1
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Hurley-Walker N, Rea N, McSweeney SJ, Meyers BW, Lenc E, Heywood I, Hyman SD, Men YP, Clarke TE, Coti Zelati F, Price DC, Horváth C, Galvin TJ, Anderson GE, Bahramian A, Barr ED, Bhat NDR, Caleb M, Dall'Ora M, de Martino D, Giacintucci S, Morgan JS, Rajwade KM, Stappers B, Williams A. A long-period radio transient active for three decades. Nature 2023; 619:487-490. [PMID: 37468588 DOI: 10.1038/s41586-023-06202-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2023] [Accepted: 05/11/2023] [Indexed: 07/21/2023]
Abstract
Several long-period radio transients have recently been discovered, with strongly polarized coherent radio pulses appearing on timescales between tens to thousands of seconds1,2. In some cases, the radio pulses have been interpreted as coming from rotating neutron stars with extremely strong magnetic fields, known as magnetars; the origin of other, occasionally periodic and less-well-sampled radio transients is still debated3. Coherent periodic radio emission is usually explained by rotating dipolar magnetic fields and pair-production mechanisms, but such models do not easily predict radio emission from such slowly rotating neutron stars and maintain it for extended times. On the other hand, highly magnetic isolated white dwarfs would be expected to have long spin periodicities, but periodic coherent radio emission has not yet been directly detected from these sources. Here we report observations of a long-period (21 min) radio transient, which we have labelled GPM J1839-10. The pulses vary in brightness by two orders of magnitude, last between 30 and 300 s and have quasiperiodic substructure. The observations prompted a search of radio archives and we found that the source has been repeating since at least 1988. The archival data enabled constraint of the period derivative to <3.6 × 10-13 s s-1, which is at the very limit of any classical theoretical model that predicts dipolar radio emission from an isolated neutron star.
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Affiliation(s)
- N Hurley-Walker
- International Centre for Radio Astronomy Research, Curtin University, Bentley, Western Australia, Australia.
| | - N Rea
- Institute of Space Sciences (ICE), Consejo Superior de Investigaciones Científicas (CSIC), Barcelona, Spain
- Institut d'Estudis Espacials de Catalunya (IEEC), Barcelona, Spain
| | - S J McSweeney
- International Centre for Radio Astronomy Research, Curtin University, Bentley, Western Australia, Australia
| | - B W Meyers
- International Centre for Radio Astronomy Research, Curtin University, Bentley, Western Australia, Australia
| | - E Lenc
- Australia Telescope National Facility (ATNF), CSIRO Space & Astronomy, Epping, New South Wales, Australia
| | - I Heywood
- Astrophysics, University of Oxford, Oxford, UK
- Department of Physics & Electronics, Rhodes University, Makhanda, South Africa
- South African Radio Astronomy Observatory (SARAO), Cape Town, South Africa
| | - S D Hyman
- Department of Engineering and Physics, Sweet Briar College, Sweet Briar, VA, USA
| | - Y P Men
- Max-Planck-Institut für Radioastronomie, Bonn, Germany
| | - T E Clarke
- Remote Sensing Division, U.S. Naval Research Laboratory, Washington, DC, USA
| | - F Coti Zelati
- Institute of Space Sciences (ICE), Consejo Superior de Investigaciones Científicas (CSIC), Barcelona, Spain
- Institut d'Estudis Espacials de Catalunya (IEEC), Barcelona, Spain
| | - D C Price
- International Centre for Radio Astronomy Research, Curtin University, Bentley, Western Australia, Australia
| | - C Horváth
- International Centre for Radio Astronomy Research, Curtin University, Bentley, Western Australia, Australia
| | - T J Galvin
- International Centre for Radio Astronomy Research, Curtin University, Bentley, Western Australia, Australia
- CSIRO, Space and Astronomy, Bentley, Western Australia, Australia
