Four Late-type Galaxies with Double Radio Lobes and Properties of Such Galaxies

The triggering mechanism for radio lobes from late-type galaxies is not fully understood.More samples are desired for a thorough investigation and statistics.By utilizing the optical data from the newly released Dark Energy Spectroscopic Instrument imaging surveys and the radio sources from the NRAO VLA Sky Survey and the Faint Images of the Radio Sky at Twenty-centimeter,we identify four Late-type Galaxies with double Radio Lobes(La GRLs):J0217-3645,J0947+6220,J1412+3723 and J1736+5108.Including previously known La GRLs,we confirm the correlation between radio power P_(1.4GHz)and stellar mass M_(*)of host galaxies.Most(25/35)La GRLs belong to the blue cloud galaxies,while the newly identified cases in this work are located within the region of the red sequence.We find a clear correlation between the differential radio power,i.e.,the offset from the P_(1.4GHz)-M_(*)relation,and the galaxy color,indicating that bluer galaxies at a fixed M_(*)tend to host more powerful radio lobes.Furthermore,the majority(31/36)of La GRLs are either located in a galaxy group or displaying a disturbed morphology.We suggest that all of the galaxy mass,color and surrounding environment could play important roles in triggering radio lobes in late-type galaxies.

The FAST Galactic Plane Pulsar Snapshot Survey.II.Discovery of 76 Galactic Rotating Radio Transients and the Enigma of RRATs

We have carried out the Galactic Plane Pulsar Snapshot(GPPS)survey by using the Five-hundred-meter Aperture Spherical radio Telescope(FAST),the most sensitive systematic pulsar survey in the Galactic plane.In addition to more than 500 pulsars already discovered through normal periodical search,we report here the discovery of 76 new transient radio sources with sporadic strong pulses,detected by using the newly developed module for a sensitive single-pulse search.Their small DM values suggest that they all are Galactic rotating radio transients(RRATs).They show different properties in the follow-up observations.More radio pulses have been detected from 26 transient radio sources but no periods can be found due to a limited small number of pulses from all FAST observations.The followup observations show that 16 transient sources are newly identified as being the prototypes of RRATs with a period already determined from more detected sporadic pulses,and 10 sources are extremely nulling pulsars,and 24 sources are weak pulsars with sparse strong pulses.On the other hand,48 previously known RRATs have been detected by the FAST,either during verification observations for the GPPS survey or through targeted observations of applied normal FAST projects.Except for one RRAT with four pulses detected in a session of 5-minute observation and four RRATs with only one pulse detected in a session,sensitive FAST observations reveal that 43 RRATs are just generally weak pulsars with sporadic strong pulses or simply very nulling pulsars,so that the previously known RRATs always have an extreme emission state together with a normal hardly detectable weak emission state.This is echoed by the two normal pulsars J1938+2213 and J1946+1449 with occasional brightening pulses.Though strong pulses of RRATs are very outstanding in the energy distribution,their polarization angle variations follow the polarization angle curve of the averaged normal pulse profile,suggesting that the predominant sparse pulses of RRATs are emitted in the same region with the same geometry as normal weak pulsars.

FAST Pulsar Database.I.Polarization Profiles of 682 Pulsars

Pulsar polarization profiles form a very basic database for understanding the emission processes in a pulsar magnetosphere.After careful polarization calibration of the 19-beam L-band receiver and verification of beamoffset observation results,we obtain polarization profiles of 682 pulsars from observations by the Five-hundredmeter Aperture Spherical radio Telescope(FAST)duringthe Galactic Plane Pulsar Snapshot survey and other normal FAST projects.Among them,polarization profiles of about 460 pulsars are observed for the first time.The profiles exhibit diverse features.Some pulsars have a polarization position angle curve with a good S-shaped swing,some with orthogonal modes;some have components with highly linearly polarized components or strong circularly polarized components;some have a very wide profile,coming from an aligned rotator,and some have an interpulse from a perpendicular rotator;some wide profiles are caused by interstellar scattering.We derive geometric parameters for 190 pulsars from the S-shaped position angle curves or with orthogonal modes.We find that the linear and circular polarization or the widths of pulse profiles have various frequency dependencies.Pulsars with a large fraction of linear polarization are more likely to have a large Edot.

