arXiv subjects

J. Quinn

Publications and source records attributed to J. Quinn.

At least 163 records · Page 9Linked to original sources

arXiv2001

Cutoff in the TeV Energy Spectrum of Markarian 421 During Strong Flares in 2001

Exceptionally strong and long lasting flaring activity of the blazar Markarian 421 (Mrk 421) occurred between January and March 2001. Based on the excellent signal-to-noise ratio of the data we derive the energy spectrum between 260 GeV - 17 TeV with unprecedented statistical precision. The spectrum is not well described by a simple power law even with a curvature term. Instead the data can be described by a power law with exponential cutoff: $\rm {{dN}\over{dE}} \propto \rm E^{-2.14 \pm 0.03_{stat}} \times e^{-E/E_{0}} m^{-2} s^{-1} TeV^{-1}$ with $\rm E_{0} = 4.3 \pm 0.3_{stat} TeV$. Mrk 421 is the second $γ$-ray blazar that unambiguously exhibits an absorption-like feature in its spectral energy distribution at 3-6 TeV suggesting that this may be a universal phenomenon, possibly due to the extragalactic infra-red background radiation.

astro-ph↗

arXiv2000

Gamma-ray Observations of the Galactic Plane at Energies E > 500 GeV

In 1998 and 1999 the Whipple Observatory 10 m telescope was used to search for diffuse gamma ray emission from the Galactic Plane. No signifiant evidence of emission was found. Assuming the TeV emission profile matches EGRET observations above 1 GeV with a differential spectral index of 2.4, we derive an upper limit of {$\rm {3.0\cdot10^{-8}cm^{-2}s^{-1}sr^{-1}}$} for the average diffuse emission above {$\rm500 GeV$} in the galactic latitude range from {$\rm-2^o$ to $\rm +2^o$} at galactic longitude {$\rm 40^o$}. Comparisons with EGRET observations provide a lower limit of 2.31 for the differential spectral index of the diffuse emission, assuming there is no break in the spectrum between 30 GeV and 500 GeV. This constrains models for diffuse emission with a significant inverse Compton contribution.

astro-ph↗

arXiv1999

Search for Pulsed TeV Gamma-ray Emission from the Crab Pulsar

We present the results of a search for pulsed TeV emission from the Crab pulsar using the Whipple Observatory's 10 m gamma-ray telescope. The direction of the Crab pulsar was observed for a total of 73.4 hours between 1994 November and 1997 March. During this period the Whipple 10 m telescope was operated at its lowest energy threshold to date. Spectral analysis techniques were applied to search for the presence of a gamma-ray signal from the Crab pulsar over the energy band 250 GeV to 4 TeV. We do not see any evidence of the 33 ms pulsations present in other energy bands from the Crab pulsar. The 99.9% confidence level upper limit for pulsed emission above 250 GeV is derived to be 4.8x10^-12 cm^-2 s^-1 or <3% of the steady flux from the Crab Nebula. These results imply a sharp cut-off of the power-law spectrum seen by the EGRET instrument on the Compton Gamma-Ray Observatory. If the cut-off is exponential, it must begin at 60 GeV or lower to accommodate these upper limits.

astro-ph↗

arXiv1999

Gravitational Microlensing Evidence for a Planet Orbiting a Binary Star System

The study of extra-solar planetary systems has emerged as a new discipline of observational astronomy in the past few years with the discovery of a number of extra-solar planets. The properties of most of these extra-solar planets were not anticipated by theoretical work on the formation of planetary systems. Here we report observations and light curve modeling of gravitational microlensing event MACHO-97-BLG-41, which indicates that the lens system consists of a planet orbiting a binary star system. According to this model, the mass ratio of the binary star system is 3.8:1 and the stars are most likely to be a late K dwarf and an M dwarf with a separation of about 1.8 AU. A planet of about 3 Jupiter masses orbits this system at a distance of about 7 AU. If our interpretation of this light curve is correct, it represents the first discovery of a planet orbiting a binary star system and the first detection of a Jovian planet via the gravitational microlensing technique. It suggests that giant planets may be common in short period binary star systems.

