A hard X-ray brightening in the symbiotic star CH Cyg.
ATel #14216; G. J. M. Luna (IAFE/Conicet), K. Mukai (NASA/GSFC), R. Lopes de Oliveira (UFS, Brazil), J. Sokoloski (Columbia University), A. Pujol (IAFE/Conicet)
on 25 Nov 2020; 19:52 UT
Credential Certification: Gerardo Juan Manuel Luna (gjmluna@iafe.uba.ar)
Subjects: X-ray, Cataclysmic Variable, Variables
During the last hundred days, Swift/BAT Hard X-ray Transient Monitor shows that there has been an increase in the 15-50 keV energy range of the symbiotic binary CH Cyg, almost doubling the flux observed in the preceding 100 days (see http://cms.iafe.uba.ar/jluna/chcyg.html ). We observed CH Cyg with the XRT instrument onboard the Swift satellite on 2020-11-20 during 3.2 ks. We used the XRT in the WT mode to minimize the effects of optical loading, and did not observe with the UVOT (filter wheel position=0, or blocked).
The source was detected at a count rate of 0.175 c/s in the 0.3-10 keV energy range. The spectrum displays the usual two-components, one soft (0.3-2 keV) thermal component with an observed flux of 1.7e-12 ergs/cm^2/s and one hard (2-10 keV), highly absorbed thermal component with an observed flux of 1.9e-11 ergs/cm^2/s.
The observed flux in the hard component is, so far, about 1/3 of those recorded by ASCA on October 1994 and with RXTE in 2009 (Atel 2245), both being the highest observed and already about 10x greater than the flux observed with Chandra on March 2001 and Suzaku on January and May 2006. On the other hand, the flux of the soft component is about half of that observed with ASCA, Chandra and Suzaku.
The last few hundred days are also marked by a steady increase in the optical brightness, with an overall increase of ~1.5 mag in the V filter since October 2019.
We wish to thank the Swift Team for making these observations possible.
