Showing papers by "Shashi B. Pandey published in 2014"
TL;DR: In this article, a multi-wavelength study of the radio-loud narrow-line Seyfert 1 galaxy (NLSy1) 1H 0323+342, detected by the Fermi Gamma-Ray Space Telescope, is presented.
Abstract: We present a multiwavelength study of the radio-loud narrow-line Seyfert 1 galaxy (NLSy1) 1H 0323+342, detected by the Fermi Gamma-Ray Space Telescope. Multiband light curves show many orphan X-ray and optical flares having no corresponding γ-ray counterparts. Such anomalous variability behavior can be due to different locations of the emission region from the central source. During a large flare, a γ-ray flux doubling timescale as small as ~3 hr is noticed. We built spectral energy distributions (SEDs) during different activity states and modeled them using a one-zone leptonic model. The shape of the optical/UV component of the SEDs is dominated by accretion disk emission in all the activity states. In the X-ray band, significant thermal emission from the hot corona is inferred during quiescent and first flaring states; however, during subsequent flares, the nonthermal jet component dominates. The γ-ray emission in all the states can be well explained by inverse-Compton scattering of accretion disk photons reprocessed by the broad-line region. The source showed violent intra-night optical variability, coinciding with one of the high γ-ray activity states. An analysis of the overall X-ray spectrum fitted with an absorbed power-law plus relativistic reflection component hints at the presence of an Fe Kα line and returns a high black hole spin value of a = 0.96 ± 0.14. We argue that 1H 0323+342 possesses dual characteristics, akin to both flat-spectrum radio quasars (FSRQs) and radio-quiet NLSy1 galaxies, though at a low jet power regime compared to powerful FSRQs.
79 citations
TL;DR: In this paper, the authors present an analysis of long-term X-ray and optical observations of the Wolf-Rayet binary, WR 25, using archival data from observations with the XMM-Newton and the Swift observatories.
Abstract: We present an analysis of long-term X-ray and optical observations of the Wolf-Rayet binary, WR 25. Using archival data from observations with the XMM-Newton and the Swift observatories, spanning over ~10 yr, we show that WR 25 is a periodic variable in X-rays with a period of 208 ± 3 days. X-ray light curves in the 0.5-10.0 keV energy band show phase-locked variability, where the flux increased by a factor of ~2 from minimum to maximum, being maximum near periastron passage. The light curve in the soft energy band (0.5-2.0 keV) shows two minima indicating the presence of two eclipses. However, the light curve in the hard energy band (2.0-10.0 keV) shows only one minimum during the apastron passage. The X-ray spectra of WR 25 were explained by a two-temperature plasma model. Both the cool and the hot plasmas were constant at 0.628 ± 0.008 and 2.75 ± 0.06 keV throughout an orbital cycle, where the cooler plasma could be due to small scale shocks in a radiation-driven outflow and the high temperature plasma could be due to the collision of winds. The column density varied with the orbital phase and was found to be maximum after the periastron passage, when the WN star is in front of the O star. The abundances of WR 25 were found to be non-solar. Optical V-band data of WR 25 also show the phase-locked variability, being at maximum near periastron passage. The results based on the present analysis indicate that WR 25 is a colliding wind binary where the presence of soft X-rays is attributed to individual components; however, hard X-rays are due to the collision of winds.
20 citations
TL;DR: A metal-free facile and efficient two-step synthetic protocol for the preparation of 1,4-benzoxazepine-5(2H)-one derivatives has been developed.
Abstract: A metal-free facile and efficient two-step synthetic protocol for the preparation of 1,4-benzoxazepine-5(2H)-one derivatives has been developed. The protocol involves Ugi reaction followed by K2CO3 mediated highly regioselective 7-exo-dig intramolecular cyclization of less-nucleophilic oxygen with the pendant alkyne moiety of an Ugi–propargyl precursor to afford the 1,4-benzoxazepine-5(2H)-one derivatives in good to excellent yields.
17 citations
Spanish National Research Council1, University of Málaga2, University of the Basque Country3, Ikerbasque4, Aryabhatta Research Institute of Observational Sciences5, Russian Academy of Sciences6, Saint Petersburg State University7, Petrozavodsk State University8, Special Astrophysical Observatory9, University of Jaén10, Chinese Academy of Sciences11, Sungkyunkwan University12
TL;DR: In this paper, the authors studied the dark nature of GRB 130528A through multi-wavelength observations and concluded that the main reason for the optical darkness is local extinction inside of the host galaxy.
