X-ray polarization evidence for a 200-year-old flare of Sgr A*

: Marin F., Churazov E., Khabibullin I., Ferrazzoli R., Di Gesu L., Barnouin T., Di Marco A., Middei R., Vikhlinin A., Costa E., Soffitta P., Muleri F., Sunyaev R., Forman W., Kraft R., Bianchi S., Donnarumma I., Petrucci P.O., Enoto T., Agudo I., Antonelli L.A., Bachetti M., Baldini L., Baumgartner W.H., Bellazzini R., Bongiorno S.D., Bonino R., Brez A., Bucciantini N., Capitanio F., Castellano S., Cavazzuti E., Chen C.T., Ciprini S., De Rosa A., Del Monte E., Di Lalla N., Doroshenko V., Dovčiak M., Ehlert S.R., Evangelista Y., Fabiani S., Garcia J.A., Gunji S., Hayashida K., Heyl J., Ingram A., Iwakiri W., Jorstad S.G., Kaaret P., Karas V., Kitaguchi T., Kolodziejczak J.J., Krawczynski H., La Monaca F., Latronico L., Liodakis Ionnis., Maldera S., Manfreda A., Marinucci A., Marscher A.P., Marshall H.L., Massaro F., Matt G., Mitsuishi I., Mizuno T., Negro M., Ng C.Y., O’Dell S.L., Omodei N., Oppedisano C., Papitto A., Pavlov G.G., Peirson A.L., Perri M., Pesce-Rollins M., Pilia M., Possenti A., Poutanen Juri., Puccetti S., Ramsey B.D., Rankin J., Ratheesh A., Roberts O.J., Romani R.W., Sgrò C., Slane P., Spandre G., Swartz D., Tamagawa T., Tavecchio F., Taverna R., Tawara Y., Tennant A.F., Thomas N.E., Tombesi F., Trois A., Tsygankov Sergey S., Turolla R., Vink J., Weisskopf M.C., Wu K., Xie F., Zane S.

Publisher: Nature Research

: 2023

: Nature

: 619

: 7968

: 41

: 45

: 1476-4687

DOI: https://doi.org/10.1038/s41586-023-06064-x

: https://doi.org/10.1038/s41586-023-06064-x

: https://arxiv.org/abs/2304.06967

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 nuclei. 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 years. 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 scenario. If this interpretation is correct, the reflected continuum emission should be polarized. 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.