The radio galaxy NGC 1275, located at the central region of Perseus cluster, is a well-known very high-energy (VHE) gamma-ray emitter. The Major Atmospheric Cherenkov Experiment Telescope has detected two distinct episodes of VHE (E > 80 GeV) gamma-ray emission from NGC 1275 during 2022 December and 2023 January. The second outburst, observed on 2023 January 10, was the more intense of the two, with flux reaching 58% of the Crab Nebula flux above 80 GeV. The differential energy spectrum measured between 80 GeV and 1.5TeV can be described by a power law with a spectral index of Gamma=-2.90 +/- 0.16(stat) for both flaring events. The broadband spectral energy distribution derived from these flares, along with quasisimultaneous low-energy counterparts, suggests that the observed gamma-ray emission can be explained using a homogeneous single-zone synchrotron self-Compton model. The physical parameters derived from this model for both flaring states are similar. The intermediate state observed between two flaring episodes is explained by a lower Doppler factor or magnetic field, which subsequently returned to its previous value during the high-activity state observed on 2023 January 10.

The Major Atmospheric Cherenkov Experiment (MACE) is a large size (21m) Imaging Atmospheric Cherenkov Telescope (IACT) installed at an altitude of 4270m above sea level at Hanle, Ladakh in northern India. Here we report the detection of Very High Energy (VHE) gamma-ray emission from Crab Nebula above 80 GeV. We analysed ~15 hours of data collected at low zenith angle between November 2022 and February 2023. The energy spectrum is well described by a log-parabola function with a flux of ~(3.46 +/- 0.26stat) x 10-10 TeV-1 cm-2 s-1, at 400 GeV with spectral index of 2.09 +/- 0.06stat and a curvature parameter of 0.08 +/- 0.07stat. The gamma-rays are detected in an energy range spanning from 80 GeV to ~5 TeV. The energy resolution improves from ~34% at an analysis energy threshold of 80 GeV to ~21% above 1 TeV. The daily light curve and the spectral energy distribution obtained for the Crab Nebula is in agreement with previous measurements, considering statistical and systematic uncertainties.

ABSTRACT 1ES 1959+650, a high-energy peaked BL Lac object (HBL) with redshift z = 0.047, is known to exhibit flux and spectral variability in different energy bands. In this work, we primarily considered the simultaneous Fermi-LAT and Swift-XRT data of 1ES 1959+650 to study the flux and spectral variability in the energy ranges (0.1–300 GeV) and (0.6–10 keV), respectively. Using the Fermi-LAT light curve, a stretch of quiescent state and three high flux states of the source were identified. The flux and the spectral variability were studied using flare profiles and flux-index loops. In the γ-ray energies, 1ES 1959+650 clearly showed the evolution ‘softer-when-brighter’ whereas in the X-rays it showed the trend ‘harder-when-brighter’. 1ES 1959+650 also showed quick changes in spectral shape in the γ-ray band when the γ-ray flux was changing during the flares. The spectral energy distributions (SEDs) of the source were constructed using simultaneous data from Fermi-LAT, Swift-XRT, Swift-UVOT during its evolution. The TeV data from TACTIC imaging telescope were also used to construct the SED in the quiescent state. The spectral modelling of the SEDs revealed that due to the spectral variability of 1ES 1959+650, the standard leptonic one zone model cannot be used to explain the emission from this source. Instead a two zone leptonic model is needed to explain the observed SEDs from this blazar.

The MACE telescope has recently been commissioned at Hanle, Ladakh, India. It had its first light in April 2021 with a successful detection of very high energy gamma-ray photons from the standard candle Crab Nebula. Equipped with a large light collector of 21 m diameter and situated at an alti-tude of similar to 4.3 km amsl, the MACE telescope is expected to explore the mysteries of the non-thermal Universe in the energy range above 20 GeV with very high sensitivity. It can also play an important role in carrying out multi-messenger astronomy in India.

