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# Discovery of 15 New Pulsars at High Galactic Latitudes with FAST

Xin Xu<sup>1,2</sup>, Shi Dai<sup>3,4</sup>, Qijun Zhi<sup>2,5</sup>, Juntao Bai<sup>6,7</sup>, Joanna Berteaud<sup>8,9</sup>, Francesca Calore<sup>10</sup>, Maïca Clavel<sup>11</sup>, Weiwei Zhu<sup>12</sup>, Di Li<sup>12,13</sup>, Rushuang Zhao<sup>2,5</sup>, Renxin Xu<sup>14</sup>, and Guojun Qiao<sup>14</sup>

## Abstract

We present the discovery and timing results for 15 pulsars discovered in a high-Galactic-latitude survey conducted with the Five-hundred-meter Aperture Spherical Telescope. The survey targeted a region as close as possible to the Galactic center, encompassing an area near the Galactic bulge. The newly discovered pulsars consist of 11 normal pulsars and four millisecond pulsars (MSPs). Among the MSPs, three are identified in binary systems with orbital periods of ~3.1, 4.6, and 12.5 days, respectively. We have successfully obtained coherent timing solutions for three of the normal pulsars (PSRs J1745−0059, J1746−0156, and J1800−0059). Furthermore, within our data set, we found that four pulsars (three new and one known) show mode-changing and/or subpulse-drifting phenomena. Comparing our discoveries with simulations of the Galactic disk and bulge MSP populations indicates that these new pulsars are most likely located in the disk. Nonetheless, our discoveries demonstrate that deep surveys at high Galactic latitudes have significant potential to enhance our understanding of the MSP population in the direction of the bulge.

*Unified Astronomy Thesaurus concepts: Radio pulsars (1353); Binary pulsars (153); Millisecond pulsars (1062)*

## 1. Introduction

To date, nearly 4000 pulsars have been discovered (e.g., R. N. Manchester et al. 2005), with the discovery rate accelerating in recent years, largely due to deep surveys conducted by the Five-hundred-meter Aperture Spherical Telescope (FAST; D. Li et al. 2018; A. D. Cameron et al. 2020; M. Cruces et al. 2021; J. L. Han et al. 2021; Z. Pan et al. 2021; W. Q. Su et al. 2023; L. Zhang et al. 2023; D. J. Zhou et al. 2023; D. Yin et al. 2024; D. Zhao et al. 2024) and the MeerKAT telescope (A. Ridolfi et al. 2022; L. Vleeschower et al. 2022; W. Chen et al. 2023; P. V. Padmanabh et al. 2023, 2024; E. Carli et al. 2024; V. Prayag et al. 2024; J. D. Turner et al. 2024). Q. J. Zhi et al. (2024) conducted a pilot survey at intermediate Galactic latitudes, demonstrating that FAST surveys in these regions have the potential to uncover hundreds of millisecond pulsars (MSPs). Most of these deep pulsar surveys have concentrated on the Galactic plane or globular clusters. At high Galactic latitudes, previous pulsar surveys have primarily utilized low radio frequencies (T. Coenen et al. 2014; S. Sanidas et al. 2019; N. D. R. Bhat et al. 2023a, 2023b), drift scans (A. N. Lommen et al. 2000;

J. Boyles et al. 2013; R. S. Lynch et al. 2013; D. Li et al. 2018; B. B. P. Perera et al. 2022), or short integration times per pointing (M. Burgay et al. 2006; M. J. Keith et al. 2010; E. F. Keane et al. 2018), making them generally sensitive only to bright or nearby pulsars compared to Galactic plane surveys. This limitation constrains our understanding of the pulsar population in these regions, particularly toward areas such as the Galactic bulge (e.g., F. Calore et al. 2016).

The dense stellar environment of the Galactic center and bulge is expected to host a substantial population of MSPs (F. Calore et al. 2016; A. Gautam et al. 2022). This population has been proposed as the origin of the enigmatic Galactic center γ-ray excess (GCE; S. Murgia 2020), although whether dark matter annihilation contributes to the observed diffuse γ-ray emission remains an open question (e.g., F. Calore et al. 2015, 2021; O. Macias et al. 2018; D. Song et al. 2024). Recent studies combining γ-ray and X-ray observations of the Galactic bulge suggest that many unidentified X-ray sources in the region are consistent with being MSPs that have yet to be identified (J. Berteaud et al. 2021). F. Calore et al. (2016) conducted simulations of the MSP population in the Galactic bulge, demonstrating that their distribution could extend up to tens of degrees above (and below) the Galactic plane, despite their distribution being strongly peaked toward the Galactic center. Given the considerable distance to the Galactic center, probing this population requires deep surveys that cover a

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Original content from this work may be used under the terms of the [Creative Commons Attribution 4.0 licence](https://creativecommons.org/licenses/by/4.0/). Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

<footnote n="1"><sup>1</sup> School of Mathematical Science, Guizhou Normal University, Guiyang 550001, People's Republic of China</footnote>

<footnote n="2"><sup>2</sup> Guizhou Provincial Key Laboratory of Radio Astronomy and Data Processing, Guizhou Normal University, Guiyang 550001, People's Republic of China;
qjzhi@gznu.edu.cn</footnote>

