X-ray polarization evidence for a 200-year-old flare of Sgr A*
Ingram, Adam; Kaaret, Philip; Wu, Kinwah; Enoto, Teruaki; Turolla, Roberto; Pavlov, George G.; Khabibullin, Ildar; Churazov, Eugene; Weisskopf, Martin C.; Tennant, Allyn F.; Slane, Patrick; Papitto, Alessandro; Hayashida, Kiyoshi; Vink, Jacco; Bianchi, Stefano; Matt, Giorgio; Vikhlinin, Alexey; Kraft, Ralph; Kitaguchi, Takao; Doroshenko, Victor; Tsygankov, Sergey S.; Poutanen, Juri; Sunyaev, Rashid; Tombesi, Francesco; Ng, C. -Y.; Mitsuishi, Ikuyuki; Mizuno, Tsunefumi; Tamagawa, Toru; Tawara, Yuzuru; Zane, Silvia; Dovčiak, Michal; Iwakiri, Wataru; Bachetti, Matteo; Tavecchio, Fabrizio; Thomas, Nicholas E.; Pesce-Rollins, Melissa; Marshall, Herman L.; Heyl, Jeremy; Ratheesh, Ajay; Marinucci, Andrea; De Rosa, Alessandra; Middei, Riccardo; Marin, Frédéric; Petrucci, Pierre-Olivier; Baumgartner, Wayne H.; Negro, Michela; Perri, Matteo; Taverna, Roberto; Muleri, Fabio; Di Marco, Alessandro; Krawczynski, Henric; Possenti, Andrea; Baldini, Luca; Agudo, Iván; Antonelli, Lucio A.; Bellazzini, Ronaldo; Bongiorno, Stephen D.; Bonino, Raffaella; Brez, Alessandro; Bucciantini, Niccolò; Capitanio, Fiamma; Castellano, Simone; Cavazzuti, Elisabetta; Ciprini, Stefano; Costa, Enrico; Del Monte, Ettore; Di Gesu, Laura; Di Lalla, Niccolò; Donnarumma, Immacolata; Ehlert, Steven R.; Evangelista, Yuri; Fabiani, Sergio; Ferrazzoli, Riccardo; Garcia, Javier A.; Gunji, Shuichi; Jorstad, Svetlana G.; Karas, Vladimir; Kolodziejczak, Jeffery J.; La Monaca, Fabio; Latronico, Luca; Liodakis, Ioannis; Maldera, Simone; Manfreda, Alberto; Marscher, Alan P.; Massaro, Francesco; O'Dell, Stephen L.; Omodei, Nicola; Oppedisano, Chiara; Peirson, Abel L.; Pilia, Maura; Puccetti, Simonetta; Ramsey, Brian D.; Rankin, John; Roberts, Oliver J.; Romani, Roger W.; Soffitta, Paolo; Spandre, Gloria; Trois, Alessio; Xie, Fei; Chen, Chien-Ting; Sgrò, Carmelo; Barnouin, Thibault; Forman, William; Swartz, Doug
France, Germany, Russia, Italy, United States, Japan, Spain, Czech Republic, Canada, United Kingdom, Finland, Hong Kong SAR, Netherlands, China
Abstract
The centre of the Milky Way Galaxy hosts a black hole with a solar mass of about 4 million (Sagittarius A* (Sgr A)) that is very quiescent at present with a luminosity many orders of magnitude below those of active galactic nuclei1. Reflection of X-rays from Sgr A* by dense gas in the Galactic Centre region offers a means to study its past flaring activity on timescales of hundreds and thousands of years2. The shape of the X-ray continuum and the strong fluorescent iron line observed from giant molecular clouds in the vicinity of Sgr A* are consistent with the reflection scenario3-5. If this interpretation is correct, the reflected continuum emission should be polarized6. Here we report observations of polarized X-ray emission in the direction of the molecular clouds in the Galactic Centre using the Imaging X-ray Polarimetry Explorer. We measure a polarization degree of 31% ± 11%, and a polarization angle of −48° ± 11°. The polarization angle is consistent with Sgr A* being the primary source of the emission, and the polarization degree implies that some 200 years ago, the X-ray luminosity of Sgr A* was briefly comparable to that of a Seyfert galaxy.