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Shashi B. Pandey

Bio: Shashi B. Pandey is an academic researcher from Aryabhatta Research Institute of Observational Sciences. The author has contributed to research in topics: Gamma-ray burst & Light curve. The author has an hindex of 31, co-authored 114 publications receiving 3320 citations. Previous affiliations of Shashi B. Pandey include University of Michigan & Central Drug Research Institute.


Papers
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Journal ArticleDOI
TL;DR: In this article, the photometric calibration of the Swift Ultraviolet/Optical Telescope (UVOT) was performed with observations of standard stars and standard star fields that represent a wide range of spectral star types.
Abstract: We present the photometric calibration of the Swift Ultraviolet/Optical Telescope (UVOT) which includes: optimum photometric and background apertures, effective area curves, colour transformations, conversion factors for count rates to flux and the photometric zero-points (which are accurate to better than 4 per cent) for each of the seven UVOT broad-band filters. The calibration was performed with observations of standard stars and standard star fields that represent a wide range of spectral star types. The calibration results include the position-dependent uniformity, and instrument response over the 1600‐8000 A operational range. Because the UVOT is a photon-counting instrument, we also discuss the effect of coincidence loss on the calibration results. We provide practical guidelines for using the calibration in UVOT data analysis. The results presented here supersede previous calibration results.

935 citations

Journal ArticleDOI
Warren Skidmore, Ian P. Dell'Antonio, Misato Fukugawa, Aruna Goswami, Lei Hao, David Jewitt, Greg Laughlin, Charles C. Steidel, Paul Hickson, Luc Simard, M. Schöck, Tommaso Treu, Judith G. Cohen, G. C. Anupama, Mark Dickinson, Fiona A. Harrison, Tadayuki Kodama, Jessica R. Lu, Bruce Macintosh, Matthew A. Malkan, Shude Mao, Norio Narita, Tomohiko Sekiguchi, Annapurni Subramaniam, Masaomi Tanaka, Feng Tian, Michael F. A'Hearn, Masayuki Akiyama, Babar Ali, Wako Aoki, Manjari Bagchi, Aaron J. Barth, Varun Bhalerao, Marusa Bradac, James S. Bullock, Adam J. Burgasser, Scott Chapman, Ranga-Ram Chary, Masashi Chiba, Michael C. Cooper, Asantha Cooray, Ian J. M. Crossfield, Thayne Currie, Mousumi Das, Gulab C. Dewangan, Richard de Grijs, Tuan Do, Subo Dong, Jarah Evslin, Taotao Fang, Xuan Fang, Christopher D. Fassnacht, Leigh N. Fletcher, Eric Gaidos, Roy R. Gal, Andrea M. Ghez, Mauro Giavalisco, Carol A. Grady, Thomas K. Greathouse, Rupjyoti Gogoi, Puragra Guhathakurta, Luis C. Ho, Priya Hasan, Gregory J. Herczeg, Mitsuhiko Honda, Masa Imanishi, Hanae Inami, Masanori Iye, Jason S. Kalirai, U.S. Kamath, Stephen R. Kane, Nobunari Kashikawa, Mansi M. Kasliwal, Vishal P. Kasliwal, Evan N. Kirby, Quinn Konopacky, Sébastien Lépine, Di Li, Jianyang Li, Junjun Liu, Michael C. Liu, Enrigue Lopez-Rodriguez, Jennifer M. Lotz, Philip Lubin, Lucas M. Macri, Keiichi Maeda, Franck Marchis, Christian Marois, Alan P. Marscher, Crystal L. Martin, Taro Matsuo, Claire E. Max, Alan W. McConnachie, Stacy McGough, Carl Melis, Leo Meyer, Michael J. Mumma, Takayuki Muto, Tohru Nagao, Joan Najita, Julio F. Navarro, Michael J. Pierce, Jason X. Prochaska, Masamune Oguri, Devendra K. Ojha, Yoshiko K. Okamoto, Glenn S. Orton, Angel Otarola, Masami Ouchi, Chris Packham, Deborah Padgett, Shashi B. Pandey, Catherine Pilachowsky, Klaus M. Pontoppidan, Joel R. Primack, Shalima Puthiyaveettil, Enrico Ramirez-Ruiz, Naveen A. Reddy, Michael Rich, Matthew J. Richter, James Schombert, Anjan A. Sen, Jianrong Shi, Kartik Sheth, Raghunathan Srianand, Jonathan C. Tan, Masayuki Tanaka, Angelle Tanner, Nozomu Tominaga, David Tytler, Vivian U, Lingzhi Wang, Xiaofeng Wang, Yiping Wang, Gillian Wilson, Shelley A. Wright, Chao Wu, Xufeng Wu, Renxin Xu, Toru Yamada, Bin Yang, Gongbo Zhao, Hongsheng Zhao 
TL;DR: The TMT Detailed Science Case describes the transformational science that the Thirty Meter Telescope (TMT) will enable as mentioned in this paper, and more than 150 astronomers from within the TMT partnership and beyond offered input in compiling the new 2015 detailed science case, including the California Institute of Technology (Caltech), the Indian Institute of Astrophysics (IIA), the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC), the NaOJ, the University of California, the Association of Canadian Universities for Research in Astronomy (ACURA) and US associate partner, AU
Abstract: The TMT Detailed Science Case describes the transformational science that the Thirty Meter Telescope will enable. Planned to begin science operations in 2024, TMT will open up opportunities for revolutionary discoveries in essentially every field of astronomy, astrophysics and cosmology, seeing much fainter objects much more clearly than existing telescopes. Per this capability, TMT's science agenda fills all of space and time, from nearby comets and asteroids, to exoplanets, to the most distant galaxies, and all the way back to the very first sources of light in the Universe. More than 150 astronomers from within the TMT partnership and beyond offered input in compiling the new 2015 Detailed Science Case. The contributing astronomers represent the entire TMT partnership, including the California Institute of Technology (Caltech), the Indian Institute of Astrophysics (IIA), the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC), the National Astronomical Observatory of Japan (NAOJ), the University of California, the Association of Canadian Universities for Research in Astronomy (ACURA) and US associate partner, the Association of Universities for Research in Astronomy (AURA).

