Three new millisecond pulsars discovered in Terzan 5 globular cluster

Top panels: Averaged pulse profiles of the best detections
of Ter5aj (on the left), Ter5ak (in the middle) and Ter5al
(on the right). Bottom panel: Intensity of the signal (gray
scale) as a function of the rotational phase and time for
each MSP. Credit: Cadelano et al., 2018.

An international team of astronomers has found three new
millisecond pulsars (MSPs) in a Milky Way globular cluster
called Terzan 5. The new discovery increases the number of
identified pulsars in Terzan 5 to 37 and makes this cluster
the most efficient factory of MSPs in the galaxy known to
date. The finding is reported January 30 in a paper published
on arXiv.org.


Millisecond pulsars spin rapidly, at hundreds of times per
second. Astronomers searching for new MSPs focus their
observations on (GCs), as such gravitationally
bound collections of stars are ideal factories for the
formation of a large variety of astronomical objects, including
pulsars. So far, 146 MSPs were detected in 28 globular
clusters, but it is believed that a very large population of
several thousand millisecond pulsars is still to be uncovered.

Now, a team of scientists led by Mario Cadelano of the
University of Bologna, Italy, has replenished the list of known
MSPs in GCs by finding three new objects of this type in the
Terzan 5 globular . Residing in the bulge of the
Milky Way galaxy, Terzan 5 is most likely a heavily obscured
globular cluster. However some studies have found that it is
probably not a genuine GC, but could be a pristine remnant of a
building block of the galactic bulge. All in all, Terzan 5 is
perceived by astronomers as a prolific MSP factory as previous
observations have detected 34 such pulsars in this cluster.

Cadelano’s team has analyzed the archival observational data of
Terzan 5 obtained by the 100-m Robert C. Byrd Green Bank
Telescope (GBT) in Green Bank, West Virginia, for over five
years—between August 2010 and October 2015. As a result, they
identified three previously unknown MSPs in the inner regions
of this cluster, designated: J1748−2446aj, J1748−2446ak and
J1748−2446al.

“We report on the discovery of three new millisecond pulsars
(namely J1748−2446aj, J1748−2446ak and J1748−2446al) in the
inner regions of the dense stellar system Terzan 5. These
pulsars have been discovered thanks to a method, alternative to
the classical search routines, that exploited the large set of
archival observations of Terzan 5 acquired with the Green Bank
Telescope over 5 years (from 2010 to 2015),” the astronomers
wrote in the paper.

According to the research, J1748−2446aj, J1748−2446ak and
J1748−2446al are isolated MSPs with spin periods of 2.96, 1.89
and 5.95 milliseconds. Therefore, J1748−2446ak turns out to be
the fourth fastest MSP in Terzan 5 and the fifth fastest among
all the known pulsars in globular clusters.

Moreover, the researchers estimated the intrinsic spin-down
rates for J1748−2446aj and J1748−2446ak, which are consistent
with those typically measured for MSPs in globular clusters. In
general, the new discovery increases the number of known MSPs
in Terzan 5 to 37, which now hosts one-fourth of the entire
population detected so far in globular
clusters.

Explore further:

Pulsar jackpot reveals globular cluster’s inner structure

More information: Discovery of three new millisecond
pulsars in Terzan 5, arXiv:1801.09929 [astro-ph.HE] arxiv.org/abs/1801.09929

Abstract
We report on the discovery of three new millisecond pulsars
(namely J1748-2446aj, J1748-2446ak and J1748-2446al) in the
inner regions of the dense stellar system Terzan 5. These
pulsars have been discovered thanks to a method, alternative to
the classical search routines, that exploited the large set of
archival observations of Terzan 5 acquired with the Green Bank
Telescope over 5 years (from 2010 to 2015). This technique
allowed the analysis of stacked power spectra obtained by
combining ~206 hours of observation. J1748-2446aj has a spin
period of ~2.96 ms, J1748-2446ak of ~1.89 ms (thus it is the
fourth fastest pulsar in the cluster) and J1748-2446al of ~5.95
ms. All the three millisecond pulsars are isolated and
currently we have timing solutions only for J1748-2446aj and
J1748-2446ak. For these two systems, we evaluated the
contribution to the measured spin-down rate of the acceleration
due to the cluster potential field, thus estimating the
intrinsic spin-down rates, which are in agreement with those
typically measured for millisecond pulsars in globular
clusters. Our results increase to 37 the number of pulsars
known in Terzan 5, which now hosts 25% of the entire pulsar
population identified, so far, in globular clusters.

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