<footnote n="3"><sup>3</sup> Australia Telescope National Facility, CSIRO, Space and Astronomy, P.O. Box 76, Epping, NSW 1710, Australia; shi.dai@csiro.au</footnote>

<footnote n="4"><sup>4</sup> Western Sydney University, Locked Bag 1797, Penrith South DC, NSW 2751, Australia</footnote>

<footnote n="5"><sup>5</sup> School of Physics and Electronic Science, Guizhou Normal University, Guiyang 550001, People's Republic of China</footnote>

<footnote n="6"><sup>6</sup> Xinjiang Astronomical Observatory, Chinese Academy of Sciences, Urumqi, Xinjiang 830011, People's Republic of China</footnote>

<footnote n="7"><sup>7</sup> School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China</footnote>

<footnote n="8"><sup>8</sup> University of Maryland, Department of Astronomy, College Park, MD 20742, USA</footnote>

<footnote n="9"><sup>9</sup> NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771, USA</footnote>

<footnote n="10"><sup>10</sup> LAPTh, CNRS, USMB, 74940 Annecy, France</footnote>

<footnote n="11"><sup>11</sup> Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France</footnote>

<footnote n="12"><sup>12</sup> National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, People's Republic of China</footnote>

<footnote n="13"><sup>13</sup> Department of Astronomy, Tsinghua University, Beijing 100190, People's Republic of China</footnote>

<footnote n="14"><sup>14</sup> School of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, People's Republic of China
Received 2024 December 22; revised 2025 February 14; accepted 2025 February 26; published 2025 March 24</footnote>
<figure><img src="image_3.png" /><figcaption>**Figure 1.** A plot of the sky coverage map of this survey in galactic coordinates. The black dots represent each survey beam position, the blue dots mark the positions of the known pulsars within the survey region, and the red stars indicate the locations of the newly discovered pulsars. The area enclosed by the solid black line represents the region we plan to survey.</figcaption></figure>

substantial portion of the bulge. The presence or absence of detectable bulge MSPs would have profound implications for understanding the origin of the GCE and could contribute to refining dark matter theories.

If such a population exists, determining whether bulge MSPs share the same formation and evolutionary history as MSPs in the Galactic disk and globular clusters would provide valuable insights into the stellar evolution and dynamics of the bulge. Discovering these MSPs would enable direct comparisons of their ages, magnetic field strengths, and binary system properties (e.g., binary fractions and orbital periods) with those of disk and globular cluster MSPs. Additionally, finding pulsars in the bulge would offer new opportunities to study the distribution of free electrons (e.g., J. M. Yao et al. 2017) and the magnetic field structure (D. H. F. M. Schnitzeler 2012) in the inner regions of our Galaxy.

In this paper, we present the results of a high-Galactic-latitude pulsar survey conducted with FAST. The survey area was selected to be as close to the Galactic bulge as possible, constrained by the sky coverage accessible with FAST's snapshot observing mode (J. L. Han et al. 2021). Thanks to FAST's exceptional sensitivity, this represents the deepest survey at mid- and high latitudes, skimming the outskirts of the Galactic bulge. Section 2 describes the survey and associated timing campaign, while Section 3 presents the results. Finally, conclusions and a discussion are provided in Section 4.

## 2. Observations and Data Reduction

### 2.1. FAST Survey and Pulsar Search

The 19-beam L-band focal plane array of FAST (D. Li et al. 2018) was used to survey a region at high Galactic latitude. The observing band covered a frequency range of 1.0–1.5 GHz (P. Jiang et al. 2020). A total of 238 observations were carried out, utilizing the FAST snapshot observing mode and covering Galactic longitudes and latitudes of $21^\circ < l < 27^\circ$ and $10^\circ < b < 16^\circ$. Each snapshot observation consists of four independent pointings, offset from one another, to ensure uniform sky coverage while minimizing slewing time. More details on the snapshot mode can be found in J. L. Han et al.

(2021). The integration time per pointing is 5 minutes. In Figure 1, we show the footprints of each pointing as the gray regions. The lower boundary in Galactic longitude of our survey is set by the limiting decl. of FAST in the snapshot mode. The FAST ROACH back end was used in its pulsar-search mode, with 4096 channels across 500 MHz of bandwidth and a 49 µs sampling rate. The total intensity was recorded with 8 bit sampling.

A periodicity search was conducted using the pulsar-searching software package PRESTO (S. M. Ransom 2001), covering a dispersion measure (DM) range of 0–1000 pc cm⁻³. Radio frequency interference (RFI) was masked using the rfifind routine. To account for the potential orbital modulation of pulsar periodic signals, we searched for signals drifting by up to ±200 $n_h^{-1}$ bins in the Fourier domain, by setting $z_{max}$ = 200 (S. M. Ransom et al. 2002), where $n_h$ is the largest harmonic at which a signal is detected (up to eight harmonics were summed). Additionally, single-pulse candidates with a signal-to-noise ratio (S/N) greater than 8 were identified using the single_pulse_search.py routine. This routine was applied to each dedispersed time series and the boxcar filtering parameters, using filter widths ranging from 1 to 300 samples. Burst candidates were manually examined after removing narrow-band and impulsive RFI.