Three New Spiral Galaxies with Active Nuclei Producing Double Radio Lobes

Double radio lobes are generally believed to be produced by active nuclei of elliptical galaxies.However,several double-lobed radio sources have been solidly found to be associated with spiral galaxies.By cross-matching~9×105 spiral galaxies selected from the Sloan Digital Sky Survey DR8 data with the full 1.4 GHz radio source catalogs of NRAO VLA Sky Survey and Faint Images of the Radio Sky at Twenty-centimeters,we identify three new spiral galaxies:J0326-0623,J1110+0321 and J1134+3046 that produce double radio lobes,and five doublelobed spirals previously known.By combining the newly discovered and all the other known cases in literature,we confirm the relation that more massive spiral galaxies could produce more powerful radio lobes.We find that most of these spiral galaxies are located in a galaxy group or a poor cluster,in which the environment is denser than in the field,and about half of them are the central brightest galaxies in their parent system.We therefore suggest that the environment is one of the key factors for a spiral to produce double radio lobes.

Cleaning Radio Frequency Interference in Pulsar-Folded Data Based on the Conditional Random Fields with an Adaptive Prior

Radio astronomy observations are frequently impacted by radio frequency interference(RFI).We propose a novel method,named 2σCRF,for cleaning RFI in the folded data of pulsar observations,utilizing a Bayesian-based model called conditional random fields(CRFs).This algorithm minimizes the“energy”of every pixel given an initial label.The standard deviations(i.e.,rms values)of the folded pulsar data are utilized as pixels for all subintegrations and channels.Non-RFI data without obvious interference is treated as“background noise,”while RFI-affected data have different classes due to their exceptional rms values.This initial labeling can be automated and is adaptive to the actual data.The CRF algorithm optimizes the label category for each pixel of the image with the prior initial labels.We demonstrate the efficacy of the proposed method on pulsar folded data obtained from Five-hundred-meter Aperture Spherical radio Telescope observations.It can effectively recognize and tag various categories of RFIs,including broadband or narrowband,constant or instantaneous,and even weak RFIs that are unrecognizable in some pixels but picked out based on their neighborhoods.The results are comparable to those obtained via manual labeling but without the need for human intervention,saving time and effort.

A New Emission Mode of PSR B1859+07

Previous studies have identified two emission modes in PSR B1859+07: a normal mode that has three prominent components in the average profile, with the trailing one being the brightest, and an anomalous mode(i.e., the A mode) where emissions seem to be shifted to an earlier phase. Within the normal mode, further analysis has revealed the presence of two submodes, i.e., the cW mode and c B mode, where the central component can appear either weak or bright. As for the anomalous mode, a new bright component emerges in the advanced phase while the bright trailing component in the normal mode disappears. New observations of PSR B1859+07 using the Fivehundred-meter Aperture Spherical Radio Telescope(FAST) have revealed the existence of a previously unknown emission mode, dubbed the Af mode. In this mode, all emission components seen in the normal and anomalous modes are detected. Notably, the mean polarization profiles of both the A and Af modes exhibit a jump in the orthogonal polarization angle modesin the bright leading component. The polarization angles for the central component in the original normal mode follow two distinct orthogonal polarization modes in the A and Af modes respectively. The polarization angles for the trailing component show almost the same but a small systematic shift in the A and Af modes, roughly following the values for the c W and cB modes. Those polarization features of this newly detected emission mode imply that the anomalous mode A of PSR B1859+07 is not a result of “phase shift”or “swooshes” of normal components, but simply a result of the varying intensities of different profile components.Additionally, subpulse drifting has been detected in the leading component of the Af mode.

The FAST Galactic Plane Pulsar Snapshot survey:I.Project design and pulsar discoveries

Discovery of pulsars is one of the main goals for large radio telescopes.The Five-hundredmeter Aperture Spherical radio Telescope(FAST),that incorporates an L-band 19-beam receiver with a system temperature of about 20 K,is the most sensitive radio telescope utilized for discovering pulsars.We designed the snapshot observation mode for a FAST key science project,the Galactic Plane Pulsar Snapshot(GPPS)survey,in which every four nearby pointings can observe a cover of a sky patch of 0.1575 square degrees through beam-switching of the L-band 19-beam receiver.The integration time for each pointing is 300 seconds so that the GPPS observations for a cover can be made in 21 minutes.The goal of the GPPS survey is to discover pulsars within the Galactic latitude of±10∘from the Galactic plane,and the highest priority is given to the inner Galaxy within±5∘.Up to now,the GPPS survey has discovered 201 pulsars,including currently the faintest pulsars which cannot be detected by other telescopes,pulsars with extremely high dispersion measures(DMs)which challenge the currently widely used models for the Galactic electron density distribution,pulsars coincident with supernova remnants,40 millisecond pulsars,16 binary pulsars,some nulling and mode-changing pulsars and rotating radio transients(RRATs).The follow-up observations for confirmation of new pulsars have polarization-signals recorded for polarization profiles of the pulsars.Re-detection of previously known pulsars in the survey data also leads to significant improvements in parameters for 64 pulsars.The GPPS survey discoveries are published and will be updated at http://zmtt.bao.ac.cn/GPPS/.