We present a long-term multi-wavelength study of the flat spectrum radio quasar 3C 279 using near simultaneous observations available from July 01, 2012 and June 31, 2018 (MJD 56109-58301). The data set includes measurements from the TACTIC, Fermi-LAT, Swift-XRT, Swift-UVOT, SMARTS, Steward-SPOL, and OVRO. The TACTIC telescope has monitored the source 3C 279 for ∼ 70 h between 2013 and 2018 in the energy range of > 0.85 TeV and yields null result. We have analysed the Fermi-LAT data to obtain the 5-day binned light curve in the energy range 0.1–300 GeV. One low and six high emission states are identified in the Fermi-LAT light curve. The high emission states are modelled with an exponential rise and decay time profile using 1-day averaged flux points and have been characterized as the asymmetric flares. The spectral analysis of near simultaneous X-ray and γ-ray data from the Swift-XRT and Fermi-LAT respectively indicates harder when brighter trend during the high activity states. The time averaged broadband spectral energy distributions corresponding to the seven states are successfully reproduced under the framework of a simple one zone leptonic emission model with IR photons originating from the dusty torus as the dominant target for the inverse Compton scattering by the relativistic electrons. Results obtained from the broadband modelling suggest that the non-thermal emission region in the jet is above the broadline region. This is also supported by the average value of seed factor estimated using the derived model parameters. A positive correlation between the bulk Lorentz factor of the emission zone and average γ-ray flux measurements for each state indicates that an increase in the bulk Lorentz factor can be the dominant cause for the observed flares from 3C 279. We also discuss the implications of the obtained model parameters in detail to understand the long-term behaviour of the source.

MACE (Major Atmospheric Cherenkov Experiment) is a Very High Energy (VHE) γ ray telescope, under installation at Hanle (32∘46′46′′ N, 78°58′35′′ E) in the Himalayan ranges of North India. It is a 21 m diameter dish and 25 m focal length Imaging Atmospheric Cherenkov Telescope (IACT) located at an altitude of 4270 m, highest for any existing IACT. In this paper, we estimate 4 performance characteristics of the MACE telescope, namely the trigger rate, the integral flux sensitivity, the angular resolution and the energy resolution in the dynamic energy range of ∼ 30 GeV–10 TeV in the low zenith angle range (< 30°). We observe that the integral rate of the MACE telescope for the 4 closed clusters nearest neighbor (CCNN) trigger with single-channel photoelectron threshold of 9.0 photoelectrons is 1.03 kHz. The integral flux sensitivity of the telescope is expected to be 2.4 % with the threshold energy of 31 GeV. We employ the Random Forest method (RFM) and show that the MACE telescope is estimated to have an angular resolution, defined as the σ of a 2-dimensional Gaussian distribution, of ∼0.21° in the energy range of 30.0–47.0 GeV. The angular resolution improves with increasing γ-ray energy and reaches to a value of ∼0.06° in the energy range of 1.8 TeV–3 TeV. We also evaluate 68% containment radius (σ0.68) for the distribution of reconstructed arrival directions as an alternative estimate of angular resolution. We find σ0.68 to steadily improve from a value of 0.36°in the energy range of 30.0–47 GeV to a value of ∼0.09° in the energy range of 1.8–3 TeV. We also reconstructed γ-ray energies using the regressive RFM and estimated the energy resolution, defined as the σ of the 1-D Gaussian fitted to distribution of fractional difference between the true and estimated energy, as a function of γ-ray energy. The MACE telescope is estimated to have energy resolution of ∼40% in the energy range (30–47) GeV (close to the analysis energy threshold of the MACE telescope), which improves to ∼19.8% in the energy bin of 1.8–3 TeV. The bias in the corresponding energy ranges improves from ∼36% to ∼−0.2%.

