J. A. Stevens

Multiwavelength Observations of a Dramatic High-Energy Flare in the Blazar 3C 279

The blazar 3C 279, one of the brightest identified extragalactic objects in the γ-ray sky, underwent a large (factor of ~10 in amplitude) flare in γ-rays toward the end of a 3 week pointing by Compton Gamma Ray Observatory (CGRO), in 1996 January-February. The flare peak represents the highest γ-ray intensity ever recorded for this object. During the high state, extremely rapid γ-ray variability was seen, including an increase of a factor of 2.6 in ~8 hr, which strengthens the case for relativistic beaming. Coordinated multifrequency observations were carried out with Rossi X-Ray Timing Explorer (RXTE), Advanced Satellite for Cosmology and Astrophysics (ASCA; or, Astro-D), Roentgen Satellite (ROSAT), and International Ultraviolet Explorer (IUE) and from many ground-based observatories, covering most accessible wavelengths. The well-sampled, simultaneous RXTE light curve shows an outburst of lower amplitude (factor of 3) well correlated with the γ-ray flare without any lag larger than the temporal resolution of ~1 day. The optical-UV light curves, which are not well sampled during the high-energy flare, exhibit more modest variations (factor of ~2) and a lower degree of correlation. The flux at millimetric wavelengths was near a historical maximum during the γ-ray flare peak, and there is a suggestion of a correlated decay. We present simultaneous spectral energy distributions of 3C 279 prior to and near to the flare peak. The γ-rays vary by more than the square of the observed IR-optical flux change, which poses some problems for specific blazar emission models. The synchrotron self-Compton (SSC) model would require that the largest synchrotron variability occurred in the mostly unobserved submillimeter/far-infrared region. Alternatively, a large variation in the external photon field could occur over a timescale of a few days. This occurs naturally in the mirror model, wherein the flaring region in the jet photoionizes nearby broad emission line clouds, which, in turn, provide soft external photons that are Comptonized to γ-ray energies.

Dust, Gas, and the Evolutionary Status of the Radio Galaxy 8C 1435+635 at z = 4.25

We present the results of new rest-frame far-IR observations of the z = 4.25 radio galaxy 8C 1435+635, which not only confirm that it contains an enormous quantity of dust (as first inferred from its millimeter-wave detection by Ivison in 1995), but also allow the first meaningful constraints to be placed on the mass of this dust and associated gas. The new measurements consist of (1) clear detections of submillimeter continuum emission at λobs = 450 and 850 μm obtained with the new submillimeter bolometer array, SCUBA, on the James Clerk Maxwell Telescope, (2) continuum upper limits at λobs = 350, 750, and 175 μm obtained with SCUBA and the PHT far-IR camera aboard the Infrared Space Observatory, and (3) a sensitive upper limit on the CO (4-3) line flux obtained with the IRAM 30 m Millimeter Radio Telescope. The resulting rest-frame 33-238 μm continuum coverage allows us to deduce that 2 × 108 M☉ of dust at a temperature of 40 ± 5 K is responsible for the observed millimeter/submillimeter emission. Using our CO upper limit, which constrains MH2/Md to less than 950, we go on to calculate robust limits on the total gas reserves (H2 + H I), which are thereby constrained to between 4 × 1010 and 1.2 × 1012 M☉. The submillimeter properties of 8C 1435+635 are thus strikingly similar to those of the z = 3.80 radio galaxy 4C 41.17, the only other high-redshift galaxy detected to date at submillimeter wavelengths whose properties appear not to be exaggerated by gravitational lensing. The inferred gas masses of both objects are sufficiently large to suggest that the formative starbursts of massive elliptical galaxies are still in progress at z simeq 4. Observations of complete samples of radio galaxies spanning a range of redshifts and radio luminosities will be required to determine whether the spectacular far-IR properties of 8C 1435+635 and 4C 41.17 are primarily due to their extreme redshifts or to their extreme radio luminosities.

Cold dust and young starbursts: spectral energy distributions of Herschel SPIRE sources from the HerMES survey

We present spectral energy distributions (SEDs) for 68 Herschel sources detected at 5σ at 250, 350 and 500 μm in the HerMES SWIRE-Lockman field. We explore whether existing models for starbursts, quiescent star-forming galaxies and active galactic nucleus dust tori are able to model the full range of SEDs measured with Herschel. We find that while many galaxies (∼56 per cent) are well fitted with the templates used to fit IRAS, Infrared Space Observatory (ISO) and Spitzer sources, for about half the galaxies two new templates are required: quiescent (‘cirrus’) models with colder (10–20 K) dust and a young starburst model with higher optical depth than Arp 220. Predictions of submillimetre fluxes based on model fits to 4.5–24 μm data agree rather poorly with the observed fluxes, but the agreement is better for fits to 4.5–70 μm data. Herschel galaxies detected at 500 μm tend to be those with the highest dust masses.

EGRET observations of the 1993 March gamma-ray flare from PKS 0528+134

EGRET observation of PKS 0528 + 134 during the 1993 March flare in gamma-rays is presented here. During the flare gamma-rays were detected at a level approximately three times greater than the observed intensity in earlier observations. Spectra of the source during the flare, as well as during the nonflaring state are presented. The flux history of PKS 0528 + 134 as observed from the start of the Compton Gamma Ray Observatory (CGRO) mission up to the end of Phase 3 (1993 October) is given. Multiwavelength observations of PKS 0528 + 134 during the flare are also presented. A detailed relativistic SSC jet model agrees well with the 1993 March Multiwavelength spectrum; the data, however, are insufficient to discriminate between this and other emission models.

