Multiwavelength study of VHE emission from Markarian 501 using TACTIC observations during April–May, 2012

Abstract

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 ∼66.3 hours of clean data revealed the presence of a TeV γ-ray signal (686±77 γ-ray events) from the source direction with a statistical significance of 8.89σ above 850 GeV. Further, a total of 375 ± 47 γ-ray like events were detected in 25.2 hours of observation from 22 -27 May, 2012 with a statistical significance of 8.05σ 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 −Γ with f 0 = (2.27 ± 0.38) × 10photons cm −2 s −1 TeV −1 and Γ = 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 Email address: chandrap@barc.gov.in (P Chandra) Preprint submitted to New AstronomyJanuary 26, 2017 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.

20 Years of Indian Gamma Ray Astronomy Using Imaging Cherenkov Telescopes and Road Ahead

“…The model predicted a tangled magnetic field of 0.12 Gauss in a spherical emission region of radius 6.1 × 10 15 cm. The energy distribution of relativistic electrons in the emission zone followed a smooth broken power law with indices 2.1 and 4.9 before and after the break, respectively [69,73]. These findings are found to be broadly consistent with the results from the multi-wavelength observations of the source during April-August, 2013, including data from MAGIC and VERITAS telescopes [74].…”

“…A multi-wavelength study of the TeV γ-ray emission from Mrk 501 was performed using TACTIC observations during April-May, 2012 [69]. Analysis of the TACTIC light curve during this period indicated a relatively high gamma-ray emission state of the source between 22 and 27 May 2012.…”

The origin of multi-TeV flares from the nearest blazar Markarian 421

“…From the continuous monitoring and dedicated multi-wavelength observations of the nearest HBLs Markarian 421 (Mrk 421, z=0.0308 [26,27]), Mrk 501 (z=0.033 [27,28]) and 1ES 1959+650 (z=0.047 [29]), several major multi-TeV flares have been observed [30][31][32][33][34]. Strong temporal correlation in different wavebands, particularly in X-rays and VHE γ-rays has been observed in some flaring events, however, in some other flaring events no such correlation is observed [35,36], which seems unusual for a leptonic origin [17][18][19]37] of the multi-TeV emissions and needs to be addressed through other alternative mechanisms [38][39][40][41][42][43][44].…”

Multi-TeV flaring in nearby high-energy blazars: A photohadronic scenario

“…From the continuous monitoring and dedicated multi-wavelength observations of the nearest HBLs Markarian 421 (Mrk 421, z=0.0308 [57,58]), Mrk 501 (z=0.033 [58,59]) and 1ES 1959+650 (z=0.047 [60]), several major multi-TeV flares have been observed [61][62][63][64][65]. Strong temporal correlation in different wavebands, particularly in X-rays and VHE γ-rays has been observed in some flaring events, however, in some other flaring events no such correlation is observed [15,16], which seems unusual for a leptonic origin [9,10,12,66] of the multi-TeV emissions and needs to be addressed through other alternative mechanisms [55,[67][68][69][70][71]98].…”