astro-ph↗

arXiv1999

Whipple Observations of BL Lac Objects

Only BL Lac objects have been detected as extragalactic sources of very high energy (E > 300 GeV) gamma rays. Using the Whipple Observatory Gamma-ray Telescope, we have attempted to detect more BL Lacs using three approaches. First, we have conducted surveys of nearby BL Lacs, which led to the detections of Mrk 501 and 1ES 2344+514. Second, we have observed X-ray bright BL Lacs when the RXTE All-Sky Monitor identifies high state X-ray emission in an object, in order to efficiently detect extended high emission states. Third, we have conducted rapid observations of several BL Lacs and QSOs located close together in the sky to search for very high flux, short time-scale flare states such as have been seen from Mrk 421. We will present the results of a survey using the third observational technique.

astro-ph↗

arXiv1999

The Very Energetic Radiation Imaging Telescope Array System (VERITAS)

We give an overview of the current status and scientific goals of VERITAS, a proposed hexagonal array of seven 10 m aperture imaging Cherenkov telescopes. The selected site is Montosa Canyon (1390 m a.s.l.) at the Whipple Observatory, Arizona. Each telescope, of 12 m focal length, will initially be equipped with a 499 element photomultiplier camera covering a 3.5 degree field of view. A central station will initiate the readout of 500 MHz FADCs upon receipt of multiple telescope triggers. The minimum detectable flux sensitivity will be 0.5% of the Crab Nebula flux at 200 GeV. Detailed simulations of the array's performance are presented elsewhere at this meeting. VERITAS will operate primarily as a gamma-ray observatory in the 50 GeV to 50 TeV range for the study of active galaxies, supernova remnants, pulsars and gamma-ray bursts.

astro-ph↗

arXiv1999

A Search for Pulsed TeV Gamma Ray Emission from the Crab Pulsar

We present the results of a search for pulsed TeV emission from the Crab pulsar using the Whipple Observatory's 10m gamma-ray telescope. The direction of the Crab pulsar was observed for a total of 73.4 hours between 1994 November and 1997 March. Spectral analysis techniques were applied to search for the presence of a gamma-ray signal from the Crab pulsar over the energy band 250GeV to 4TeV. At these energies we do not see any evidence of the 33ms pulsations present at lower energies from the Crab pulsar. The 99.9% confidence level upper limit for pulsed emission above 250GeV is derived to be 4.8 10^-12 cm^-2 s^-1 or <3% of the steady flux from the Crab Nebula. These results imply a sharp cut-off of the power-law spectrum seen by the EGRET instrument on the Compton Gamma-Ray Observatory. If the cut-off is exponential, it must begin at 60GeV or lower to accommodate these upper limits.

astro-ph↗

arXiv1999

Hour-Scale Multiwavelength Variability in Markarian 421

Markarian 421 was observed for about four days with BeppoSAX and the Whipple Observatory gamma-ray telescope in April 1998. A pronounced, well-defined, flare with hour-scale variability was observed simultaneously in X-rays and very high energy gamma-rays. These data provide the first evidence that the X-ray and TeV intensities are well correlated on time-scales of hours. While the rise of the flare occurred on a similar time-scale in the two wavebands, the decay of the flare was much more rapid in gamma rays, providing the first clear indication that the X-ray and gamma-ray emission may not be completely correlated in Markarian 421.

astro-ph↗

arXiv1999

VHE gamma-ray observations of Markarian 501

Markarian 501, a nearby (z=0.033) X-ray selected BL Lacertae object, is a well established source of Very High Energy (VHE, E>=300 GeV) gamma rays. Dramatic variability in its gamma-ray emission on time-scales from years to as short as two hours has been detected. Multiwavelength observations have also revealed evidence that the VHE gamma-ray and hard X-ray fluxes may be correlated. Here we present results of observations made with the Whipple Collaboration's 10 m Atmospheric Cerenkov Imaging Telescope during 1999 and discuss them in the context of observations made on Markarian 501 during the period from 1996-1998.

