Effelsberg Research Articles

Multi-epoch searches for relativistic binary pulsars and fast transients in the Galactic Centre

ABSTRACT The high stellar density in the central parsecs around the Galactic Centre makes it a seemingly favourable environment for finding relativistic binary pulsars. These include pulsars orbiting other neutron stars, stellar-mass black holes, or the central supermassive black hole, Sagittarius A*. Here, we present multi-epoch pulsar searches of the Galactic Centre at four observing frequencies, $4.85,\, 8.35,\, 14.6,\, 18.95\, {\rm GHz}$, using the Effelsberg 100-m radio telescope. Observations were conducted 1 yr prior to the discovery of, and during monitoring observations of, the Galactic Centre magnetar PSR J1745−2900. Our data analysis features acceleration searches on progressively shorter time series to maintain sensitivity to relativistic binary pulsars. The multi-epoch observations increase the likelihood of discovering transient or nulling pulsars, or ensure orbital phases are observed at which acceleration search methods work optimally. In ${\sim}147\, {\rm h}$ of separate observations, no previously undiscovered pulsars have been detected. Through calibration observations, we conclude this might be due to insufficient instantaneous sensitivity, caused by the intense continuum emission from the Galactic Centre, its large distance, and, at higher frequencies, the aggregate effect of steep pulsar spectral indices and atmospheric contributions to the system temperature. Additionally, we find that for millisecond pulsars in wide circular orbits $({\lesssim}800\, {\rm d})$ around Sagittarius A*, linear acceleration effects cannot be fully corrected in deep observations $(9\, {\rm h})$ with existing software tools. Pulsar searches of the Galactic Centre with the next generation of radio telescopes – such as MeerKat, ngVLA, and SKA1-mid – will have improved chances of uncovering this elusive population.

Project MOMO: Multiwavelength Observations and Modeling of OJ 287

Our project MOMO (Multiwavelength observations and modeling of OJ 287) consists of dedicated, dense, long-term flux and spectroscopic monitoring, and deep follow-up observations of the blazar OJ 287 at >13 frequencies from the radio to the X-ray band since late 2015. In particular, we are using Swift to obtain optical-UV-X-ray spectral energy distributions (SEDs) and the Effelsberg telescope to obtain radio measurements between 2 and 40 GHz. MOMO is the densest long-term monitoring of OJ 287 involving X-rays and broad-band SEDs. The theoretical part of the project aims at understanding jet and accretion physics of the blazar central engine in general and the supermassive binary black hole scenario in particular. Results are presented in a sequence of publications and so far included: detection and detailed analysis of the bright 2016/17 and 2020 outbursts and the long-term light curve; Swift, XMM, and NuSTAR spectroscopy of the 2020 outburst around maximum; and interpretation of selected events in the context of the binary black hole scenario of OJ 287 (papers I–IV). Here, we provide a description of the project MOMO, a summary of previous results, the latest results, and we discuss future prospects.

A search for pulsar companions around low-mass white dwarfs

ABSTRACT We report on a search for pulsars at the positions of eight low-mass white dwarfs and one higher mass white dwarf with the 100-m Effelsberg Radio Telescope. These systems have orbital parameters suggesting that their unseen companions are either massive white dwarfs or neutron stars (NSs). Our observations were performed at 1.36 GHz, reaching sensitivities of 0.1–0.2 mJy. We searched our data accounting for the possible acceleration and jerk of the pulsar signals due to orbital motion, but found no significant pulsar signals. Considering our result jointly with 20 non-detections of similar systems with the Greenbank Radio Telescope, we infer fNS ≤ 0.10, for the fraction of NSs orbiting these white dwarfs. We discuss the sensitivity of this result to the underlying assumptions and conclude with a brief discussion on the prospects of targeted surveys for discovering millisecond pulsars.

