Magnetic fields appear to be ubiquitous in the astrophysical environments of our Universe,but are still poorly understood despite playing an important role in understanding different-scale celestial objects(e.g.,Earth...Magnetic fields appear to be ubiquitous in the astrophysical environments of our Universe,but are still poorly understood despite playing an important role in understanding different-scale celestial objects(e.g.,Earth,planets,stars,normal galaxies,active galactic nuclei,clusters etc.).We briefly review the results and progress in magnetic field estimation based on rotation measures from the large-scale interstellar medium,megaparsec-scale radio jets to the plasma near the black-hole horizon.We find that there is no evident correlation between electron density and magnetic field in warm ionized plasma,which suggests that the estimation of the magnetic field from the ratio of the rotation measure and dispersion measure correctly reflects the intrinsic field.The estimation of the magnetic field from the rotation measure is also discussed near the black hole horizon in M 87.The Square Kilometre Array will greatly improve the understanding of the magnetic field in our Universe,which will provide high-quality polarization imaging and extragalactic rotation measures in the near future.展开更多
The Five-hundred-meter Aperture Spherical radio Telescope(FAST)is the most sensitive radio telescope for pulsar observations.We make polarimetric measurements of a large number of faint and distant pulsars using the F...The Five-hundred-meter Aperture Spherical radio Telescope(FAST)is the most sensitive radio telescope for pulsar observations.We make polarimetric measurements of a large number of faint and distant pulsars using the FAST.We present the new measurements of Faraday rotation for 134 faint pulsars in the Galactic halo.Significant improvements are also made for some basic pulsar parameters for 15 of them.We analyse the newly determined rotation measures(RMs)for the Galactic magnetic fields by using these 134 halo pulsars,together with previously available RMs for pulsars and extragalactic radio sources and also the newly determined RMs for another 311 faint pulsars which are either newly discovered in the project of the Galactic Plane Pulsar Snapshot(GPPS)survey or previously known pulsars without RMs.The RM tomographic analysis in the first Galactic quadrant gives roughly the same field strength of around 2μG for the large-scale toroidal halo magnetic fields.The scale height of the halo magnetic fields is found to be at least 2.7±0.3 kpc.The RM differentiation of a large number of pulsars in the Galactic disk in the Galactic longitude range of 26°<l<90°gives evidence for the clockwise magnetic fields(viewed from the north Galactic pole)in two interarm regions inside the Scutum arm and between the Scutum and Sagittarius arm,and the clockwise fields in the Local-Perseus interarm region and field reversals in the Perseus arm and beyond.展开更多
A 5°×7°sky area containing two large radio structures of G203.1+6.6 and G206.7+5.9 with a size of about 2.°5 and 3.°5 respectively is scanned by using the L-band 19-beam receiver of the Five-h...A 5°×7°sky area containing two large radio structures of G203.1+6.6 and G206.7+5.9 with a size of about 2.°5 and 3.°5 respectively is scanned by using the L-band 19-beam receiver of the Five-hundred-meter Aperture Spherical radio Telescope(FAST).The FAST L-band receiver covers a frequency range of 1.0-1.5 GHz.Commissioning of the receiving system,including the measurements of the half-power beam width,gain,and main-beam efficiency is made by observing the calibrators.The multi-channel spectroscopy backend mounted to the receiver allows an in-band spectral-index determination.The brightness-temperature spectral indices of both objects are measured to beβ~-2.6 to-2.7.Polarized emission is detected from the archival Effelsbergλ11 cm data for all the shell structures of G203.1+6.6 and G206.7+5.9.These results clearly indicate a non-thermal synchrotron emitting nature,confirming that G203.1+6.6 and G206.7+5.9 are large shell-type supernova remnants(SNRs).Based on morphological correlation between the radio continuum emission of G206.7+5.9 and the H i structures,the kinematic distance to this new SNR is estimated to be about 440 pc,placing it in the Local Arm.展开更多
