Detection of 16 gamma-ray pulsars through blind frequency searches using the Fermi LAT

Bridging the μHz Gap in the Gravitational-Wave Landscape with Binary Resonances

Gravitational-wave (GW) astronomy is transforming our understanding of the Universe by probing phenomena invisible to electromagnetic observatories. A comprehensive exploration of the GW frequency spectrum is essential to fully harness this potential. Remarkably, current methods have left the μHz frequency band almost untouched. Here, we show that this μHz gap can be filled by searching for deviations in the orbits of binary systems caused by their resonant interaction with GWs. In particular, we show that laser ranging of the Moon and artificial satellites around the Earth, as well as timing of binary pulsars, may discover the first GW signals in this band, or otherwise set stringent new constraints. To illustrate the discovery potential of these binary resonance searches, we consider the GW signal from a cosmological first-order phase transition, showing that our methods will probe models of the early Universe that are inaccessible to any other near-future GW mission. We also discuss how our methods can shed light on the possible GW signal detected by NANOGrav, either constraining its spectral properties or even giving an independent confirmation.

Fermi-LAT Observation of PSR B1259-63 during Its 2021 Periastron Passage

PSR B1259-63 is a γ-ray binary system, where the compact object is a pulsar. The system has an orbital period of 1236.7 days and shows peculiar γ-ray flares (in 100 MeV–300 GeV) after its periastron time. We analyzed the Fermi-LAT observation of PSR B1259-63 during its latest periastron passage, as well as its previous three periastrons. The bright GeV flares started about 60 days after the periastron epoch in 2021. This delay is larger than that around the 2017 periastron and much larger than earlier periastrons. The delay of the GeV flux peak time in each periastron passage is apparent in our results. We discussed the possible origin of this delay and made a prediction of the GeV flux peak time in next periastron passage, based on observation of the previous delays.

Proper motion, spectra, and timing of PSR J1813-1749 using Chandra and NICER

PSR J1813-1749 is one of the most energetic rotation-powered pulsars known, producing a pulsar wind nebula (PWN) and gamma-ray and TeV emission, but whose spin period is only measurable in X-ray. We present analysis of two Chandra datasets that are separated by more than ten years and recent NICER data. The long baseline of the Chandra data allows us to derive a pulsar proper motionμ R.A. = - ( 0 . ″ 067 ± 0 . ″ 010 ) yr-1 andμ decl. = - ( 0 . ″ 014 ± 0 . ″ 007 ) yr-1 and velocity v ⊥ ≈ 900-1600 km s-1 (assuming a distance d = 3 - 5 kpc), although we cannot exclude a contribution to the change in measured pulsar position due to a change in brightness structure of the PWN very near the pulsar. We model the PWN and pulsar spectra using an absorbed power law and obtain best-fit absorption N H = (13.1 ± 0.9) × 1022 cm-2, photon index Γ = 1.5 ± 0.1, and 0.3-10 keV luminosity L X ≈ 5.4 × 1034 erg s-1(d/ 5 kpc)2 for the PWN and Γ = 1.2 ± 0.1 and L X « 9.3 × 1033 erg s-1(d/ 5 kpc)2 for PSR J1813-1749. These values do not change between the 2006 and 2016 observations. We use NICER observations from 2019 to obtain a timing model of PSR J1813-1749, with spin frequency ν = 22.35 Hz and spin frequency time derivativev . = ( - 6.428 ± 0.003 ) × 10 - 11 Hz s-1. We also fit ν measurements from 2009-2012 and our 2019 value and find a long-term spin-down ratev . = ( - 6.3445 ± 0.0004 ) × 10 - 11 Hz s-1. We speculate that the difference in spin-down rates is due to glitch activity or emission mode switching.

Identification and functional characterization of Lys-trimethylation of lactate dehydrogenase A

Background: Trimethylation of histones has been extensively studied, where histone methyltransferases catalyze the transfer of methyl groups from S-adenosyl methionine. Thus far, there have been no researches on the trimethylation of non-histone proteins. The precise mechanisms by which trimethylation affects cell progress and the related protein functions remain unclear.

Purpose: The objective of this study was to identify the Lys-trimethylated proteins in kidney-derived cells and tissues, as well as to better understand the mechanisms underlying Lys-trimethylation-mediated cell metabolism.

Methods: The levels of Lys-trimethylation in kidney-derived cells and tissues were assayed by Western blotting. Additionally, high-resolution mass spectrometry was used to analyze kidney-derived cells and tissues, and the eukaryotic expression vectors that led to the mutations of lysine were constructed and transfected into HEK293T cells. The LDHA activity of HEK293T cells was detected under conditions of Lys-trimethylation inhibition, and the proliferation of HEK293T cells was measured using EdU and Western blotting analyses.

Results: The different proteins in kidney-derived cells and tissues showed different levels of Lys-trimethylation. In particular, lactate dehydrogenase A (LDHA) was Lys-trimethylated on lysine (K5). Inhibition of the Lys-trimethylation in LDHA increased the LDH activity of HEK293T cells and upregulated their proliferation.

Conclusion: We suggested that LDHA affects the metabolism and proliferation of cells via a Lys-trimethylation-mediated mechanism; Lys-trimethylation might be a potential target for therapeutic research or used as a prognostic and treatment biomarker of several diseases.

Disentangling Coalescing Neutron-Star-White-Dwarf Binaries for LISA

The prime candidate sources for the upcoming space-borne gravitational wave (GW) observatory LISA are the numerous Galactic tight binaries of white dwarfs (WDs) and neutron stars (NSs), many of which will coalesce and undergo mass transfer, leading to simultaneous emission of x rays and GWs. Here, detailed and coherent numerical stellar models are explored for the formation and evolution of these systems, including finite-temperature effects and complete calculations of mass transfer from a WD to a NS accretor. Evolutionary tracks of characteristic strain amplitude are computed, and the unique pattern of their evolution in the GW frequency-dynamical chirp mass parameter space enables a firm identification of the nature of the systems. Furthermore, it is demonstrated that a precise detection of the chirp allows determination of the NS mass to an accuracy of a few percent; with applications to constraining its equation of state, in particular for dual-line GW sources observed simultaneously at high and low frequencies.

Einstein@Home discovers a radio-quiet gamma-ray millisecond pulsar

Millisecond pulsars (MSPs) are old neutron stars that spin hundreds of times per second and appear to pulsate as their emission beams cross our line of sight. To date, radio pulsations have been detected from all rotation-powered MSPs. In an attempt to discover radio-quiet gamma-ray MSPs, we used the aggregated power from the computers of tens of thousands of volunteers participating in the Einstein@Home distributed computing project to search for pulsations from unidentified gamma-ray sources in Fermi Large Area Telescope data. This survey discovered two isolated MSPs, one of which is the only known rotation-powered MSP to remain undetected in radio observations. These gamma-ray MSPs were discovered in completely blind searches without prior constraints from other observations, raising hopes for detecting MSPs from a predicted Galactic bulge population.

Astronomy. Pulsar beams--big and bright

Recent studies of gamma-ray beams emitted from rotating neutron stars are providing a better understanding of the mechanism underlying pulsars.

Gamma-Ray Pulsars Old and New

The Fermi Gamma-ray Space Telescope is discovering neutron stars that are high-energy gamma-ray emitters.