First detection of X-ray polarization from the accreting neutron star 4U 1820-303

This paper reports the first detection of polarization in the X-rays for atoll-source 4U 1820-303, obtained with the Imaging X-ray Polarimetry Explorer (IXPE) at 99.999% confidence level (CL). Simultaneous polarimetric measurements were also performed in the radio with the Australia Telescope Compact Array (ATCA). The IXPE observations of 4U 1820-303 were coordinated with Swift-XRT, NICER, and NuSTAR aiming to obtain an accurate X-ray spectral model covering a broad energy interval. The source shows a significant polarization above 4 keV, with a polarization degree of 2.0(0.5)% and a polarization angle of -55(7) deg in the 4-7 keV energy range, and a polarization degree of 10(2)% and a polarization angle of -67(7) deg in the 7-8 keV energy bin. This polarization also shows a clear energy trend with polarization degree increasing with energy and a hint for a position-angle change of about 90 deg at 96% CL around 4 keV. The spectro-polarimetric fit indicates that the accretion disk is polarized orthogonally to the hard spectral component, which is presumably produced in the boundary/spreading layer. We do not detect linear polarization from the radio counterpart, with a 99.97% upper limit of 50% at 7.25 GHz

The accretion/ejection link in the neutron star X-ray binary 4U 1820-30 I: a boundary layer-jet coupling?

The accretion flow/jet correlation in neutron star (NS) low-mass X-ray binaries (LMXBs) is far less understood when compared to black hole (BH) LMXBs. In this paper we will present the results of a dense multiwavelength observational campaign on the NS LMXB 4U 1820-30, including X-ray (NICER, NuSTAR, and AstroSat) and quasi-simultaneous radio (ATCA) observations in 2022. 4U 1820-30 shows a peculiar 170 d super-orbital accretion modulation, during which the system evolves between ‘modes’ of high and low X-ray flux. During our monitoring, the source did not show any transition to a full hard state. X-ray spectra were well described using a disc blackbody, a Comptonization spectrum along with a Fe K emission line at ∼6.6 keV. Our results show that the observed X-ray flux modulation is almost entirely produced by changes in the size of the region providing seed photons for the Comptonization spectrum. This region is large (∼15 km) in the high mode and likely coincides with the whole boundary layer, while it shrinks significantly (≲10 km) in low mode. The electron temperature of the corona and the observed rms variability in the hard X-rays also exhibit a slight increase in low mode. As the source moves from high to low mode, the radio emission due to the jet becomes ∼5 fainter. These radio changes appear not to be strongly connected to the hard-to-soft transitions as in BH systems, while they seem to be connected mostly to variations observed in the boundary layer.AM, FCZ, and NR are supported by the H2020 ERC Consolidator Grant ‘MAGNESIA’ under grant agreement number 817661 (PI: Rea) and National Spanish grant PGC2018-095512-BI00. This work was also partially supported by the programme Unidad de Excelencia Maria de Maeztu CEX2020-001058-M, and by the PHAROS COST Action (No. CA16214). MDS and TDR acknowledge support from the INAF grant ‘ACE-BANANA’. AB is grateful to the Royal Society, United Kingdom. She is supported by an INSPIRE Faculty grant (DST/INSPIRE/04/2018/001265) by the Department of Science and Technology, Govt. of India. AB also acknowledges the financial support of ISRO under the AstroSat Archival Data Utilization Programme (No. DS-2B-13013(2)/4/2019-Sec. 2). TDS and AS acknowledge financial support from PRIN-INAF 2019 with the project ‘Probing the geometry of accretion: from theory to observations’ (PI: Belloni). FCZ is supported by a Ramón y Cajal fellowship (grant agreement RYC2021-030888-I). EA acknowledges funding from the Italian Space Agency, contract ASI/INAF n. I/004/11/4. FC acknowledges support from the Royal Society through the Newton International Fellowship programme (NIF/R1/211296). JvdE acknowledges a Warwick Astrophysics prize post-doctoral fellowship made possible thanks to a generous philanthropic donation, and was supported by a Lee Hysan Junior Research Fellowship awarded by St. Hilda’s College, Oxford, during part of this work. We thank Jamie Stevens and ATCA staff for making the radio observations possible. ATCA is part of the Australia Telescope National Facility (https://ror.org/05qajvd42) which is funded by the Australian Government for operation as a National Facility managed by CSIRO. We acknowledge the Wiradjuri people as the Traditional Owners of the ATCA observatory site. NICER is a 0.2–12 keV X-ray telescope operating on the International Space Station, funded by NASA. NuSTAR is a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory and funded by NASA. This publication uses the data from the AstroSat mission of the Indian Space Research Organization (ISRO), archived at the Indian Space Science Data Centre (ISSDC).With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2020-001058-M).Peer reviewe