150 citations

Journal ArticleDOI
TL;DR: In this paper, an extremely bright gamma-ray burst (GRB) 160625B was observed in both gamma and optical wavelengths, with three isolated episodes separated by long quiescent intervals, with the durations of each sub-burst being approximately 0.8, 35, and 212 seconds.
Abstract: The ejecta composition is an open question in gamma-ray burst (GRB) physics 1 . Some GRBs possess a quasi-thermal spectral component in the time-resolved spectral analysis 2 , suggesting a hot fireball origin. Others show a featureless non-thermal spectrum known as the Band function3–5, consistent with a synchrotron radiation origin5,6 and suggesting that the jet is Poynting-flux dominated at the central engine and probably in the emission region as well7,8. There are also bursts showing a sub-dominant thermal component and a dominant synchrotron component 9 , suggesting a probable hybrid jet composition 10 . Here, we report an extraordinarily bright GRB 160625B, simultaneously observed in gamma-ray and optical wavelengths, whose prompt emission consists of three isolated episodes separated by long quiescent intervals, with the durations of each sub-burst being approximately 0.8 s, 35 s and 212 s, respectively. Its high brightness (with isotropic peak luminosity Lp,iso ≈ 4 × 1053 erg s−1) allows us to conduct detailed time-resolved spectral analysis in each episode, from precursor to main burst and to extended emission. The spectral properties of the first two sub-bursts are distinctly different, allowing us to observe the transition from thermal to non-thermal radiation between well-separated emission episodes within a single GRB. Such a transition is a clear indication of the change of jet composition from a fireball to a Poynting-flux-dominated jet. The extremely bright GRB 160625B, consisting of three sub-bursts separated by quiescent intervals, shows a transition from thermal to non-thermal radiation that indicates a change of jet composition from a fireball to a Poynting-flux-dominated jet.