Study of the thermal and nonthermal emission components in M31: the Sardinia Radio Telescope view at 6.6 GHz

Context. The Andromeda galaxy is the best-known large galaxy besides our own Milky Way. Several images and studies exist at all wavelengths from radio to hard X-ray. Nevertheless, only a few observations are available in the microwave range where its average radio emission reaches the minimum. Aims. In this paper, we want to study the radio morphology of the galaxy, decouple thermal from nonthermal emission, and extract the star formation rate. We also aim to derive a complete catalog of radio sources for the mapped patch of sky. Methods. We observed the Andromeda galaxy with the Sardinia Radio Telescope at 6.6 GHz with very high sensitivity and angular resolution, and an unprecedented sky coverage. Results. Using new 6.6 GHz data and Effelsberg radio telescope ancillary data, we confirm that, globally, the spectral index is ∼0.7−0.8, while in the star forming regions it decreases to ∼0.5. By disentangling (gas) thermal and nonthermal emission, we find that at 6.6 GHz, thermal emission follows the distribution of HII regions around the ring. Nonthermal emission within the ring appears smoother and more uniform than thermal emission because of diffusion of the cosmic ray electrons away from their birthplaces. This causes the magnetic fields to appear almost constant in intensity. Furthermore, we calculated a map of the star formation rate based on the map of thermal emission. Integrating within a radius of Rmax = 15 kpc, we obtained a total star formation rate of 0.19 ± 0.01 M⊙ yr−1 in agreement with previous results in the literature. Finally, we correlated our radio data with infrared images of the Andromeda galaxy. We find an unexpectedly high correlation between nonthermal and mid-infrared data in the central region, with a correlation parameter r = 0.93. Finally, by computing the logarithmic 24μm/21cm ratio q24 μm, we find a decreasing trend with increasing galactocentric distance and an increasing dispersion. The logarithmic far-infrared-to-radio ratio is found to be 2.41 ± 0.04.

A Search for Cloud Cores Affected by Shocked Carbon Chain Chemistry in L1251

Abstract We searched for shocked carbon chain chemistry (SCCC) sources with C3S abundances surpassing those of HC5N toward the dark cloud L1251, using the Effelsberg telescope at the K band (18–26 GHz). L1251-1 and L1251-3 are identified as the most promising SCCC sources. The two sources harbor young stellar objects. We conducted mapping observations toward L1251-A, the western tail of L1251, at λ ∼ 3 mm with the Purple Mountain Observatory 13.7 m and the Nobeyama Radio Observatory 45 m telescopes in lines of C2H, N2H+, CS, HCO+, SO, HC3N, and C18O as well as in CO 3–2 using the James Clerk Maxwell Telescope (JCMT). The spectral data were combined with archival data including Spitzer and Herschel continuum maps for further analysis. Filamentary substructures labeled as F1–F6 were extracted in L1251, with F1 being associated with L1251-A hosting L1251-1. The peak positions of dense gas traced by HCO+ are misaligned relative to those of the dust clumps. Episodic outflows are common in this region. The twisted morphology of F1 and velocity distribution along L1251-A may originate from stellar feedback. SCCC in L1251-1 may have been caused by outflow activities originated from the infrared source IRS1. The signposts of ongoing SCCC and the broadened line widths of C3S and C4H in L1251-1 as well as the distribution of HC3N are also related to outflow activities in this region. L1251-1 (IRS1) together with the previously identified SCCC source IRS3 demonstrate that L1251-A is an excellent region to study SCCC.

Repeating behaviour of FRB 121102: periodicity, waiting times, and energy distribution

ABSTRACT Detections from the repeating fast radio burst FRB 121102 are clustered in time, noticeable even in the earliest repeat bursts. Recently, it was argued that the source activity is periodic, suggesting that the clustering reflected a not-yet-identified periodicity. We performed an extensive multiwavelength campaign with the Effelsberg telescope, the Green Bank telescope, and the Arecibo Observatory to shadow the Gran Telescope Canaria (optical), NuSTAR (X-ray) and INTEGRAL (γ-ray). We detected 36 bursts with Effelsberg, one with a pulse width of 39 ms, the widest burst ever detected from FRB 121102. With one burst detected during simultaneous NuSTAR observations, we place a 5σ upper limit of 5 × 1047 erg on the 3–79 keV energy of an X-ray burst counterpart. We tested the periodicity hypothesis using 165 h of Effelsberg observations and find a periodicity of 161 ± 5 d. We predict the source to be active from 2020 July 9 to October 14 and subsequently from 2020 December 17 to 2021 March 24. We compare the wait times between consecutive bursts within a single observation to Weibull and Poisson distributions. We conclude that the strong clustering was indeed a consequence of a periodic activity and show that if the few events with millisecond separation are excluded, the arrival times are Poisson distributed. We model the bursts’ cumulative energy distribution with energies from ∼1038–1039 erg and find that it is well described by a power law with slope of γ = −1.1 ± 0.2. We propose that a single power law might be a poor descriptor of the data over many orders of magnitude.

