Falcon Research in Greenland, 1973

... During the summer of 1972 a research team initiated the first in-depth study of the peregrine falcon (Falco peregrinus) in West Greenland. Eight eyries (nests) of this endangered species were located in an inland sample area of 700 sq. mi. Detailed observations were taken of peregrine breeding behaviour at one eyrie. Seven of the eyries produced young, containing an average of 2.57 young per successful eyrie. This high reproductive rate indicates a healthy population, but analyses of 2 addled eggs revealed high p,p'-DDE as well as polychlorinated biphenyl (PCB) residues and eggshell fragments from 9 eggs showed a 14 per cent decrease in thickness compared with 42 eggs collected in Greenland before the introduction of DDT into the environment. ... The [1973] survey area consisted of 900 sq. mi. (2,330 sq. km.), including ice-cap, lakes, fjords, and other unsuitable habitat totalling about 150 sq. mi. (388 sq. km.). We found 10 occupied peregrine falcon nesting cliffs in the survey area in 1973. ... 9 eyries produced young. Of these 9, 7 were also successful in 1972, while another was occupied throughout the season by an aggressive pair, and at the ninth a lone female mildly defended the cliff. Of the 9 producing eyries in 1973, 1 contained 4 young, 5 contained 3 young each, 2 had 2 young each, and 1 held 1 young. This gives a total of 24 young peregrines and a production rate of 2.4 young per occupied eyrie, or 2.67 young per successful eyrie. These young were counted at advanced ages varying from 2.5 weeks to just before fledging. It is believed that all or almost all fledged. We found 1 occupied eyrie per 90 sq. mi. (233 sq. km.), or 1 successful eyrie per 100 sq. mi. (260 sq. km.). All young were banded with a metal band on the left tarsus and a red plastic band on the right. ... The colour bands signify the beginning of an international peregrine colour banding system established for quick geographical identification of banding locality. During the 2 summers, 9 gyrfalcon nesting cliffs were located in the survey area. We believe that at least 6 of the 9 locations were occupied in 1972. In 1973, 8 of the 9 cliffs were checked. Young were found at 4 sites. A fifth was observed from an aircraft and appeared to be active. Lone adults were observed at 2 other locations. Seven young gyrfalcons were banded out of 10 young found. One nest site was inaccessible and the young were not banded, accounting for the difference in number located and banded. The production rate per producing pair of gyrfalcons was 2.50 young. ... Our sample survey indicates that in 1973, as in 1972, the peregrine falcon reproduced normally in West Greenland. The slightly higher production rate in 1973 can possibly be attributed to warmer temperatures during the nesting period, as the summer of 1972 was unseasonably cool. However, the 1972 data on eggshell thinning and high DDE and PCB residues reveal that this population is precariously balanced, and severe reproductive failure threatens. Analysis of the 1973 addled egg and measurement of the additional eggshell fragments will supplement the 1972 results to provide a larger data base. ..