129 citations

Journal ArticleDOI
TL;DR: Spectral analysis of the Swift observations of GRB 060614 shows that the burst presents standard optical, ultraviolet and X-ray afterglows, detected beginning 4 ks after the trigger, and that the peak energy of the burst has decreased to as low as 8 keV at the beginning of the XRT observation.
Abstract: GRB 060614 is a remarkable gamma-ray burst (GRB) observed by Swift with puzzling properties, which challenge current progenitor models. In particular, the lack of any bright supernova (SN) down to very strict limits and the vanishing spectral lags during the whole burst are typical of short GRBs, strikingly at odds with the long (102 s) duration of this event. Here we present detailed spectral and temporal analysis of the Swift observations of GRB 060614. We show that the burst presents standard optical, ultraviolet and X-ray afterglows, detected beginning 4 ks after the trigger. An achromatic break is observed simultaneously in the optical and X-ray bands, at a time consistent with the break in the R-band light curve measured by the VLT. The achromatic behaviour and the consistent postbreak decay slopes make GRB 060614 one of the best examples of a jet break for a Swift burst. The optical and ultraviolet afterglow light curves have also an earlier break at 29.7 ± 4.4 ks, marginally consistent with a corresponding break at 36.6 ± 2.4 ks observed in the X-rays. In the optical, there is strong spectral evolution around this break, suggesting the passage of a break frequency through the optical/ultraviolet band. The very blue spectrum at early times suggests this may be the injection frequency, as also supported by the trend in the light curves: rising at low frequencies, and decaying at higher energies. The early X-ray light curve (from 97 to 480 s) is well interpreted as the X-ray counterpart of the burst extended emission. Spectral analysis of the BAT and XRT data in the ∼80 s overlap time interval show that the peak energy of the burst has decreased to as low as 8 keV at the beginning of the XRT observation. Spectral analysis of following XRT data shows that the peak energy of the burst continues to decrease through the XRT energy band and exits it at about 500 s after the trigger. The average peak energy Ep of the burst is likely below the BAT energy band (<24 keV at the 90% confidence level) but larger than 8 keV. The initial group of peaks observed by BAT (∼5 s) is however distinctly harder than the rest of the prompt emission, with a peak energy of about 300 keV as measured by Konus Wind. Considering the time-averaged spectral properties, GRB 060614 is consistent with the Eiso − E rest , Eγ − E rest ,a ndLp,iso − E rest correlations.

121 citations

Journal ArticleDOI
01 Jun 2003
TL;DR: It is suggested that the bump can be modeled with a SN having the same temporal profile as the other proposed hypernova SN2002ap, but 1.3 mag brighter at peak, and located at the GRB redshift.
Abstract: We report on photometric, spectroscopic and polarimetric monitoring of the optical and near-infrared (NIR) afterglow of GRB020405. Ground-based optical observations, performed with 8 different telescopes, started about 1 day after the high-energy prompt event and spanned a period of ∼10 days; the addition of archival HST data extended the coverage up to ∼150 days after the GRB. We report the first detection of the afterglow in NIR bands. The detection of Balmer and oxygen emission lines in the optical spectrum of the host galaxy indicates that the GRB is located at redshift z = 0.691. Fe II and Mg II absorption systems are detected at z = 0.691 and at z = 0.472 in the afterglow optical spectrum. The latter system is likely caused by absorbing clouds in the galaxy complex located ∼2" southwest of the GRB020405 host. Hence, for the first time, the galaxy responsible for an intervening absorption line system in the spectrum of a GRB afterglow is spectroscopically identified. Optical and NIR photometry of the afterglow indicates that, between 1 and 10 days after the GRB, the decay in all bands is consistent with a single power law of index a = 1.54 ′0.06. The late-epoch VLT J-band and HST optical points lie above the extrapolation of this power law, so that a plateau (or "bump") is apparent in the VRIJ light curves at 10-20 days after the GRB. The light curves at epochs later than day ∼20 after the GRB are consistent with a power-law decay with index α' = 1.85 ′ 0.15. While other authors have proposed to reproduce the bump with the template of the supernova (SN) 1998bw, considered the prototypical "hypernova", we suggest that it can also be modeled with a SN having the same temporal profile as the other proposed hypernova SN2002ap, but 1.3 mag brighter at peak, and located at the GRB redshift. Alternatively, a shock re-energization may be responsible for the rebrightening. A single polarimetric R-band measurement shows that the afterglow is polarized, with P = 1.5 ′ 0.4% and polarization angle 0 = 172° ′8°. Broad-band optical-NIR spectral flux distributions show, in the first days after the GRB, a change of slope across the J band which we interpret as due to the presence of the electron cooling frequency v c . The analysis of the multiwavelength spectrum within the standard fireball model suggests that a population of relativistic electrons with index p ∼ 2.7 produces the optical-NIR emission via synchrotron radiation in an adiabatically expanding blastwave, with negligible host galaxy extinction, and the X-rays via Inverse Compton scattering off lower-frequency afterglow photons.

