Tian Ma Radio Telescope Research Articles

Shanghai Tianma Radio Telescope and Its Role in Pulsar Astronomy

After two phases of on-site construction and testing (2010–2013 and 2013–2017), the Shanghai Tianma Radio Telescope (TMRT) can work well, with efficiencies better than 50% from 1.3 to 50.0 GHz, mainly benefiting from its low-noise cryogenic receivers and active surface system. Pulsars were chosen as important targets of research at the TMRT because of their important scientific and applied values. To meet the demands of pulsar-related observations, TMRT is equipped with some necessary backends, including a digital backend system (DIBAS) supporting normal pulsar observation modes, a real-time fast-radio-burst-monitoring backend, and baseband backends for very-long-baseline interferometry (VLBI) observations. Utilizing its high sensitivity and simultaneous dual-frequency observation capacity, a sequence of pulsar research endeavors has been undertaken, such as long-term pulsar timing, magnetar monitoring, multi-frequency (or high-frequency) observations, interstellar scintillation, pulsar VLBI, etc. In this paper, we give a short introduction about pulsar observation systems at the TMRT and briefly review the results obtained by these pulsar research projects.

Distribution Properties of the 6.7 GHz Methanol Masers and Their Surrounding Gases in the Milky Way

An updated catalog consisting of 1092 6.7 GHz methanol maser sources is reported in this work. Additionally, the NH3 (1, 1), NH3 (2, 2), and NH3 (3, 3) transitions were observed toward 214 star-forming regions using the Shanghai Tianma radio telescope in order to examine the differences in physical environments, such as the excitation temperature and column density of molecular clouds associated with methanol masers on the Galactic scale. Statistical results reveal that the number of 6.7 GHz methanol masers in the Perseus arm is significantly lower than that in the other three main spiral arms. In addition, the Perseus arm also has the lowest gas column density among the main spiral arms traced by the NH3 observations. Both findings suggest that the Perseus arm has the lowest rate of high-mass star formation compared to the other three main spiral arms. We also observed a trend in which both the luminosity of the 6.7 GHz methanol masers and the ammonia gas column density decreased with the galactocentric distance. This finding indicates that the density of material in the inner Milky Way is generally higher than that in the outer Milky Way. This further suggests that high-mass stars are more easily formed at the head of the spiral arms. Furthermore, we found that the column density of ammonia gas is higher in the regions on the arms than in the inter-arm regions, supporting that the former is more likely to be the birthplace of high-mass stars.

Observations of Nine Millisecond Pulsars at 8600 MHz Using the TMRT

We report detection results of nine millisecond pulsars (MSPs) at 8600 MHz using simultaneous 2250 and 8600 MHz observations conducted with the Shanghai Tian Ma Radio Telescope. Mainly benefiting from updated ephemerids with 2250 MHz observations, integrated profiles of all nine MSPs at 8600 MHz are successfully obtained by coherently adding multi-epoch (3–83 epochs) observation data spanning from 19–1210 days, which significantly increases the number of MSPs with published profiles (from 4 to 11) above 8000 MHz, as seven of our target MPSs had no related results previously. Combining our new flux density and pulse width measurements with previous low-frequency results, we study their integrated profile evolution and spectral behaviors in a wider frequency range. We find their component separations and pulse widths remain almost constant, which is consistent with previous findings. While dramatic evolution of integrated profiles exists at low frequencies, we observe a potential end of the related evolution around 5 GHz in eight MSPs. The spectra of four MSPs are found to deviate from a single power law, and we fit them with a broken power law. The change in the profile of PSR J1713+0747, which started around MJD 59320−59321, seems to be more prominent as the observation frequency increases. Compared with the effects of the interstellar medium, we prefer to explain this event as some changes in the magnetosphere. We also find its integrated profile possibly had not recovered to the pre-event state until MJD 59842–59857.

Distributed Control Software for the Active Surface System of Tian-ma Radio Telescope

The Tian-ma Radio Telescope (TMRT) applies an Active Surface System (ASFS), which corrects for large-scale deformations due to gravity and thermal on the primary reflector. The centralized and automated management of the ASFS using software has become a challenge, for which we have developed the TMRT Active Surface System Control Software (TASCS). This paper describes the design and implementation of TASCS for device control, status monitoring, human-computer interaction, and data management functionalities. TASCS adopts the open-source Tango Controls framework and distributes middleware technology to realize real-time automated adjustment of the primary reflector through remote centralized control of a large number of actuators. At present, it has been successfully deployed on the TMRT and has played an important role in Event Horizon Telescope observations.