| | - G E Anderson
- International Centre for Radio Astronomy Research, Curtin University, Bentley, Western Australia, Australia
| | - A Bahramian
- International Centre for Radio Astronomy Research, Curtin University, Bentley, Western Australia, Australia
| | - E D Barr
- Max-Planck-Institut für Radioastronomie, Bonn, Germany
| | - N D R Bhat
- International Centre for Radio Astronomy Research, Curtin University, Bentley, Western Australia, Australia
| | - M Caleb
- Sydney Institute for Astronomy, School of Physics, The University of Sydney, Sydney, New South Wales, Australia
- ASTRO3D: ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions, Canberra, Australian Capital Territory, Australia
| | - M Dall'Ora
- INAF Capodimonte Astronomical Observatory Naples, Naples, Italy
| | - D de Martino
- INAF Capodimonte Astronomical Observatory Naples, Naples, Italy
| | - S Giacintucci
- Remote Sensing Division, U.S. Naval Research Laboratory, Washington, DC, USA
| | - J S Morgan
- International Centre for Radio Astronomy Research, Curtin University, Bentley, Western Australia, Australia
| | - K M Rajwade
- ASTRON, the Netherlands Institute for Radio Astronomy, Dwingeloo, The Netherlands
| | - B Stappers
- Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, The University of Manchester, Manchester, UK
| | - A Williams
- International Centre for Radio Astronomy Research, Curtin University, Bentley, Western Australia, Australia
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2
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Kirsten F, Marcote B, Nimmo K, Hessels JWT, Bhardwaj M, Tendulkar SP, Keimpema A, Yang J, Snelders MP, Scholz P, Pearlman AB, Law CJ, Peters WM, Giroletti M, Paragi Z, Bassa C, Hewitt DM, Bach U, Bezrukovs V, Burgay M, Buttaccio ST, Conway JE, Corongiu A, Feiler R, Forssén O, Gawroński MP, Karuppusamy R, Kharinov MA, Lindqvist M, Maccaferri G, Melnikov A, Ould-Boukattine OS, Possenti A, Surcis G, Wang N, Yuan J, Aggarwal K, Anna-Thomas R, Bower GC, Blaauw R, Burke-Spolaor S, Cassanelli T, Clarke TE, Fonseca E, Gaensler BM, Gopinath A, Kaspi VM, Kassim N, Lazio TJW, Leung C, Li DZ, Lin HH, Masui KW, Mckinven R, Michilli D, Mikhailov AG, Ng C, Orbidans A, Pen UL, Petroff E, Rahman M, Ransom SM, Shin K, Smith KM, Stairs IH, Vlemmings W. A repeating fast radio burst source in a globular cluster. Nature 2022; 602:585-589. [PMID: 35197615 DOI: 10.1038/s41586-021-04354-w] [Citation(s) in RCA: 23] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2021] [Accepted: 12/15/2021] [Indexed: 11/09/2022]
Abstract
Fast radio bursts (FRBs) are flashes of unknown physical origin1. The majority of FRBs have been seen only once, although some are known to generate multiple flashes2,3. Many models invoke magnetically powered neutron stars (magnetars) as the source of the emission4,5. Recently, the discovery6 of another repeater (FRB 20200120E) was announced, in the direction of the nearby galaxy M81, with four potential counterparts at other wavelengths6. Here we report observations that localized the FRB to a globular cluster associated with M81, where it is 2 parsecs away from the optical centre of the cluster. Globular clusters host old stellar populations, challenging FRB models that invoke young magnetars formed in a core-collapse supernova. We propose instead that FRB 20200120E originates from a highly magnetized neutron star formed either through the accretion-induced collapse of a white dwarf, or the merger of compact stars in a binary system7. Compact binaries are efficiently formed inside globular clusters, so a model invoking them could also be responsible for the observed bursts.
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Affiliation(s)
- F Kirsten
- Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, Onsala, Sweden. .,ASTRON, Netherlands Institute for Radio Astronomy, Dwingeloo, The Netherlands.
