期刊
ASTROPHYSICAL JOURNAL
卷 778, 期 2, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/778/2/106
关键词
gamma rays: stars; globular clusters: individual (M28); pulsars: individual (B1821-24)
资金
- NSERC Discovery Grant
- Canada Foundation for Innovation
- NASA DPR [S-15633-Y]
- Office Of Internatl Science &Engineering
- Office Of The Director [0968296] Funding Source: National Science Foundation
- Science and Technology Facilities Council [ST/J001562/1] Funding Source: researchfish
- STFC [ST/J001562/1] Funding Source: UKRI
We report a 5.4 sigma detection of pulsed gamma rays from PSR B1821-24 in the globular cluster M28 using similar to 44 months of Fermi Large Area Telescope (LAT) data that have been reprocessed with improved instrument calibration constants. We constructed a phase-coherent ephemeris, with post-fit residual rms of 3 mu s, using radio data spanning similar to 23.2 yr, enabling measurements of the multi-wavelength light-curve properties of PSR B1821-24 at the milliperiod level. We fold RXTE observations of PSR B1821-24 from 1996 to 2007 and discuss implications on the emission zones. The gamma-ray light curve consists of two peaks separated by 0.41 +/- 0.02 in phase, with the first gamma-ray peak lagging behind the first radio peak by 0.05 +/- 0.02 in phase, consistent with the phase of giant radio pulses. We observe significant emission in the off-peak interval of PSR B1821-24 with a best-fit LAT position inconsistent with the core of M28. We do not detect significant gamma-ray pulsations at the spin or orbital periods from any other known pulsar in M28, and we place limits on the number of energetic pulsars in the cluster. The derived gamma-ray efficiency, similar to 2%, is typical of other gamma-ray pulsars with comparable spin-down power, suggesting that the measured spin-down rate (2.2 x 10(36) erg s(-1)) is not appreciably distorted by acceleration in the cluster potential. This confirms PSR B1821-24 as the second very energetic millisecond pulsar in a globular cluster and raises the question of whether these represent a separate class of objects that only form in regions of very high stellar density.
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