Through the methods described above, we discovered 15 new pulsars, all of which have been successfully confirmed by follow-up observations. In Figure 1, the blue circles represent the positions of known pulsars within the survey region, and the red stars show the locations of newly discovered pulsars. The basic parameters of our discoveries are presented in Table 1. Detailed descriptions of these new pulsars are provided in the next section. A further search of this data set is currently ongoing and updates will be continuously provided on our project webpage.<fnref n="15" />

We detected single pulses from the newly discovered pulsars J1736−0245, J1745−0059, J1746−0156, J1800−0059, and J1801−0108 and from the known pulsars B1740−03, J1735−0243, J1745−0129, and J1800−0125. Studies of their single pulses are presented in Section 3.3. No rotating radio transient sources or fast radio bursts were detected in this survey. Assuming a system equivalent flux density of 1.25 Jy (P. Jiang et al. 2020), our sensitivity to detecting single pulses with a width of 5 ms and an S/N of 8 is 4.5 mJy.

### 2.2. Follow-up Timing Observations

Three pulsars underwent regular timing observations, namely J1745−0059, J1746−0156, and J1800−0059. Among these, J1745−0059 and J1800−0059, two of the brightest pulsars in our sample, were observed with Murriyang, CSIRO's Parkes 64 m telescope. The ultra-wideband low system (G. Hobbs et al. 2020) was employed in coherently dedispersed search mode, recording data with 2 bit sampling every 64 µs in each of the 1 MHz wide frequency channels, covering a total bandwidth of 3328 MHz between 704 and 4032 MHz. Only total intensity data were recorded. The integration times of J1745−0059 and J1800−0059 ranges from 10 to 30 minutes and 45 to 80 minutes per observation, respectively. PSR J1746−0156 was observed and timed with FAST using the central beam of the 19-beam receiver. Data were recorded in pulsar-search mode with configurations identical to those used in the

<footnote n="15">¹⁵ https://astrolab.gznu.edu.cn/kxyj.htm</footnote>
<table><caption>**Table 1**
The Basic Parameters of All 15 New Pulsars, Where Three of the Pulsars for Which Coherent Timing Solutions Have Been Obtained Are Indicated by Asterisks</caption><thead><tr><th rowspan="2">Pulsar</th><th rowspan="2">R.A.<br>(J2000)</th><th rowspan="2">Decl.<br>(J2000)</th><th rowspan="2">Period<br>(s)</th><th rowspan="2">DM<br>(pc cm<sup>-3</sup>)</th><th colspan="2">Dist<br>(kpc)</th><th rowspan="2">P<sub>b</sub><br>(days)</th><th rowspan="2">χ<sub>p</sub><br>(ls)</th><th rowspan="2">Companion Mass<br>(M<sub>☉</sub>)</th><th rowspan="2">Type</th></tr><tr><th>YMW16</th><th>NE2001</th></tr></thead><tbody><tr><td colspan="11" style="text-align:center; font-weight:bold;">Normal Pulsars</td></tr><tr><td>J1736-0245</td><td>17:36:41</td><td>-02:45</td><td>0.139298</td><td>44.3(1)</td><td>0.7</td><td>1.6</td><td>...</td><td>...</td><td>...</td><td>Isolated</td></tr><tr><td>J1738-0319</td><td>17:38:55</td><td>-03:19</td><td>1.369302</td><td>85.0(4)</td><td>2.3</td><td>2.9</td><td>...</td><td>...</td><td>...</td><td>Isolated</td></tr><tr><td>J1745-0059<sup>*</sup></td><td>17:45:56.70</td><td>-00:58:54.0</td><td>0.679457</td><td>68.63(3)</td><td>3.3</td><td>2.4</td><td>...</td><td>...</td><td>...</td><td>Isolated</td></tr><tr><td>J1746-0156<sup>*</sup></td><td>17:46:30.93</td><td>-01:56:31</td><td>1.829039</td><td>92.94(8)</td><td>5.2</td><td>3.2</td><td>...</td><td>...</td><td>...</td><td>Isolated</td></tr><tr><td>J1750-0043</td><td>17:50:57</td><td>-00:43</td><td>0.571810</td><td>85.1(4)</td><td>5.3</td><td>2.9</td><td>...</td><td>...</td><td>...</td><td>Isolated</td></tr><tr><td>J1753-0006</td><td>17:53:02</td><td>-00:06</td><td>0.263349</td><td>101(1)</td><td>8.9</td><td>3.6</td><td>...</td><td>...</td><td>...</td><td>Isolated</td></tr><tr><td>J1753-0217</td><td>17:53:58</td><td>-02:17</td><td>1.039570</td><td>91.5(5)</td><td>4.5</td><td>3.0</td><td>...</td><td>...</td><td>...</td><td>Isolated</td></tr><tr><td>J1754+0000</td><td>17:54:07</td><td>+00:00</td><td>0.0611325</td><td>104.71(5)</td><td>10.0</td><td>3.7</td><td>...</td><td>...</td><td>...</td><td>Isolated</td></tr><tr><td>J1800-0059<sup>*</sup></td><td>18:00:39.07</td><td>-00:59:13.6</td><td>1.192542</td><td>84.2(2)</td><td>4.5</td><td>2.7</td><td>...</td><td>...</td><td>...</td><td>Isolated</td></tr><tr><td>J1801-0108</td><td>18:01:25</td><td>-01:08</td><td>1.072109</td><td>86.3(4)</td><td>4.6</td><td>2.7</td><td>...</td><td>...</td><td>...</td><td>Isolated</td></tr><tr><td>J1804-0046</td><td>18:04:51</td><td>-00:46</td><td>0.635152</td><td>86.8(2)</td><td>4.7</td><td>2.7</td><td>...</td><td>...</td><td>...</td><td>Isolated</td></tr><tr><td colspan="11" style="text-align:center; font-weight:bold;">MSPs</td></tr><tr><td>J1742-0237</td><td>17:42:08</td><td>-02:37</td><td>0.00366367</td><td>65.685(6)</td><td>1.5</td><td>2.2</td><td>12.48</td><td>14.14</td><td>0.39 &lt; 0.46 &lt; 1.12</td><td>Binary</td></tr><tr><td>J1748-0224</td><td>17:48:48</td><td>-02:24</td><td>0.00176509</td><td>75.899(3)</td><td>2.8</td><td>2.5</td><td>3.09</td><td>2.74</td><td>0.18 &lt; 0.21 &lt; 0.45</td><td>Binary</td></tr><tr><td>J1750-0112</td><td>17:50:07</td><td>-01:12</td><td>0.00889597</td><td>72.97(3)</td><td>3.5</td><td>2.5</td><td>...</td><td>...</td><td>...</td><td>Isolated</td></tr><tr><td>J1801-0144</td><td>18:01:15</td><td>-01:44</td><td>0.00303345</td><td>60.021(2)</td><td>2.1</td><td>2.0</td><td>4.76</td><td>4.64</td><td>0.23 &lt; 0.27 &lt; 0.60</td><td>Binary</td></tr></tbody></table>