Revisiting profile instability of PSR J1022+1001

ABSTRACT Millisecond pulsars in timing arrays can act as probes for gravitational wave detection and improving the Solar system ephemerides among several other applications. However, the stability of the integrated pulse profiles can limit the precision of the ephemeris parameters and in turn the applications derived from it. It is thus crucial for the pulsars in the array to have stable integrated pulse profiles. Here we present evidence for long-term profile instability in PSR J1022+1001 which is currently included in the European and Parkes pulsar timing arrays. We apply a new evaluation method to an expanded data set ranging from the Effelsberg Pulsar Observing System backend used in the 1990s to that of data from the current PSRIX backend at the Effelsberg Radio Telescope. We show that this intrinsic variability in the pulse shape persists over time-scales of years. We investigate if systematic instrumental effects like polarization calibration or signal propagation effects in the interstellar medium causes the observed profile instability. We find that the total variation cannot be fully accounted for by instrumental and propagation effects. This suggests additional intrinsic effects as the origin for the variation. We finally discuss several factors that could lead to the observed behaviour and comment on the consequent implications.

Measuring interstellar delays of PSR J0613−0200 over 7 yr, using the Large European Array for Pulsars

ABSTRACT Using data from the Large European Array for Pulsars, and the Effelsberg telescope, we study the scintillation parameters of the millisecond pulsar PSR J0613−0200 over a 7 yr timespan. The ‘secondary spectrum’ – the 2D power spectrum of scintillation – presents the scattered power as a function of time delay, and contains the relative velocities of the pulsar, observer, and scattering material. We detect a persistent parabolic scintillation arc, suggesting scattering is dominated by a thin, anisotropic region. The scattering is poorly described by a simple exponential tail, with excess power at high delays; we measure significant, detectable scattered power at times out to ${\sim}5 \, \mu {\rm s}$, and measure the bulk scattering delay to be between 50 to 200 ns with particularly strong scattering throughout 2013. These delays are too small to detect a change of the pulse profile shape, yet they would change the times of arrival as measured through pulsar timing. The arc curvature varies annually, and is well fitted by a one-dimensional scattering screen ${\sim}40{{\ \rm per\ cent}}$ of the way towards the pulsar, with a changing orientation during the increased scattering in 2013. Effects of uncorrected scattering will introduce time delays correlated over time in individual pulsars, and may need to be considered in gravitational wave analyses. Pulsar timing programmes would benefit from simultaneously recording in a way that scintillation can be resolved, in order to monitor the variable time delays caused by multipath propagation.