Located in the Perseus galaxy cluster, NGC 1275 (z = 0.0179), is the brightest radio galaxy detected in both high energy (HE; E > 100 MeV) and very high energy (VHE; E > 100 GeV) regimes. Here we present the results from the observations of NGC 1275 with TACTIC for 37.1 h between December, 2016 and February, 2017. In the absence of a statistically significant VHE gamma-ray detection from the TACTIC observations, we estimate the 3 sigma upper limit on the integral flux above 0.85 TeV to be 2.85 x 10(-11) erg cm(-2) s(-1). We also report the results of near simultaneous multiwavelength observations of the source from the Fermi-LAT, Swift-XRT/UVOT and OVRO. We find the source to be in flaring state on the night of 31 December, 2016 - 1 January, 2017 when the HE gamma-ray flux above 0.1 GeV went up to 2.0 x 10(-6) ph cm(-2) s(-1) which is approximately 4 times the flux level during its low state. We present the broad-band spectral energy distributions (SED) of the source during its flaring and low states. It is evident from the SED that the VHE upper limit obtained from the TACTIC observations is consistent with the low emission state of the source.

High Energy Physics (HEP) Experiments produce large amounts of data. The data produced in these experiments are in the range of terabytes and petabytes. The explosion of data has posed a challenge in data capture, storage, data integrity, searching, querying, visualization and analysis. This has led to the development of domain-specific file formats like FITS, HDF5, analysis frameworks like ROOT, storage architectures like relational and NoSQL databases, and parallel and distributed data handling methodologies. In this paper, we investigate the read–write performance by comparing the HEP domain-specific framework ROOT and a NoSQL database Berkeley DB in the context of a gamma-ray Cerenkov experiment to meet the requirement of real-time data analysis. Major Atmospheric Cerenkov Experiment (MACE) is a 21 m gamma-ray telescope set up by BARC at HANLE, India. It will generate a few hundred gigabytes of data per observational night. Aiming at the real-time analysis of the data we have developed a dynamic reading mechanism by implementing a binary type provider for data retrieval from the Berkeley DB database. Data analysis queries were performed and compared both in ROOT files using ROOT query methods and in Berkeley DB using Language Integrated Queries (LINQ). Finally, a generic framework facilitating the online analysis of the data is proposed in this paper.

In this work, we study the short term flaring activity from the high synchrotron peaked blazar Mrk 501 detected by the FACT and H.E.S.S. telescopes in the energy range 2-20 TeV during June 23-24, 2014 (MJD 56831.86-56831.94). We revisit this major TeV flare of the source in the context of near simultaneous multi-wavelength observations of gamma-rays in MeV-GeV regime with Fermi-LAT, soft X-rays in 0.3-10 keV range with Swift-XRT, hard X-rays in 10-20 keV and 15-50 keV bands with MAXI and Swift-BAT respectively, UV-Optical with Swift-UVOT and 15 GHz radio with OVRO telescope. We have performed a detailed temporal and spectral analysis of the data from Fermi-LAT, Swift-XRT and Swift-UVOT during the period June 15-30, 2014 (MJD 56823-56838). Near simultaneous archival data available from Swift-BAT, MAXI and OVRO telescope along with the V-band optical polarization measurements from SPOL observatory are also used in the study of giant TeV flare of Mrk 501 detected by the FACT and H.E.S.S. telescopes. No significant change in the multi-wavelength emission from radio to high energy gamma-rays during the TeV flaring activity of Mrk 501 is observed except variation in soft X-rays. The varying soft X-ray emission is found to be correlated with the gamma-ray emission at TeV energies during the flaring activity of the source. The soft X-ray photon spectral index is observed to be anti-correlated with the integral flux showing-harder-when-brighter behavior. An average value of 4.5% for V-band optical polarization is obtained during the above period whereas the corresponding electric vector position angle changes significantly. We have used the minimum variability timescale from the H.E.S.S. observations to estimate the Doppler factor of the emission region which is found to be consistent with the previous studies of the source. (C) 2018 COSPAR. Published by Elsevier Ltd. All rights reserved.