**Note.** For three MSPs in binary systems, their orbital parameters were determined by fitting a circular orbit model to the variation of their barycentric periods in time. The minimum, median, and maximum companion masses for binary systems were estimated assuming a pulsar mass of 1.35 $M_{☉}$ and inclination angles of 90°, 60°, and 26°, respectively. The pulsar distances were estimated using the free electron density models of J. M. Cordes & T. J. W. Lazio (2002) and J. M. Yao et al. (2017).

survey, including full polarization information. The integration time of this pulsar ranges from 180 to 300 s per observation.

Furthermore, we carried out eight follow-up observations of three MSPs (J1742-0237, J1748-0224, and J1801-0144) in binary systems with FAST, aiming to obtain their basic orbital parameters. The data recording and configuration were identical to those used for J1746-0156, with each pulsar having an integration time of 5 minutes. Additionally, we performed six observations of J1801-0144 using Murriyang, to refine its orbital parameters. The other two MSPs are too faint to be detected by Murriyang with an integration time of ~1 hr and were therefore not followed up with Murriyang.

To obtain a coherent timing solution, search-mode observations were folded, with the apparent spin period of each pulsar determined at each observing epoch using the DSPSR software package (W. van Straten & M. Bailes 2011), with a subintegration length of 30 s. Narrowband and impulsive RFIs were manually removed from each subintegration. Then, each observation was averaged in time to create subintegrations with a length of a few minutes, and pulse times of arrival (ToAs) were measured for each subintegration, using the PAT routine of the PSRCHIVE software package (W. van Straten et al. 2012). Finally, the timing analysis was performed for each pulsar using the TEMPO2 software package (G. B. Hobbs et al. 2006), where the timing analysis was performed using the Barycentric Coordinate Time TT(TAI) clock standard and JPL DE438 solar system ephemeris.

We successfully obtained coherent timing solutions for three pulsars (J1745-0059, J1746-0156, and J1800-0059). For these pulsars, we refolded the search-mode data and averaged the time and frequency of each observation to generate high-S/N pulse profiles. ToAs were measured using these high-S/N profiles and we repeated our timing analysis to measure their spin

and astrometric parameters. Throughout our timing analysis, TEMPO2 fitting with ToA errors (known as “MODE 1”) was used and the weighted rms (Wrms) of the timing residuals are reported in Table 2. To refine our DM measurements, for each pulsar we selected a high-S/N observation and divided the bandwidth into four frequency subbands. We then measured a ToA from each subband and fitted for the DM using TEMPO2. Our timing results will be presented in the next section.

