Spectroscopic observations of the flaring gamma-ray narrow-line Seyfert 1 PKS 2004-447
ATel #13259; M. Berton (FINCA/Metsahovi), S. Ciroi (UniPD), E. Congiu (Carnegie), S. Chen (UniPD), L. Crepaldi (UniPD), F. Di Mille (Carnegie), L. Foschini (INAF - OA Brera), E. Jarvela (UCSB), S. Komossa (MPIfR), J. Kotilainen (FINCA), A. Lahteenmaki (Metsahovi), A. Vietri (UniPD)
on 4 Nov 2019; 10:03 UT
Credential Certification: Marco Berton (marco.berton@utu.fi)
In the framework of ESO project P104.B-0587 (P.I. Berton) we obtained a spectrum of the flaring gamma-ray emitting narrow-line Seyfert 1 (NLS1) galaxy PKS 2004-447 (ATel#13229, #13233, #13244, #13249) at z = 0.240. We observed the target on 2019-10-31 UT00:28 with EFOSC2 on the 3.58m New Technology Telescope (NTT) of La Silla Observatory, using grism#5 with an exposure time of 1200s. The spectrum was wavelength calibrated using HeAr lamp, and flux calibrated using the spectrophotometric standard star LTT9491. We compared our new spectrum with a previous observation of the target during a non-flaring state. The observation was carried out on 2019-04-16 UT09:51 with LDSS3 on the 6.5m Clay Telescope of Las Campanas Observatory, using VPH-ALL and an exposure time of 900s. For wavelength calibration we used a HeAr lamp, and for flux calibration the standard star LTT9491. To compensate for the different observing conditions, we rescaled the spectra assuming a constant [O III] flux.
The 5100A continuum luminosity has increased approximately by a factor 5, going from 9.7e43 erg/s in the Clay spectrum to 4.6e44 erg/s in the NTT spectrum. The equivalent width of the Hbeta line decreased from 86.7A to 26.7A, in agreement with the typical behavior of flaring blazars (e.g., Foschini 2012). Also the Hbeta luminosity has increased, going from 1.8e42 erg/s in the Clay spectrum to 2.1e42 erg/s. This 20% increase in the line luminosity is significantly less prominent than that of the continuum. Since the Hbeta luminosity depends on the accretion disk luminosity where the ionizing continuum originates, while both the disk and the relativistic jet contributes to the continuum luminosity, we can conclude that the jet is responsible for a vast majority of the luminosity increase.
These results can finally be compared with the spectrum by Drinkwater et al. (1997), observed with the Anglo-Australian Telescope in 1984. The continuum luminosity we estimate is 1.8e44 erg/s, while the Hbeta luminosity was 1.6e42 erg/s. Both values are slightly closer to what we observe in the Clay spectrum than those measured in the flaring state, possibly suggesting that the source was in a quiescent state during the 1984 observation.
