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Exploring the nature of Galactic unassociated sources detected by the Fermi-LAT
F. Acero, A. Acharyya, A. Adelfio +120
We investigate the nature of the unassociated sources detected by the Fermi-LAT close (|b|<10°) to the Galactic plane, representing 16% of all sources in the 4FGL-DR4 catalog. The…
Gamma-ray signature of superluminous supernovae: Fermi-LAT GeV detection of SN 2017egm and evidence of a central engine
F. Acero, A. Acharyya, A. Adelfio +116
Superluminous supernovae (SLSNe) are a rare class of transients with peak luminosities 10-100 times greater than those of standard core-collapse supernovae (SNe). The mechanisms po…
Magnetic-field Order in the Southwestern Rim of RCW 86 Constrained Using X-Ray Polarimetry
Stefano Silvestri, Dmitry Prokhorov, Jacco Vink +97
RCW 86 is a supernova remnant whose origin has recently been linked to an off-center explosion within a cavity created by its progenitor star. In the southwestern region, the forwa…
Satellite-borne -ray astrophysics from coherent interactions in oriented crystals
Pietro Monti-Guarnieri, Gianfranco Paternò, Alexei Sytov +20
High-density and high-Z crystals are key elements of most space-borne -ray telescopes operating at gigaelectronvolt energies (such as Fermi-LAT). The lattice structure is usuall…
Super-Eddington Accretion Geometry: a Remarkable Stability of the Hidden Ultraluminous X-Ray Source Cygnus X-3
Romana Mikušincová, Alexandra Veledina, Fabio Muleri +112
We report on the average and orbital phase-resolved polarization of Cyg X-3 in the hard state during the 2023 Imaging X-ray Polarimetry Explorer (IXPE) observational campaign. We f…
Polarization of reflected X-ray emission from the Sgr A molecular complex: multiple flares, multiple sources?
Ildar Khabibullin, Eugene Churazov, Riccardo Ferrazzoli +100
The extended X-ray emission observed in the direction of several molecular clouds in the central molecular zone of our Galaxy exhibits spectral and temporal properties consistent w…
X-ray Polarization Detection of the Pulsar Wind Nebula in G21.5-0.9 with IXPE
Niccolò Di Lalla, Nicola Omodei, Niccolò Bucciantini +98
We present the X-ray polarization observation of G21.5-0.9, a young Galactic supernova remnant (SNR), conducted with the Imaging X-ray Polarimetry Explorer (IXPE) in October 2023,…
IXPE Observations of the Blazar Mrk 501 in 2022: A Multiwavelength View
L. Lisalda, E. Gau, H. Krawczynski +157
The blazar Markarian 501 (Mrk 501) was observed on three occasions over a 4-month period between 2022 March and 2022 July with the Imaging X-ray Polarimetry Explorer (IXPE). In thi…
A Systematic Search for MeV-GeV Pulsar Wind Nebulae without Gamma-ray Detected Pulsars
Jordan Eagle, Daniel Castro, Wei Zhang +3
An increasing number of pulsar wind nebulae (PWNe) are being identified in the TeV band by ground-based Imaging Air Cherenkov Telescopes such that they constitute the dominant sour…
High optical to X-ray polarization ratio reveals Compton scattering in BL Lacertae's jet
Ivan Agudo, Ioannis Liodakis, Jorge Otero-Santos +147
Blazars, supermassive black hole systems (SMBHs) with highly relativistic jets aligned with the line of sight, are the most powerful long-lived emitters of electromagnetic emission…
Puzzling Variation of Gamma Rays from the Sun over the Solar Cycle Revealed with Fermi-LAT
A. Acharyya, A. Adelfio, M. Ajello +100
The steady-state gamma-ray emission from the Sun is thought to consist of two emission components due to interactions with Galactic cosmic rays: (1) a hadronic disk component, and…
X-ray Polarization of the High-Synchrotron-Peak BL Lacertae Object 1ES 1959+650 during Intermediate and High X-ray Flux States
Luigi Pacciani, Dawoon E. Kim, Riccardo Middei +97