## 3. Results

We discovered 15 new pulsars, including 11 normal pulsars and four MSPs, with a total observing time of 118.5 hr, covering approximately ~27 deg² (see Table 1). Additionally, we detected six previously known pulsars in the surveyed area: B1740-03 (R. N. Manchester et al. 1978), J1735-0243 (J. Boyles et al. 2013), J1737-0314A (Z. Pan et al. 2021), J1742-0203 (A. E. McEwen et al. 2020), J1745-0129 (R. T. Edwards et al. 2001), and J1800-0125 (F. Crawford et al. 2006), with J1737-0314A being a pulsar in the globular cluster NGC 6402 (Z. Pan et al. 2021). This globular cluster hosts six MSPs, but due to our limited sensitivity (with a 5 minutes integration time per pointing), we could not detect the remaining five pulsars. This section will provide a detailed discussion of all newly discovered pulsars and pulsars with special single-pulse phenomena.

### 3.1. Normal Pulsars

The newly discovered pulsars include 11 isolated normal pulsars. Their basic parameters are listed in Table 1, including their names, coordinates (R.A. and decl.), spin periods, and DM. One of them, J1754+0000, has a spin period of ~0.06 s, making it potentially a young pulsar. Measurements of its
<figure><img src="image_4.png" /><figcaption>**Figure 2.** Integrated pulse profiles of the 15 new pulsars were obtained with FAST at the center frequency of 1250 MHz. The first 11 panels display the 5 minutes integrated pulse profiles of the 11 normal pulsars, while the next four panels present the 20 minutes integrated pulse profiles of the four MSPs. All pulse profiles have been normalized.</figcaption></figure>

<table><caption>**Table 2**

Parameters for Three Normal Pulsars with Timing Solutions, Including R.A., Decl., Rotation Period, and Derived Parameters</caption><thead><tr><th></th><th>J1745-0059</th><th>J1746-0156</th><th>J1800-0059</th></tr></thead><tbody><tr><td>RAJ (J2000)</td><td>17:45:56.70(1)</td><td>17:46:30.93(4)</td><td>18:00:39.07(3)</td></tr><tr><td>DECJ (J2000)</td><td>-00:58:54.0(1)</td><td>-01:56:31(1)</td><td>-00:59:13.6(3)</td></tr><tr><td>ν (Hz)</td><td>1.47163492631(2)</td><td>0.54673292488(3)</td><td>0.83854355767(3)</td></tr><tr><td>ν (Hz s<sup>-1</sup>)</td><td>-9.4(2) × 10<sup>-16</sup></td><td>-5.3(3) × 10<sup>-16</sup></td><td>-1.9(2) × 10<sup>-17</sup></td></tr><tr><td>PEPOCH (MJD)</td><td>60396.3</td><td>60353.5</td><td>60400.8</td></tr><tr><td>Time span (MJD)</td><td>60273-60519</td><td>60243-60463</td><td>60282-60519</td></tr><tr><td>DM (cm<sup>-3</sup> pc)</td><td>68.63(3)</td><td>92.94(8)</td><td>84.2(2)</td></tr><tr><td>W<sub>rms</sub> (ms)</td><td>0.085</td><td>0.21</td><td>0.14</td></tr><tr><td colspan="4">Derived Parameters</td></tr><tr><td>GL (deg)</td><td>24.41</td><td>23.61</td><td>26.18</td></tr><tr><td>GB (deg)</td><td>14.07</td><td>13.48</td><td>10.82</td></tr><tr><td>P (s)</td><td>0.679516354310(8)</td><td>1.82904660482(9)</td><td>1.19254389453(4)</td></tr><tr><td>Ṗ (s s<sup>-1</sup>)</td><td>4.36(7) × 10<sup>-16</sup></td><td>1.77(8) × 10<sup>-15</sup></td><td>2.8(3) × 10<sup>-16</sup></td></tr><tr><td>τ<sub>c</sub> (Myr)</td><td>24.73</td><td>16.401</td><td>68.33</td></tr><tr><td>B<sub>s</sub> (G)</td><td>5.51 × 10<sup>11</sup></td><td>1.82 × 10<sup>12</sup></td><td>5.81 × 10<sup>11</sup></td></tr></tbody></table>

spindown rate through follow-up timing observations are required to understand its nature.

We estimated the distances to these pulsars using the free electron density models of YMW16 (J. M. Yao et al. 2017) and

NE2001 (J. M. Cordes & T. J. W. Lazio 2002). The distances are provided in the sixth and seventh columns of Table 1. For several pulsars, the distances estimated by the two models differ significantly, as seen in cases like PSRs J1754+0000 and
J1753−0006, where the YMW16 model predicts substantially greater distances compared to the NE2001 model.

The integrated pulse profiles of these normal pulsars observed with FAST are shown in the first 11 panels of Figure 2, using a 5 minutes integration at a central frequency of 1250 MHz. The results indicate that the integrated profiles of five pulsars (PSRs J1753−0006, J1800−0059, J1801−0108, J1753−0217, and J1736−0244) exhibit a single-component pulse shape, with PSR J1753−0217 having the narrowest radiation window of just a few degrees. In contrast, the integrated pulse profiles of J1753−0006 and J1736−0244 are asymmetric, with the much steeper right side of the former and the opposite of the latter suggesting the presence of multiple underlying components that require verification through longer observations. The other six pulsars—PSRs J1754+0000, J1750−0043, J1746−0156, J1804−0046, J1745−0059, and J1738−0319—display relatively complex integrated pulse profiles, each consisting of at least two components. J1746−0156’s integrated profile features two closely separated components, while J1754+0000, J1745−0059, and J1738−0319 show two distinctly separated components with a clear bridge of radiation between them. However, J1738−0319 appears to have a multicomponent profile. Furthermore, the pulse profile of J1804−0046 shows a weak component at −8°, with a peak intensity that is only one-fifth of the overall integral profile. It is worth noting that the 5 minutes integration with FAST does not provide an integrated pulse profile with a high S/N. The shapes of the integrated pulse profiles of these pulsars may change under longer observations.

