J. M. Bai

A population of radio-loud narrow-line Seyfert 1 galaxies with blazar-like properties?

Blazars having strong emission lines were found to be associated mostly with broad-line type 1 active galactic nuclei (AGNs). Hitherto, evidence for blazars identified with narrow-line Seyfert 1 (NLS1) AGNs was limited to only a very few individual cases. Here we present a comprehensive study of a sample of 23 genuine radio-loud NLS1 AGNs with radio loudness larger than 100. The radio sources of the sample are ubiquitously compact, unresolved on scales of several arcseconds. Some of these objects show interesting radio to X-ray properties that are unusual to most of the previously known radio-loud NLS1 AGNs, but are reminiscent of blazars. These include flat radio spectra, large-amplitude flux and spectral variability, compact VLBI cores, very high variability brightness temperatures, enhanced optical continuum emission, flat X-ray spectra, and blazar-like spectral energy distributions (SEDs). We interpret them as signatures of the postulated blazar nature of some of the objects, which likely possess at least moderately relativistic jets. Intrinsically, some of them have relatively low radio power and would have been classified as radio-intermediate AGNs. The black hole masses are estimated to be within 10(6)-10(8) M-circle dot, and the Eddington ratios close to unity, as in normal NLS1 AGNs. The results imply that radio-loud AGNs may be powered by black holes of moderate masses (similar to 10(6)-10(7) M-circle dot) accreting at high rates. Some of the objects, despite having strong emission lines, resemble high-energy-peaked BL Lac objects (HBLs) in their SEDs. Given the peculiarities of blazar-like NLS1 AGNs, questions arise as to whether they are plain downsizing extensions of normal radio-loud AGNs, or form a previously unrecognized population.

The Afterglow of GRB 130427A from 1 to 10^(16) GHz

We present multiwavelength observations of the afterglow of GRB 130427A, the brightest (in total fluence) gamma-ray burst (GRB) of the past 29 yr. Optical spectroscopy from Gemini-North reveals the redshift of the GRB to be z = 0.340, indicating that its unprecedented brightness is primarily the result of its relatively close proximity to Earth; the intrinsic luminosities of both the GRB and its afterglow are not extreme in comparison to other bright GRBs. We present a large suite of multiwavelength observations spanning from 300 s to 130 days after the burst and demonstrate that the afterglow shows relatively simple, smooth evolution at all frequencies, with no significant late-time flaring or rebrightening activity. The entire data set from 1 GHz to 10 GeV can be modeled as synchrotron emission from a combination of reverse and forward shocks in good agreement with the standard afterglow model, providing strong support to the applicability of the underlying theory and clarifying the nature of the GeV emission observed to last for minutes to hours following other very bright GRBs. A tenuous, wind-stratified circumburst density profile is required by the observations, suggesting a massive-star progenitor with a low mass-loss rate, perhaps due to low metallicity. GRBs similar in nature to GRB 130427A, inhabiting low-density media and exhibiting strong reverse shocks, are probably not uncommon but may have been difficult to recognize in the past owing to their relatively faint late-time radio emission; more such events should be found in abundance by the new generation of sensitive radio and millimeter instruments.

RADIATION MECHANISMS AND PHYSICAL PROPERTIES OF GeV-TeV BL Lac OBJECTS

Broadband spectral energy distributions (SEDs) are complied from literature for 24 TeV BL Lac objects. Two SEDs, which are identified as low and high states with their flux densities at

A Narrow-Line Seyfert 1-Blazar Composite Nucleus in 2MASX J0324+3410

1\ {\rm TeV}

Absorption of 10-200 GeV Gamma Rays by Radiation from Broad-Line Regions in Blazars

(

Optical Monitoring Sample of the GeV Gamma-Ray-loud Blazars

F_{1 TeV}

SUPERMASSIVE BLACK HOLES WITH HIGH ACCRETION RATES IN ACTIVE GALACTIC NUCLEI. I. FIRST RESULTS FROM A NEW REVERBERATION MAPPING CAMPAIGN

), are available for each of 11 objects. We fit the SEDs with the single-zone synchrotron + synchrotron-self-Compton (SSC) model and determine the physical parameters of the jets. The model well represents the SEDs, and the observed relation between two peak frequencies

Search for short variability timescale of the GeV gamma-ray-loud blazars

\nu_{\rm s}

OPTICAL INTRA-DAY VARIABILITY IN BLAZARS

and

XMM-Newton view of PKS 2155-304: Characterizing the X-ray variability properties with EPIC pn

\nu_{\rm c}