Peregrine Falcon Survey, West Greenland, 1972

... The main purpose of the 1972 survey was to study a sample area of West Greenland to supply baseline data about peregrine falcons from which future surveys could determine the status and trends of this bird in Greenland. The main part of the study had as its goals: 1) to determine the density, distribution, and reproductive success of nesting peregrines in a sample area; 2) to band all peregrine nestlings found; 3) to determine prey species of the peregrine; 4) to make interspecific observations of peregrines and gyrfalcons; 5) to make detailed observations from a blind of a sample peregrine falcon eyrie; 6) to conduct a small-bird census in the area of the sample eyrie; 7) to make a photographic record in colour slides and movies of the investigations. ... Eight peregrine falcon eyries and 3 gyrfalcon eyries were found in the survey area. In all, 18 nestlings were found in the 8 peregrine eyries. Of the 8 eyries, 1 had no young, but showed signs of occupancy ... and was defended by an aggressive pair of falcons. Of the other 7 eyries where we found hatched young, 1 had 4 young, 4 had 3 young, and 2 had 1 young bird each. Of the total of 18 nestling peregrines, 13 were banded and 5 were fully-fledged, on the wing, and unable to be caught for banding. Of the peregrine nestlings banded, 9 were males and 4 were females. The number of nestlings (18) in the 8 peregrine eyries gave a production rate of 2.25 per eyrie, or 2.57 if an average is taken of the 7 eyries actually producing young. At 1 eyrie a young falcon was found dead (the eyrie with 4 young). We know that at least 8 of the remaining 17 young fledged successfully, but we are uncertain about the success of the others and cannot therefore make a definite statement on fledging ratio. We estimate, however, that the fledging rate of the peregrines in our survey area was at least 2.00 per producing eyrie. The maximum dimensions of our irregularly-shaped survey area were 39 x 34 miles (63 x 55 km). The estimated area of the survey was about 800 sq. mi. (2,072 sq. km), or about 700 sq. mi. (1,800 sq. km) when the surface area of fiords and lakes is excluded. The nesting density of the active, young-producing peregrine eyries (7) was about 1 pair per 100 sq. mi. (260 sq. km). ... At the 3 gyrfalcon (Falco rusticolus) eyries we found 8 nestlings or fully-fledged young, of which we were able to band 3. Peregrines and gyrfalcons (and a rare white-tailed sea eagle, Haliaetus albicilla) are the only avian predators nesting in southern West Greenland, although ravens (Corvus corax) competed for some nesting cliff sites. We collected remains of prey species and pellets at each falcon eyrie. Addled eggs (2) from 2 peregrine eyries were collected for pesticide analysis. Eggshell fragments for thickness determination were gathered at 5 peregrine eyries. ... Peregrine falcons in West Greenland appear to be in a healthy state as evidenced by a high nesting density (1/100 sq. mi.) and a high production rate (2.25/eyrie), especially in light of the unusually severe conditions in West Greenland during the winter and late spring of 1971-72. We found little interspecific competition for prey species between peregrines and gyrfalcons. The gyrfalcon is already nesting in West Greenland before the peregrines arrive from their winter migration to the south. The gyrfalcons could therefore be expected to be aggressive in defence of their nesting cliffs and thereby occupy optimal cliffs. Despite this, all the peregrines we studied occupied high, sheer, and quite optimal nesting cliffs. Gyrfalcons seemed to prefer a nesting site lower down on a cliff face than peregrines, and both falcons preferred high, sheer cliffs with a southern exposure. Ravens were relegated to lower, less desirable (more accessible) cliffs for nesting. We await pesticide analysis of the peregrine falcon eggs and prey species collected, as well as eggshell thickness determination. Before these facts are determined we can say nothing definite about the status of peregrines in Greenland. Nesting density and production, however, suggest that the status of the peregrine is better in Greenland than in other areas of the north. ..

Parsec Scale Properties of Markarian 501

We present the results of a high angular resolution study of the BL Lac object Markarian 501 in the radio band. We consider data taken at 14 different epochs, ranging between 1.6 GHz and 22 GHz in frequency, and including new Space VLBI observations obtained on 2001 March 5 and 6 at 1.6 and 5 GHz. We study the kinematics of the parsec-scale jet and estimate its bulk velocity and orientation with respect to the line of sight. Limb brightened structure in the jet is clearly visible in our data and we discuss its possible origin in terms of velocity gradients in the jet. Quasi-simultaneous multi-wavelength observations allow us to map the spectral index distribution and to compare it to the jet morphology. Finally, we estimate the physical parameters of the parsec-scale jet.Comment: accepted for publication in ApJ; 24 pages with 17 figures (fig. 1 and fig. 2 available only as .jpg files

Complex Spectral Variability from Intensive Multi-wavelength Monitoring of Mrk421 in 1998