Abstract: Aims. We study the dark nature of GRB 130528A through multi-wavelength observations and conclude that the main reason for the optical darkness is local extinction inside of the host galaxy. Methods. Automatic observations were performed at the Burst Optical Observer and Transient Exploring System (BOOTES)-4 /MET robotic telescope. We also triggered target of opportunity (ToO) observations at Observatorio de Sierra Nevada (OSN), IRAM Plateau de Bure Interferometer (PdBI) and Gran Telescopio Canarias (GTC + OSIRIS). The host galaxy photometric observations in optical to near-infrared (nIR) wavelengths were achieved through large ground-based aperture telescopes, such as 10.4 m Gran Telescopio Canarias (GTC), 4.2 m William Herschel Telescope (WHT), 6 m Bolshoi Teleskop Alt-azimutalnyi (BTA) telescope, and 2 m Liverpool Telescope (LT). Based on these observations, spectral energy distributions (SED) for the host galaxy and afterglow were constructed. Results. Thanks to millimetre (mm) observations at PdBI, we confirm the presence of a mm source within the XRT error circle that faded over the course of our observations and identify the host galaxy. However, we do not find any credible optical source within early observations with BOOTES-4 /MET and 1.5 m OSN telescopes. Spectroscopic observation of this galaxy by GTC showed a single faint emission line that likely corresponds to [OII] 3727 angstrom at a redshift 1.250 +/- 0.001, implying a star formation rate (M-circle dot/yr) > 6.18 M-circle dot/yr without correcting for dust extinction. The probable line-of-sight extinction towards GRB130528A is revealed through analysis of the afterglow SED, resulting in a value of A(V)(GRB) >= 0.9 at the rest frame; this is comparable to extinction levels found among other dark GRBs. The SED of the host galaxy is explained well (chi(2)/d.o.f. = 0.564) by a luminous (M-B = -21.16), low-extinction (A(V) = 0, rest frame), and aged (2.6 Gyr) stellar population. We can explain this apparent contradiction in global and line-of-sight extinction if the GRB birth place happened to lie in a local dense environment. In light of having relatively small specific star formation rate similar to 5.3 M circle dot/yr (L/L*)(-1), this also could explain the age of the old stellar population of host galaxy.
16 citations
Spanish National Research Council1, University of Málaga2, Ikerbasque3, University of the Basque Country4, Aryabhatta Research Institute of Observational Sciences5, Saint Petersburg State University6, Russian Academy of Sciences7, Petrozavodsk State University8, Special Astrophysical Observatory9, University of Jaén10, Chinese Academy of Sciences11, Sungkyunkwan University12
TL;DR: In this article, the authors studied the dark nature of GRB 130528A through multi-wavelength observations and concluded that the main reason for the optical darkness is local extinction inside of the host galaxy.
Abstract: We study the dark nature of GRB 130528A through multi-wavelength observations and conclude that the main reason for the optical darkness is local extinction inside of the host galaxy. Automatic observations were performed at BOOTES-4/MET robotic telescope. We also triggered target of opportunity (ToO) observation at the OSN, IRAM PdBI and the GTC+OSIRIS. The host galaxy photometric observations in optical to near-infrared (nIR) wavelengths were achieved through large ground-based aperture telescopes, such as the 10.4m GTC, the 4.2m WHT, 6m BTA, and the 2m LT. Based on these observations, spectral energy distributions (SED) for the host galaxy and afterglow were constructed. Thanks to mm observations at PdBI, we confirm the presence of a mm source within the XRT error circle that faded over the course of our observations and identify the host galaxy. However, we do not find any credible optical source within early observations with BOOTES-4/MET and 1.5m OSN telescopes. Spectroscopic observation of this galaxy by GTC showed a single faint emission line that likely corresponds to [OII] 3727\{AA} at a redshift of 1.250+/-0.001 implying a SFR(M_sun/yr) > 6.18 M_sun/yr without correcting for dust extinction. The probable extinction was revealed through analysis of the afterglow SED, resulting in a value of AV >= ~ 0.9 at the rest frame, this is comparable to extinction levels found among other dark GRBs. The SED of the host galaxy is explained well (chi2/d.o.f.=0.564) by a luminous (MB=-21.16), low-extinction (AV =0, rest frame), and aged (2.6 Gyr) stellar population. We can explain this apparent contradiction in global and line-of-sight extinction if the GRB birth place happened to lie in a local dense environment. In light of having relatively small specific SFR (SSFR) ~ 5.3 M_sun/yr (L/L_star)-1, this also could explain the age of the old stellar population of host galaxy.
12 citations
TL;DR: In this article, the authors present the results based on R-band polarimetric follow-up observations of the nearby (~10 Mpc) Type II-plateau SN 2012aw.
Abstract: We present the results based on R-band polarimetric follow-up observations of the nearby (~10 Mpc) Type II-plateau SN 2012aw. Starting from ~10 days after the SN explosion, these polarimetric observations cover ~90 days (during the plateau phase) and are distributed over 9 epochs. To characterize the Milky Way interstellar polarization (ISP_MW ), we have observed 14 field stars lying in a radius of 10 degree around the SN. We have also tried to subtract the host galaxy dust polarization component assuming that the dust properties in the host galaxy are similar to that observed for Galactic dust and the general magnetic field follow the large scale structure of the spiral arms of a galaxy. After correcting the IS_PMW , our analysis infer that SN 2012aw has maximum polarization of 0.85% +- 0.08% but polarization angle does not show much variation with a weighted mean value of ~138 degree. However, if both ISP_MW and host galaxy polarization (ISP_HG ) components are subtracted from the observed polarization values of SN, maximum polarization of the SN becomes 0.68% +- 0.08%. The distribution of Q and U parameters appears to follow a loop like structure. The evolution of polarimetric light curve (PLC) properties of this event is also compared with other well studied core-collapse supernovae of similar type.