The HERMES-technologic and scientific pathfinder

HERMES-TP/SP (High Energy Rapid Modular Ensemble of Satellites Technologic and Scientific Pathfinder) is a constellation of six 3U nano-satellites hosting simple but innovative X-ray detectors, characterized by a large energy band and excellent temporal resolution, and thus optimized for the monitoring of Cosmic High Energy transients such as Gamma Ray Bursts and the electromagnetic counterparts of Gravitational Wave Events, and for the determination of their positions. The projects are funded by the Italian Ministry of University and Research and by the Italian Space Agency, and by the European Union's Horizon 2020 Research and Innovation Program under Grant Agreement No. 821896. HERMES-TP/SP is an in-orbit demonstration, that should be tested starting from 2022. It is intrinsically a modular experiment that can be naturally expanded to provide a global, sensitive all sky monitor for high-energy transients

The scientific payload on-board the HERMES-TP and HERMES-SP CubeSat missions

none103siHERMES (High Energy Rapid Modular Ensemble of Satellites) Technological and Scientific pathfinder is a space borne mission based on a LEO constellation of nano-satellites. The 3U CubeSat buses host new miniaturized detectors to probe the temporal emission of bright high-energy transients such as Gamma-Ray Bursts (GRBs). Fast transient localization, in a field of view of several steradians and with arcmin-level accuracy, is gained by comparing time delays among the same event detection epochs occurred on at least 3 nano-satellites. With a launch date in 2022, HERMES transient monitoring represents a keystone capability to complement the next generation of gravitational wave experiments. In this paper we will illustrate the HERMES payload design, highlighting the technical solutions adopted to allow a wide-energy-band and sensitive X-ray and gamma-ray detector to be accommodated in a CubeSat 1U volume together with its complete control electronics and data handling system.noneEvangelista, Yuri; Fiore, Fabrizio; Fuschino, Fabio; Campana, Riccardo; Ceraudo, Francesco; Demenev, Evgeny; Guzman, Alejandro; Labanti, Claudio; La Rosa, Giovanni; Fiorini, Mauro; Gandola, Massimo; Grassi, Marco; Mele, Filippo; Morgante, Gianluca; Nogara, Paolo; Piazzolla, Raffaele; Pliego Caballero, Samuel; Rashevskaya, Irina; Russo, Francesco; Sciarrone, Giulia; Sottile, Giuseppe; Milankovich, Dorottya; Pál, András; Ambrosino, Filippo; Auricchio, Natalia; Barbera, Marco; Bellutti, Pierluigi; Bertuccio, Giuseppe; Borghi, Giacomo; Cao, Jiewei; Chen, Tianxiang; Dilillo, Giuseppe; Feroci, Marco; Ficorella, Francesco; Lo