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 $\gamma$-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 $\sim21.05\pm 0.41$ degree of polarization (DP) with steady position angle (PA) at 43$^\circ$ 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 ($\sim$ 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$^\circ$) 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

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

Optical intra-day variability in 3C 66A: a decade of observations

We present results based on the observations of the blazar 3C 66A from 2005 November 06 to 2016 February 14 in the BVR and I broad-bands using the 1.2-m telescope of the Mt Abu InfraRed Observatory (MIRO). The source was observed on 160 nights; on 89 of these nights, it was monitored for more than 1 h to check for the presence of any intra-day variability (IDV). The blazar 3C 66A exhibited significant variations in the optical flux on short- and long-term time-scales. However, unlike the highly variable S5 0716+71, it showed an IDV duty cycle of about 8 per cent only. Our statistical studies suggest IDV time-scales ranging from ∼37 min to about 3.12 h and, in one case, the possibility of quasi-periodic variations with a characteristic time-scale of ∼1.4 h. The IDV amplitudes in the R band were found to vary from 0.03 mag to as much as 0.6 mag, with a larger amplitude of variation when the source was relatively fainter. The typical rate of the flux variation was estimated to be ∼0.07 mag h−1 in both the rising and the falling phases. However, rates of brightness variation as high as 1.38 mag h−1 were also detected. The shortest time-scale of the variation (i.e. 37 min) sets an upper limit of 6.92 × 1014 cm on the size of the emission region and about 3.7 × 108 M⊙ as an estimate of the mass of the black hole, assuming that the origin of the rapid optical variability is in close vicinity to the central supermassive black hole. The long-term study suggests a mild bluer-when-brighter behaviour, typical for BL Lacertae objects.by Navpreet Kaur, Sameer, Kiran S. Baliyan and S. Ganes

Study of AGNs using blazar variability as a tool

by Navpreet Kaur et.a