12 citations
TL;DR: In this article, a multi-wavelength study of the radio-loud narrow line Seyfert 1 galaxy (NLSy1), 1H 0323+342, detected by Fermi Gamma Ray Space Telescope is presented.
Abstract: We present a multi-wavelength study of the radio-loud narrow line Seyfert 1 galaxy (NLSy1), 1H 0323+342, detected by Fermi Gamma Ray Space Telescope. Multi-band light curves show many orphan X-ray and optical flares having no corresponding {\gamma}-ray counterparts. Such anomalous variability behavior can be due to different locations of the emission region from the central source. During a large flare, {\gamma}-ray flux doubling time scale as small as $\sim$ 3 hours is noticed. We built spectral energy distribution (SED) during different activity states and modeled them using an one-zone leptonic model. The shape of the optical/UV component of the SEDs is dominated by accretion disk emission in all the activity states. In the X-ray band, significant thermal emission from the hot corona is inferred during quiescent and first flaring states, however, during subsequent flares, non-thermal jet component dominates. The {\gamma}-ray emission in all the states can be well explained by inverse-Compton scattering of accretion disk photons reprocessed by the broad line region. The source showed violent intra-night optical variability, coinciding with one of the high {\gamma}-ray activity states. An analysis of the overall X-ray spectrum fitted with an absorbed power-law plus relativistic reflection component hints for the presence of Fe K-{\alpha} line and returns a high black hole spin value of a=0.96 $\pm$ 0.14. We argue that 1H 0323+342 possesses dual characteristics, akin to flat spectrum radio quasars (FSRQs) as well as radio-quiet NLSy1s, though at a low jet power regime compared to powerful FSRQs.
4 citations
Chinese Academy of Sciences1, Purple Mountain Observatory2, Australian National University3, University of California, Berkeley4, Guangxi University5, University of Michigan6, University of New South Wales7, University of Hawaii8, Sabancı University9, Istanbul University10, Middle East Technical University11, Ariès12, SLAC National Accelerator Laboratory13, Chulalongkorn University14, Institute for the Physics and Mathematics of the Universe15, Louisiana State University16, University of Texas at Austin17, College of Saint Benedict18
TL;DR: In this article, the optical luminosity function (LF) of gamma-ray bursts (GRBs) estimated from a uniform sample of 58 GRBs from observations with the Robotic Optical Transient Search Experiment III (ROTSE-III) was presented.
Abstract: We present the optical luminosity function (LF) of gamma-ray bursts (GRBs) estimated from a uniform sample of 58 GRBs from observations with the Robotic Optical Transient Search Experiment III (ROTSE-III) Our GRB sample is divided into two sub-samples: detected afterglows (18 GRBs) and those with upper limits (40 GRBs) We derive R-band fluxes for these two sub-samples 100 s after the onset of the burst The optical LFs at 100 s are fitted by assuming that the co-moving GRB rate traces the star formation rate While fitting the optical LFs using Monte Carlo simulations, we take into account the detection function of ROTSE-III We find that the cumulative distribution of optical emission at 100 s is well described by an exponential rise and power-law decay, a broken power law, and Schechter LFs A single power-law (SPL) LF, on the other hand, is ruled out with high confidence
3 citations
TL;DR: In this article, the authors present an analysis of long-term X-ray and optical observations of the Wolf-Rayet binary WR 25 and show that it is a periodic variable in X-rays with a period of $208 \pm 3$ days.
Abstract: We present an analysis of long-term X-ray and optical observations of the Wolf-Rayet binary WR 25. Using archival data from observations with the XMM-Newton and the Swift observatories spanning over ~10 yr, we show that WR 25 is a periodic variable in X-rays with a period of $208 \pm 3$ days. X-ray light curves in the 0.5-10.0 keV energy band show phase-locked variability, where the flux increased by a factor of ~2 from minimum to maximum, being maximum near periastron passage. The light curve in the soft energy band (0.5-2.0 keV) shows two minima indicating the presence of two eclipses. However, the light curve in the hard energy band (2.0-10.0 keV) shows only one minimum during the apastron passage. The X-ray spectra of WR 25 were explained by a two-temperature plasma model. Both the cool and the hot plasmas were constant at 0.628+/-0.008 and 2.75+/-0.06 keV throughout an orbital cycle, where the cooler plasma could be due to the small scale shocks in a radiation-driven outflow and the high temperature plasma could be due to the collision of winds. The column density varied with the orbital phase and was found to be maximum after the periastron passage, when the WN star is in front of the O star. The abundances of WR 25 were found to be non-solar. Optical V-band data of WR 25 also show the phase-locked variability, being at maximum near periastron passage. The results based on the present analysis indicate that WR 25 is a colliding wind binary where the presence of soft X-rays is attributed to individual components; however, hard X-rays are due to the collision of winds.
1 citations