In this work, we report on the detection of enhanced TeV gamma- ray emission from the high synchrotron peaked blazar Mrk 421 with the TACTIC telescope on the night of December 28, 2014 (MJD 57019). We use data from the TACTIC observations of Mrk 421 for one week during December 25-31, 2014 (MJD 57016-57022) in this study. The TACTIC observation on December 28, 2014 (MJD 57019) alone results in the detection of 86 17 gamma- ray like events from Mrk 421 with a statistical significance of 5.17 sigma in a live time of similar to 2.2 hours above an energy threshold of 0.85 TeV. The high statistics (higher than three Crab Units) of TeV photons enables us to study the very high energy (VHE) gamma- ray emission from the source at shorter timescales. A minimum variability timescale of similar to 0.72 days is obtained for the TeV gamma- ray emission from Mrk 421 during the above flaring activity of the source. The intrinsic VHE spectrum is described by a power law with spectral index of 2.99 +/- 0.38 in the energy range 0.85-8.5 TeV. The integral VHE gamma- ray flux above 0.85 TeV is determined to be (3.68 +/- 0.64) x 10(-11) ph cm(-2) s(-1) from the TACTIC observations of Mrk 421 on the night of December 28, 2014 (MJD 57019). Near simultaneous measurements by the HAWC observatory give an integral flux of (2.90 +/- 0.40) x 10(-11) ph cm(-2) s(-1) above 2 TeV from Mrk 421 observations on December 29, 2014 (MJD 57020.33-57020.58). We have also analysed the contemporaneous data from Fermi-LAT to study the high energy (HE) gamma- ray emission during the high activity state of the source. The HE gamma- ray emission is observed to be increasing after the TeV flaring activity detected with the TACTIC. We also use other near simultaneous archival data available from the Swift-BAT in hard X-rays and from SPOL at Steward Observatory in optical V and R bands to characterize the multi-wavelength emission of Mrk 421 during the high activity state observed at TeV energies. The TeV gamma- ray emission observed on December 28, 2014 (MJD 57019) is found to be more prominent than the emissions in lower energy bands during the same period. The TeV gamma- ray observation of Mrk 421 in high activity state with the TACTIC telescope is also used to understand the physical mechanism for blazar emission under the frame work of the leptonic single zone synchrotron self Compton process. (C) 2018 Elsevier B.V. All rights reserved.

•Long term observation (three years) with TACTIC telescope in search for TeV gamma-rays from IC 310.•Nearly simultaneous observation with Fermi-LAT and from ARIES observatory to understand emission mechanism.•Upper limits on integral flux in GeV and TeV energies indicate the source to be at low- state of emission.•Optical fluxes from the source, possibilily contaminated with host-galaxy emission, show variability.

We observed the TeV blazar Mrk421 in the very high energy (VHE) region with TACTIC from 21 December, 2014 to 21 February, 2015. The VHE gamma-ray signal is detected from the source at a statistical significance of similar to 9 sigma with 648 +/- 74 gamma-ray like events using a total observation time of 65.6 h of clean data. To denote the active period of the source, the entire observation has been divided into two spells: Spell I (21-30 December, 2014; MJD: 57012-57021) and Spell II (15 January-21 February, 2015; MJD: 57037-57074). The Spell I corresponds to relatively higher activity state wherein 337 +/- 47 gamma-rays are detected at a statistical significance of 7.39 sigma in 21.7 h. During Spell II, 311 +/- 57 gamma-ray events have been detected in similar to 44c at a statistical significance of 5.6 sigma. The analysis of high energy (HE) gamma-ray data from Fermi-LAT has been carried out for the period of TACTIC observations. In addition, near simultaneous multi-wavelength data from Swift-BAT and MAXI in the X-ray region, SPOL in optical V-band and OVRO at 15 GHz radio band have also been considered. The HE gamma-ray and optical observations indicate variability during both the spells whereas hard X-ray observations are consistent with the average emission through out the TACTIC observations. The broad-band spectral energy distributions of the source are reproduced by single zone homogeneous synchrotron self Compton process for the two spells. The model parameters estimated for the two spells are similar except for the particle energy density which is obtained to be slightly higher during Spell I.