Water megamaser emission in hard X-ray selected AGN

Context. Water megamaser emission at 22 GHz has proven to be a powerful tool for astrophysical studies of active galactic nuclei (AGN) because it allows an accurate determination of the mass of the central black hole and of the accretion disc geometry and dynamics. However, after searches among thousands of galaxies, only about 200 of them have shown such spectroscopic features, most of them of uncertain classification. In addition, the physical and geometrical conditions under which a maser activates are still unknown. Aims. We characterize the occurrence of water maser emission in an unbiased sample of AGN by investigating the relation with the X-ray properties and the possible favourable geometry that is required to detect water maser. Methods. We searched for 22 GHz maser emission in a hard X-ray selected sample of AGN, taken from the INTEGRAL/IBIS survey above 20 keV. Only half of the 380 sources in the sample have water maser data. We also considered a volume-limited sub-sample of 87 sources, for which we obtained new observations with the Green Bank and Effelsberg telescopes (for 35 sources). We detected one new maser and increased its radio coverage to 75%. Results. The detection rate of water maser emission in the total sample is 15 ± 3%. This fraction increases to 19 ± 5% for the complete sub-sample, especially when we consider type 2 (22 ± 5% and 31 ± 10% for the total and complete samples, respectively) and Compton-thick AGN (56 ± 18% and 50 ± 35% for the total and complete samples, respectively). No correlation is found between water maser and X-ray luminosity. We note that all types of masers (disc and jet) are associated with hard X-ray selected AGN. Conclusions. These results demonstrate that the hard X–ray selection may significantly enhance the maser detection efficiency over comparably large optical or infrared surveys. A possible decline in detection fraction with increasing luminosity might suggest that an extremely luminous nuclear environment does not favour maser emission. The large fraction of CT AGN with water maser emission could be explained in terms of geometrical effects. The maser medium would then be the very edge-on portion of the obscuring medium.

Subpulse drifting and periodic nulling in single pulse emission of PSR B2000+40

ABSTRACT We have carried out a detailed study of single pulse emission from the pulsar B2000+40 (J2002+4050), observed at 1.6-GHz frequencies using the Effelsberg radio telescope. The pulsar has three components, which are not well separated, with the central component resembling core emission. We have investigated modulations in single pulse behaviour using the fluctuation spectral analysis, which showed the presence of two prominent periodicities, around 2.5P and 40P, respectively. The shorter periodicity was associated with the phenomenon of subpulse drifting and was seen to be absent in the central core component. Drifting showed large phase variations in conal components. Additionally, the periodic modulations had significant evolution with time, varying between very sharp and highly diffuse features. In addition to drifting the pulsar also had the presence of nulling in the single pulse sequence. The longer periodic feature in the fluctuation spectra was associated with nulling behaviour. The pulsar joins a select group, which shows the presence of the phase-modulated drifting as well as periodic nulling in the presence of core emission. This provides further evidence for the two phenomena to be distinct from each other with different physical origins.

Interstellar glycolamide: A comprehensive rotational study and an astronomical search in Sgr B2(N).

Glycolamide is a glycine isomer and also one of the simplest derivatives of acetamide (e.g., one hydrogen atom is replaced with a hydroxyl group), which is a known interstellar molecule. In this context, the aim of our work is to provide direct experimental frequencies of the ground vibrational state of glycolamide in the centimeter-, millimeter- and submillimeter-wavelength regions in order to enable its identification in the interstellar medium. We employed a battery of state-of-the-art rotational spectroscopic techniques in the frequency and time domain to measure the frequencies of glycolamide. We used the spectral line survey named Exploring Molecular Complexity with ALMA (EMoCA), which was performed toward the star forming region Sgr B2(N) with ALMA to search for glycolamide in space. We also searched for glycolamide toward Sgr B2(N) with the Effelsberg radio telescope. The astronomical spectra were analyzed under the local thermodynamic equilibrium approximation. We used the gas-grain chemical kinetics model MAGICKAL to interpret the results of the astronomical observations. About 1500 transitions have been newly assigned up to 460 GHz to the most stable conformer, and a precise set of spectroscopic constants was determined. Spectral features of glycolamide were then searched for in the prominent hot molecular core Sgr B2(N2). We report the nondetection of glycolamide toward this source with an abundance at least six and five times lower than that of acetamide and glycolaldehyde, respectively. Our astrochemical model suggests that glycolamide may be present in this source at a level just below the upper limit, which was derived from the EMoCA survey. We could also not detect the molecule in the region's extended molecular envelope, which was probed with the Effelsberg telescope. We find an upper limit to its column density that is similar to the column densities obtained earlier for acetamide and glycolaldehyde with the Green Bank Telescope.