Simultaneous 2.25/8.60 GHz Observations of the Magnetar XTE J1810-197

We did 194 epochs of simultaneous 2.25/8.60 GHz observations of XTE J1810−197 in 926 days shortly following its reactivation in 2018 with Shanghai Tian Ma Radio Telescope (TMRT). Although its integrated profiles changed with both time and frequency during this period, they could be classified into 12 types according to phase areas of active radiation components. After MJD 59015, XTE J1810−197 turned from the normal emission state into the spiky emission state that was manifesting as a series of bright narrow sub-pulse bursts at both 2.25 and 8.60 GHz. Due to its variable integrated profiles and unsteady rotations, we got the spin frequency ν and spin-frequency derivatives with the piecewise fitting method. In addition, its long-term declining trend of ν was also obtained as s−2 with the linear fitting method based on our observations spanning a comparatively longer period. We found its flux densities went through three stages: sharp decrease, stabilization, and day-to-day fluctuations in our dual-frequency observations. Although the flux density showed different stages, XTE J1810−197 showed a relatively flat spectrum (α > –1) in most observations. Assuming an ideal dipole magnetic field as some previous research works, we obtained the emission heights of XTE J1810−197 were about 7.5(9) × 104 km and 2.38(7) × 104 km at 2.25 and 8.60 GHz, respectively. We also found that its emission heights would decrease rapidly with the degree of magnetic field twisting.

The automation software of Tian-Ma radio telescope RFI monitoring system

The automation software of Tian-Ma radio telescope RFI monitoring system

Luminosity Outburst Energized by the Collision between the Infalling Streamer and Disk in W51 North

We report the detection of the disk/torus, outflow, and inflow structures traced by H2O masers toward a high-mass young stellar object W51 North during its H2O maser outburst stage using the Karl G. Jansky Very Large Array (VLA). It is found that the disk has a radius of ∼4000 au and an inclination angle with respect to the sky plane of ∼60° by combining the VLA and the Atacama Large Millimeter/submillimeter Array data. Additionally, a peculiar flow perpendicular to the SiO bipolar outflow is detected in the H2O maser, SiO, and HC3N lines, which is newly-identified as an infalling streamer rather than an old outflow from this source, as reported in previous studies. Combining the VLA map and the Tianma radio telescope monitoring of the H2O masers suggests that the origin of the luminosity outburst of H2O masers during 2020 January–April is likely related to the energy release from the collision between the infalling streamer and the disk. This may provide an additional mechanism to account for the luminosity outburst or episodic accretion beyond disk fragmentation caused by gravitational instability.

Application of Infrared Thermal Imager to measure the temperature of Back-Up Structure of the TianMa radio telescope

Application of Infrared Thermal Imager to measure the temperature of Back-Up Structure of the TianMa radio telescope

Physical Environments of the Luminosity Outburst Source NGC 6334I Traced by Thermal and Maser Lines of Multiple Molecules

We have conducted a systematic line survey, primarily focused on transitions of the methanol and ammonia molecules, and monitoring observations of masers toward the high-mass star-forming region NGC 6334I. These observations were undertaken between 2019 and 2022 in the C, K, Ka, and Q bands with the Tianma Radio Telescope. In total, 63 CH3OH (including 11 class I and nine class II maser or maser candidate), 18 13CH3OH, and 34 NH3 (including seven maser or maser candidate) transitions were detected. The emission is likely associated with the luminosity outburst source MM1. Rotation diagram analysis of multiple ammonia transitions shows that the gas temperature in the molecular core was a factor of 2 higher than that measured in previous observations in the pre-burst stage. This suggests that the molecular core has likely been heated by radiation originating from the luminosity outburst. Maser variability in the methanol and excited-state OH masers shows a general trend that the maser components associated with the luminosity outburst have decreased in their intensity since 2020. The decay in the maser luminosity indicates that the outburst is possibly declining, and as a result, the duration of the MM1 luminosity outburst may be shorter than the predicted 40 yr duration. Compared to the masers detected toward another luminosity outburst source, G358.93-0.03, abundant class I methanol masers and strong water maser flares were also detected toward NGC 633I, but masers from rare class II methanol transitions and new molecules were absent toward NGC 6334I. The large number of detections of maser transitions toward the two burst sources provided a database for further maser modeling to explore the physical environments associated with accretion burst events.