Interaction of the solar wind with the interstellar medium leads to the formation of the heliosphere and termination shock. This article addresses three aspects of the plasma and magnetic field on two sides of the hel...Interaction of the solar wind with the interstellar medium leads to the formation of the heliosphere and termination shock. This article addresses three aspects of the plasma and magnetic field on two sides of the heliopause： （1） The interstellar magnetic field surrounding the heliopause. In the limit of very low plasma β-ratio an analytical solution is obtained for the 3D interstellar magnetic field by means of a line dipole method. The undisturbed magnetic field in the upstream is allowed to have an arbitrary inclination angle. The solution describes the heliosphere as having a blunt-nosed geometry on the upwind side and approaching a cylindrical geometry on the downwind side. The distortion of the magnetic field can penetrate very deep into the interstellar space. （2） Interaction of the interstellar neutral hydrogen with the global solar wind. The ionization process leads to removal of interstellar neutral hydrogen in the heliosphere： on the upwind side, 90% of hydrogen depletion occurs inside 60 AU, the hydrogen density changes rapidly inside 10 AU. A hydrogen cavity forms inside -4 AU; the cavity extends on the downwind side to form a long cavity wake. Outside the cavity and cavity wake, pickup protons are produced, they cause deceleration and heating of the solar wind. The wind speed and temperature also increase steadily with heliolatitude caused by the latitudinal increase in wind speed at the inner boundary. （3） The global geometry of the termination shock. The termination shock has been treated as having a closed geometry in previous heliosphere models. This study presents a new perspective that the global termination shock may have a bow-shaped open geometry. The termination shock forms on the upwind side because the forward motion of the supersonic solar wind is blocked at the blunt-nosed heliopause. However, the heliopause likely to be open on the downwind side; the motion of the supersonic solar wind is unobstructed for shock formation. Thus, the global termination shock likely has an open geometry. On the upwind side the shock flares out and weakens from the nose to its flanks. Eventually, the shock asymptotically reduces to a Mach wave. The supersonic solar wind remains shock free in the heliotail.展开更多
基金the support of the National SKA Program of China(No.2022SKA0120101)National Natural Science Foundation of China(Nos.U1931203 and 12233007)
文摘Magnetic fields appear to be ubiquitous in the astrophysical environments of our Universe,but are still poorly understood despite playing an important role in understanding different-scale celestial objects(e.g.,Earth,planets,stars,normal galaxies,active galactic nuclei,clusters etc.).We briefly review the results and progress in magnetic field estimation based on rotation measures from the large-scale interstellar medium,megaparsec-scale radio jets to the plasma near the black-hole horizon.We find that there is no evident correlation between electron density and magnetic field in warm ionized plasma,which suggests that the estimation of the magnetic field from the ratio of the rotation measure and dispersion measure correctly reflects the intrinsic field.The estimation of the magnetic field from the rotation measure is also discussed near the black hole horizon in M 87.The Square Kilometre Array will greatly improve the understanding of the magnetic field in our Universe,which will provide high-quality polarization imaging and extragalactic rotation measures in the near future.
基金supported by the National Natural Science Foundation of China(Grant Nos.11988101,11833009,and U2031115)the Key Research Program of the Chinese Academy of Sciences(Grant No.QYZDJSSW-SLH021)+2 种基金the National SKA Program of China(Grant No.2022SKA0120103)supported by the National Natural Science Foundation of China(Grant Nos.11873058,and 12133004)the National SKA Program of China(Grant No.2020SKA0120200)。
文摘The Five-hundred-meter Aperture Spherical radio Telescope(FAST)is the most sensitive radio telescope for pulsar observations.We make polarimetric measurements of a large number of faint and distant pulsars using the FAST.We present the new measurements of Faraday rotation for 134 faint pulsars in the Galactic halo.Significant improvements are also made for some basic pulsar parameters for 15 of them.We analyse the newly determined rotation measures(RMs)for the Galactic magnetic fields by using these 134 halo pulsars,together with previously available RMs for pulsars and extragalactic radio sources and also the newly determined RMs for another 311 faint pulsars which are either newly discovered in the project of the Galactic Plane Pulsar Snapshot(GPPS)survey or previously known pulsars without RMs.The RM tomographic analysis in the first Galactic quadrant gives roughly the same field strength of around 2μG for the large-scale toroidal halo magnetic fields.The scale height of the halo magnetic fields is found to be at least 2.7±0.3 kpc.The RM differentiation of a large number of pulsars in the Galactic disk in the Galactic longitude range of 26°<l<90°gives evidence for the clockwise magnetic fields(viewed from the north Galactic pole)in two interarm regions inside the Scutum arm and between the Scutum and Sagittarius arm,and the clockwise fields in the Local-Perseus interarm region and field reversals in the Perseus arm and beyond.