| | - B Marcote
- Joint Institute for VLBI ERIC, Dwingeloo, The Netherlands
| | - K Nimmo
- ASTRON, Netherlands Institute for Radio Astronomy, Dwingeloo, The Netherlands.,Anton Pannekoek Institute for Astronomy, University of Amsterdam, Amsterdam, The Netherlands
| | - J W T Hessels
- ASTRON, Netherlands Institute for Radio Astronomy, Dwingeloo, The Netherlands.,Anton Pannekoek Institute for Astronomy, University of Amsterdam, Amsterdam, The Netherlands
| | - M Bhardwaj
- Department of Physics, McGill University, Montreal, Quebec, Canada.,McGill Space Institute, McGill University, Montreal, Quebec, Canada
| | - S P Tendulkar
- Department of Astronomy and Astrophysics, Tata Institute of Fundamental Research, Mumbai, India.,National Centre for Radio Astrophysics, Pune, India
| | - A Keimpema
- Joint Institute for VLBI ERIC, Dwingeloo, The Netherlands
| | - J Yang
- Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, Onsala, Sweden
| | - M P Snelders
- Anton Pannekoek Institute for Astronomy, University of Amsterdam, Amsterdam, The Netherlands
| | - P Scholz
- Dunlap Institute for Astronomy & Astrophysics, University of Toronto, Toronto, Ontario, Canada
| | - A B Pearlman
- Department of Physics, McGill University, Montreal, Quebec, Canada.,McGill Space Institute, McGill University, Montreal, Quebec, Canada.,Division of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena, CA, USA
| | - C J Law
- Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA, USA.,Owens Valley Radio Observatory, California Institute of Technology, Pasadena, CA, USA
| | - W M Peters
- Remote Sensing Division, US Naval Research Laboratory, Washington, DC, USA
| | - M Giroletti
- Istituto Nazionale di Astrofisica, Istituto di Radioastronomia, Bologna, Italy
| | - Z Paragi
- Joint Institute for VLBI ERIC, Dwingeloo, The Netherlands
| | - C Bassa
- ASTRON, Netherlands Institute for Radio Astronomy, Dwingeloo, The Netherlands
| | - D M Hewitt
- Anton Pannekoek Institute for Astronomy, University of Amsterdam, Amsterdam, The Netherlands
| | - U Bach
- Max Planck Institute for Radio Astronomy, Bonn, Germany
| | - V Bezrukovs
- Engineering Research Institute Ventspils International Radio Astronomy Centre (ERI VIRAC), Ventspils University of Applied Sciences (VUAS), Ventspils, Latvia
| | - M Burgay
- Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Cagliari, Selargius, Italy
| | - S T Buttaccio
- Istituto Nazionale di Astrofisica, Istituto di Radioastronomia Radiotelescopio di Noto, Noto, Italy
| | - J E Conway
- Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, Onsala, Sweden
| | - A Corongiu
- Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Cagliari, Selargius, Italy
| | - R Feiler
- Institute of Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Toruń, Poland
| | - O Forssén
- Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, Onsala, Sweden
| | - M P Gawroński
- Institute of Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Toruń, Poland
| | - R Karuppusamy
- Max Planck Institute for Radio Astronomy, Bonn, Germany
| | - M A Kharinov
- Institute of Applied Astronomy of the Russian Academy of Sciences, St. Petersburg, Russia
| | - M Lindqvist
- Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, Onsala, Sweden
| | - G Maccaferri
- Istituto Nazionale di Astrofisica, Istituto di Radioastronomia, Bologna, Italy
| | - A Melnikov
- Institute of Applied Astronomy of the Russian Academy of Sciences, St. Petersburg, Russia
| | - O S Ould-Boukattine
- Anton Pannekoek Institute for Astronomy, University of Amsterdam, Amsterdam, The Netherlands
| | - A Possenti
- Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Cagliari, Selargius, Italy.,Dipartimento di Fisica, Università di Cagliari, Monserrato, Italy
| | - G Surcis
- Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Cagliari, Selargius, Italy
| | - N Wang
- Xinjiang Astronomical Observatory, Urumqi, China
| | - J Yuan
- Xinjiang Astronomical Observatory, Urumqi, China
| | - K Aggarwal
- Department of Physics and Astronomy, West Virginia University, Morgantown, WV, USA.,Center for Gravitational Waves and Cosmology, West Virginia University, Morgantown, WV, USA
| | - R Anna-Thomas
- Department of Physics and Astronomy, West Virginia University, Morgantown, WV, USA.,Center for Gravitational Waves and Cosmology, West Virginia University, Morgantown, WV, USA
| | - G C Bower
- Academia Sinica Institute of Astronomy and Astrophysics, Hilo, HI, USA
| | - R Blaauw
- ASTRON, Netherlands Institute for Radio Astronomy, Dwingeloo, The Netherlands
| | - S Burke-Spolaor
- Department of Physics and Astronomy, West Virginia University, Morgantown, WV, USA.,Center for Gravitational Waves and Cosmology, West Virginia University, Morgantown, WV, USA.,Canadian Institute for Advanced Research, CIFAR Azrieli Global Scholar, Toronto, Ontario, Canada
| | - T Cassanelli
- Dunlap Institute for Astronomy & Astrophysics, University of Toronto, Toronto, Ontario, Canada.,David A. Dunlap Department of Astronomy & Astrophysics, University of Toronto, Toronto, Ontario, Canada
| | - T E Clarke
