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Register a new userMulti-color Optical Variability of the TeV Blazar Mrk 501 in the Low-State
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A. C. Gupta
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We report results based on the monitoring of the BL Lac object Mrk 501 in the optical (B, V and R) passbands from March to May 2000. Observations spread over 12 nights were carried out using 1.2 meter Mount Abu Telescope, India and 61 cm Telescope at Sobaeksan Astronomy Observatory, South Korea. The aim is to study the intra-day variability (IDV), short term variability and color variability in the low state of the source. We have detected flux variation of 0.05 mag in the R-band in time scale of 15 min in one night. In the B and V passbands, we have less data points and it is difficult to infer any IDVs. Short term flux variations are also observed in the V and R bands during the observing run. No significant variation in color (B$-$R) has been detected but (V$-$R) shows variation during the present observing run. Assuming the shortest observed time scale of variability (15 min) to represent the disk instability or pulsation at a distance of 5 Schwarschild radii from the black hole (BH), mass of the central BH is estimated $sim$ 1.20 $times$ 10$^{8} M_{odot}$.
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We have monitored the BL Lac object Mrk 501 in optical $V$, $R$ and $I$ bands from 2010 to 2015. For Mrk 501, the presence of strong host galaxy component can affect the results of photometry. After subtracting the host galaxy contributions, the source shows intraday and long-term variabilities for optical flux and color indices. The average variability amplitudes of $V$, $R$ and $I$ bands are $22.05%, 22.25%, 23.82%$ respectively, and the value of duty cycle 14.87 per cent. A minimal variability timescale of 106 minutes is detected. No significant time lag between $V$ and $I$ bands is found on one night. The bluer-when-brighter (BWB) trend is dominant for Mrk 501 on intermediate, short and intraday timescales which supports the shock-in-jet model. For the long timescale, Mrk 501 in different state can have different BWB trend. The corresponding results of non-correcting host galaxy contributions are also presented.
Mrk 421 and Mrk 501 are two close, bright and well-studied high-synchrotron-peaked blazars, which feature bright and persistent GeV and TeV emission. We use the longest and densest dataset of unbiased observations of these two sources, obtained at TeV and GeV energies during five years with FACT and Fermi-LAT. To characterize the variability and derive constraints on the emission mechanism, we augment the dataset with contemporaneous multi-wavelength observations from radio to X-rays. We correlate the light curves, identify individual flares in TeV energies and X-rays, and look for inter-band connections, which are expected from the shock propagations within the jet. For Mrk 421, we find that the X-rays and TeV energies are well correlated with close to zero lag, supporting the SSC emission scenario. The timing between the TeV, X-ray flares in Mrk 421 is consistent with periods expected in the case of Lense-Thirring precession of the accretion disc. The variability of Mrk 501 on long-term periods is also consistent with SSC, with a sub-day lag between X-rays and TeV energies. Fractional variability for both blazars shows a two bump structure with the highest variability in the X-ray and TeV bands.
We present our observations of the optical intra-day variability (IDV) in $gamma$-ray BL Lac object Mrk 501. The observations were run with the 1.02 m and 2.4 m optical telescopes at Yunnan Observatories from 2005 April to 2012 May. The light curve at the $R$ band on 2010 May 15 passes both variability tests (the $F$ test and the ANOVA test). A flare within the light curve on 2010 May 15 has a magnitude change $Delta m = 0.03 pm 0.005_{rm{stat}} pm 0.007_{rm{sys}}$ mag, textbf{a darkening timescale of $tau_{rm{d}}=$ 26.7 minutes}, and an amplitude of IDV $Amp=2.9% pm0.7%$. A decline textbf{described by 11 consecutive flux measurements} within the flare can be fitted linearly with a Pearsons correlation coefficient $r = 0.945$ at the confidence level of $> 99.99%$. Under the assumptions that the IDV is tightly connected to the mass of the black hole, textbf{and that the flare duration, being two times $tau_{rm{d}}$, is representative of the minimum characteristic timescale, we can derive upper bounds to the mass of the black hole}. In the case of the Kerr black hole, the timescale of $Delta t_{rm{min}}^{rm{ob}}=$ 0.89 hours gives $M_{bullet}la 10^{9.20} M_{odot}$, which is consistent with measurements reported in the literature. This agreement indicates that the hypothesis about $M_{bullet}$ and $Delta t_{rm{min}}^{rm{ob}}$ is consistent with the measurements/data.
Energy spectra of gamma-ray blazars may contain an imprint from the cosmic infrared background radiation due to gamma-ray absorption (pair-production) by soft photons constituting the extragalactic background light (EBL). The signature of this imprint depends on the spectral shape of the EBL. In this work we correct the observed spectra of Mrk 421 and Mrk 501 for absorption using different possible realizations of the EBL, consistent with the most recent detections and limits. We present the intrinsic gamma-ray spectrum of these sources for the different EBL scenarios. These spectra reveal their true peak energy and luminosities, which provide important information on the nature and physical characteristics of the particle acceleration mechanism operating in these sources.
High-resolution millimeter wave very-long-baseline interferometry (mm-VLBI) is an ideal tool for probing the structure at the base of extragalactic jets in detail. The TeV blazar Mrk 501 is one of the best targets among BL Lac objects for studying the nature of off-axis jet structures because it shows different jet position angles at different scales. The aim of this study is to investigate the properties of the off-axis jet structure through high-resolution mm-VLBI images at the jet base and physical parameters such as kinematics, flux densities, and spectral indices. We performed Very Long Baseline Array (VLBA) observations over six epochs from 2012 February to 2013 February at 43 GHz. Quasi-simultaneous Global Millimeter VLBI Array (GMVA) observations at 86 GHz were performed in May 2012. We discover a new jet component at the northeast direction from the core in all the images at 43 and 86 GHz. The new component shows the off-axis location from the persistent jet extending to the southeast. The 43 GHz images reveal that the scattering of the positions of the NE component is within ~0.2 mas. The 86 GHz data reveals a jet component located 0.75 mas southeast of the radio core. We also discuss the spectral indices between 43 and 86 GHz, where the northeast component has steeper spectral index and the southeast component has comparable or flatter index than the radio core does.
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