astro-ph↗

arXiv1999

Search for TeV Gamma-Rays from Shell-Type Supernova Remnants

If cosmic rays with energies <100 TeV originate in the galaxy and are accelerated in shock waves in shell-type supernova remnants (SNRs), gamma-rays will be produced as the result of proton and electron interactions with the local interstellar medium, and by inverse Compton emission from electrons scattering soft photon fields. We report on observations of two supernova remnants with the Whipple Observatory's 10 m gamma-ray telescope. No significant detections have been made and upper limits on the >500 GeV flux are reported. Non-thermal X-ray emission detected from one of these remnants (Cassiopeia A) has been interpreted as synchrotron emission from electrons in the ambient magnetic fields. Gamma-ray emission detected from the Monoceros/Rosette Nebula region has been interpreted as evidence of cosmic-ray acceleration. We interpret our results in the context of these observations.

astro-ph↗

arXiv1999

The Flux Variability of Markarian 501 in Very High Energy Gamma Rays

The BL Lacertae object Markarian 501 was identified as a source of gamma-ray emission at the Whipple Observatory in March 1995. Here we present a flux variability analysis on several times-scales of the 233 hour data set accumulated over 213 nights (from March 1995 to July 1998) with the Whipple Observatory 10 m atmospheric Cherenkov imaging telescope. In 1995, with the exception of a single night, the flux from Markarian 501 was constant on daily and monthly time-scales and had an average flux of only 10% that of the Crab Nebula, making it the weakest VHE source detected to date. In 1996, the average flux was approximately twice the 1995 flux and showed significant month-to-month variability. No significant day-scale variations were detected. The average gamma-ray flux above ~350 GeV in the 1997 observing season rose to 1.4 times that of the Crab Nebula -- 14 times the 1995 discovery level -- allowing a search for variability on time-scales shorter than one day. Significant hour-scale variability was present in the 1997 data, with the shortest, observed on MJD 50607, having a doubling time of ~2 hours. In 1998 the average emission level decreased considerably from that of 1997 (to ~20% of the Crab Nebula flux) but two significant flaring events were observed. Thus, the emission from Markarian 501 shows large amplitude and rapid flux variability at very high energies as does Markarian 421. It also shows large mean flux level variations on year-to-year time-scales, behaviour which has not been seen from Markarian 421 so far.

astro-ph↗

arXiv1999

Correlated variability of Mkn 421 at X-ray and TeV wavelengths on timescales of hours

Mkn 421 was observed for about two days with BeppoSAX, prior to and partly overlapping the start of a 1 week continuous exposure with ASCA in April 1998, as part of a world-wide multiwavelength campaign. A pronounced, well defined, flare observed in X-rays was also observed simultaneously at TeV energies by the Whipple Observatory's 10 m gamma-ray telescope. These data provide the first evidence that the X-ray and TeV intensities are well correlated on time-scales of hours.

astro-ph↗

arXiv1998

Observations of the Binary Microlens Event MACHO-98-SMC-1 by the Microlensing Planet Search Collaboration

We present the observations of the binary lensing event MACHO-98-SMC-1 conducted at the Mt.~Stromlo 74" telescope by the Microlensing Planet Search (MPS) collaboration. The MPS data constrain the first caustic crossing to have occurred after 1998 June 5.55 UT and thus directly rule out one of the two fits presented by the PLANET collaboration (model II). This substantially reduces the uncertainty in the the relative proper motion estimations of the lens object. We perform joint binary microlensing fits of the MPS data together with the publicly available data from the EROS, MACHO/GMAN and OGLE collaborations. We also study the binary lens fit parameters previously published by the PLANET and MACHO/GMAN collaborations by using them as initial values for $χ^2$ minimization. Fits based on the PLANET model I appear to be in conflict with the GMAN-CTIO data. From our best fit, we find that the lens system has a proper motion of $μ= 1.3\pm 0.2 \kmsk$ with respect to the source, which implies that the lens system is most likely to be located in the Small Magellanic Cloud strengthening the conclusion of previous reports.

astro-ph↗

arXiv1998

Tev Blazars: Status of Observations

The close relation between ground-based TeV observations and satellite borne $γ$-ray measurements has been important for the understanding of blazars. The observations which involve the TeV component in blazar studies are reviewed.

