Search Publications
Cygnus X-3 revealed as a Galactic ultraluminous X-ray source by IXPE
Ingram, Adam; Kaaret, Philip; Wu, Kinwah +127 more
The accretion of matter by compact objects can be inhibited by radiation pressure if the luminosity exceeds a critical value known as the Eddington limit. The discovery of ultraluminous X-ray sources has shown that accretion can proceed even when the apparent luminosity considerably exceeds this limit. A high apparent luminosity might be produced …
Discovery of a variable energy-dependent X-ray polarization in the accreting neutron star GX 5−1
Kaaret, Philip; Wu, Kinwah; Steiner, James F. +116 more
We report on the coordinated observations of the neutron star low-mass X-ray binary (NS-LMXB) GX 5−1 in X-rays (IXPE, NICER, NuSTAR, and INTEGRAL), optical (REM and LCO), near-infrared (REM), mid-infrared (VLT VISIR), and radio (ATCA). This Z-source was observed by IXPE twice in March-April 2023 (Obs. 1 and 2). In the radio band the source was det…
A magnetar giant flare in the nearby starburst galaxy M82
Thuillot, William; Mereghetti, Sandro; Esposito, Paolo +32 more
Magnetar giant flares are rare explosive events releasing up to 1047 erg in gamma rays in less than 1 second from young neutron stars with magnetic fields up to 1015−16 G (refs. 1,2). Only three such flares have been seen from magnetars in our Galaxy3,4 and in the Large Magellanic Cloud5 in ro…
GRB 180128A: A second magnetar giant flare candidate from the Sculptor Galaxy
Andreoni, Igor; Frederiks, Dmitry D.; Svinkin, Dmitry S. +14 more
Magnetars are slowly rotating neutron stars that possess the strongest magnetic fields known in the cosmos (1014 − 1015 G). They display a range of transient high-energy electromagnetic activity. The brightest and most energetic of these events are the gamma-ray bursts (GRBs) known as magnetar giant flares (MGFs), with isotro…
Astrophysical constraints on decaying dark gravitons
Obied, Georges; Law-Smith, Jamie A. P.; Prabhu, Anirudh +1 more
In the dark dimension scenario, which predicts an extra dimension of micron scale, dark gravitons (KK modes) are a natural dark matter candidate. In this paper, we study observable features of this model. In particular, their decay to standard matter fields can distort the CMB and impact other astrophysical signals. Using this we place bounds on t…
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…
Freeze-in production of sterile neutrino dark matter in a gauged U(1)‧ model with inverse seesaw
Poddar, Tanmay Kumar; Das, Arindam; Goswami, Srubabati +1 more
We consider a general, anomaly free U(1)‧ extension of the Standard Model (SM) where the neutrino mass is generated at the tree level via the inverse seesaw mechanism. The model contains three right handed neutrinos, three additional singlet fermions, one extra complex scalar and a neutral gauge boson (Z‧). Instead of resorting to a specific U(1) …
21cm signal sensitivity to dark matter decay
Qin, Y.; Mesinger, A.; Facchinetti, G. +1 more
The redshifted 21cm signal from the Cosmic Dawn is expected to provide unprecedented insights into early Universe astrophysics and cosmology. Here we explore how dark matter can heat the intergalactic medium before the first galaxies, leaving a distinctive imprint in the 21cm power spectrum. We provide the first dedicated Fisher matrix forecasts o…
Multimessenger search for electrophilic feebly interacting particles from supernovae
Carenza, Pierluca; Balaji, Shyam; Luque, Pedro De la Torre
We study MeV-scale electrophilic feebly interacting particles (FIPs), that may be abundantly produced in supernova explosions, escape the star and decay into electrons and positrons. This exotic injection of leptons in the Milky Way leaves an imprint in both photon and cosmic ray fluxes. Specifically, positrons lose energy and annihilate almost at…
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…