Search Publications
New 511 keV Line Data Provide Strongest sub-GeV Dark Matter Constraints
Silk, Joseph; De la Torre Luque, Pedro; Balaji, Shyam
We explore the 511 keV emission associated with sub-GeV dark matter (DM) particles that can produce electron–positron pairs and form positronium after thermalizing. We use ∼16 yr of data from the Spectrometer on INTEGRAL to constrain DM properties, including the full positron propagation and losses, and the suppression of free electron density awa…
An IXPE-led X-Ray Spectropolarimetric Campaign on the Soft State of Cygnus X-1: X-Ray Polarimetric Evidence for Strong Gravitational Lensing
Ingram, Adam; Kaaret, Philip; Wu, Kinwah +134 more
We present the first X-ray spectropolarimetric results for Cygnus X-1 in its soft state from a campaign of five IXPE observations conducted during 2023 May–June. Companion multiwavelength data during the campaign are likewise shown. The 2–8 keV X-rays exhibit a net polarization degree PD = 1.99% ± 0.13% (68% confidence). The polarization signal is…
Primordial Black Holes in Scalar Field Inflation Coupled to the Gauss–Bonnet Term with Fractional Power-law Potentials
Ashrafzadeh, Ali; Karami, Kayoomars
In this study, we investigate the formation of primordial black holes (PBHs) in a scalar field inflationary model coupled to the Gauss–Bonnet term with fractional power-law potentials. The coupling function enhances the curvature perturbations, then results in the generation of PBHs and detectable secondary gravitational waves (GWs). We identify t…
NICER Discovery that SRGA J144459.2–604207 Is an Accreting Millisecond X-Ray Pulsar
Chakrabarty, Deepto; Ray, Paul S.; Wolff, Michael T. +17 more
We present the discovery, with the Neutron Star Interior Composition Explorer (NICER), that SRGA J144459.2‑604207 is a 447.9 Hz accreting millisecond X-ray pulsar (AMXP), which underwent a 4 week long outburst starting on 2024 February 15. The AMXP resides in a 5.22 hr binary, orbiting a low-mass companion donor with M d > 0.1 M
High Hard X-Ray Polarization in Cygnus X-1 Confined to the Intermediate Hard State: Evidence for a Variable Jet Component
Rao, A. R.; Bhalerao, Varun; Mithun, N. P. S. +7 more
Cygnus X-1, the well-known accreting black hole system, exhibits several observational features hinting at an intricate interplay between the accretion disk, its atmosphere known as the corona, and the putative relativistic jet. It has been extensively studied using all available observational methods, including using the newly available technique…
What Is the Black Hole Spin in Cyg X-1?
Zdziarski, Andrzej A.; Szanecki, Michał; Dewangan, Gulab +6 more
We perform a detailed study of the black hole spin of Cyg X-1, using accurate broadband X-ray data obtained in the soft spectral state by simultaneous NICER and NuSTAR observations, supplemented at high energies by INTEGRAL data. We use the relativistic disk model kerrbb together with different models of the Comptonization high-energy tail and the…
The Cause of the Difference in the Propagation Distances between Compact and Transient Jets in Black Hole X-Ray Binaries
Zdziarski, Andrzej A.; Heinz, Sebastian
Accreting black hole binaries change their properties during evolution, passing through two main luminous states, dominated by either hard or soft X-rays. In the hard state, steady compact jets emitting multiwavelength radiation are present. Those jets are usually observed in radio, and when resolved, their extent is ≲1015 cm. Then, dur…
An X-Ray and Radio View of the 2022 Reactivation of the Magnetar SGR J1935+2154
Campana, S.; Tiengo, A.; Götz, D. +19 more
Recently, the Galactic magnetar SGR J1935+2154 has garnered attention due to its emission of an extremely luminous radio burst, reminiscent of fast radio bursts (FRBs). SGR J1935+2154 is one of the most active magnetars, displaying flaring events nearly every year, including outbursts as well as short and intermediate bursts. Here, we present our …
GRB 231115A: A Nearby Magnetar Giant Flare or a Cosmic Short Gamma-Ray Burst?
Zhou, Hao; Jin, Zhi-Ping; Wang, Yun +3 more
There are two classes of gamma-ray transients with a duration shorter than 2 s. One consists of cosmic short gamma-ray bursts (GRBs) taking place in the deep Universe via the neutron star mergers, and the other is the magnetar giant flares (GFs) with energies of ∼1044 ‑ 1046 erg from "nearby" galaxies. Though the magnetar GFs…
Constraints on Neutron Star Structure from the Clocked X-Ray Burster 1RXS J180408.9-342058
Nagataki, S.; Hashimoto, M.; Dohi, A. +3 more
Type I X-ray bursts are rapid-brightening transient phenomena on the surfaces of accreting neutron stars (NSs). Some X-ray bursts, called clocked bursters, exhibit regular behavior with similar light-curve profiles in their burst sequences. The periodic nature of clocked bursters has the advantage of constraining X-ray binary parameters and physic…