- Remote Sensing Division, US Naval Research Laboratory, Washington, DC, USA
| | - E Fonseca
- Department of Physics, McGill University, Montreal, Quebec, Canada.,McGill Space Institute, McGill University, Montreal, Quebec, Canada.,Department of Physics and Astronomy, West Virginia University, Morgantown, WV, USA.,Center for Gravitational Waves and Cosmology, West Virginia University, Morgantown, WV, USA
| | - B M Gaensler
- Dunlap Institute for Astronomy & Astrophysics, University of Toronto, Toronto, Ontario, Canada.,David A. Dunlap Department of Astronomy & Astrophysics, University of Toronto, Toronto, Ontario, Canada
| | - A Gopinath
- Anton Pannekoek Institute for Astronomy, University of Amsterdam, Amsterdam, The Netherlands
| | - V M Kaspi
- Department of Physics, McGill University, Montreal, Quebec, Canada.,McGill Space Institute, McGill University, Montreal, Quebec, Canada
| | - N Kassim
- Remote Sensing Division, US Naval Research Laboratory, Washington, DC, USA
| | - T J W Lazio
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
| | - C Leung
- MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA, USA.,Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - D Z Li
- Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA, USA
| | - H H Lin
- Canadian Institute for Theoretical Astrophysics, University of Toronto, Toronto, Ontario, Canada.,Institute of Astronomy and Astrophysics, Academia Sinica, Taipei, Taiwan
| | - K W Masui
- MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA, USA.,Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - R Mckinven
- Dunlap Institute for Astronomy & Astrophysics, University of Toronto, Toronto, Ontario, Canada
| | - D Michilli
- Department of Physics, McGill University, Montreal, Quebec, Canada.,McGill Space Institute, McGill University, Montreal, Quebec, Canada.,MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA, USA.,Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - A G Mikhailov
- Institute of Applied Astronomy of the Russian Academy of Sciences, St. Petersburg, Russia
| | - C Ng
- Dunlap Institute for Astronomy & Astrophysics, University of Toronto, Toronto, Ontario, Canada
| | - A Orbidans
- Engineering Research Institute Ventspils International Radio Astronomy Centre (ERI VIRAC), Ventspils University of Applied Sciences (VUAS), Ventspils, Latvia
| | - U L Pen
- Dunlap Institute for Astronomy & Astrophysics, University of Toronto, Toronto, Ontario, Canada.,Canadian Institute for Advanced Research, CIFAR Azrieli Global Scholar, Toronto, Ontario, Canada.,Canadian Institute for Theoretical Astrophysics, University of Toronto, Toronto, Ontario, Canada.,Perimeter Institute for Theoretical Physics, Waterloo, Ontario, Canada.,Institute of Astronomy and Astrophysics, Academia Sinica, Taipei, Taiwan
| | - E Petroff
- Anton Pannekoek Institute for Astronomy, University of Amsterdam, Amsterdam, The Netherlands.,Department of Physics, McGill University, Montreal, Quebec, Canada.,McGill Space Institute, McGill University, Montreal, Quebec, Canada
| | - M Rahman
- Sidrat Research, Toronto, Ontario, Canada
| | - S M Ransom
- National Radio Astronomy Observatory, Charlottesville, VA, USA
| | - K Shin
- MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA, USA.,Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - K M Smith
- Perimeter Institute for Theoretical Physics, Waterloo, Ontario, Canada
| | - I H Stairs
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada
| | - W Vlemmings
- Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, Onsala, Sweden
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3
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Hallinan G, Corsi A, Mooley KP, Hotokezaka K, Nakar E, Kasliwal MM, Kaplan DL, Frail DA, Myers ST, Murphy T, De K, Dobie D, Allison JR, Bannister KW, Bhalerao V, Chandra P, Clarke TE, Giacintucci S, Ho AYQ, Horesh A, Kassim NE, Kulkarni SR, Lenc E, Lockman FJ, Lynch C, Nichols D, Nissanke S, Palliyaguru N, Peters WM, Piran T, Rana J, Sadler EM, Singer LP. A radio counterpart to a neutron star merger. Science 2017; 358:1579-1583. [PMID: 29038372 DOI: 10.1126/science.aap9855] [Citation(s) in RCA: 325] [Impact Index Per Article: 46.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2017] [Accepted: 10/09/2017] [Indexed: 11/02/2022]
Abstract
Gravitational waves have been detected from a binary neutron star merger event, GW170817. The detection of electromagnetic radiation from the same source has shown that the merger occurred in the outskirts of the galaxy NGC 4993, at a distance of 40 megaparsecs from Earth. We report the detection of a counterpart radio source that appears 16 days after the event, allowing us to diagnose the energetics and environment of the merger. The observed radio emission can be explained by either a collimated ultrarelativistic jet, viewed off-axis, or a cocoon of mildly relativistic ejecta. Within 100 days of the merger, the radio light curves will enable observers to distinguish between these models, and the angular velocity and geometry of the debris will be directly measurable by very long baseline interferometry.
