25 research outputs found
Optical polarimetry of the blazar CGRaBS~ J0211+1051 from MIRO
We report the detection of high polarization in the first detailed optical
linear polarization measurements on the BL Lac object CGRaBS J0211+1051, which
flared in -rays on 2011 January 23 as reported by Fermi. The
observations were made during 2011 January 30 - February 3 using
photo-polarimeter mounted at the 1.2m telescope of Mt Abu InfraRed
Observatory(MIRO). The CGRaBS J0211+1051 was detected to have degree of polarization (DP) with steady position angle (PA) at
43 on 2011 January 30. During Jan 31 and Feb 1, while polarization
shows some variation, position angle remains steady for the night. Several
olarization flashes occurred during February 2 and 3 resulting in changes in
the DP by more than 4% at short time scales ( 17 to 45 mins). A mild
increase in the linear polarization with frequency is noticed during the nights
of February 2 & 3. The source exhibited significant inter-night variations in
the degree of polarization (changed by about 2 to 9%) and position angle
(changed by 2 to 22) during the five nights of observations. The
intra-night activity shown by the source appears to be related to turbulence in
the relativistic jet. Sudden change in the PA accompanied by a rise in the DP
could be indicative of the fresh injection of electrons in the jet. The
detection of high and variable degree of polarization categorizes the source as
low energy peaked blazar.Comment: 14-pages including 3-figure
Electronics design and development of Near-Infrared Imager, Spectrometer and Polarimeter
NISP, a multifaceted near-infrared instrument for the upcoming 2.5m IR
telescope at MIRO Gurushikhar, Mount Abu, Rajasthan, India is being developed
at PRL, Ahmedabad. NISP will have wide (FOV = 10' x 10') field imaging,
moderate (R=3000) spectroscopy and imaging polarimetry operating modes. It is
designed based on 0.8 to 2.5 micron sensitive, 2048 X 2048 HgCdTe (MCT) array
detector from Teledyne. Optical, Mechanical and Electronics subsystems are
being designed and developed in-house at PRL. HAWAII-2RG (H2RG) detector will
be mounted along with controlling SIDECAR ASIC inside LN2 filled cryogenic
cooled Dewar. FPGA based controller for H2RG and ASIC will be mounted outside
the Dewar at room temperature. Smart stepper motors will facilitate motion of
filter wheels and optical components to realize different operating modes.
Detector and ASIC temperatures are servo controlled using Lakeshore's
Temperature Controller (TC) 336. Also, several cryogenic temperatures will be
monitored by TC for health checking of the instrument. Detector, Motion and
Temperature controllers onboard telescope will be interfaced to USB Hub and
fiber-optic trans-receiver. Remote Host computer interface to remote end
trans-receiver will be equipped with in-house developed GUI software to control
all functionalities of NISP. Design and development aspects of NISP Electronics
will be presented in this conference.Comment: 6 pages, 3 figures, Submitted to SPIE Conference Astronomical
Telescopes + Instrumentation 202
35th International Cosmic Ray Conference, ICRC 2017
PKS1510-089 is a flat spectrum radio quasar located at a redshift of 0.36. It is one of only a few such sources detected in very-high-energy (VHE, >100 GeV) gamma rays. Though PKS1510-089 is highly variable at GeV energies, until recently no variability has been observed in the VHE band. In 2015 May PKS1510-089 showed a high state in optical and in the GeV range. A VHE gamma-ray flare was detected with MAGIC at that time, showing the first instance of VHE gamma-ray flux variability on the time scale of days in this source. We will present the MAGIC results from this observation, discuss their temporal and spectral properties in the multi-wavelength context and present modelling of such emission in the external Compton scenario.</p
CTA 102 in exceptionally high state during 2016-2017
Blazars in outburst provide a unique opportunity to study their spectral behavior, correlated variations at different frequencies, and jet structure. An unprecedented flaring activity in FSRQ CTA 102, occuring from 2016 November to 2017 January, is used here for a detailed study to understand flaring mechanisms at short and long timescales, spectral behavior in different energy regimes, and to estimate sizes and location of the high-energy emitting region in the jet. Multiwavelength (MW) data for CTA 102 during its outburst period, were obtained from Fermi-LAT, Swift-XRT/UVOT, Steward Observatory, Mt Abu Infrared Observatory, and OVRO. These were analyzed to construct MW light curves, extract the spectral information, and to perform the correlated variability studies. Our study shows that CTA 102 attained the highest ever flux levels across the electromagnetic spectrum (EMS) while flaring and otherwise, with rapid and prolonged activities at all the frequencies. A number of short-term (three to eight days) and long-term (more than a month) variability events are noticed across the EMS. We infer a redder when brighter trend in faint state and a bluer when brighter trend during a few optical flares. Based on the flux doubling timescale, the size of γ-ray emitting region is estimated as ≈8.76 × 1015 cm, located at a distance of about 5.58 × 1016 cm from the central engine. CTA 102 was in extremely bright phase during 2016–2017, possibly due to, successive high energy particle injections into the jet, creating shocks traveling down the jet which lead to the overall flux enhancement across the EMS. Alternatively, a decreasing viewing angle could also lead to such flux enhancement. The study reveals correlated variations in all the energy bands, with lags within time bins, indicating co-spatial origin of the emissions. During the flaring event, a bluer-when-brighter color in the optical and harder when brighter trend in the X-ray and γ-ray spectra are noticed. During some flares softer γ-ray spectra are observed.by Navpreet Kaur and Kiran S. Baliya
Optical intra-day variability in 3C 66A: 10 years of observations
by Navpreet Kaur, Baliyan Sameer, S. Kiran and S. Ganes