In this work, we have reported the results of multiwavelength study of the Fermi hard spectrum blazar B2 0806+35 using data from Swift, Fermi, and TACTIC observations. We analysed Swift/UVOT, Swift/XRT, Fermi/LAT, and TACTIC data to construct the sepctral energy distribution for different epochs over last 7 yr. We modelled the spectral energy distributions using one zone leptonic blazar emission model and emission from optically thick geometrically thin accretion disc around the black hole. It is shown that the photon spectrum in the GeV-TeV energy range is steep and the source is not a good candidate to study intergalactic magnetic field. It is also shown that the accretion disc is systematically receding from the central black hole and the accretion flow is possibly advection dominated.

Strong X-ray and gamma-ray flares have been detected in February 2010 from the high synchrotron peaked blazar Mrk 421 (z = 0.031). With the motivation of understanding the physics involved in this flaring activity, we study the variability of the source in X-ray and gamma-ray energy bands during the period February 10-23, 2010 (MJD 55237-55250). We use near simultaneous X-ray data collected by MAXI, Swift-XRT and gamma-ray data collected by Fermi-LAT and TACTIC along with the optical V-band observations by SPOL at Steward Observatory. We observe that the variation in the one day averaged flux from the source during the flare is characterized by fast rise and slow decay. Besides, the TeV gamma-ray flux shows a strong correlation with the X-ray flux, suggesting the former to be an outcome of synchrotron self Compton emission process. To model the observed X-ray and gamma-ray light curves, we numerically solve the kinetic equation describing the evolution of particle distribution in the emission region. The injection of particle distribution into the emission region, from the putative acceleration region, is assumed to be a time dependent power law. The synchrotron and synchrotron self Compton emission from the evolving particle distribution in the emission region are used to reproduce the X-ray and gamma-ray flares successfully. Our study suggests that the flaring activity of Mrk 421 can be an outcome of an efficient acceleration process associated with the increase in underlying non-thermal particle distribution. (C) 2016 Elsevier B.V. All rights reserved.

List of contributions from the Cherenkov Telescope Array Consortium presented at the 35th International Cosmic Ray Conference, July 12-20 2017, Busan, Korea.

We have observed Markarian 501 in Very High Energy (VHE) gamma-ray wavelength band for 70.6 hours from 15 April to 30 May, 2012 using TACTIC telescope. Detailed analysis of similar to 66.3 hours of clean data revealed the presence of a TeV gamma-ray signal (686 +/- 77 gamma-ray events) from the source direction with a statistical significance of 8.89? above 850 GeV. Further, a total of 375 +/- 47 gamma-ray like events were detected in 25.2 hours of observation from 22 - 27 May, 2012 with a statistical significance of 8.05 sigma indicating that the source has possibly switched over to a relatively high gamma-ray emission state. We have derived time-averaged differential energy spectrum of the state in the energy range 850 GeV - 17.24 TeV which fits well with a power law function of the form dF/dE=f(0)E(-Gamma) with f(0)=(2.27 +/- 0.38)x10(-11) photons cm(-2) s(-1) TeV-1 and Gamma=2.57 +/- 0.15. In order to investigate the source state, we have also used almost simultaneous multiwavelength observations viz: high energy data collected by Fermi-LAT, X-ray data collected by Swift-XRT and MAXI, optical and UV data collected by Swift-UVOT, and radio data collected by OVRO, and reconstructed broad-band Spectral Energy Distribution (SED). The obtained SED supports leptonic model (homogeneous single zone) for VHE gamma-ray emission involving synchrotron and synchrotron self Compton (SSC) processes. (C) 2017 Elsevier B.V. All rights reserved.

