Jules P. Halpern

Rejection of the Binary Broad-Line Region Interpretation of Double-peaked Emission Lines in Three Active Galactic Nuclei

It has been suggested that the peculiar double-peaked Balmer lines of certain broad-line radio galaxies come from individual broad-line regions associated with the black holes of a supermassive binary. We continue to search for evidence of the radial velocity variations characteristics of a double-lined spectroscopic binary that are required in such a model. After spectroscopic monitoring of three suitable candidates (Arp 102B, 3C 390.3, and 3C 332) spanning two decades, we find no such long-term systematic changes in radial velocity. A trend noticed by Gaskell in one of the Balmer-line peaks of 3C 390.3 before 1988 did not continue after that year, invalidating his inferred orbital period and mass. Instead, we find lower limits on the plausible orbital periods that would require the assumed supermassive binaries in all three objects to have total masses in excess of 1010 M☉. In the case of 3C 390.3, the total binary mass must exceed 1011 M☉ to satisfy additional observational constraints on the inclination angle. We argue that such large binary black hole masses are difficult to reconcile with other observations and with theory. In addition, there are peculiar properties of the line profiles and flux ratios in these objects that are not explained by ordinary broad-line region cloud models. We therefore doubt that the double-peaked line profiles of Arp 102B, 3C 390.3, and 3C 332 arise in pairs of broad-line regions. Rather, they are much more likely to be intimately associated with single black holes. The recent discoveries of transient but otherwise similar double-peaked emission lines in nearby active galactic nuclei bolster the view that double-peaked emission lines are commonly produced by a single compact source.

Measurement of an Active Galactic Nucleus Central Mass on Centiparsec Scales: Results of Long-Term Optical Monitoring of Arp 102B

The optical spectrum of the broad-line radio galaxy Arp 102B has been monitored for more than 13 yr to investigate the nature of the source of its broad, double-peaked hydrogen Balmer emission lines. The shape of the lines varied subtly; there was an interval during which the variation in the ratio of the fluxes of the two peaks appeared to be sinusoidal, with a period of 2.16 yr and an amplitude of about 16% of the average value. The variable part of the broad Hα line is well fitted by a model in which a region of excess emission (a quiescent hot spot) within an accretion disk (fitted to the nonvarying portion of the double-peaked line) completes at least two circular orbits and eventually fades. Fits to spectra from epochs when the hot spot is not present allow determination of the disk inclination, while fits for epochs when it is present provide a measurement of the radius of the hot spots orbit. From these data and the period of variation, we find that the mass within the hot spots orbit is 2.2 -->+ 0.2−0.7×10 -->8 M☉, within the range of previous estimates of masses of active galactic nuclei. Because this mass is determined at a relatively small distance from the central body, it is extremely difficult to explain without assuming that a supermassive black hole lies within Arp 102B. Our collection of spectra allows us to apply several tests to models of the source of the double peaks. The ratio of Hα to Hβ flux at a given velocity displays no turning points or points of inflection at the velocity associated with the blue peak in flux; thus, this peak should not correspond to a turning point in physical conditions. This behavior is consistent with simple accretion disk and, possibly, spiral shock models but not with models that attribute the double peaks to separate broad-line regions around a binary black hole or to broad, subrelativistic jets. The lack of systematic change in the velocity of the blue peak over time provides a further constraint on binary broad-line region models; this yields a lower limit on the mass of such a binary black hole system of at least 1010 M☉. The variability properties of the double-peaked emission lines in Arp 102B therefore continue to favor an accretion disk origin over other models.

OPTICAL AND X-RAY SPECTROSCOPY OF 1E 0449.4(1823: DEMISE OF THE ORIGINAL TYPE 2 QSO

New optical spectra of the original narrow-line quasar 1E 0449.4-1823 show that it now has broad emission lines of considerable strength, eliminating it as a type 2 QSO candidate. Although broad emission line components were probably weakly present in 1981 and 1984, they have certainly increased in strength and are accompanied by Balmer continuum emission that makes the spectrum bluer than it was previously. We suggest that the behavior of 1E 0449.4-1823 is the same as that of some Seyfert 1.8 and 1.9 galaxies, in which Goodrich attributed long-term variations of their broad Balmer lines to dynamical motions of obscuring material located in or around the broad-line region. The optical continuum and broad emission line regions of 1E 0449.4-1823 may still be partly covered in our line of sight, which would explain its large forbidden-line equivalent widths and flat αox relative to other low-redshift QSOs. Also present are apparent absorption features in the broad Balmer lines and in Mg II, which may be related to the past obscuration and current emergence of the broad-line region. However, it is difficult to distinguish absorption from broad emission line peaks that are displaced in velocity; we consider the latter a plausible competing interpretation of these peculiar line profiles. An ASCA X-ray spectrum of 1E 0449.4-1823 can be fitted with a power law of Γ=1.63 -->+ 0.12−0.09, intrinsic NH < 9 × 1020 cm-2, and no Fe Kα line emission. Its 2-10 keV luminosity is 6.7 × 1044 ergs s-1. Thus, there is no evidence for Seyfert 2 properties in the X-ray emission from 1E 0449.4-1823, which resembles that of an ordinary QSO. With regard to the still hypothetical type 2 QSOs, we argue that there is little evidence for the existence of any among X-ray-selected samples.

E 0336-248 : a new bl lac object found by an old Einstein

We obtained new ROSAT HRI and optical observations in the field of the Einstein X-ray source E 0336-248, which we use to identify it as a 19th magnitude BL Lacertae object at z=0.251 with an X-ray luminosity of 10^45 erg/s. It is also a 14 mJy radio source at 20 cm. An emission-line galaxy at z=0.043 that was previously considered a Seyfert identification for E 0336-248 is shown instead to be an unrelated, non-active H II region galaxy that lies 78 arcseconds from the X-ray source. The resolution of this historical case of mistaken identity illustrates that discoveries of non-AGN emission-line galaxies with high X-ray luminosity should be tested carefully. The properties of E 0336-248 are similar to those of other X-ray selected BL Lacs, including its location in an apparent group or cluster of galaxies. Somewhat unusual is the weak contribution of nonstellar optical light relative to the starlight in the spectrum of its host galaxy, which raises once again the possibility that even high-luminosity BL Lac objects may be difficult to identify in X-ray selected samples. We discuss a possible manifestation of this problem that appeared in the recent literature.