New Methanol Maser Transitions and Maser Variability Identified from an Accretion Burst Source G358.93-0.03

The high-mass young stellar object G358.93-0.03 underwent an accretion burst during the period from 2019 January to June. Given its extraordinary conditions, a number of new maser transitions may have been naturally excited during the burst stage. Searching for new maser lines and monitoring maser variability associated with the accretion burst event are important for understanding the complex conditions of the massive star formation toward G358.93-0.03. In this work, using the Shanghai 65 m Tianma Radio Telescope, we continuously monitored the multiple maser (including methanol and water) transitions toward G358.93-0.03 during the burst in the period from 2019 March 14 to May 20. There were 23 CH3OH maser transitions and one H2O maser transition detected from the monitoring. Nearly all the detected maser transitions toward this source have dramatic variations in their intensities within a short period of ∼2 months. Eight new methanol transitions from G358.93-0.03 were identified to be masering in our observations based on their spectral profile, line width, intensity, and the rotation diagram. During the monitoring, the gas temperature of the clouds in the case of saturated masers can show a significant decline, indicating that the maser clouds were going through a cooling process, possibly associated with the propagation of a heat wave induced by the accretion burst. Some of the maser transitions were even detected with the second flares in 2019 April, which may be associated with the process of the heat-wave propagation induced by the same accretion burst acting on different maser positions.

A Q-band Line Survey toward Orion KL Using the Tianma Radio Telescope

We have conducted a line survey toward Orion KL using the Q-band receiver of the Tianma 65 m radio telescope (TMRT), covering 34.8–50 GHz with a velocity resolution between 0.79 and 0.55 km s−1, respectively. The observations reach a sensitivity of the level of 1–8 mK, proving that the TMRT is sensitive for conducting deep-line surveys. In total, 597 Gaussian features are extracted. Among them, 177 radio recombination lines (RRLs) are identified, including 126, 40, and 11 RRLs of hydrogen, helium, and carbon, with a maximum Δn of 16, 7, and 3, respectively. The carbon RRLs are confirmed to originate from photodissociation regions with a V LSR ∼ 9 km s−1. In addition, 371 molecular transitions of 53 molecular species are identified. Twenty-one molecular species of this survey were not firmly detected in the Q band by Rizzo et al., including species such as H2CS, HCOOH, C2H5OH, CO, H2CCO, CH3CHO, CH2OCH2, HCN υ 2 = 1, and CH3OCHO υ t = 1. In particular, the vibrationally excited states of ethyl cyanide (C2H5CN υ13/υ21) are for the first time firmly detected in the Q band. NH3 (15,15) and (16,16) are identified, and they are so far the highest transitions of the NH3 inversion lines detected toward Orion KL. All of the identified lines can be reproduced by a radiative transfer model.

Thermal Analysis of the Backup Structure of the Tianma Telescope

Taking the Tianma Radio Telescope (TMRT) as an object, this paper focuses on the determination of temperature gradients and thermal deformations of the backup structure (BUS) with the finite element method. To this end, a modeling and analysis method, which consists of a simplified FEM and a four-component simulation process, is proposed. In the development, only solar radiation is considered and thermal convection is neglected. Based on the thermal time constant of the BUS, the simulations of temperature gradients are simplified as static analysis. The superposed temperature gradients agree well with the ones measured by thermometers with a 0.57°C root mean square (rms) error. In addition, the illuminated-weighted rms errors of the primary reflector surface calculated by the simulation and measured by the extended out-of-focus holography are in good agreement. The rms error increases approximately 170 μm when the Sun persistently illuminated the BUS for 3 hr. The optimized initial temperature of the antenna structure is 20°C by comparing the results between the finite element analysis and the e-OOF measurement. The thermal deformation database can support the real-time compensation of the active surface system if the traces of the radio telescope are known in advance.

The Tian Ma 65-m Telescope Automatic Early Warning System

The Tian Ma Radio Telescope (TMRT), which is mainly used for deep space exploration and radio astronomy observations, is the largest fully steerable radio telescope in Asia. For promoting the automation of the telescope, an automatic early warning system is designed and implemented. The system can conveniently aggregate heterogeneous sensor data, make use of established strategies to implement an alert system, and send real-time alarms through multiple channels, which is helpful to promote unmanned operation. In addition, we adopt DevOps (a compound of development (Dev) and operations (Ops) which means end-to-end automation in software development and delivery) to simplify the development, upgrading, and maintenance of the telescope automatic early warning system.

