Spectroscopic identification of a flaring AGN in the Chandra observations of the JWST-NEP-TDF
ATel #12049; F. Civano (CfA), D. Stern (JPL), W. P. Maksym (CfA), S. H. Cohen (ASU), R. A. Jansen (ASU), C. L. MacLeod (CfA), R. Windhorst (ASU)
on 19 Sep 2018; 17:24 UT
Credential Certification: Francesca Civano (fcivano@cfa.harvard.edu)
Subjects: Optical, X-ray, AGN, Black Hole
We report the redshift measurement of a recently discovered X-ray transient in Chandra observations of the James Webb Space Telescope North Ecliptic Pole Time Domain Field (JWST NEP-TDF) obtained in late July 2018. The location of the X-ray flare (RA, Dec)=(17:24:21.72, +65:48:47.3) is consistent with SDSS J172421.74+654847.5. The discovery of this X-ray flare was reported in ATel #11906.
A spectrum of SDSS J172421.74+654847.5 was obtained by D. Stern using the Double Spectrograph (DBSP) on the Hale 200 inch Telescope at the Palomar Observatory on UT 2018 August 11. Two 900 s observations of the target were taken using the 1.5 arcsecs slit at the parallactic angle. The night was not photometric due to a combination of ash produced by nearby fires and high clouds. The data were processed using standard procedures and flux calibrated with observations of the white dwarf spectro-photometric standard star Wolf 1346 obtained on the same night.
The spectrum quality is high enough to identify the following high signal to noise ratio emission lines: broad (FWHM~5000 km/s) MgII 2799A, narrow [OII] 3727A, and broad Hbeta 4861A. The redshift of the source measured from these emission lines is z=0.833. The source luminosity in the X-ray band is therefore Lx=1.4e^44 erg/s, assuming the flux measured from the X-ray spectra reported in ATel #11906. From the observed optical emission lines and the X-ray luminosity, we can confirm this source is an Active Galactic Nucleus (AGN).
We plan to obtain more spectra of this AGN to search for continuum variability. A detailed analysis of the emission line profiles and widths, as well as of the various absorption lines observed in the spectrum, will be presented in future publication(s).
We thank F. Harrison (PI of the Palomar night) and the (large) Palomar crew on the night of this observations: post-PhD: Murray Brightman, Gael Noirot and Joe Simon; Caltech Summer Undergraduate Research Fellows: Honghui Liu, Renata Koontz, Andrew Sosanya and Julian Sander; and friends/relatives: Karin Emmenegger, Ingrid Kocsardi, Asher Stern, Eden Stern, Wendy Herry and Alienor Bernardie.