To date, we have successfully obtained coherent timing solutions for three (J1745−0059, J1746−0156, and J1800−0059) of the newly discovered pulsars. The best-fit timing parameters for these pulsars are presented in Table 2, while the corresponding timing residuals are shown in Figure 3. For other normal pulsars where coherent timing solutions have not yet been achieved, the results will be reported in a future publication. Notably, we carried out three 1 hr observations of J1801−0108 using Murriyang, the Parkes telescope, but no pulsar signals were detected. Consequently, follow-up timing studies for this pulsar will need to rely on high-sensitivity telescopes like FAST.

## 3.2. MSPs

So far, we have discovered four new MSPs, all with spin periods of less than 10 ms. Except for PSR J1750−0112, the spin periods of the other three MSPs (PSRs J1742−0237, J1748−0224, and J1801−0144) exhibit significant variations in each observation, indicating that they are in binary systems. For those three pulsars in binary systems, we measured their orbital parameters by fitting the variation of their barycentric periods as a function of time obtained from FAST and Murriyang observations using the *fitorbit*<fnref n="16" /> program. The fitting results indicate that all three pulsars are in nearly circular orbits with small eccentricities ($e < 10^{-3}$). Figure 4 shows the fitting results for their period changes and the corresponding residuals, where the blue circles indicate FAST observations and the red triangles indicate Murriyang observations. The binary orbital period ($P_b$) and the projection of the semimajor axis along the line of sight ($\chi_p$) for these pulsars are listed in the eighth and ninth columns of Table 1, respectively.

<figure><img src="image_5.png" /><figcaption>**Figure 3.** The time residuals of the three normal pulsars are plotted as a function of MJD. The Wrms of the timing residuals for each pulsar are listed in Table 2. The timing of J1746−0156 was carried out with FAST, while J1745−0059 and J1800−0059 were observed with Murriyang.</figcaption></figure>

Additional timing observations are currently underway to obtain coherent timing solutions and determine their orbital parameters.

PSR J1750−0112 is an MSP with a spin period of ~8.896 ms. Three observations with FAST showed negligible changes in its observed period, within the limits of uncertainty. Therefore, it is likely an isolated MSP. Using the NE2001 and YMW16 models, we estimated the distance to this pulsar, finding it to be the most distant of the four new MSPs. Its integrated pulse profile, shown in Figure 2, is based on 20 minutes of FAST observation. The profile displays two obvious components, with a wide pulse emission window covering almost half of the entire pulse period. The separation between the two components is ~85°. Due to the low S/N, the presence of bridge radiation between the components remains uncertain and requires verification through longer observations.

For the three pulsars in binary systems—J1748−0224, J1801−0144, and J1742−0237—preliminary orbital solutions suggest orbital periods of approximately 3.09, 4.76, and 12.48 days, respectively. Meanwhile, these pulsars all have very short spin periods, with J1748−0224 having the shortest, at 1.765 ms. To estimate their companion masses, we employed the D. R. Lorimer & M. Kramer (2004) method, assuming the pulsar mass to be $M_p = 1.35 M_\odot$, and the minimum, median, and maximum companion masses were estimated with inclination angles of $i = 90°, 60°, \text{and } 26°$, respectively. The minimum, median, and maximum companion masses of these

<footnote n="16">¹⁶ https://github.com/vivekvenkris/fitorbit</footnote>
<figure><img src="image_6.png" /><figcaption>**Figure 4.** Variations in the observation periods of three pulsars in binary systems were recorded using FAST and Murriyang. Each data point corresponds to a 5 minutes (FAST) or 1 hr (Murriyang) observation plotted against a single orbital period. The black curves depict the orbital fits of the period changes, while the lower panels show the residuals of the fits.</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>**Figure 5.** The single-pulse stacks of four pulsars exhibiting unique single-pulse phenomena are presented, with the first three being newly discovered and the fourth being a known pulsar. All display either mode-switching or subpulse-drifting behavior.</figcaption></figure>

three pulsars are listed in the 10th column of Table 1. The results suggest that all three MSPs have a white dwarf (WD) as their companion. Among them, J1742−0237 has the largest companion mass, while J1748−0224 has the smallest.

We obtained the integrated pulse profiles of these three pulsars using FAST observations with 20 minutes of integration at a central frequency of 1250 MHz. The results are shown in the last three panels of Figure 2. For J1748−0224, the integrated pulse profile is single-component pulse shape. For J1801−0144, the integrated pulse profile shows both the main pulse (MP) and the interpulse (IP), with a separation of ~150°. The peak intensity of the IP is only one-fifth that of the MP. Additionally, the MP has a weak leading component. We did not detect any bridge radiation between the MP and IP. The integrated profile of J1742−0237 exhibits a distinct tail component.

