J/A+A/686/A144ivo://CDS.VizieR/J/A+A/686/A144doi:10.26093/cds/vizier.36860144CDSBause M.L.Herrmann W.Spitler L.G.2024-11-29T20:02:47Z2024-06-05T12:09:09ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frneutron-starsradio-sourcesSince the detection of a burst resembling a fast radio burst (FRB) from the Galactic magnetar SGR 1935+2154, magnetars have joined the set of favourable candidates for FRB progenitors. However, the emission mechanism of magnetars remains poorly understood. Observations of magnetars with a high cadence over extended timescales have allowed for their emission properties to be determined, in particular, their temporal variations. In this work, we present the results of the long-term monitoring campaign of the magnetar XTE J1810-197 since its second observed active phase from December 2018 until November 2021, with the Stockert 25m radio telescope. We present a single pulse search method, improving on commonly used neural network classifiers thanks to the filtering of radio frequency interference based on its spectral variance and the magnetar's rotation. Results. With this approach, we were able to lower the signal to noise ratio (S/N) detection threshold from 8 to 5. This allowed us to find over 115000 spiky single pulses - compared to 56000 from the neutral network approach. Here, we present the temporal variation of the overall profile and single pulses. Two distinct phases of different single pulse activity can be identified: phase 1 from December 2018 to mid-2019, with a few single pulses per hour, and phase 2 from September 2020 with hundreds of single pulses per hour (with a comparable average flux density). We find that the single pulse properties and folded profile in phase 2 exhibit a change around mid-March 2021. Before this date, the folded profile consists of a single peak and single pulses, with fluences of up to 1000Jy.ms and a single-peaked width distribution at around 10 ms. After mid-March 2021, the profile consists of a two peaks and the single pulse population shows a bimodal width distribution with a second peak at 1ms and fluences of up to 500Jy.ms. We also present asymmetries in the phase-resolved single pulse width distributions beginning to appear in 2020, where the pulses arriving earlier in the rotational phase appear wider than those appearing later. This asymmetry persists despite the temporal evolution of the other single pulse and emission properties. Conclusions. We argue that a drift in the emission region in the magnetosphere may explain this observed behaviour. Additionally, we find that the fluence of the detected single pulses depends on the rotational phase and the highest fluence is found in the centre of the peaks in the profile. While the majority of the emission can be linked to the detected single pulses, we cannot exclude another weak mode of emission. In contrast to the pulses from SGR 1935+2154, we have not found any spectral feature or bursts with energies in the order of magnitude of an FRB during our observational campaign. Therefore, the question of whether this magnetar is capable of emitting such highly energetic bursts remains open.2024A&A...686A.144Bhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/686/A144CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/686/A144https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/686/A144http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/686/A144https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/686/A144https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/686/A144http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/686/A144GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapRadiodefaultJ/A+A/686/A144/tablea1Number of pulses and average flux density per observationrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintDateDate of observationtime.epochnullablen_Date[-S1 -S2] Note on Datemeta.notecharMJDMJD of observationdtime.epoch;obsdoubleNspsNumber of detected single pulses in observation (no_sps_filtering)meta.numberdoublee_NspsUncertainty of detected single pulses in observationstat.errordoubletobsDuration of observationstime.duration;obsdoubleFluxAverage flux density of overall profile in observationJyphot.flux.density;em.radiodoublee_FluxUncertainty of FluxJystat.error;phot.fluxdoubleJ/A+A/686/A144/tablea2List of single pulses with the properties discussed in the publicationrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMJDMJD of observationdtime.epoch;obsdoubleindexedTcandTopocentric time since start of observation when the SP was detected (centre of pulse)stime;arith.diffdoublePhaseRotational phase when the SP was detected (centre of pulse)stime.phasedoubleFluxmeanMean flux density of the single pulseJyphot.flux.density;em.radiodoubleFluenceFluence of the single pulseJy.msphot.fluence;em.gamma.harddoubleWidthDuration of the single pulsemssrc.var.pulsefloatHalf[1/2] The half of the profile, in which the single pulse was detected (1=left, 2=right)meta.codeint