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Broadband spectral fitting of blazars using XSPEC

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Research in Astronomy and Astrophysics 2018年第3期18卷 105-120页

作者： Sunder Sahayanathan Atreyee Sinha ranjeev misra Astrophysical Sciences Division Bhabha Atomic Research Centre Mumbai - 400085 India Inter-University Centre for Astronomy and Astrophysics Pune-411007 India

The broadband spectral energy distribution（SED） of blazars is generally interpreted as radiation arising from synchrotron and inverse Compton mechanisms. Traditionally,the underlying source parameters responsible for these emission processes,like particle energy density,magnetic field,etc.,are obtained through simple visual reproduction of the observed fluxes. However,this procedure is incapable of providing confidence ranges for the estimated parameters. In this work,we propose an efficient algorithm to perform a statistical fit of the observed broadband spectrum of blazars using different emission models. Moreover,we use the observable quantities as the fit parameters,rather than the direct source parameters which govern the resultant SED. This significantly improves the convergence time and eliminates the uncertainty regarding initial guess parameters. This approach also has an added advantage of identifying the degenerate parameters,which can be removed by including more observable information and/or additional constraints. A computer code developed based on this algorithm is implemented as a user-defined routine in the standard X-ray spectral fitting package,XSPEC. Further,we demonstrate the efficacy of the algorithm by fitting the well sampled SED of blazar 3 C 279 during its gamma ray flare in 2014.

关键词： galaxies active-BL Lacertae objects general - quasars individual (3C 279) - relativistic processes - radiation mechanisms non-thermal

The kilosecond variability of X-ray sources in nearby galaxies

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Research in Astronomy and Astrophysics 2013年第12期13卷 1445-1454页

作者： Soma Mandal ranjeev misra Gulab C.Dewangan Department of Physics Taki Government College Inter-University Centre for Astronomy and Astrophysics

Chandra observations of 17 nearby galaxies were analyzed and 166 bright sources with X-ray counts 〉 100 were chosen for temporal analysis. Fractional root mean square （rms） variability amplitudes were estimated for light curves, binned at 4 kilosecond （ks）, with length 〈 40 ks. While there are nine ultra-luminous X- ray sources （ULXs） with unabsorbed luminosity （in the 0.3-8.0 keV band） L 〉 1039 erg s-1 in the sample for which the fractional rms variability is constrained to be 〈 10%, only two of them show variability. One of the variable ULXs exhibits a secular transition and has an ultra-soft spectrum with temperature - 0.3 keV while the other is a rapidly varying source in NGC 0628, which has previously been com- pared to the Galactic microquasar GRS 1915＋105. These results seem to indicate that ULXs are typically not highly variable on ks timescales, except for some ultra-soft ones. Among the relatively low luminosity sources （L - 10^38 erg s-1）, we find five of them to be variable. Apart from an earlier known source in NGC 1569, we identify a source in NGC 2403 that exhibits persistent high amplitude fluctuations. In general, the variability of the sources does not seem to be correlated with hardness, which indicates that they may not be due to variations in any absorbing material, but instead could reflect instabilities in the inner accretion disk.

关键词： galaxies: general --X-rays: binaries

AstroSat observation of the Be/X-ray binary Pulsar 3A 0726–260(4U 0728–25)

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Research in Astronomy and Astrophysics 2020年第9期20卷 349-357页

作者： Jayashree Roy Prahlad C.Agrawal Baibhav Singari ranjeev misra UM-DAE Centre for Excellence in Basic Sciences University of MumbaiVidyanagari CampusMumbai400098MaharashtraIndia Inter-University Center for Astronomy and Astrophysics Post Bag 4Pune411007MaharashtraIndia School of Physical Sciences National Institute of Science Education and Research BhubaneswarKhurda752050OdishaIndia