### 3.3. Single-pulse Phenomenon

By examining the single-pulse stacks of the new and known pulsars from this survey, we observed that five of the pulsars display mode-changing or subpulse-drifting behavior during the observations. The single-pulse stacks of these pulsars are shown in Figure 5.

For J1745−0059, a distinct intensity modulation is observed in its second component, which is not evident in the first

component. This suggests two distinct emission modes, distinguished by the intensity of the second component. J1800−0059 and J1801−0108 both exhibit subpulse-drifting behavior, with the distinction that their subpulse drift trajectories are in opposite directions. For J1735−0243, a known pulsar discovered by J. Boyles et al. (2013), using the Green Bank Telescope at 350 MHz, our 5 minutes observations reveal a mode change at around pulse number 200. In the normal mode, the first component is more intense relative to the others, while in the anomalous mode, the intensity of each component is comparable. Notably, in our observations, the anomalous pattern accounts for only about one-tenth of the total observation time. While we observed single-pulse phenomena in these pulsars over a short period, detailed and statistical characterization of their single pulses will require longer and more sensitive observations.

### 4. Discussion and Conclusion

This study reports the results of a high-Galactic-latitude survey conducted with FAST. Within a survey area of approximately 15 deg², we discovered 15 new pulsars, comprising 11 normal pulsars and four MSPs. Among the MSPs, one is isolated, while the other three are in binary systems. Notably, these are the first Galactic field MSPs discovered in this region. For the 11 newly discovered normal
<figure><img src="image_8.png" /><figcaption>**Figure 6.** The sensitivity of the three surveys (SUPERB, CRAFTS, and this work) as a function of the pulsar spin period for different DM values, assuming a 10% duty cycle. The solid and dashed lines represent DM = 50 pc cm⁻³ and 300 pc cm⁻³, respectively. The estimated flux densities of our discoveries are shown as the red dots. The flux densities of the known pulsars in the surveyed region were obtained from the ATNF pulsar catalog and are shown as the blue dots.</figcaption></figure>

pulsars, follow-up timing observations with Murriyang or FAST allowed us to successfully obtain coherent timing solutions for three pulsars: J1745−0059, J1746−0156, and J1800−0059. Furthermore, we analyzed the single pulses of both new and known pulsars observed in this survey and found that four pulsars exhibited interesting single-pulse phenomena. J1800−0059 and J1801−0108 display subpulse drift behavior, with opposite drift trajectories, while J1745−0059 and J1735−0243 exhibit two distinct emission modes. Detailed and statistical properties of these single pulses require longer and highly sensitive observations.

Three of our discoveries are MSPs in binary systems. The orbital period ($P_b$) and companion mass ($M_c$) of PSRs J1748−0224 and J1801−0144 are consistent with the $P_b-M_c$ relation for low-mass WD–MSP binary systems (e.g., T. M. Tauris & G. J. Savonije 1999), suggesting that their companions are likely helium (HE) WDs. The companion of PSR J1742−0237 has a mass of $0.46 M_\odot$ (at an inclination angle of 60°), significantly more massive than the prediction for an HE–MSP binary with an orbital period of 12.5 days. Therefore, PSR J1742−0237 could potentially be in a binary system with a carbon–oxygen WD (e.g., C. Y. Hui et al. 2018). Optical identifications and/or precise mass measurements of MSP companions are required to confirm the nature of these systems.

We estimated the sensitivity of our survey to MSPs using the radiometer equation (D. R. Lorimer & M. Kramer 2004). We used a gain of $G = 16 \text{ K Jy}^{-1}$ for FAST and the observing parameters described in Section 2. Our sensitivity was compared with previous surveys at high Galactic latitudes, including SUPERB (E. F. Keane et al. 2018) and CRAFTS (K. Zhang et al. 2019). In Figure 6, we show the sensitivities as a function of the spin period for different DMs, assuming a 10% duty cycle. The sensitivity of our survey is more than 1 order of magnitude higher than that of SUPERB. Compared to CRAFTS, a drift scan survey, our survey is approximately three times more sensitive, primarily due to the longer integration time per pointing. In addition, we estimated the flux densities of the newly discovered pulsars using the profiles in Figure 2 and the radiometer equation (D. R. Lorimer &

<figure><img src="image_9.png" /><figcaption>**Figure 7.** Galactic distribution of 15 pulsars discovered in this survey (green: normal pulsars; blue: MSPs). The distances were estimated using the YMW16 electron density model (J. M. Yao et al. 2017). The known normal pulsars and MSPs are indicated by the gray and orange dots, respectively. We only include known pulsars with a distance from the Galactic plane (|Z|) of less than 2.5 kpc. The black dashed line shows a distance of 3 kpc from the Galactic center, which is indicative of the GCE extension (F. Calore et al. 2015). The blue and red dashed lines indicate the innermost boundaries of a similar survey if the FAST snapshot mode could extend to declinations of −15°and −10°, respectively.</figcaption></figure>

M. Kramer 2004) and showed them as red dots in Figure 6. For comparison, the flux densities of the known pulsars in our survey region, obtained from the ATNF pulsar catalog (R. N. Manchester et al. 2005),<fnref n="17" /> are shown as the blue dots. Our newly discovered pulsars exhibit significantly lower flux densities, further highlighting FAST’s capability to detect faint pulsars.