98 citations


Cited by
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Journal Article
TL;DR: The first direct detection of gravitational waves and the first observation of a binary black hole merger were reported in this paper, with a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ.
Abstract: On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10(-21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410(-180)(+160) Mpc corresponding to a redshift z=0.09(-0.04)(+0.03). In the source frame, the initial black hole masses are 36(-4)(+5)M⊙ and 29(-4)(+4)M⊙, and the final black hole mass is 62(-4)(+4)M⊙, with 3.0(-0.5)(+0.5)M⊙c(2) radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

4,375 citations

01 Jan 2005
TL;DR: The Monthly Notices as mentioned in this paper is one of the three largest general primary astronomical research publications in the world, published by the Royal Astronomical Society (RAE), and it is the most widely cited journal in astronomy.
Abstract: Monthly Notices is one of the three largest general primary astronomical research publications. It is an international journal, published by the Royal Astronomical Society. This article 1 describes its publication policy and practice.

2,091 citations

Journal ArticleDOI
M. P. van Haarlem1, Michael W. Wise2, Michael W. Wise1, A. W. Gunst1  +219 moreInstitutions (27)
TL;DR: In dit artikel zullen the authors LOFAR beschrijven: van de astronomische mogelijkheden met de nieuwe telescoop tot aan een nadere technische beshrijving of het instrument.
Abstract: LOFAR, the LOw-Frequency ARray, is a new-generation radio interferometer constructed in the north of the Netherlands and across europe. Utilizing a novel phased-array design, LOFAR covers the largely unexplored low-frequency range from 10-240 MHz and provides a number of unique observing capabilities. Spreading out from a core located near the village of Exloo in the northeast of the Netherlands, a total of 40 LOFAR stations are nearing completion. A further five stations have been deployed throughout Germany, and one station has been built in each of France, Sweden, and the UK. Digital beam-forming techniques make the LOFAR system agile and allow for rapid repointing of the telescope as well as the potential for multiple simultaneous observations. With its dense core array and long interferometric baselines, LOFAR achieves unparalleled sensitivity and angular resolution in the low-frequency radio regime. The LOFAR facilities are jointly operated by the International LOFAR Telescope (ILT) foundation, as an observatory open to the global astronomical community. LOFAR is one of the first radio observatories to feature automated processing pipelines to deliver fully calibrated science products to its user community. LOFAR's new capabilities, techniques and modus operandi make it an important pathfinder for the Square Kilometre Array (SKA). We give an overview of the LOFAR instrument, its major hardware and software components, and the core science objectives that have driven its design. In addition, we present a selection of new results from the commissioning phase of this new radio observatory.

2,067 citations

15 Mar 1979
TL;DR: In this article, the experimental estimation of parameters for models can be solved through use of the likelihood ratio test, with particular attention to photon counting experiments, and procedures presented solve a greater range of problems than those currently in use, yet are no more difficult to apply.
Abstract: Many problems in the experimental estimation of parameters for models can be solved through use of the likelihood ratio test. Applications of the likelihood ratio, with particular attention to photon counting experiments, are discussed. The procedures presented solve a greater range of problems than those currently in use, yet are no more difficult to apply. The procedures are proved analytically, and examples from current problems in astronomy are discussed.

1,748 citations

Journal ArticleDOI
TL;DR: In this article, the authors reported that NGC 2617 went through a dramatic outburst, during which its X-ray flux increased by over an order of magnitude followed by an increase of its optical/ultraviolet (UV) continuum flux.
Abstract: After the All-Sky Automated Survey for SuperNovae discovered a significant brightening of the inner region of NGC 2617, we began a ∼70 day photometric and spectroscopic monitoring campaign from the X-ray through near-infrared (NIR) wavelengths. We report that NGC 2617 went through a dramatic outburst, during which its X-ray flux increased by over an order of magnitude followed by an increase of its optical/ultraviolet (UV) continuum flux by almost an order of magnitude. NGC 2617, classified as a Seyfert 1.8 galaxy in 2003, is now a Seyfert 1 due to the appearance of broad optical emission lines and a continuum blue bump. Such 'changing look active galactic nuclei (AGNs)' are rare and provide us with important insights about AGN physics. Based on the Hβ line width and the radius-luminosity relation, we estimate the mass of central black hole (BH) to be (4 ± 1) × 10{sup 7} M {sub ☉}. When we cross-correlate the light curves, we find that the disk emission lags the X-rays, with the lag becoming longer as we move from the UV (2-3 days) to the NIR (6-9 days). Also, the NIR is more heavily temporally smoothed than the UV. This can largely be explained bymore » a simple model of a thermally emitting thin disk around a BH of the estimated mass that is illuminated by the observed, variable X-ray fluxes.« less

1,473 citations