2 research outputs found
Optical Spectral Variability of the Very-High-Energy Gamma-Ray Blazar 1ES 1011+496
We present results of five years of optical (UBVRI) observations of the
very-high-energy gamma-ray blazar 1ES 1011+496 at the MDM Observatory. We
calibrated UBVRI magnitudes of five comparison stars in the field of the
object. Most of our observations were done during moderately faint states of
1ES 1011+496 with R > 15.0. The light curves exhibit moderate, closely
correlated variability in all optical wavebands on time scales of a few days. A
cross-correlation analysis between optical bands does not show significant
evidence for time lags. We find a positive correlation (Pearson's r = 0.57;
probability of non-correlation P(>r) ~ 4e-8) between the R-band magnitude and
the B - R color index, indicating a bluer-when-brighter trend. Snap-shot
optical spectral energy distributions (SEDs) exhibit a peak within the optical
regime, typically between the V and B bands. We find a strong (r = 0.78;
probability of non-correlation P (>r) ~ 1e-15) positive correlation between the
peak flux and the peak frequency, best fit by a relation with k = 2.05 +/- 0.17. Such a correlation is
consistent with the optical (synchrotron) variability of 1ES 1011+496 being
primarily driven by changes in the magnetic field.Comment: Accepted for publication in ApJ. 16 pages, including 7 figure
Multiwavelength Observations of the Previously Unidentified Blazar RX J0648.7+1516.
We report on the VERITAS discovery of very-high-energy (VHE) gamma- ray
emission above 200 GeV from the high-frequency-peaked BL Lac object
RXJ0648.7+1516 (GBJ0648+1516), associated with 1FGLJ0648.8+1516. The photon
spectrum above 200 GeV is fit by a power law dN/dE = F0(E/E0)-{\Gamma} with a
photon index {\Gamma} of 4.4 {\pm} 0.8stat {\pm}0.3syst and a flux
normalization F0 of (2.3 {\pm}0.5stat {\pm} 1.2sys) {\times} 10-11 TeV-1cm-2s-1
with E0 = 300 GeV. No VHE vari- ability is detected during VERITAS observations
of RXJ0648.7+1516 between 2010 March 4 and April 15. Following the VHE
discovery, the optical identifica- tion and spectroscopic redshift were
obtained using the Shane 3-m Telescope at the Lick Observatory, showing the
unidentified object to be a BL Lac type with a redshift of z = 0.179. Broadband
multiwavelength observations contemporaneous with the VERITAS exposure period
can be used to sub-classify the blazar as a high-frequency-peaked BL Lac (HBL)
object, including data from the MDM ob- servatory, Swift-UVOT and XRT, and
continuous monitoring at photon energies above 1 GeV from the Fermi Large Area
Telescope (LAT). We find that in the absence of undetected, high-energy rapid
variability, the one-zone synchrotron self-Compton model (SSC) overproduces the
high-energy gamma-ray emission measured by the Fermi-LAT over 2.3 years. The
SED can be parameterized sat- isfactorily with an external-Compton or
lepto-hadronic model, which have two and six additional free parameters,
respectively, compared to the one-zone SSC model