A radio continuum and polarization study of the pulsar wind nebula CTB 87 (G74.9+1.2)

ABSTRACT We present radio continuum and linear polarization observations of the pulsar wind nebula (PWN) CTB 87 (G74.9+1.2) with the Effelsberg 100-m Radio Telescope between 4.75 and 32 GHz. An analysis of these new data including archived low-frequency observations at 1420 and 408 MHz from the Canadian Galactic Plane Survey shows that CTB 87 consists of two distinct emission components: a compact kidney-shaped component, 14 × 8.5 pc2 (7.8 × 4.8 arcmin2) in size and a larger diffuse, spherical, and centrally peaked component of about 30 pc (17 arcmin) in diameter. The kidney-shaped component with a much steeper radio continuum spectrum is highly linearly polarized and likely represents a relic PWN. The diffuse component represents the undisturbed part of the PWN expanding inside a cavity or stellar wind bubble. The previously reported spectral break above 10 GHz is likely the result of missing large-scale emission and insufficient sensitivity of the high-frequency radio continuum observations. The simulation of the system’s evolution yields an age of about 18 000 yr as the result of a Type II supernova explosion with ejecta mass of about 12 M⊙ and explosion energy of about 7 × 1050 erg. We also found evidence for a radio shell in our polarization data that represents the blast wave that entered the molecular cloud complex at a radius of about 13 pc.

Observing superluminous supernovae and long gamma-ray bursts as potential birthplaces of repeating fast radio bursts

ABSTRACT Superluminous supernovae (SLSNe) and long gamma-ray bursts (LGRBs) have been proposed as progenitors of repeating fast radio bursts (FRBs). In this scenario, bursts originate from the interaction between a young magnetar and its surrounding supernova remnant (SNR). Such a model could explain the repeating, apparently non-Poissonian nature of FRB121102, which appears to display quiescent and active phases. This bursting behaviour is better explained with a Weibull distribution, which includes parametrization for clustering. We observed 10 SLSNe/LGRBs for 63 h, looking for repeating FRBs with the Effelsberg 100-m radio telescope, but have not detected any bursts. We scale the burst rate of FRB121102 to an FRB121102-like source inhabiting each of our observed targets, and compare this rate to our upper burst rate limit on a source by source basis. By adopting a fiducial beaming fraction of 0.6, we obtain 99.99 per cent and 83.4 per cent probabilities that at least one, and at least half of our observed sources are beamed towards us, respectively. One of our SLSN targets, PTF10hgi, is coincident with a persistent radio source, making it a possible analogue to FRB121102. We performed further observations on this source using the Effelsberg 100-m and Parkes 64-m radio telescopes. Assuming that PTF10hgi contains an FRB121102-like source, the probabilities of not detecting any bursts from a Weibull distribution during our observations are 14 per cent and 16 per cent for Effelsberg and Parkes, respectively. We conclude by showing that a survey of many short observations increases burst detection probability for a source with Weibull distributed bursting activity.

Discovery of a new supernova remnant G21.8−3.0

ABSTRACT Sensitive radio continuum surveys of the Galactic plane are ideal for discovering new supernova remnants (SNRs). From the Sino-German λ6-cm polarization survey of the Galactic plane, an extended shell-like structure has been found at ℓ = 21${^{\circ}_{.}}$8, b = −3${^{\circ}_{.}}$0, which has a size of about 1°. New observations were made with the Effelsberg 100-m radio telescope at λ11 cm to estimate the source spectrum, together with Urumqi λ6-cm and Effelsberg λ21-cm data. The spectral index of G21.8−3.0 was found to be α = −0.72 ± 0.16. Polarized emission was mostly detected in the eastern half of G21.8−3.0 at both λ6 and λ11 cm. These properties, together with the Hα filament along its northern periphery and the lack of infrared emission, indicate that the emission is non-thermal, as is usual in shell-type SNRs.