We report the Imaging X-ray Polarimetry Explorer (IXPE) polarimetric and simultaneous multiwavelength observations of the high-energy-peaked BL Lacertae (HBL) object 1ES 1959+650,…
Fermi detection of gamma-ray Emission from the Hot Coronae of Radio-quiet Active Galactic Nuclei
Jun-Rong Liu, Jian-Min Wang, Fermi-LAT Collaboration
Relativistic jets around supermassive black holes (SMBHs) are well-known powerful -ray emitters. In absence of the jets in radio-quiet active galactic nuclei (AGNs), how the SMB…
Characterizing Candidate Blazar Counterparts of the Ultra-High-Energy Event KM3-230213A
KM3NeT Collaboration, MessMapp Group, LAT Collaboration +13
High-energy astrophysical neutrinos serve as crucial messengers for understanding hadronic acceleration processes and identifying the origins of cosmic rays, with blazars among the…
The AGILE space mission: an Italian success story and its legacy for future space astronomy
Carlotta Pittori, Marco Tavani, Andrea Argan +10
AGILE (Astrorivelatore Gamma ad Immagini LEggero) has been a unique and hugely successful mission of Italian Space Agency (ASI), built and operated with the programmatic and techni…
Periodic Gamma-ray Modulation of the blazar PG 1553+113 Confirmed by Fermi-LAT and Multi-wavelength Observations
S. Abdollahi, L. Baldini, G. Barbiellini +98
A 2.1-year periodic oscillation of the gamma-ray flux from the blazar PG 1553+113 has previously been tentatively identified in almost 7 year of data from the Fermi Large Area Tele…
Search for Extended GeV Sources in the Inner Galactic Plane
S. Abdollahi, F. Acero, A. Acharyya +108
The recent detection of extended -ray emission around middle-aged pulsars is interpreted as inverse-Compton scattering of ambient photons by electron-positron pairs escaping the…
IXPE Observation of the Low-Synchrotron Peaked Blazar S4 0954+65 During An Optical-X-ray Flare
Pouya M. Kouch, Ioannis Liodakis, Francesco Fenu +134
The X-ray polarization observations made possible with the Imaging X-ray Polarimetry Explorer (IXPE) offer new ways of probing high-energy emission processes in astrophysical jets…
Evidence for a shock-compressed magnetic field in the northwestern rim of Vela Jr. from X-ray polarimetry
Dmitry A. Prokhorov, Yi-Jung Yang, Riccardo Ferrazzoli +97
Synchrotron X-ray emission has been detected from nearly a dozen young supernova remnants (SNRs). X-rays of synchrotron origin exhibit linear polarization in a regular, non-randoml…
A Two-Week Monitoring Campaign on Mrk 421
W. Peter Maksym, Ioannis Liodakis, M. Lynne Saade +153
X-ray polarization is a unique new probe of the particle acceleration in astrophysical jets made possible through the Imaging X-ray Polarimetry Explorer. Here we report on the firs…
GRB 221009A: the B.O.A.T Burst that Shines in Gamma Rays
M. Axelsson, M. Ajello, M. Arimoto +151
We present a complete analysis of Fermi Large Area Telescope (LAT) data of GRB 221009A, the brightest Gamma-Ray Burst (GRB) ever detected. The burst emission above 30 MeV detected…
Analysis of Crab X-ray Polarization using Deeper IXPE Observations
Josephine Wong, Tsunefumi Mizuno, Niccoló Bucciantini +98
We present Crab X-ray polarization measurements using IXPE data with a total exposure of 300ks, three times more than the initial 2022 discovery paper. Polarization is detected in…
X-ray and multiwavelength polarization of Mrk 501 from 2022 to 2023
Chien-Ting J. Chen, Ioannis Liodakis, Riccardo Middei +143
We present multiwavelength polarization measurements of the luminous blazar Mrk~501 over a 14-month period. The 2--8 keV X-ray polarization was measured with the Imaging X-ray Pola…
An IXPE-Led X-ray Spectro-Polarimetric Campaign on the Soft State of Cygnus X-1: X-ray Polarimetric Evidence for Strong Gravitational Lensing
James F. Steiner, Edward Nathan, Kun Hu +134
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 multiwav…