The nearby (z = 0.031) TeV gamma-ray emitter BL Lac object Mrk 421 has been observed with the TACTIC telescope for nearly 118 hours during 01 February to 26 April, 2012 (MJD 55958-56044). Detailed analysis reveals the detection of 529 +/- 76 gamma-rays with 6.9 sigma significance above 850 GeV energy threshold during the period of 15-26 March, 2012 (MJD 56001-56013). Nearly simultaneous multiwavelength observations of the source also indicate a comparatively higher flux state during this period (MJD 56001-56013). In this paper, we present the study of Mrk 421 during this period in very high energy (VHE) domain along with the results from high energy (HE), X-ray, optical and radio observations. We reproduce the spectral energy distribution (SED) of the source during this period using the synchrotron and synchrotron self-Compton (SSC) process. The model parameters of the emission region of the source are found to be consistent with the values reported in the literature. (C) 2016 Elsevier B.V. All rights reserved.

The MACE (Major Atmospheric Cherenkov Experiment) is an upcoming Very High Energy (VHE) gamma-ray telescope, based on imaging atmospheric Cherenkov technique, being installed at Hanle, a high altitude astronomical site in Ladakh, India. Here we present Monte Carlo simulation studies of trigger rates and threshold energies of MACE in the zenith angle range of 0 degrees-60 degrees for on-axis gamma-ray coming from point source and various cosmic ray species. We have simulated the telescope's response to gamma-rays, proton, electron and alpha initiated atmospheric Extensive Air Showers (EAS) in the broad energy range of 5 GeV to 20 TeV. For gamma-rays we consider power law and log parabolic spectra while other particles are simulated with their respective cosmic ray spectrum. Trigger rates and threshold energies are estimated for the trigger configuration of 4 Close Cluster Nearest Neighbour(CCNN) pixels as implemented in MACE hardware, in combination with single channel discriminator threshold ranging from 6-10 photo electrons (pe). We find that MACE can achieve the gamma-ray trigger energy threshold of similar to 17 GeV (4 CCNN, 9 pe) at 0 degrees zenith angle for power law spectrum. The total trigger rate at 0 degrees zenith is expected to be similar to 650 Hz, with protons contributing similar to 80% to it. For the zenith range of 0 degrees-40 degrees we find that the telescope can achieve gamma-gray trigger threshold energies of similar to 22 GeV at 20 degrees zenith angle and similar to 40 GeV at 40 degrees zenith angle. Integral rates are also almost constant for this zenith angle range. At zenith angle of 60 degrees, trigger energy threshold increases to similar to 173 GeV and total integral rate falls down to similar to 305 Hz. (C) 2016 Elsevier B.V. All rights reserved.

List of contributions from the CTA Consortium presented at the 34th International Cosmic Ray Conference, 30 July - 6 August 2015, The Hague, The Netherlands.

In this paper, we present results of TeV gamma-ray observations of the high synchrotron peaked BL Lac object 1ES 1218+304 (z = 0.182) with the TACTIC (TeV Atmospheric Cherenkov Telescope with Imaging Camera). The observations are primarily motivated by the unusually hard GeV-TeV spectrum of the source despite its relatively large redshift. The source is observed in the TeV energy range with the TACTIC from March 1, 2013 to April 15, 2013 (MJD 56352-56397) for a total observation time of 39.62 h and no evidence of TeV gamma-ray activity is found from the source. The corresponding 99% confidence level upper limit on the integral flux above a threshold energy of 1.1 TeV is estimated to be 3.41 x10(-12) photons cm(-2) s(-1) (i.e. <23% Crab Nebula flux) assuming a power law differential energy spectrum with photon index 3.0, as previously observed by the MAGIC and VERITAS telescopes. For the study of multi-wavelength emission from the source, we use nearly simultaneous optical, UV and X-ray data collected by the UVOT and XRT instruments on board the Swift satellite and high energy gamma-ray data collected by the Large Area Telescope on board the Fermi satellite. We also use radio data at 15 GHz from OVRO 40 m telescope in the same period. No significant increase of activity is detected from radio to TeV gamma-rays from 1ES1218+304 during the period from March 1, 2013 to April 15, 2013. (C) 2014 Elsevier B.V. All rights reserved.