We conducted a multi-frequency campaign for the TeV blazar Mrk~421 in 1998 April. The campaign started from a pronounced high amplitude flare recorded by SAX and Whipple; ASCA observation started three days later. In the X-ray data, we detected multiple flares, occuring on time scales of about one day. ASCA data clearly reveal spectral variability. The comparison of the data from ASCA, EUVE and RXTE indicates that the variability amplitudes in the low energy synchrotron component are larger at higher photon energies. In TeV Gamma-rays, large intra-day variations -- which were correlated with the X-ray flux -- were observed when results from three Cherenkov telescopes are combined. The RMS variability of TeV Gamma--rays was similar to that observed in hard X-rays, above 10 keV. The X-ray light curve reveals flares which are almost symmetric for most of cases, implying the dominant time scale is the light crossing time through the emitting region. The structure function analysis based on the continuous X-ray light curve of seven days indicates that the characteristic time scale is ~0.5 day. The analysis of ASCA light curves in various energy bands appears to show both soft (positive) and hard (negative) lags. These may not be real, as systematic effects could also produce these lags, which are all much smaller than an orbit. If the lags of both signs are real, these imply that the particle acceleration and X-ray cooling time scales are similar.Comment: 10 pages, 4 figures, accepted for publication in ApJ Letter

Might some gamma ray bursts be an observable signature of natural wormholes?

The extragalactic microlensing scenario for natural wormholes is examined. It is shown that the main features of wormhole lensing events upon the light of distant Active Galactic Nuclei (AGNs) are similar to some types of already observed Gamma Ray Bursts (GRBs). Using recent satellite data on GRBs, an upper limit to the negative mass density -- ${\cal O} (10^{-36})$ g cm$^{-3}$ -- under the form of wormhole-like objects is presented.Comment: extended version, additions on GRB physics, background sources and cosmological consequences. Two ps figures. Accpeted for publication in Phys. Rev.

The Identification of EGRET Sources with Flat-Spectrum Radio Sources

We present a method to assess the reliability of the identification of EGRET sources with extragalactic radio sources. We verify that EGRET is detecting the blazar class of AGN. However, many published identifications are found to be questionable. We provide a table of 42 blazars which we expect to be robust identifications of EGRET sources. This includes one previously unidentified EGRET source, the lensed AGN PKS 1830-210 near the direction of the Galactic center. We provide the best available positions for 16 more radio sources which are also potential identifications for previously unidentified EGRET sources. All high Galactic latitude EGRET sources (b>3 degrees) which demonstrate significant variability can be identified with flat spectrum radio sources. This suggests that EGRET is not detecting any type of AGN other than blazars. This identification method has been used to establish with 99.998% confidence that the peak gamma-ray flux of a blazar is correlated with its average 5 GHz radio flux. An even better correlation is seen between gamma-ray flux and the 2.29 GHz flux density measured with VLBI at the base of the radio jet. Also, using high confidence identifications, we find that the radio sources identified with EGRET sources have larger correlated VLBI flux densities than the parent population of flat radio spectrum sources.Comment: To be published in Ap J, May 20, 1997 issue, Vol. 481. The complete paper is available at http://bu-ast.bu.edu/~mattox/src_id.htm

Modeling the Emission Processes in Blazars

Blazars are the most violent steady/recurrent sources of high-energy gamma-ray emission in the known Universe. They are prominent emitters of electromagnetic radiation throughout the entire electromagnetic spectrum. The observable radiation most likely originates in a relativistic jet oriented at a small angle with respect to the line of sight. This review starts out with a general overview of the phenomenology of blazars, including results from a recent multiwavelength observing campaign on 3C279. Subsequently, issues of modeling broadband spectra will be discussed. Spectral information alone is not sufficient to distinguish between competing models and to constrain essential parameters, in particular related to the primary particle acceleration and radiation mechanisms in the jet. Short-term spectral variability information may help to break such model degeneracies, which will require snap-shot spectral information on intraday time scales, which may soon be achievable for many blazars even in the gamma-ray regime with the upcoming GLAST mission and current advances in Atmospheric Cherenkov Telescope technology. In addition to pure leptonic and hadronic models of gamma-ray emission from blazars, leptonic/hadronic hybrid models are reviewed, and the recently developed hadronic synchrotron mirror model for TeV gamma-ray flares which are not accompanied by simultaneous X-ray flares (``orphan TeV flares'') is revisited.Comment: Invited Review at "The Multimessenger Approach to Gamma-Ray Sources", Barcelona, Spain, July 2006; submitted to Astrophysics and Space Science. 10 pages, including 6 eps figures. Uses Springer's ApSS macro

