REM follow-up observations of the flaring flat spectrum radio quasar TXS 0646-176
ATel #14999; Filippo D'Ammando (INAF-IRA Bologna)
on 26 Oct 2021; 09:48 UT
Credential Certification: Filippo D'Ammando (dammando@ira.inaf.it)
Subjects: Optical, AGN, Black Hole, Blazar, Quasar
Referred to by ATel #: 15000
Following the flaring activity from the flat spectrum radio quasar TXS 0646-176 (z = 1.232) observed by Fermi-LAT, AGILE-GRID, and DAMPE in gamma-rays (ATel #14980, ATel #14981, ATel #14993) and by Swift-XRT and SRG/eROSITA in X-rays (ATel #14987, ATel #14991), we have activated follow-up observations with the robotic 60-cm REM telescope located at La Silla (Chile) with a DDT request (PI: D'Ammando).
DDT observations were carried out with REM on 2021 October 23 and 24 with 180 s integration images in r and i bands. Recent observations of the source with REM were carried out on 2021 October 1, at the beginning of the gamma-ray activity period, for a Guest Observer program (ID: 43004, PI: D'Ammando). Optical calibration was performed against the APASS catalog. Preliminary results are reported in the following table.
Band | 2021-10-01 | 2021-10-23 | 2021-10-24 |
r | 18.08 +/- 0.08 | 18.08 +/- 0.12 | 17.17 +/- 0.05 |
i | 17.56 +/- 0.08 | 17.52 +/- 0.12 | 17.37 +/- 0.10 |
REM observed a significant enhancement of the activity of TXS 0646-176 in r-band in October 2021, with an optical flare occurred on October 24. As a comparison, the SDSS r-band magnitudes of the source are 18.82 and 18.58 in DR8 (Aihara et al. 2011, ApJS, 193, 29) and 18.84 in DR7 (Abazajian et al. 2009, ApJS, 182, 543). The r-band magnitude observed by REM on 2021 October 24 is brighter than the value observed in 2018 December 9 by NOT (ATel #12293), at the time of the 2018 gamma-ray flaring activity (ATel #12327). The SDSS i-band magnitude of the source is 18.22, confirming the enhancement of the activity of TXS 0646-176 in 2021 October also in i-band.
In consideration of the ongoing activity of this source, we encourage multi-wavelength observations. REM will continue to monitor TXS 0646-176 in the next days.
We would like to thank the REM Team and Director for making these observations possible.