Three-month Monitoring of the Variability toward W51 IRS2 with Ammonia, Water, and Methanol Transitions

A four-epoch monitoring program spanning ∼three months (from 2020 January 8 to April 7) for ammonia, water, and methanol transitions toward the high-mass star-forming region W51 IRS2 was conducted using the Shanghai 65 m Tianma Radio Telescope with its K-band (18–26.5 GHz) receiver. In total, 33 ammonia transitions and 16 methanol transitions were detected toward the target at least once during this monitoring program. Among them, 14 ammonia and 4 methanol transitions show maser emission characteristics. Rapid variabilities (including both increases and decreases) in the ammonia and methanol transitions were detected from both maser and thermal emissions during the three months of the monitoring. In addition, H2O masers with obvious variability were also detected. The results of the rotation diagram analysis for the ammonia and methanol quasi-thermal transitions show the variations in their rotational temperatures during the monitoring. The derived temperatures from the transitions with larger upper energies (E u /κ) generally decreased over the whole monitoring period, from January 8 to April 7, but those with smaller E u /κ first increased from January 8 to April 1, then rapidly decreased from April 1 to April 7. These findings support the suggestion that an inside-out heatwave propagation in W51 IRS2 was involved with the accretion burst over a short duration (only on the order of months) and caused the drastic variability behaviors of the different line transitions during high-mass star formation.

An Excited-state OH Maser Survey toward WISE Point Sources

We report a survey of excited-state hydroxyl (ex-OH) masers at the 4.7 and 6.0 GHz transitions toward a sample consisting of 3348 massive star-forming region candidates selected from the all-sky Wide-field Infrared Survey Explorer point-source catalog. The survey was conducted with the Shanghai Tianma Radio Telescope. In total, 6, 9, and 30 sources were detected with the ex-OH masers at the 4766, 6031, and 6035 MHz transitions, respectively. Among them, one 4766 MHz, one 6031 MHz, and five 6035 MHz ex-OH maser sources are newly identified. A series of statistical analyses derived that the ex-OH masers were detected efficiently toward the subsamples associated with both the 6.7 GHz CH3OH maser and radio recombination lines (RRLs), whereas compared to the CH3OH masers, the ex-OH masers are more likely to be produced toward the sources with stronger 22 μm band emission. A significant luminosity correlation is found between the ex-OH masers and RRLs. In addition, we found that the magnetic field strength of most sources with the 6.7 GHz CH3OH maser was stronger relative to that of sources without the CH3OH maser. Combined with these, it demonstrates that the ex-OH maser is associated with more evolved star-forming regions, likely associated with thicker dust envelopes. Meanwhile, the ex-OH masers might be a potential tracer for measuring the Galactic magnetic field information on the large-scale views using their Zeeman pairs.

Pulse Profile Variations Associated with Two Glitches of PSR B1822–09

We reported two new glitches of PSR B1822−09 that were detected at the Shanghai Tian Ma Radio Telescope. The glitches occurred around MJD 58,025 and 58,474.5, respectively. The shapes of the integrated mean pulse profiles in both the radio-bright (B-mode) and the radio-quiet (Q-mode) modes changed after two glitches. Such changes are probably related to the trigger mechanisms of the glitches. According to the Gaussian fitting to the integrated mean pulse profiles, variations of the integrated mean pulse profiles can be attributed to variations of the Gaussian components. The fitting also indicates that there may be changes in only a part of the Gaussian components after glitches. We proposed an interpretation of the relation between the precursor and the interpulse of PSR B1822−09 according to variations of Gaussian components. We analyzed the cumulative distributions of the glitch sizes and the waiting times of all 14 glitches of PSR B1822−09. The cumulative distribution of the glitch sizes can be fitted well by a power law with an index α of 0.985 ± 0.005. The cumulative distribution of the waiting times follows a Poisson model with a mean waiting time λ of 466 ± 66 days. The correlation coefficient between the waiting times and the sizes of the corresponding preceding glitches is 0.906. In contrast, there is no apparent correlation between the waiting times and the sizes of the corresponding trailing glitches.

A highly directional eight‐hole coupling circular waveguide coupler

Aiming at the system noise temperature calibration of the K-band seven-beam cryogenic receiver on Tianma Radio Telescope, a design of K-band highly directional coupler is proposed in this paper. Based on the hole coupling principle proposed by Gian Guido Gentili, an eight-hole coupling circular waveguide directional coupler is designed by ANSYS HFSS software. Through the distribution mode of eight coupling holes, the excellent performance and compact structure have been realized. Measurement shows that the reflection coefficient is less than −25 dB, coupling degree is stable within −25 ± 1 dB, isolation degree is lower than −35 dB, and directivity coefficient is greater than 10 dB in its operating frequency range.