基金supported by the National Key R&D Program of China(Grant Nos.2021YFA1600401,and 2021YFA1600400)the National Natural Science Foundation of China(Grant No.11988101)+4 种基金and the National SKA Program of China(Grant No.2022SKA0120103)the CAS-NWO Cooperation Program(Grant No.GJHZ1865)the Open Project Program of the Key Laboratory of FAST,NAOC,Chinese Academy of Sciencessupported by the Cultivation Project for FAST Scientific Payoff and Research Achievement of CAMS-CAS,and the Science&Technologysupported by the National Natural Science Foundation of China(Grant No.12003044)。
文摘A 5°×7°sky area containing two large radio structures of G203.1+6.6 and G206.7+5.9 with a size of about 2.°5 and 3.°5 respectively is scanned by using the L-band 19-beam receiver of the Five-hundred-meter Aperture Spherical radio Telescope(FAST).The FAST L-band receiver covers a frequency range of 1.0-1.5 GHz.Commissioning of the receiving system,including the measurements of the half-power beam width,gain,and main-beam efficiency is made by observing the calibrators.The multi-channel spectroscopy backend mounted to the receiver allows an in-band spectral-index determination.The brightness-temperature spectral indices of both objects are measured to beβ~-2.6 to-2.7.Polarized emission is detected from the archival Effelsbergλ11 cm data for all the shell structures of G203.1+6.6 and G206.7+5.9.These results clearly indicate a non-thermal synchrotron emitting nature,confirming that G203.1+6.6 and G206.7+5.9 are large shell-type supernova remnants(SNRs).Based on morphological correlation between the radio continuum emission of G206.7+5.9 and the H i structures,the kinematic distance to this new SNR is estimated to be about 440 pc,placing it in the Local Arm.
文摘Interaction of the solar wind with the interstellar medium leads to the formation of the heliosphere and termination shock. This article addresses three aspects of the plasma and magnetic field on two sides of the heliopause： （1） The interstellar magnetic field surrounding the heliopause. In the limit of very low plasma β-ratio an analytical solution is obtained for the 3D interstellar magnetic field by means of a line dipole method. The undisturbed magnetic field in the upstream is allowed to have an arbitrary inclination angle. The solution describes the heliosphere as having a blunt-nosed geometry on the upwind side and approaching a cylindrical geometry on the downwind side. The distortion of the magnetic field can penetrate very deep into the interstellar space. （2） Interaction of the interstellar neutral hydrogen with the global solar wind. The ionization process leads to removal of interstellar neutral hydrogen in the heliosphere： on the upwind side, 90% of hydrogen depletion occurs inside 60 AU, the hydrogen density changes rapidly inside 10 AU. A hydrogen cavity forms inside -4 AU; the cavity extends on the downwind side to form a long cavity wake. Outside the cavity and cavity wake, pickup protons are produced, they cause deceleration and heating of the solar wind. The wind speed and temperature also increase steadily with heliolatitude caused by the latitudinal increase in wind speed at the inner boundary. （3） The global geometry of the termination shock. The termination shock has been treated as having a closed geometry in previous heliosphere models. This study presents a new perspective that the global termination shock may have a bow-shaped open geometry. The termination shock forms on the upwind side because the forward motion of the supersonic solar wind is blocked at the blunt-nosed heliopause. However, the heliopause likely to be open on the downwind side; the motion of the supersonic solar wind is unobstructed for shock formation. Thus, the global termination shock likely has an open geometry. On the upwind side the shock flares out and weakens from the nose to its flanks. Eventually, the shock asymptotically reduces to a Mach wave. The supersonic solar wind remains shock free in the heliotail.