FAST Observations of an Extremely Active Episode of FRB 20201124A.Ⅳ.Spin Period Search

We report the properties of more than 800 bursts detected from the repeating fast radio burst(FRB)source FRB 20201124A with the Five-hundred-meter Aperture Spherical radio Telescope during an extremely active episode on UTC 2021 September 25th-28th in a series of four papers.In this fourth paper of the series,we present a systematic search of the spin period and linear acceleration of the source object from both 996 individual pulse peaks and the dedispersed time series.No credible spin period was found from this data set.We rule out the presence of significant periodicity in the range between 1 ms and 100 s with a pulse duty cycle<0.49±0.08(when the profile is defined by a von-Mises function,not a boxcar function)and linear acceleration up to 300 m s^(-2)in each of the four one-hour observing sessions,and up to 0.6 m s^(-2)in all 4 days.These searches contest theoretical scenarios involving a 1 ms–100 s isolated magnetar/pulsar with surface magnetic field<10^(15)G and a small duty cycle(such as in a polar-cap emission mode)or a pulsar with a companion star or black hole up to 100 M_(⊙)and P_(b)>10 hr.We also perform a periodicity search of the fine structures and identify 53 unrelated millisecond-timescale“periods”in multicomponents with the highest significance of 3.9σ.The“periods”recovered from the fine structures are neither consistent nor harmonically related.Thus they are not likely to come from a spin period.We caution against claiming spin periodicity with significance below~4σwith multi-components from one-off FRBs.We discuss the implications of our results and the possible connections between FRB multi-components and pulsar microstructures.

FAST Observations of an Extremely Active Episode of FRB 20201124A:Ⅰ.Burst Morphology

We report the properties of more than 600 bursts(including cluster-bursts)detected from the repeating fast radio burst(FRB)source FRB 20201124A with the Five-hundred-meter Aperture Spherical radio Telescope during an extremely active episode on UTC 2021 September 25–28,in a series of four papers.The observations were carried out in the band of 1.0–1.5 GHz by using the center beam of the L-band 19-beam receiver.We monitored the source in sixteen1 hr sessions and one 3 hr session spanning 23 days.All the bursts were detected during the first four days.In this first paper of the series,we perform a detailed morphological study of 624 bursts using the two-dimensional frequencytime“waterfall”plots,with a burst(or cluster-burst)defined as an emission episode during which the adjacent emission peaks have a separation shorter than 400 ms.The duration of a burst is therefore always longer than 1 ms,with the longest up to more than 120 ms.The emission spectra of the sub-bursts are typically narrow within the observing band with a characteristic width of~277 MHz.The center frequency distribution has a dominant peak at about 1091.9 MHz and a secondary weak peak around 1327.9 MHz.Most bursts show a frequencydownwarddrifting pattern.Based on the drifting patterns,we classify the bursts into five main categories:downward drifting(263)bursts,upward drifting(3)bursts,complex(203),no drifting(35)bursts,and no evidence for drifting(121)bursts.Subtypes are introduced based on the emission frequency range in the band(low,middle,high and wide)as well as the number of components in one burst(1,2,or multiple).We measured a varying scintillation bandwidth from about 0.5 MHz at 1.0 GHz to 1.4 MHz at 1.5 GHz with a spectral index of 3.0.

Extragalactic dispersion measures of fast radio bursts

Fast radio bursts show large dispersion measures, much larger than the Galactic dispersion measure foreground. Therefore, they evidently have an extragalac- tic origin. We investigate possible contributions to the dispersion measure from host galaxies. We simulate the spatial distribution of fast radio bursts and calculate the dis- persion measures along the sightlines from fast radio bursts to the edge of host galaxies by using the scaled NE2001 model for thermal electron density distributions. We find that contributions to the dispersion measure of fast radio bursts from the host galaxy follow a skew Gaussian distribution. The peak and the width at half maximum of the dispersion measure distribution increase with the inclination angle of a spiral galaxy, to large values when the inclination angle is over 70~. The largest dispersion measure produced by an edge-on spiral galaxy can reach a few thousand pc cm-3, while the dispersion measures from dwarf galaxies and elliptical galaxies have a maximum of only a few tens of pc cm-3. Notice, however, that additional dispersion measures of tens to hundreds of pc cm-3 can be produced by high density clumps in host galaxies. Simulations that include dispersion measure contributions from the Large Magellanic Cloud and the Andromeda Galaxy are shown as examples to demonstrate how to ex- tract the dispersion measure from the intergalactic medium.