The new model of fitting the spectral energy distributions of Mkn 421 and Mkn 501

The spectral energy distribution (SED) of TeV blazars has a double-humped shape that is usually interpreted as Synchrotron Self Compton (SSC) model. The one zone SSC model is used broadly but cannot fit the high energy tail of SED very well. It need bulk Lorentz factor which is conflict with the observation. Furthermore one zone SSC model can not explain the entire spectrum. In the paper, we propose a new model that the high energy emission is produced by the accelerated protons in the blob with a small size and high magnetic field, the low energy radiation comes from the electrons in the expanded blob. Because the high and low energy photons are not produced at the same time, the requirement of large Doppler factor from pair production is relaxed. We present the fitting results of the SEDs for Mkn 501 during April 1997 and Mkn 421 during March 2001 respectively.Comment: 5 pages, 1 figures, 1table. accepted for publication in Sciences in China --

A new ordering parameter of spectral energy distributions from synchrotron-self-Compton emitting blazars

The broadband SEDs of blazars exhibit two broad spectral components, which in leptonic emission models are attributed to synchrotron radiation and synchrotron self-Compton (SSC) radiation of relativistic electrons. During high state phases, the high-frequency SSC component often dominates the low-frequency synchrotron component, implying that the inverse Compton SSC losses of electrons are at least equal to or greater than the synchrotron losses of electrons. We calculate from the analytical solution of the kinetic equation of relativistic electrons, subject to the combined linear synchrotron and nonlinear synchrotron self-Compton cooling, for monoenergetic injection the time-integrated total synchrotron and SSC radiation fluences and spectral energy distributions (SED). Depending on the ratio of the initial cooling terms, displayed by the injection parameter $\alpha$, we find for $\alpha\ll 1$, implying complete linear cooling, that the synchrotron peak dominates the inverse Compton peak and the usual results of the spectra are recovered. For $\alpha\gg 1$ the SSC peak dominates the synchrotron peak, proving our assumption that in such a case the cooling becomes initially non-linear. The spectra also show some unique features, which can be attributed directly to the non-linear cooling. To show the potential of the model, we apply it to outbursts of 3C 279 and 3C 454.3, successfully reproducing the SEDs. The results of our analysis are promising, and we argue that this non-equilibrium model should be considered in future modeling attempts for blazar flares.Comment: accepted by MNRAS, 32 pages (single column), 7 figure

Simultaneous multi-wavelength observations of the TeV Blazar Mrk 421 during February - March 2003: X-ray and NIR correlated variability

In the present paper, we have reported the result of simultaneous multi-wavelength observations of the TeV blazar Mrk 421 during February $-$ March 2003. In this period, we have observed Mrk 421 using Pachmarhi Array of \v{C}erenkov Telescopes (PACT) of Tata Institute of Fundamental Research at Pachmarhi, India. Other simultaneous data were taken from the published literature and public data archives. We have analyzed the high quality X-ray (2-20 keV) observations from the NASA Rossi X-Ray Timing Explorer (RXTE). We have seen a possible correlated variability between X-ray and J band (1.25 $\mu$) near infrared (NIR) wavelength. This is the first case of X-ray and NIR correlated variability in Mrk 421 or any high energy peaked (HBL) blazar. The correlated variability reported here is indicating a similar origin for NIR and X-ray emission. The emission is not affected much by the environment of the surrounding medium around the central engine of the Mrk 421. The observations are consistent with the shock-in-jet model for the emission of radiations.Comment: 11 pages, 5 figures, Accepted for Publication in ChJA

BeppoSAX and multiwavelength observations of BL Lacertae in 2000

We present two BeppoSAX observations of BL Lac (2200+420) as part of a multiwavelength campaign performed in 2000. The source was in different states of activity: in June, the X-ray spectrum was faint and hard (alpha sim 0.8), with positive residuals towards low energies. In October we detected the highest [2-10] keV flux ever measured for the source. During this observation, the spectrum was soft (alpha sim 1.56) up to 10 keV, while above this energy a hard component was dominating. The BeppoSAX data are confirmed by simultaneous RXTE short observations. During the first observation the soft X-ray flux was variable on timescales of a few hours, while the hard X-ray flux was almost constant. During the second observation, instead, the soft spectrum displayed an erratic behaviour with large variations (up to factors 3-4) on timescales smaller than 2 hrs. The analysis of the multiwavelength SED of October evidenced an intriguing feature: the optical and X-ray sections of the SED are misaligned, while in the prevailing standard picture, they are both thought to be produced via synchrotron emission. We suggested four scenarios to account for this discrepancy: a higher than galactic dust-to-gas ratio towards the source, the first detection of bulk Compton emission in the X-ray band, the presence of two synchrotron emitting regions located at different distances from the nucleus, the detection of a Klein-Nishina effect on the synchrotron spectrum. We evidenced the favorable and critical points of each scenario, but, at present, we cannot discriminate between them.Comment: 13 pages, 8 figures, accepted by A&

Observations of TeV gamma-rays from Mrk 421 during Dec. 2005 to Apr. 2006 with the TACTIC telescope

The TACTIC $\gamma$-ray telescope has observed Mrk 421 on 66 clear nights from Dec. 07, 2005 to Apr. 30, 2006, totalling $\sim$ 202 hours of on-source observations. Here, we report the detection of flaring activity from the source at $\geq$ 1 TeV energy and the time-averaged differential $\gamma$-ray spectrum in the energy range 1-11 TeV for the data taken between Dec. 27, 2005 to Feb. 07, 2006 when the source was in a relatively higher state as compared to the rest of the observation period. Analysis of this data spell, comprising about $\sim$97h reveals the presence of a $\sim 12.0 \sigma$ $\gamma$-ray signal with daily flux of $>$ 1 Crab unit on several days. A pure power law spectrum with exponent $-3.11\pm0.11$ as well as a power law spectrum with an exponential cutoff $(\Gamma = -2.51\pm0.26$ and $E_0=(4.7\pm2.1) TeV)$ are found to provide reasonable fits to the inferred differential spectrum within statistical uncertainties. We believe that the TeV light curve presented here, for nearly 5 months of extensive coverage, as well as the spectral information at $\gamma$-ray energies of $>$ 5 TeV provide a useful input for other groups working in the field of $\gamma$-ray astronomy.Comment: 13pages,4figures; Accepted for publication in Astroparticle Physic

Wide band X-ray and optical observations of the BL Lac object 1ES 1959+650 in high state

The blazar 1ES 1959+650 was observed twice by BeppoSAX in September 2001 simultaneously with optical observations. We report here the X-ray data together with the optical, R_C magnitude, light curve since August 1995. The BeppoSAX observations were triggered by an active X-ray status of the source. The X-ray spectra are brighter than the previously published X-ray observations, although the source was in an even higher state a few months later, as monitored by the ASM onboard RossiXTE, when it was also detected to flare in the TeV band. Our X-ray spectra are well represented by a continuosly curved model up to 45 keV and are interpreted as synchrotron emission, with the peak moving to higher energies. This is also confirmed by the slope of the X-ray spectrum which is harder than in previous observations. Based on our optical and X-ray data, the synchrotron peak turns out to be in the range 0.1-0.7 keV. We compare our data with non simultaneous radio to TeV data and model the spectral energy distribution with a homogeneous, one-zone synchrotron inverse Compton model. We derive physical parameters that are typical of low power High Energy peaked Blazar, characterised by a relatively large beaming factor, low luminosity and absence of external seed photons.Comment: 12 pages, 6 figures, accepted by A&