Results on timing and spectral properties of the Be/X-ray binary pulsar 3A 0726-260(4U 0728-25)are *** binary was observed on 2016 May 6-7 with the Large Area X-ray Proportional Counter(LAXPC)and Soft X-ray Telescope(SXT)instruments onboard the AstroSat *** this observation,the source was in non-flaring persistent state at a flux level of^8.6±0.3×10^-11 erg cm^-2 s^-1in 0.4-20 *** X-ray pulsations with a period of 103.144±0.001 s are detected in 0.3-7 keV with the SXT and in 3-40 keV with the *** pulse profile is energy dependent,and there is an indication that the pulse shape changes from a broad single pulse to a double pulse at higher *** energies above20 keV,we report the first time detection of pulsation period 103.145±0.001 s and the double peaked pulse profile from the *** energy spectrum of the source is derived from the combined analysis of the SXT and LAXPC spectral data in 0.4-20 *** best spectral fit is obtained by a power law model with a photon index(1.7±0.03)with high energy spectral cut-off at 12.9±0.7 keV.A broad iron line at^6.3 keV is detected in the energy *** briefly discuss the implications of these results.

关键词： Be/X ray binary pulsar 4U 0728–25

Comprehensive spectral analysis of Cyg X-1 using RXTE data

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Research in Astronomy and Astrophysics 2012年第10期12卷 1427-1438页

作者： Rizwan Shahid ranjeev misra S.N.A.Jaaffrey Department of Physics M.L.Sukhadia UniversityUdaipur-313001India Inter University Centre for Astronomy and Astrophysics Pune-411007India

We analyze a large number （〉 500） of pointed Rossi X-Ray Timing Explorer （RXTE） observations of Cyg X- 1 and model the spectrum of each one. A subset of the observations for which there is a simultaneous reliable measure of the hardness ratio by the All Sky Monitor shows that the sample covers nearly all the spectral shapes of Cyg X-1. Each observation is fitted with a generic empirical model consisting of a disk black body spectrum, a Comptonized component whose input photon shape is the same as the disk emission, a Gaussian to represent the iron line and a reflection feature. The relative strength, width of the iron line and the reflection parameter are in general correlated with the high energy photon spectral index F. This is broadly consistent with a geometry where for the hard state （low F ~ 1.7） there is a hot in- ner Comptonizing region surrounded by a truncated cold disk. The inner edge of the disk moves inwards as the source becomes softer till finally in the soft state （high F 〉 2.2） the disk fills the inner region and active regions above the disk produce the Comptonized component. However, the reflection parameter shows non-monotonic behavior near the transition region （F ~ 2）, which suggests a more complex geometry or physical state of the reflector. In addition, the inner disk temperature, during the hard state, is on average higher than in the soft one, albeit with large scatter. These inconsistencies could be due to limitations in the data and the empirical model used to fit them. The flux of each spectral component is well correlated with F, which shows that unlike some other black hole systems, Cyg X- 1 does not show any hysteresis be- havior. In the soft state, the flux of the Comptonized component is always similar to the disk one, which confirms that the ultra-soft state （seen in other brighter black hole systems） is not exhibited by Cyg X-1. The rapid variation of the Compton amplifica- tion factor with F naturally explains the absence of spec

关键词： accretion accretion disks -- X-rays: binaries

Nonlinear time series analysis of the light curves from the black hole system GRS1915+105

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Research in Astronomy and Astrophysics 2011年第1期11卷 71-90页

作者： K.P.Harikrishnan ranjeev misra G.Ambika Department of Physics The Cochin College Inter University Centre for Astronomy and Astrophysics Indian Institute of Science Education and Research

GRS 1915＋105 is a prominent black hole system exhibiting variability over a wide range of time scales and its observed light curves have been classified into 12 temporal states. Here we undertake a complete analysis of these light curves from all the states using various quantifiers from nonlinear time series analysis, such as the correlation dimension （D2）, the correlation entropy （K2）, singular value decomposition （SVD） and the multifractal spectrum （f（α） spectrum）. An important aspect of our analysis is that, for estimating these quantifiers, we use algorithmic schemes which we have recently proposed and successfully tested on synthetic as well as practical time series from various fields. Though the schemes are based on the conventional delay embedding technique, they are automated so that the above quantitative measures can be computed using conditions prescribed by the algorithm and without any intermediate subjective analysis. We show that nearly half of the 12 temporal states exhibit deviation from randomness and their complex temporal behavior could be approximated by a few （three or four） coupled ordinary nonlinear differential equations. These results could be important for a better understanding of the processes that generate the light curves and hence for modeling the temporal behavior of such complex systems. To our knowledge, this is the first complete analysis of an astrophysical object （let alone a black hole system） using various techniques from nonlinear dynamics.

