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Discovery of two new millisecond pulsars towards the Galactic bulge

J. Berteaud, F. Calore, M. Clavel, S. Dai, J. S. Deneva, S. Hyman, F. K. Schinzel, A. Ridolfi, S. M. Ransom, F. Abbate, C. J. Clark, M. Kramer, T. Thongmeearkom, B. W. Stappers, E. D. Barr, R. P. Breton

TL;DR

This work addresses whether a hidden population of millisecond pulsars in the Galactic bulge could explain the Galactic Center Excess. It combines an innovative multi-wavelength candidate-selection strategy with deep radio pulsation searches across MeerKAT, Murriyang, and GBT to target X-ray MSP candidates and gamma-ray associations. The study reports two MSP discoveries, PSRs J1740-28 and J1740-2805, both in binary systems and likely associated with bulge populations, effectively doubling the MSP count within the innermost 2 degrees of the Galactic center. These results demonstrate the viability of the X-ray–guided, deep radio-search approach for uncovering bulge MSPs and highlight the ongoing need for high-sensitivity, high-frequency pulsation surveys to map the MSP population in the inner Galaxy and assess its relation to the GCE.

Abstract

The mysterious Galactic Center Excess of gamma rays could be explained by a large population of millisecond pulsars hiding in the Galactic bulge, too faint to be detected as individual high-energy point sources by the Fermi Large Area Telescope, as well as too fast and too dispersed to be detected in shallow radio pulsation surveys. Motivated by an innovative candidate selection method, we aim at detecting millisecond pulsars associated with the Galactic Center Excess by carrying deep radio pulsation searches towards promising candidates detected in the inner Galaxy, in X rays by Chandra, and in radio or gamma rays by the Very Large Array or Fermi. We conducted deep radio observation and follow-up campaigns with MeerKAT, the Murriyang and the Green Bank telescopes towards 9 X-ray candidate sources. We here report the detection of two new millisecond pulsars, including a black widow candidate, towards the Galactic bulge: PSRs J1740-2805 and J1740-28. These discoveries double the number of MSPs discovered within the innermost 2 degree from the Galactic center.

Discovery of two new millisecond pulsars towards the Galactic bulge

TL;DR

This work addresses whether a hidden population of millisecond pulsars in the Galactic bulge could explain the Galactic Center Excess. It combines an innovative multi-wavelength candidate-selection strategy with deep radio pulsation searches across MeerKAT, Murriyang, and GBT to target X-ray MSP candidates and gamma-ray associations. The study reports two MSP discoveries, PSRs J1740-28 and J1740-2805, both in binary systems and likely associated with bulge populations, effectively doubling the MSP count within the innermost 2 degrees of the Galactic center. These results demonstrate the viability of the X-ray–guided, deep radio-search approach for uncovering bulge MSPs and highlight the ongoing need for high-sensitivity, high-frequency pulsation surveys to map the MSP population in the inner Galaxy and assess its relation to the GCE.

Abstract

The mysterious Galactic Center Excess of gamma rays could be explained by a large population of millisecond pulsars hiding in the Galactic bulge, too faint to be detected as individual high-energy point sources by the Fermi Large Area Telescope, as well as too fast and too dispersed to be detected in shallow radio pulsation surveys. Motivated by an innovative candidate selection method, we aim at detecting millisecond pulsars associated with the Galactic Center Excess by carrying deep radio pulsation searches towards promising candidates detected in the inner Galaxy, in X rays by Chandra, and in radio or gamma rays by the Very Large Array or Fermi. We conducted deep radio observation and follow-up campaigns with MeerKAT, the Murriyang and the Green Bank telescopes towards 9 X-ray candidate sources. We here report the detection of two new millisecond pulsars, including a black widow candidate, towards the Galactic bulge: PSRs J1740-2805 and J1740-28. These discoveries double the number of MSPs discovered within the innermost 2 degree from the Galactic center.

Paper Structure

This paper contains 24 sections, 3 equations, 3 figures, 5 tables.

Table of Contents

  1. Introduction
  2. Observations and data reduction
  3. Radio-motivated targets
  4. Initial observations
  5. Pulsation search
  6. Timing and positions
  7. $\gamma$-ray motivated targets
  8. Observations
  9. Pulsation search
  10. Results
  11. Detections
  12. PSR J1740--28
  13. PSR J1740--2805
  14. Non-detections
  15. Methodology
  16. ...and 9 more sections

Figures (3)

  • Figure 1: Integrated pulse profile and frequency-phase waterfall of PSRs J1740--2805 (top) and J1740--28 (bottom). Data from all available Murriyang observing epochs were combined to enhance the signal-to-noise ratio.
  • Figure 2: Maximum rotation period $P_\mathrm{max}$ for two different distances as a function of radio spectral index for our 6 MSP candidates detected by Chandra and the VLA, and observed in this work by Murriyand and/or the GBT.
  • Figure 3: The naturally weighted S-band radio image obtained by the VLA. The image has an rms of 100$\mu$Jy/beam. The cross marks the position of MSP J1740-2805. The white ellipse in the lower left corner shows the synthesized beam shape, representing the image resolution. The color bar on the right relates the color scale to the intensity in Jy/beam.