Cicero, Ugo; Malcovati, Piero; Morbidini, Alfredo; Pauletta, Giovanni; Picciotto, Antonino; Rachevski, Alexandre; Santangelo, Andrea; Tenzer, Chistoph; Vacchi, Andrea; Wang, Lingjun; Xu, Yupeng; Zampa, Gianluigi; Zampa, Nicola; Zorzi, Nicola; Burderi, Luciano; Lavagna, Michèle; Bertacin, Roberto; Lunghi, Paolo; Monge, Angel; Negri, Barbara; Pirrotta, Simone; Puccetti, Simonetta; Sanna, Andrea; Amarilli, Fabrizio; Amelino-Camelia, Giovanni; Bechini, Michele; Citossi, Marco; Colagrossi, Andrea; Curzel, Serena; Della Casa, Giovanni; Cinelli, Marco; Del Santo, Melania; Di Salvo, Tiziana; Feruglio, Chiara; Ferrandi, Fabrizio; Fiorito, Michele; Gacnik, Dejan; Galgóczi, Gabor; Gambino, Angelo Francesco; Ghirlanda, Giancarlo; Gomboc, Andreja; Karlica, Mile; Efremov, Pavel; Kostic, Uros; Clerici, Aurora; Lopez Fernandez, Borja; Maselli, Alessandro; Nava, Lara; Ohno, Masanori; Ottolina, Daniele; Pasquale, Andrea; Perri, Matteo; Piccinin, Margherita; Prinetto, Jacopo; Riggio, Alessandro; Ripa, Jakub; Papitto, Alessandro; Piranomonte, Silvia; Scala, Francesca; Selcan, David; Silvestrini, Stefano; Rotovnik, Tomaz; Virgilli, Enrico; Troisi, Ivan; Werner, Norbert; Zanotti, Giovanni; Anitra, Alessio; Manca, Arianna; Clerici, AuroraEvangelista, Yuri; Fiore, Fabrizio; Fuschino, Fabio; Campana, Riccardo; Ceraudo, Francesco; Demenev, Evgeny; Guzman, Alejandro; Labanti, Claudio; La Rosa, Giovanni; Fiorini, Mauro; Gandola, Massimo; Grassi, Marco; Mele, Filippo; Morgante, Gianluca; Nogara, Paolo; Piazzolla, Raffaele; Pliego Caballero, Samuel; Rashevskaya, Irina; Russo, Francesco; Sciarrone, Giulia; Sottile, Giuseppe; Milankovich, Dorottya; Pál, András; Ambrosino, Filippo; Auricchio, Natalia; Barbera, Marco; Bellutti, Pierluigi; Bertuccio, Giuseppe; Borghi, Giacomo; Cao, Jiewei; Chen, Tianxiang; Dilillo, Giuseppe; Feroci, Marco; Ficorella, Francesco; Lo Cicero, Ugo; Malcovati, Piero; Morbidini, Alfredo; Pauletta, Giovanni; Picciotto, Antonino; Rachevski, Alexandre; Santangelo, Andrea; Tenzer, Chistoph; Vacchi, Andrea; Wang, Lingjun; Xu, Yupeng; Zampa, Gianluigi; Zampa, Nicola; Zorzi, Nicola; Burderi, Luciano; Lavagna, Michèle; Bertacin, Roberto; Lunghi, Paolo; Monge, Angel; Negri, Barbara; Pirrotta, Simone; Puccetti, Simonetta; Sanna, Andrea; Amarilli, Fabrizio; Amelino-Camelia, Giovanni; Bechini, Michele; Citossi, Marco; Colagrossi, Andrea; Curzel, Serena; Della Casa, Giovanni; Cinelli, Marco; Del Santo, Melania; Di Salvo, Tiziana; Feruglio, Chiara; Ferrandi, Fabrizio; Fiorito, Michele; Gacnik, Dejan; Galgóczi, Gabor; Gambino, Angelo Francesco; Ghirlanda, Giancarlo; Gomboc, Andreja; Karlica, Mile; Efremov, Pavel; Kostic, Uros; Clerici, Aurora; Lopez Fernandez, Borja; Maselli, Alessandro; Nava, Lara; Ohno, Masanori; Ottolina, Daniele; Pasquale, Andrea; Perri, Matteo; Piccinin, Margherita; Prinetto, Jacopo; Riggio, Alessandro; Ripa, Jakub; Papitto, Alessandro; Piranomonte, Silvia; Scala, Francesca; Selcan, David; Silvestrini, Stefano; Rotovnik, Tomaz; Virgilli, Enrico; Troisi, Ivan; Werner, Norbert; Zanotti, Giovanni; Anitra, Alessio; Manca, Arianna; Clerici, Auror