astro-ph↗

arXiv1998

A Study of High Energy Emission from the TeV blazar Mrk 501 during Multiwavelength Observations in 1996

We present the results of a multiwavelength campaign for Mrk 501 performed in March 1996 with ASCA, EGRET, Whipple, and optical telescopes. In the X-ray band, a spectral break was observed around 2 keV. We report here for the first time the detection of high-energy gamma-ray flux from Mrk 501 with EGRET with 3.5 sigma significance (E>100 MeV). Higher flux was also observed in April/May 1996, with 4.0 sigma significance for E>100 MeV, and 5.2 sigma significance for E>500 MeV. The gamma-ray spectrum was measured to be flatter than most of the gamma-ray blazars. We find that the multiband spectrum in 1996 is consistent with that calculated from a one-zone SSC model in a homogeneous region. In the context of this model, we investigate the values of the magnetic field strength and the beaming factor allowed by the observational results. We compare the March 1996 multiwavelength spectrum with that in the flare state in April 1997. Between these two epochs, the TeV flux increase is well correlated with that observed in keV range. The keV and TeV amplitudes during the April 1997 flare are accurately reproduced, assuming that the population of synchrotron photons in 1996 are scattered by the newly injected relativistic electrons, having maximum energies of G_max = 6.0e6. However, the TeV spectrum observed during March 1996 campaign is flatter than predicted by our models. We find that this cannot be explained by either higher order Comptonization or the contribution of the `seed' IR photons from the host galaxy for the first-order external radiation Comptonization.

astro-ph↗

arXiv1998

Limits to Quantum Gravity Effects from Observations of TeV Flares in Active Galaxies

We have used data from the TeV gamma-ray flare associated with the active galaxy Markarian 421 observed on 15 May 1996 to place bounds on the possible energy-dependence of the speed of light in the context of an effective quantum gravitational energy scale. The possibility of an observable time dispersion in high energy radiation has recently received attention in the literature, with some suggestions that the relevant energy scale could be less than the Planck mass and perhaps as low as 10^16 GeV. The limits derived here indicate this energy scale to be in excess of 4x10^16 GeV at the 95% confidence level. To the best of our knowledge, this constitutes the first convincing limit on such phenomena in this energy regime.

gr-qc↗

arXiv1998

New Limits to the IR Background: Bounds on Radiative Neutrino Decay and on VMO Contributions to the Dark Matter Problem

From considering the effect of gamma-gamma interactions on recently observed TeV gamma-ray spectra, improved limits are set to the density of extragalactic infrared (IR) photons which are robust and essentially model-independent. The resulting limits are up to two orders of magnitude more restrictive than direct observations in the 0.025-0.3eV regime. These limits are used to improve constraints on radiative neutrino decay in the mass range above 0.05eV and on Very Massive Objects (VMOs) as providing the dark matter needed to explain galaxy rotation curves.

astro-ph↗

arXiv1997

Discovery of >350 GeV Gamma Rays from the BL Lacertae Object 1ES 2344+514

We present the discovery of >350 GeV gamma-ray emission from the BL Lacertae object 1ES 2344+514 with the Whipple Observatory 10m gamma-ray telescope. This is the third BL Lac object detected at gamma-ray energies above 300 Gev, the other two being Markarian 421 (Mrk 421) and Mrk501. These three active galactic nuclei are all X-ray selected and have the lowest known redshifts of any BL Lac objects currently identified. The evidence for emission derives primarily from an apparent flare on December 20, 1995 when a 6 sigma excess was detected with a flux approximately 63% of the very high energy gamma-ray emission from the Crab Nebula, the standard candle for TeV gamma-ray sources. Excluding the flare, observations between October 1995 and January 1996 yield a 4 sigma detection corresponding to 11% of the VHE Crab Nebula flux. Observations spanning September 1996 to January 1997 failed to yield a significant detection of a steady flux or any flaring. For this period, the 99.9% confidence level upper limit is <8% of the Crab Nebula. The low baseline emission level and variations in nightly and yearly flux of 1ES 22344+514 are the same as the VHE emission characteristics of Mrk 421 and Mrk 501

astro-ph↗