关键词： accretion accretion disks -- X-rays: binaries

Log-normal flux distribution of bright Fermi blazars

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Research in Astronomy and Astrophysics 2018年第11期18卷 111-122页

作者： Zahir Shah Nijil Mankuzhiyil Atreyee Sinha ranjeev misra Sunder Sahayanathan Naseer Iqbal Department Of Physics University of KashmirSrinagar-190006India Astrophysical Sciences Division Bhabha Atomic Research CentreMumbai-400085India in Inter-University Centre for Astronomy and Astrophysics Pune-411007India AstroParticule et Cosmoligie CNRS/University Paris Diderot10Rue Alice Domon et Leonie DuquetParis 75013France

We present the results of the γ-ray flux distribution study on the brightest blazars which were observed by Fermi-LAT. We selected 50 of the brightest blazars based on the maximum number of detections reported in the Third LAT AGN Catalog. We performed standard unbinned maximum likelihood analysis on the LAT data during the period between August 2008 and December 2016, in order to obtain the average monthly flux. After quality cuts, blazars for which at least 90% of the total flux had survived were selected for further study, and this included 19 FSRQs and 19 BL Lacs. The Anderson-Darling and χ2 tests suggest that the integrated monthly flux follows a log-normal distribution for all sources, except for three FSRQs for which neither a normal nor a log-normal distribution was preferred. A double log-normal flux distribution tendency was observed in these sources, though this has to be confirmed with improved statistics. We also found that the standard deviation of the log-normal flux distribution increases with the mean spectral index of the blazar, and can be fitted with a line of slope 0.24±0.04. We repeat our study on three additional brightest unclassified blazars to identify their flux distribution properties. Based on the features of their log-normal flux distribution, we infer these unclassified blazars may be closely associated with FSRQs. We also highlight that considering the lognormal behavior of the flux distribution of blazars, averaging their long term flux on a linear scale can largely underestimate the nominal flux and this discrepancy can propagate down to the estimation of source parameters through spectral modeling.

关键词： active galaxy: blazar FSRQ BL Lac gamma-rays

On the reality of broad iron L lines from the narrow line Seyfert 1 galaxies 1H0707–495 and IRAS 13224–3809

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Research in Astronomy and Astrophysics 2016年第11期16卷 37-42页

作者： Pramod Karbhari Pawar Gulab Chand Dewangan Madhav Khushalrao Patil ranjeev misra Sharada Keshav Jogadand S. R. T. M. University Nanded- 431 606 India Inter-University Center for Astronomy and Astrophysics Pune - 411 007 India

We performed time resolved spectroscopy of 1H0707-495 and IRAS 13224-3809 using long XMM-Newton observations. These are strongly variable narrow line Seyfert 1 galaxies and show broad features around 1 keV that have been interpreted as relativistically broad Fe Lc~ lines. Such features are not clearly observed in other active galactic nuclei despite sometimes having high iron abundance required by the best fitted blurred reflection models. Given the importance of these lines, we explore whether the rapid variability of spectral parameters may introduce broad bumps/dips artificially in the time averaged spectrum, which may then be mistaken as broadened lines. We tested this hypothesis by performing time resolved spectroscopy using long （〉 100 ks） XMM-Newton observations and by dividing them into segments with typical exposures of a few ks. We extracted spectra from each such segment and modeled them using a two component phenomenological model consisting of a power law to represent the hard component and a black body to represent the soft emission. As expected, both the sources showed variations in the spectral parameters. Using these variation trends, we simulated model spectra for each segment and then co-added to get a combined simulated spectrum. In the simulated spectra, we found no broad features below 1 keV and in particular no deviation near 0.9 keV as seen in the real averaged spectra. This implies that the broad Fe Lα line that is seen in the spectra of these sources is not an artifact of the variation of spectral components and, hence, provides evidence that the line is indeed genuine.