The existence of a population of MSPs within the Galactic bulge remains an open question. If the GCE originates from a population of MSPs, several studies (e.g., F. Calore et al. 2016; J. Berteaud et al. 2021) have shown that their spatial distribution could extend to Galactic latitudes as high as ~20° and differs from that of the Galactic disk population. Furthermore, F. Calore et al. (2016) have demonstrated that the absence of detected MSPs in the bulge is primarily due to the limited sensitivity of pulsar searches in these regions. These findings highlight the importance of deep pulsar surveys at high Galactic latitudes near the bulge.

To determine whether any of our detected MSPs are associated with the Galactic bulge population, we compared

<footnote n="17">¹⁷ http://www.atnf.csiro.au/research/pulsar/psrcat</footnote>
our findings with simulations of both disk and bulge MSPs. For the Galactic disk population, we employed the *PSRPOPPY* software (S. D. Bates et al. 2014), following the procedure described in S. Dai et al. (2017). Our simulations incorporated spin period, luminosity, and spectral distributions based on previous studies (e.g., I. Yusifov & I. Küçük 2004; C.-A. Faucher-Giguère & V. M. Kaspi 2006; D. R. Lorimer et al. 2006, 2015; L. Levin et al. 2013). For the bulge MSP population, we adopted a model based on the distribution of red clump giants (L. Cao et al. 2013), informed by recent γ-ray results (R. Bartels et al. 2018). This model was implemented in J. Berteaud et al. (2021) with an updated Sun–Galactic center distance of 8.3 kpc. The other characteristics of the bulge population are similar to those of the disk population. Our simulations predict that approximately nine disk MSPs should be detectable in our survey, whereas no bulge MSPs are expected to be detected (averaged over 100 simulations). Based on these results, we conclude that the MSPs discovered in this survey are most likely located in the Galactic disk.

Due to FAST’s snapshot-mode decl. limit, our survey only covers a region near the bulge’s edge (see Figure 7). However, FAST’s full observing range extends to −14°, so observing at declinations of −15° or even −10° would allow us to probe further into the bulge. To evaluate the feasibility of detecting bulge MSPs in future FAST observations, we estimated the number of detectable bulge MSPs for a survey similar to ours but with an extended decl. limit. Using the same methodology employed to estimate the number of bulge MSPs in our current observations, we predict FAST would detect approximately ~one (or three) bulge MSPs if it observed as far south as 10° (or 15°). This low detection rate is likely due to the angle between the Galactic Bar’s major axis and the Sun–Galactic center line (e.g., J. Bland-Hawthorn & O. Gerhard 2016), resulting in fewer bulge MSPs being visible in the FAST sky. Our simulations indicate that deep surveys of the Galactic bulge from the southern hemisphere have greater potential for discovering bulge MSPs, as they provide direct observations through the Galactic Bar. However, large-scale FAST surveys at high Galactic latitudes remain valuable for studying the spatial distribution of disk MSPs and probing the bulge MSP population, given the current gaps in our understanding.

## Acknowledgments

This work has made use of data from FAST (the Five-hundred-meter Aperture Spherical radio Telescope; https://cstr.cn/31116.02.FAST). FAST is a Chinese national mega-science facility, operated by the National Astronomical Observatories, Chinese Academy of Sciences. Murriyang, the Parkes radio telescope, is part of the Australia Telescope National Facility (https://ror.org/05qajvd42), which is funded by the Australian Government for operation as a National Facility, managed by CSIRO. This work is supported by the National Natural Science Foundation of China (Nos. 12273008, 11988101, 12041303, and 12041304), the National SKA Program of China (Nos. 2022SKA0130100 and 2022SKA0130104), the Natural Science and Technology Foundation of Guizhou Province (No. [2023]024), and the Foundation of Guizhou Provincial Education Department (No. KY (2020) 003).

## ORCID iDs

Xin Xu https://orcid.org/0009-0006-3224-4319

Shi Dai https://orcid.org/0000-0002-9618-2499

Qijun Zhi https://orcid.org/0000-0001-9389-5197

Juntao Bai https://orcid.org/0000-0002-1052-1120

Joanna Berteaud https://orcid.org/0000-0003-4962-145X

Francesca Calore https://orcid.org/0000-0001-7722-6145

Maïca Clavel https://orcid.org/0000-0003-0724-2742

Weiwei Zhu https://orcid.org/0000-0001-5105-4058

Di Li https://orcid.org/0000-0003-3010-7661

Rushuang Zhao https://orcid.org/0000-0002-1243-0476

Renxin Xu https://orcid.org/0000-0002-9042-3044

Guojun Qiao https://orcid.org/0000-0002-9042-3044

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