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Affiliation(s)
- G Hallinan
- Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA.
| | - A Corsi
- Department of Physics and Astronomy, Texas Tech University, Lubbock, TX 79409, USA
| | - K P Mooley
- Astrophysics, Department of Physics, University of Oxford, Oxford OX1 3RH, UK
| | - K Hotokezaka
- Center for Computational Astrophysics, Flatiron Institute, 162 5th Avenue, New York, NY 10010, USA.,Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
| | - E Nakar
- Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel
| | - M M Kasliwal
- Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
| | - D L Kaplan
- Department of Physics, University of Wisconsin, Milwaukee, WI 53201, USA
| | - D A Frail
- National Radio Astronomy Observatory, Socorro, NM 87801, USA
| | - S T Myers
- National Radio Astronomy Observatory, Socorro, NM 87801, USA
| | - T Murphy
- Sydney Institute for Astronomy, School of Physics, University of Sydney, Sydney, NSW 2006, Australia.,Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO)
| | - K De
- Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
| | - D Dobie
- Sydney Institute for Astronomy, School of Physics, University of Sydney, Sydney, NSW 2006, Australia.,Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO).,Australia Telescope National Facility, Commonwealth Scientific and Industrial Research Organisation, Astronomy and Space Science, Epping, NSW 1710, Australia
| | - J R Allison
- Sydney Institute for Astronomy, School of Physics, University of Sydney, Sydney, NSW 2006, Australia.,Australian Research Council Centre of Excellence for All-sky Astrophysics in 3 Dimensions (ASTRO 3D)
| | - K W Bannister
- Australia Telescope National Facility, Commonwealth Scientific and Industrial Research Organisation, Astronomy and Space Science, Epping, NSW 1710, Australia
| | - V Bhalerao
- Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - P Chandra
- National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Pune University Campus, Ganeshkhind Pune 411007, India
| | - T E Clarke
- Remote Sensing Division, Naval Research Laboratory, Washington, DC 20375, USA
| | - S Giacintucci
- Remote Sensing Division, Naval Research Laboratory, Washington, DC 20375, USA
| | - A Y Q Ho
- Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
| | - A Horesh
- Racah Institute of Physics, Hebrew University of Jerusalem, Jerusalem 91904, Israel
| | - N E Kassim
- Remote Sensing Division, Naval Research Laboratory, Washington, DC 20375, USA
| | - S R Kulkarni
- Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
| | - E Lenc
- Sydney Institute for Astronomy, School of Physics, University of Sydney, Sydney, NSW 2006, Australia.,Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO)
| | - F J Lockman
- Green Bank Observatory, Green Bank, WV 24944, USA
| | - C Lynch
- Sydney Institute for Astronomy, School of Physics, University of Sydney, Sydney, NSW 2006, Australia.,Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO)
| | - D Nichols
- Institute of Mathematics, Astrophysics and Particle Physics, Radboud University, 6525 AJ Nijmegen, Netherlands
| | - S Nissanke
- Institute of Mathematics, Astrophysics and Particle Physics, Radboud University, 6525 AJ Nijmegen, Netherlands
| | - N Palliyaguru
- Department of Physics and Astronomy, Texas Tech University, Lubbock, TX 79409, USA
| | - W M Peters
- Remote Sensing Division, Naval Research Laboratory, Washington, DC 20375, USA
| | - T Piran
- Racah Institute of Physics, Hebrew University of Jerusalem, Jerusalem 91904, Israel
| | - J Rana
- Inter University Centre for Astronomy and Astrophysics, Pune University Campus, Pune, Maharashtra 411007, India
| | - E M Sadler
- Sydney Institute for Astronomy, School of Physics, University of Sydney, Sydney, NSW 2006, Australia.,Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO)
| | - L P Singer
- Astroparticle Physics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
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