Timing techniques applied to distributed modular high-energy astronomy: the H.E.R.M.E.S. project

The association of GW170817 with GRB170817A proved that electromagnetic counterparts of gravitational wave events are the key to deeply understand the physics of NS-NS merges. Upgrades of the existing GW antennas and the construction of new ones will allow to increase sensitivity down to several hundred Mpc vastly increasing the number of possible electromagnetic counterparts. Monitoring of the hard X-ray/soft gamma-ray sky with good localisation capabilities will help to effectively tackle this problem allowing to fully exploit multi-messenger astronomy. However, building a high energy all-sky monitor with large collective area might be particularly challenging due to the need to place the detectors onboard satellites of limited size. Distributed astronomy is a simple and cheap solution to overcome this difficulty. Here we discuss in detail dedicated timing techniques that allow to precisely locate an astronomical event in the sky taking advantage of the spatial distribution of a swarm of detectors orbiting Earth

GrailQuest and HERMES: hunting for gravitational wave electromagnetic counterparts and probing space-time quantum foam

106nonenoneBurderi, Luciano; Di Salvo, Tiziana; Riggio, Alessandro; Gambino, Angelo Francesco; Sanna, Andrea; Fiore, Fabrizio; Amarilli, Fabrizio; Amati, Lorenzo; Ambrosino, Filippo; Amelino-Camelia, Giovanni; Anitra, Alessio; Barbera, Marco; Bechini, Michele; Bellutti, Paolo; Bertaccin, Roberto; Bertuccio, Giuseppe; Campana, Riccardo; Cao, Jiewei; Capozziello, Salvatore; Ceraudo, Francesco; Chen, Tianxiang; Cinelli, Marco; Citossi, Marco; Clerici, Aurora; Colagrossi, Andrea; Costa, Enrico; Curzel, Serena; De Laurentis, Mariafelicia; Della Casa, Giovanni; Della Valle, Massimo; Demenev, Evgeny; Del Santo, Melania; Dilillo, Giuseppe; Efremov, Pavel; Evangelista, Yuri; Feroci, Marco; Ferruglio, Chiara; Ferrandi, Fabrizio; Fiorini, Mauro; Fiorito, Michele; Frontera, Filippo; Fuschino, Fabio; Gacnik, Dejan; Galgoczi, Gabor; Gao, Na; Gandola, Massimo; Ghirlanda, Giancarlo; Gamboc, Andreja; Grassi, Marco; Guidorzi, Cristiano; Guzman, Alejandro; Iaria, Rosario; Karlica, Mile; Kostic, Uros; Labanti, Claudio; La Rosa, Giovanni; Lo Cicero, Ugo; Lopez Fernandez, Borja; Lunghi, Paolo; Malcovati, Piero; Maselli, Alessandro; Manca, Arianna; Mele, Filippo; Milankovich, Dorottya; Monge, Angel; Morgante, Gianluca; Nava, Lara; Negri, Barbara; Nogara, Paolo; Ohno, Masanori; Ottolina, Daniele; Pasquale, Andrea; Pal, Andras; Perri, Matteo; Piccinin, Margherita; Piazzolla, Raffaele; Pirrotta, Simone; Pliego-Caballero, Samuel; Prinetto, Jacopo; Pucacco, Giuseppe; Puccetti, Simonetta; Rapisarda, Massimo; Rashevskaya, Irina; Rashevsky, Alexander; Ripa, Jakub; Russo, Francesco; Papitto, Alessandro; Piranomonte, Silvia; Santangelo, Andrea; Scala, Francesca; Sciarrone, Giulia; Selcan, David; Silvestrini, Stefano; Sottile, Giuseppe; Rotovnik, Tomaz; Tenzer, Christoph; Troisi, Ivan; Vacchi, Andrea; Virgilli, Enrico; Werner, Norbert; Wang, Lingjun; Xu, Yupeng; Zampa, Gianluigi; Zampa, Nicola; Zane, Silvia; Zanotti, GiovanniBurderi, Luciano; Di Salvo, Tiziana; Riggio, Alessandro; Gambino, Angelo Francesco; Sanna, Andrea; Fiore, Fabrizio; Amarilli, Fabrizio; Amati, Lorenzo; Ambrosino, Filippo; Amelino-Camelia, Giovanni; Anitra, Alessio; Barbera, Marco; Bechini, Michele; Bellutti, Paolo; Bertaccin, Roberto; Bertuccio, Giuseppe; Campana, Riccardo; Cao, Jiewei; Capozziello, Salvatore; Ceraudo, Francesco; Chen, Tianxiang; Cinelli, Marco; Citossi, Marco; Clerici, Aurora; Colagrossi, Andrea; Costa, Enrico; Curzel, Serena; De Laurentis, Mariafelicia; Della Casa, Giovanni; Della Valle, Massimo; Demenev, Evgeny; Del Santo, Melania; Dilillo, Giuseppe; Efremov, Pavel; Evangelista, Yuri; Feroci, Marco; Ferruglio, Chiara; Ferrandi, Fabrizio; Fiorini, Mauro; Fiorito, Michele; Frontera, Filippo; Fuschino, Fabio; Gacnik, Dejan; Galgoczi, Gabor; Gao, Na; Gandola, Massimo; Ghirlanda, Giancarlo; Gamboc, Andreja; Grassi, Marco; Guidorzi, Cristiano; Guzman, Alejandro; Iaria, Rosario; Karlica, Mile; Kostic, Uros; Labanti, Claudio; La Rosa, Giovanni; Lo Cicero, Ugo; Lopez Fernandez, Borja; Lunghi, Paolo; Malcovati, Piero; Maselli, Alessandro; Manca, Arianna; Mele, Filippo; Milankovich, Dorottya; Monge, Angel; Morgante, Gianluca; Nava, Lara; Negri, Barbara; Nogara, Paolo; Ohno, Masanori; Ottolina, Daniele; Pasquale, Andrea; Pal, Andras; Perri, Matteo; Piccinin, Margherita; Piazzolla, Raffaele; Pirrotta, Simone; Pliego-Caballero, Samuel; Prinetto, Jacopo; Pucacco, Giuseppe; Puccetti, Simonetta; Rapisarda, Massimo; Rashevskaya, Irina; Rashevsky, Alexander; Ripa, Jakub; Russo, Francesco; Papitto, Alessandro; Piranomonte, Silvia; Santangelo, Andrea; Scala, Francesca; Sciarrone, Giulia; Selcan, David; Silvestrini, Stefano; Sottile, Giuseppe; Rotovnik, Tomaz; Tenzer, Christoph; Troisi, Ivan; Vacchi, Andrea; Virgilli, Enrico; Werner, Norbert; Wang, Lingjun; Xu, Yupeng; Zampa, Gianluigi; Zampa, Nicola; Zane, Silvia; Zanotti, Giovann