Detection of gamma rays with E> 100 MeV from BL Lacertae

We present evidence for the first detection of gamma rays from the extragalactic object BL Lacertae. Observations taken with EGRET on the Compton Gamma Ray Observatory between 1995 January 24 and 1995 February 14 indicate a 4.4 σ excess from the direction of BL Lacertae. The corresponding flux is (40 ± 12) × 10-8 photons cm-2 s-1 above 100 MeV. The combination of all previous observations where BL Lacertae was in EGRETs field of view result in a 2.4 σ excess and a corresponding 95% confidence upper limit of 14 × 10-8 photons cm-2 s-1, indicating that its gamma-ray emission is variable, at least on timescales of several months. Observations of BL Lacertae between 22 and 375 GHz were also taken between 1995 January 24 and 1995 February 14, and the flux levels for those measurements are similar to the historical average values for this object. A deep exposure on BL Lacertae with the Whipple Observatory 10 m gamma-ray telescope shows no evidence of emission above 350 GeV during a period 9 months after the EGRET observations. The 99.9% confidence flux upper limit derived from these observations is 0.53 × 10-11 photons cm-2 s-1, which implies a large reduction in the gamma-ray emission of BL Lacertae between EGRET and Whipple Observatory energies. This reduction should result from processes intrinsic to BL Lacertae because it is near enough to Earth that intergalactic background IR fields should not significantly reduce the flux of gamma rays to which the Whipple Observatory telescope is sensitive.

A strongly starforming group: three massive galaxies associated with a QSO

We present here photometric redshift conrmation of the presence of large scale structure around the z = 1:82 QSO RX J0941, which shows an overdensity of submm sources. Radio imaging conrms the presence of the submm sources and pinpoints their likely optical-NIR counterparts. Four of the ve submm sources present in this eld (including the QSO) have counterparts with redshifts compatible with z = 1:82. We show that our photometric redshifts are robust against the use of dierent spectral templates. We have measured the galaxy stellar mass of the submm galaxies from their rest-frame K-band luminosity obtaining log(M =M ) 11:5 0:2, slightly larger than the Schechter mass of present day galaxies, and hence indicating that most of the stellar mass is already formed. We present optical-to-radio spectral energy distributions (SEDs) of the ve SCUBA sources. The emission of RX J0941 is dominated by reprocessed AGN emission in the observed MIR range, while the starburst contribution completely dominates in the submm range. The SEDs of the other three counterparts are compatible with a dominant starburst contribution above 24 m, with star formation rates SFR 2000M /yr, central dust masses log(Mdust=M ) 9 0:5 and hence central gas masses log(Mgas=M ) 10:7. There is very little room for an AGN contribution. From X-ray upper limits and the observed 24 m ux, we derive a maximum 2-10keV X-ray luminosity of 10 44 erg/s for any putative AGN, even if they are heavily obscured. This in turn points to relatively small black holes with log(M =M ) . 8 and hence stellar-to-black hole mass ratios about one order of magnitude higher than those observed in the present Universe: most of their central black hole masses are still to be accreted. Local stellar-to-black hole masses ratios can be reached if 1:3% of the available nuclear gas mass is accreted.

Modelling the millimetre–infrared flaring behaviour of the quasar 1253–055 (3C 279)

The infrared through millimetre light curve of 3C279 is investigated for the period of 1986 until mid-1994, during which time several flares were observed. A quiescent spectrum (identified with emission from an underlying jet) is presented. Both the near-IR and 375–150 GHz regimes are shown to be well described by power laws, with no evidence for any thermal contribution in the IR. Successful isolation of the flaring component by subtraction of a base level is found to be difficult. Dividing each individual flare into two regimes corresponding to before and after maximum flux, we find strong linear correlations between log 90 GHz flux and 22–90 GHz spectral slope. Furthermore, the gradient of the linear correlation steepens as the flare decays after maximum. This trend is observed for several successive flares, and can be successfully explained in terms of evolution of the flare according to the the shocked-jet model of Marscher & Gear (1985).

The Spitzer Extragalactic Representative Volume Survey (SERVS): Survey Definition and Goals (PASP, 124, 714, [2012])

The print version of this article contained some errors and omissions by the publishers and authors

A Gamma-Ray Flare in NRAO 190

We describe observations of the quasi-stellar object (QSO) NRAO 190 during a gamma-ray flare from 1994 August 9 to 1994 August 29. This QSO was serendipitously detected by the EGRET instrument on the Compton Gamma Ray Observatory in a gamma-ray flare with a luminosity at least 10 times that of its quiescent state. Optical, radio, and microwave data were obtained during or near the gamma-ray observations. The historical behavior of this object places it in the category of bright, flat-spectrum radio sources with strong optical variability that appear to form the largest class of non-Galactic high-energy gamma-ray sources. During the gamma-ray flare the source is observed with l(E > 100 MeV) = 8.4 ± 1.2 × 10-7 photons s-1 cm-2. A single power-law model gives a best-fit photon index of γ = -1.83 ± 0.14. Little evidence for major radio variability is seen during the flare or immediately afterward, although there is some increase in the 10-100 GHz flux over the next several months. There may be a slight hardening of the radio spectrum. In the optical region there are significant fluctuations on timescales of 1 day or less, although the overall optical luminosity is within the range of previous measurements. Optical observations a few weeks after the gamma-ray observations show a drop of about 60% and reduced variability. A contemporary optical spectrum shows that the source may be slightly harder than seen in a previously published spectrum. Radio monitoring of the source over the year subsequent to the flare has shown a very substantial drop in the flux at many frequencies.

Radio to γ-ray observations of 3C 454.3:1993–1995

Results from a multiwaveband study of the γ-ray-bright compact radio source 3C 454.3 are presented.