Statistics of VHEγ-rays in temporal association with radio giant pulses from the Crab pulsar

Aims.The aim of this study is to search for evidence of a common emission engine between radio giant pulses (GPs) and very-high-energy (VHE,E > 100 GeV)γ-rays from the Crab pulsar.Methods.We performed 16 h of simultaneous observations of the Crab pulsar at 1.4 GHz with the Effelsberg radio telescope and the Westerbork Synthesis Radio Telescope (WSRT), and at energies above 60 GeV we used the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes. We searched for a statistical correlation between the radio and VHEγ-ray emission with search windows of different lengths and different time lags to the arrival times of a radio GP. A dedicated search for an enhancement in the number of VHEγ-rays correlated with the occurrence of radio GPs was carried out separately for the P1 and P2 phase ranges, respectively.Results.In the radio data sample, 99444 radio GPs were detected. We find no significant correlation between the GPs and VHE photons in any of the search windows. Depending on phase cuts and the chosen search windows, we find upper limits at a 95% confidence level on an increase in VHEγ-ray events correlated with radio GPs between 7% and 61% of the average Crab pulsar VHE flux for the P1 and P2 phase ranges, respectively. This puts upper limits on the flux increase during a radio GP between 12% and 2900% of the pulsed VHE flux, depending on the search window duration and phase cuts. This is the most stringent upper limit on a correlation betweenγ-ray emission and radio GPs reported so far.

CHANG-ES

Aims.NGC 4631 is an interacting galaxy that exhibits one of the largest, gaseous halos observed among edge-on galaxies. We aim to examine the synchrotron and cosmic-ray propagation properties of its disk and halo emission with new radio continuum data.Methods.Radio continuum observations of NGC 4631 were performed with theKarl G. JanskyVery Large Array atC-band (5.99 GHz) in the C and D array configurations, and atL-band (1.57 GHz) in the B, C, and D array configurations. Complementary observations of NGC 4631 with the Effelsberg telescope were performed at 1.42 and 4.85 GHz. The interferometric total intensity data were combined with the single-dish Effelsberg data in order to recover the missing large-scale total power emission. The thermal and nonthermal components of the total radio emission were separated by estimating the thermal contribution through the extinction-corrected Hαemission. The Hαradiation was corrected for extinction using a linear combination of the observed Hαand 24μm data.Results.NGC 4631 has a global thermal fraction at 5.99 (1.57) GHz of 14 ± 3% (5.4 ± 1.1%). The mean scale heights of the total emission in the radio halo (thick disk) at 5.99 (1.57) GHz are 1.79 ± 0.54 kpc (1.75 ± 0.27 kpc) and have about the same values for the synchrotron emission. The total magnetic field of NGC 4631 has a mean strength of ⟨Beq⟩≃9 μG in the disk, and a mean strength of ⟨Beq⟩≃7 μG in the halo. We also studied a double-lobed background radio galaxy southwest of NGC 4631, which is an FR II radio galaxy according to the distribution of spectral index across the lobes.Conclusions.From the halo scale heights we estimated that the radio halo is escape-dominated with convective cosmic ray propagation, and conclude that there is a galactic wind in the halo of NGC 4631.

Radio spectral index distribution of SDSS-FIRST sources across optical diagnostic diagrams

Context. The empirical relations between supermassive black holes and their host spheroids point towards the crucial role of galactic nuclei in affecting the properties of their hosts. A detailed understanding of how the activity of a galactic nucleus regulates the growth of its host is still missing. Aims. To understand the activity and the types of accretion of supermassive black holes in different hosts, it is essential to study the radio-optical properties of a large sample of extragalactic sources. In particular, we aim to study the radio spectral index trends across the optical emission line diagnostic diagrams to search for potential (anti)correlations. Methods. To this goal, we combined flux densities from the radio FIRST survey at 1.4 GHz (with the flux density range 10 mJy ≤ F1.4 ≤ 100 mJy) for 396 SDSS sources at intermediate redshift (0.04 ≤ z ≤ 0.4) with the Effelsberg radiotelescope measurements at 4.85 GHz and 10.45 GHz. The information about the optical emission-line ratios is obtained from the SDSS-DR7 catalogue. Results. Using the Effelsberg data, we were able to infer the two-point radio spectral index distributions for star-forming galaxies, composite galaxies (with a combined contribution to the line emission from the star formation and AGN activity), Seyferts, and low ionization narrow emission region (LINER) galaxies. Conclusions. While studying the distribution of steep, flat, and inverted sources across optical diagnostic diagrams, we found three distinct classes of radio emitters for our sample: (i) sources with a steep radio index, high ionization ratio, and high radio loudness, (ii) sources with a flat radio index, lower ionization ratio, and intermediate radio loudness, (iii) sources with an inverted radio index, low ionization ratio, and low radio loudness. The classes (i), (ii), and (iii) cluster mainly along the transition from Seyfert to LINER sources in the optical diagnostic (Baldwin, Phillips & Telervich; BPT) diagram. We interpret these groups as a result of the recurrent nuclear-jet activity.