6 cm OH Masers in Northern Star Formation Regions

Abstract We have used the Shanghai Tianma Radio Telescope to search for three OH transitions at 4.7 GHz toward 155 northern star formation regions. We detect 4.7 GHz OH masers in 18 star formation regions, 8 of which are reported here for the first time. From these 18 sources, we detect 6 4660 MHz masers, 13 4765 MHz masers, and no 4750 MHz masers. A further 1 source (Sgr B2N) has been re-detected with broad quasi-thermal emission in all three OH lines. W49SW was re-detected with broad quasi-thermal emission at both 4660 and 4750 MHz. One source (W31, G010.626−0.387) was re-detected with quasi-thermal emission at both 4750 and 4765 MHz. One source (G005.885−0.392) was first detected with quasi-thermal emission at 4660 MHz. We have investigated the associations between the detected 4.7 GHz OH masers with ground-state OH masers near 1.7 GHz, 6.7 GHz methanol masers and 22 GHz water masers reported in the literature. We find that the presence of 1665 MHz OH masers is a better indicator of the presence of 4.7 GHz OH masers than 1720 MHz OH masers. The majority of the 4.7 GHz OH masers are associated with 6.7 GHz methanol and/or 22 GHz water masers. We have compared the characteristics of our detections with those reported previously in the literature and found that only five sources are fairly stable.

A 12.2 GHz Methanol Maser Survey toward the 6.7 GHz Counterparts Associated with/without UC H ii Regions

Abstract We report a new survey of the 12.2 GHz Class II methanol masers toward a sample of 367 sources with the 6.7 GHz methanol masers conducted with the Shanghai 65 m Tianma Radio Telescope. This sample has been previously made with observations of the radio continuum emission of UC H ii regions by the VLA. A total of 176 sources were detected with the 12.2 GHz methanol maser, with a detection rate of 48%, including 8 new detections. A lower detection rate (<10%) was determined toward the sources in the Galactic longitude ranges of 60°–180°, revealing that the physical environments from those sources in the Local arm or the tails of Galactic arms do not easily excite the 12.2 GHz masers. In addition, two detections of highly excited-state OH masers at the 13.4 GHz transition were made, one of which is a new detection. Compared to previous surveys, one-third of the detected 12.2 GHz masers show considerable flux variations, implying the possible changes of their physical environments associated with variable radiation fields from their host high-mass young stellar objects. A positive log–log correlation is found between the luminosities of the 6.7 and 12.2 GHz masers in our observed sample, suggesting that both the transition masers have similar excitation conditions. The statistical analysis for the relationships between the methanol maser luminosity and UC H ii region spatial size indicates that the maser luminosities of both the 6.7 and 12.2 GHz transitions have a decreasing trend with the spatial sizes of the associated UC H ii regions, indicating that the Class II methanol masers might fade away with the H ii region evolution.

The TMRT K band observations towards 26 infrared dark clouds: NH3, CCS, and HC3N

We present one of the first Shanghai Tian Ma Radio Telescope (TMRT) K Band observations towards a sample of 26 infrared dark clouds (IRDCs). We observed the (1,1), (2,2), (3,3), and (4,4) transitions of NH$_{3}$ together with CCS (2$_{1}$-1$_{0}$) and HC$_{3}$N $J\,$=2-1, simultaneously. The survey dramatically increases the existing CCS-detected IRDC sample from 8 to 23, enabling a better statistical study of the ratios of carbon-chain molecules (CCM) to N-bearing molecules in IRDCs. With the newly developed hyperfine group ratio (HFGR) method of fitting NH$_{3}$ inversion lines, we found the gas temperature to be between 10 and 18 K. The column density ratios of CCS to NH$_{3}$ for most of the IRDCs are less than 10$^{-2}$, distinguishing IRDCs from low-mass star-forming regions. We carried out chemical evolution simulations based on a three-phase chemical model NAUTILUS. Our measurements of the column density ratios between CCM and NH$_{3}$ are consistent with chemical evolutionary ages of $\lesssim$10$^{5}$ yr in the models. Comparisons of the data and chemical models suggest that CCS, HC$_{3}$N, and NH$_{3}$ are sensitive to the chemical evolutionary stages of the sources.