Erratum for Atel #14872

ATel #14873; G. J.M. Luna (IAFE-UBA), R. Carrera (INAF-Padova), T. Enoto (Cluster for Pioneering Research, Riken), J. Mikolajewska (Nicolaus Copernicus Astronomical Center), M. Orio (INAF Padova and University of Wisconsin), N. Ospina (INFN and Padova University), E. Aydi (Michigan State University), J. Carbajo-Hijarrubia (University of Barcelona), K. Gendreau (NASA), Hiroyuki Maehara (National Astronomical Observatory of Japan), M. Giese (University of Wisconsin), S. Pei (Padova University)
on 24 Aug 2021; 22:27 UT
Credential Certification: Gerardo Juan Manuel Luna (gjmluna@iafe.uba.ar)

Tweet

The names of co-authors R. Carrera and H. Maehara were incorrect in the original telegram and also small html code correction were added. A NuSTAR observation of the recurrent nova RS Oph was obtained on 2021-08-17T03:41:09 until 2021-08-18T03:21:09 (8.2 days after the reported discovery on August 8.93 UT by K. Geary, VSNET alert N.26131). The total, non continuous exposure time was almost 40 kiloseconds. A bright X-ray source is detected in both FPMA and FPMB camera with an average count rate of 14.14±0.2 c/s in the 3-40 keV energy range. No counts were measured above 40 keV. During the exposure, the count rate decreased smoothly and constantly from 9.02 ± 0.06 c/s to 7.53±0.05 c/s in the 5-30 keV energy range, while no decrease was not observed in the 3-5 keV energy range. NICER snapshot exposures lasting for a total time of 3840 seconds (observation 4202300108) started 90 minutes earlier than the NuSTAR observation and overlapped with the NuSTAR exposure, detecting the source with an average count rate 151.2±0.6 counts/s. Three optical spectra were obtained at a time close to the X-ray exposures, starting on 2021-08-16T20:46:08, with the HERMES echelle spectrograph at the MECATOR 1.2 m telescope in the 3800-9000 Angstrom range. Our preliminary fit of NICER+NuSTAR spectra in the 0.2-40 keV range shows that a single temperature plasma (kT~ 5 keV) does not yield an acceptable fit, especially at energies above ~20 keV where the model underestimates the data. A still "tentative", but better fitting model includes an absorbed (N(H)~0.8x10²² cm^-2) two-temperatures, collisionally ionized plasma (kT1~4 keV; kT2~12 keV). The total estimated absorbed flux with this model is 8.4 x 10^-10 erg/cm²/s, while the unabsorbed flux would be about 1x10^-9 erg/cm²/s. However, there are still significant residuals at the lowest energy with this model, in fact the spectrum is altogether very complex and appears to have several different components. While the optical spectra do not indicate a rapid evolution after the SALT spectra described in ATel #14852, the broad absorption component at ~ - 4200 km/s in HI lines disappeared, and two satellite components appeared at about ±2500 km/s velocity in the H&alpha and H&beta emission line wings. They may be due to a bipolar collimated outflow, similar to the profiles observed during the 2006 outburst ~10-30 days after optical maximum (see Skopal et al., 2008, ASPC, 401, 227). Continued observations will provide information about acceleration or deceleration of these bipolar outflows. We speculate that the complexity of the X-ray spectrum is due to different regions of X-ray emission with different characteristics, possibly a shell and a bipolar outflow like suggested by Rupen et al. (2008, ApJ, 688, 559) on the basis of radio observations.