Optical and radio variability of the BL Lac object AO 0235+16: a possible 5-6 year periodicity

New optical and radio data on the BL Lacertae object AO 0235+16 have been collected in the last four years by a wide international collaboration, which confirm the intense activity of this source. The optical data also include the results of the Whole Earth Blazar Telescope (WEBT) first-light campaign organized in November 1997. The optical spectrum is observed to basically steepen when the source gets fainter. We have investigated the existence of typical variability time scales and of possible correlations between the optical and radio emissions by means of visual inspection, Discrete Correlation Function analysis, and Discrete Fourier Transform technique. The major radio outbursts are found to repeat quasi-regularly with a periodicity of about 5.7 years; this period is also in agreement with the occurrence of some of the major optical outbursts, but not all of them.Comment: to be published in A&

Rapid Synchrotron Flares from BL Lacertae Detected by ASCA and RXTE

We report the variable X-ray emission from BL Lacertae detected in the ASCA ToO observation conducted during the EGRET and RXTE pointings, coincident with the 1997 July outburst. The source showed a historically high state of X-ray, optical, and gamma-ray emission, with its 2-10 keV flux peaking at ~3.3 E-11 erg/cm2/s. This is more than 3 times higher than the value measured by ASCA in 1995. We detected two rapid flares which occured only in the soft X-ray band, while the hard X-ray flux also increased, but decayed with a much longer time scale. Together with the requirement of a very steep and varying power law dominating the soft X-ray band in addition to the hard power law, we suggest that both the high energy end of the synchrotron spectrum and the hard inverse Compton spectrum were visible in this source during the outburst. We discuss the possible origins of the observed variability time scales, and interpret the short time scales of the soft X-ray variability as reflecting the size of the emission region.Comment: 20 pages, 4 figures, accepted for publication in the Astrophysical Journa

Multifrequency monitoring of the blazar 0716+714 during the GASP-WEBT-AGILE campaign of 2007

Since the CGRO operation in 1991-2000, one of the primary unresolved questions about the blazar gamma-ray emission has been its possible correlation with the low-energy (in particular optical) emission. To help answer this problem, the Whole Earth Blazar Telescope (WEBT) consortium has organized the GLAST-AGILE Support Program (GASP) to provide the optical-to-radio monitoring data to be compared with the gamma-ray detections by the AGILE and GLAST satellites. This new WEBT project started in early September 2007, just before a strong gamma-ray detection of 0716+714 by AGILE. We present the GASP-WEBT optical and radio light curves of this blazar obtained in July-November 2007, about various AGILE pointings at the source. We construct NIR-to-UV spectral energy distributions (SEDs), by assembling GASP-WEBT data together with UV data from the Swift ToO observations of late October. We observe a contemporaneous optical-radio outburst, which is a rare and interesting phenomenon in blazars. The shape of the SEDs during the outburst appears peculiarly wavy because of an optical excess and a UV drop-and-rise. The optical light curve is well sampled during the AGILE pointings, showing prominent and sharp flares. A future cross-correlation analysis of the optical and AGILE data will shed light on the expected relationship between these flares and the gamma-ray events.Comment: 5 pages, 5 figures, to be published in A&A (Letters); revised to match the final version (changes in Fig. 5 and related text