An Unusually Powerful Water-Maser Flare in the Galactic Source W49N

The most powerful flare ever registered in the Galactic water-maser source W49N has been detected in long-term monitoring data in the 616–523 transition with line frequency f = 22.235 GHz carried out on the 22-m Simeiz, 32-m Torun, 100-m Effelsberg, and 32-m Medicina radio telescopes, beginning in September 2017 and continuing in 2018. Some stages of the flare were monitored daily. Detailed variations of the source spectral flux density with time have been obtained. At the flare maximum, the flux exceeded P ≈ 8 × 104 Jy, and this was record highest flux registered over the entire history of observations of this source. Important conclusions related to details of the mechanism for the H2O line emission have been drawn. An exponential increase in the flare flux density was detected during both the rise and decline of the flare. The data obtained indicate that the maser is unsaturated, and remained in this state up to the maximum observed flux densities. Additional support for the idea that the maser is unsaturated is the shape of the dependence of the line width on the flux. The characteristics of the variations of the spectral flux density are probably associated with a sharp increase in the density of the medium and the photon flux that led to an increase in the temperature from an initial level of 10–40 K to hundreds of Kelvins. Interferometric maps of the object during the increase in the spectral flux density of the flare have been obtained. A possible mechanism for the primary energy release in W49N is considered.

Spin frequency evolution and pulse profile variations of the recently re-activated radio magnetar XTE J1810–197

Abstract After spending almost a decade in a radio-quiet state, the Anomalous X-ray Pulsar XTE J1810–197 turned back on in early 2018 December. We have observed this radio magnetar at 1.5 GHz with nearly daily cadence since the first detection of radio re-activation on 2018 December 8. In this paper, we report on the current timing properties of XTE J1810–197 and find that the magnitude of the spin frequency derivative has increased by a factor of 2.6 over our 48-d data set. We compare our results with the spin-down evolution reported during its previous active phase in the radio band. We also present total intensity pulse profiles at five different observing frequencies between 1.5 and 8.4 GHz, collected with the Lovell and the Effelsberg telescopes. The profile evolution in our data set is less erratic than what was reported during the previous active phase, and can be seen varying smoothly between observations. Profiles observed immediately after the outburst show the presence of at least five cycles of a very stable ∼50 ms periodicity in the main pulse component that lasts for at least tens of days. This remarkable structure is seen across the full range of observing frequencies.

The relativistic jet of the γ-ray emitting narrow-line Seyfert 1 galaxy PKS J1222+0413

ABSTRACT We present a multifrequency study of PKS J1222+0413 (4C +04.42), currently the highest redshift γ-ray emitting narrow-line Seyfert 1 (γ-NLS1). We assemble a broad spectral energy distribution (SED) including previously unpublished datasets: X-ray data obtained with the NuSTAR and Neil Gehrels Swift observatories; near-infrared, optical, and UV spectroscopy obtained with VLT X-shooter; and multiband radio data from the Effelsberg telescope. These new observations are supplemented by archival data from the literature. We apply physical models to the broad-band SED, parametrizing the accretion flow and jet emission to investigate the disc–jet connection. PKS J1222+0413 has a much greater black hole mass than most other NLS1s, MBH ≈ 2 × 108 M$\odot$, similar to those found in flat spectrum radio quasars (FSRQs). Therefore this source provides insight into how the jets of γ-NLS1s relate to those of FSRQs.