关键词： galaxies: general -- galaxies: active -- galaxies: individual (1H0707-495 IRAS 13224-3809)

Systematic analysis of low/hard state RXTE spectra of GX 339–4 to constrain the geometry of the system

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Research in Astronomy and Astrophysics 2018年第5期18卷 37-46页

作者： Kalyani Bagri ranjeev misra Anjali Rao Jagdish Singh Yadav Shiv Kumar Pandey Pt. Ravishankar Shukla University Raipur Chhattisgard 492010 India Inter-University Centre for Astronomy and Astrophysics Ganeshkhind Pune 411007 India Tata Institute of Fundamental Research Colaba Mumbai 400005 India

One of the popular models for the low/hard state of black hole binaries is that the standard accretion disk is truncated and the hot inner region produces, via Comptonization, hard X-ray *** is supported by the value of the high energy photon index, which is often found to be small,～ 1.7（〈 2）, implying that the hot medium is starved of seed photons. On the other hand, the suggestive presence of a broad relativistic Fe line during the hard state would suggest that the accretion disk is not truncated but extends all the way to the innermost stable circular orbit. In such a case, it is a puzzle why the hot medium would remain photon starved. The broad Fe line should be accompanied by a broad smeared reflection hump at ～ 30 ke V and it may be that this additional component makes the spectrum hard and the intrinsic photon index is larger, i.e. 〉2. This would mean that the medium is not photon deficient, reconciling the presence of a broad Fe line in the observed hard state. To test this hypothesis,we have analyzed the RXTE observations of GX 339–4 from the four outbursts during 2002–2011 and identify observations when the system was in the hard state and showed a broad Fe line. We have then attempted to fit these observations with models, which include smeared reflection, to understand whether the intrinsic photon index can indeed be large. We find that, while for some observations the inclusion of reflection does increase the photon index, there are hard state observations with a broad Fe line that have photon indices less than 2.

关键词： accretion accretion disks - stars black holes - X-rays binaries - X-rays individual(GX 339-4)

Time-resolved spectral analysis of prompt emission from long gamma-ray bursts with GeV emission

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Research in Astronomy and Astrophysics 2014年第1期14卷 35-46页

作者： Arikkala Raghurama Rao Rupal Basak Jishnu Bhattacharya Sarthak Chandra Nikunj Maheshwari Manojendu Choudhury ranjeev misra Tata Institute of Fundamental Research Indian Institute of Technology Centre for Excellence in Basic Sciences Inter-University Centre for Astronomy and Astrophysics

We performed detailed time-resolved spectroscopy of bright tong gamma- ray bursts （GRBs） which show significant GeV emissions （GRB 080916C, GRB 090902B and GRB 090926A）. In addition to the standard Band model, we also use a model consisting of a black body and a power law to fit the spectra. We find that for the latter model there are indications of an additional soft component in the spectra. While previous studies have shown that such models are required for GRB 090902B, here we find that a composite spectral model consisting of two blackbodies and a power law adequately fits the data of all the three bright GRBs. We investigate the evolution of the spectral parameters and find several interesting features that appear in all three GRBs, like （a） temperatures of the blackbodies are strongly correlated with each other, （b） fluxes in the black body components are strongly correlated with each other, （c） the temperatures of the black body trace the profile of the individual pulses of the GRBs, and （d） the characteristics of power law components like the spectral index and the delayed onset bear a close similarity to the emission characteristics in the GeV regions. We discuss the implications of these results and the possibility of identifying the radiation mechanisms during the prompt emission of GRBs.

关键词： gamma rays: bursts - gamma rays: observations - methods: data analysis