out the timing campaign with the 100-m Effelsberg radio-telescope at L-band around 1.36 GHz. Along with 11 FAST pulsars previously reported, FAST seems to be uncovering a population of older pulsars, bordering and/or even across the pulsar death-lines. We report here two sources with notable characteristics. PSR J1951+4724 is a young and energetic pulsar with nearly 100 per cent of linearly polarized flux density and visible up to an observing frequency of 8 GHz. PSR J2338+4818, a mildly recycled pulsar in a 95.2-d orbit with a Carbon–Oxygen white dwarf (WD) companion of $\gtrsim 1\, \rm {M}_{\odot }$, based on estimates from the mass function. This system is the widest WD binary with the most massive companion known to-date. Conspicuous discrepancy was found between estimations based on NE2001 and YMW16 electron density models, which can be attributed to underrepresentation of pulsars in the sky region between Galactic longitudes 70° < l < 100°. This work represents one of the early CRAFTS results, which start to show potential to substantially enrich the pulsar sample and refine the Galactic electron density model.