J. Nousek

Pennsylvania State University, University Park, MD, United States

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Publications (114)152.34 Total impact

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    ABSTRACT: Long-duration Gamma-Ray Bursts (GRBs) are an extremely rare outcome of the collapse of massive stars, and are typically found in the distant Universe. Because of its intrinsic luminosity (L ∼ 3 × 10(53) erg s(-1)) and its relative proximity (z = 0.34), GRB 130427A was a unique event that reached the highest fluence observed in the γ-ray band. Here we present a comprehensive multiwavelength view of GRB 130427A with Swift, the 2-m Liverpool and Faulkes telescopes and by other ground-based facilities, highlighting the evolution of the burst emission from the prompt to the afterglow phase. The properties of GRB 130427A are similar to those of the most luminous, high-redshift GRBs, suggesting that a common central engine is responsible for producing GRBs in both the contemporary and the early Universe and over the full range of GRB isotropic energies.
    Science 11/2013; · 31.20 Impact Factor
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    ABSTRACT: We present a comprehensive statistical analysis of Swift X-ray light-curves of Gamma-Ray Bursts (GRBs) collecting data from more than 650 GRBs discovered by Swift and other facilities. The unprecedented sample size allows us to constrain the REST FRAME X-ray properties of GRBs from a statistical perspective, with particular reference to intrinsic time scales and the energetics of the different light-curve phases in a common rest-frame 0.3-30 keV energy band. Temporal variability episodes are also studied and their properties constrained. Two fundamental questions drive this effort: i) Does the X-ray emission retain any kind of "memory"of the prompt gamma-ray phase? ii) Where is the dividing line between long and short GRB X-ray properties? We show that short GRBs decay faster, are less luminous and less energetic than long GRBs in the X-rays, but are interestingly characterized by similar intrinsic absorption. We furthermore reveal the existence of a number of statistically significant relations that link the X-ray to prompt gamma-ray parameters in long GRBs; short GRBs are outliers of the majority of these 2-parameter relations. However and more importantly, we report on the existence of a universal 3-parameter scaling that links the X-ray and the gamma-ray energy to the prompt spectral peak energy of BOTH long and short GRBs: E_{X,iso}\propto E_{gamma,iso}^{1.00\pm 0.06}/E_{pk}^{0.60\pm 0.10}.
    Monthly Notices of the Royal Astronomical Society 03/2012; 428(1). · 5.52 Impact Factor
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    ABSTRACT: We searched for X-ray serendipitous sources in over 370 Swift-XRT fields centered on gamma ray bursts detected between 2004 and 2008 and observed with total exposures ranging from 10 ks to over 1 Ms. This defines the Swift Serendipitous Survey in deep XRT GRB fields, which is quite broad compared to existing surveys (~33 square degrees) and medium depth, with a faintest flux limit of 7.2e-16 erg cm^-2 s^-1 in the 0.5 to 2 keV energy range. The survey has a high degree of uniformity thanks to the stable point spread function and small vignetting correction factors of the XRT, moreover is completely random on the sky as GRBs explode in totally unrelated parts of the sky. In this paper we present the sample and the X-ray number counts of the high Galactic-latitude sample, estimated with high statistics over a wide flux range (i.e., 7.2e-16 to ~5e-13 erg cm^-2 s^-1 in the 0.5-2 keV band and 3.4e-15 to ~6e-13 erg cm^-2 s^-1 in the 2-10 keV band). We detect 9387 point-like sources, while 7071 point-like sources are found at high Galactic-latitudes (i.e. >=20 deg). The large number of detected sources resulting from the combination of large area and deep flux limits make this survey a new important tool for investigating the evolution of AGN. In particular, the large area permits finding rare high-luminosity objects like QSO2, which are poorly sampled by other surveys, adding precious information for the luminosity function bright end. The high Galactic-latitude logN-logS relation is well determined over all the flux coverage, and it is nicely consistent with previous results at 1 sigma confidence level. By the hard X-ray color analysis, we find that the Swift Serendipitous Survey in deep XRT GRB fields samples relatively unobscured and mildly obscured AGN, with a fraction of obscured sources of ~37% (~15%) in the 2-10 (0.3-3 keV) band.
    Astronomy and Astrophysics 02/2011; 528. · 5.08 Impact Factor
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    ABSTRACT: The Table contains the SwiftFT catalog of the serendipitous sources detected in over 370 Swift-XRT fields centered on gamma ray bursts, which were detected between 2004 and 2008 and observed with total exposures ranging from 10ks to over 1Ms. (2 data files).
    VizieR Online Data Catalog. 02/2011;
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    ABSTRACT: The Joint Astrophysics Nascent Universe Satellite (JANUS) is a proposed multiwavelength cosmic dawn science investigation. The mission's primary objectives are to: measure the cosmic star formation rate over the redshift range of 5-12, map the growth of massive black holes that seed galaxy formation at z>6, and enable detailed studies of the history of reionization and metal enrichment in the early Universe. Over the baseline mission, the wide-field X-ray Coded Aperture Telescope (XCAT; 1-20 keV) on JANUS is designed to localize high redshift (z>5) GRBs. After a prompt slew, the Near-Infrared Telescope (NIRT; 0.7-1.7 microns) refines the XCAT position by observing the early afterglow of each burst. The position, brightness, and redshift are telemetered to ground-based astronomers in real time. Concurrently, a wide-angle objective-prism survey of the entire extragalactic sky yields detection of high redshift quasars in the 6-10 redshift range.
    12/2010; 43:42502.
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    ABSTRACT: The hard X-ray all-sky survey with the Swift/BAT instrument has provided a detailed census of local AGN activity. The Swift/BAT AGN catalog from 9-months of operation has allowed the determination of the X-ray properties, SEDs, accretion rates and absorption properties of AGN in the local Universe. Here we present preliminary results from a complete subsample of AGN in the recently published 22-month catalog (extending this soon to the 36- and 54-month BAT catalogs currently in preparation), covering 4800 square degrees of the sky, in the Northern Galactic Cap. The ultimate aim is to present a complete and in-depth X-ray spectral characterization of this representative sample, determining detailed X-ray spectral properties such as absorbing column density/complexity, iron K emission and luminosity, while also making use of the extensive archival multi-wavelength coverage available (for example from SDSS) in this part of the sky to determine SEDs and accretion properties in these AGN. This in-depth study of a complete local sample will aid greatly in the understanding of distant AGNs in deep surveys.
    01/2010;
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    ABSTRACT: Gamma-ray bursts (GRBs) are produced by rare types of massive stellar explosion. Their rapidly fading afterglows are often bright enough at optical wavelengths that they are detectable at cosmological distances. Hitherto, the highest known redshift for a GRB was z = 6.7 (ref. 1), for GRB 080913, and for a galaxy was z = 6.96 (ref. 2). Here we report observations of GRB 090423 and the near-infrared spectroscopic measurement of its redshift, z = 8.1(-0.3)(+0.1). This burst happened when the Universe was only about 4 per cent of its current age. Its properties are similar to those of GRBs observed at low/intermediate redshifts, suggesting that the mechanisms and progenitors that gave rise to this burst about 600,000,000 years after the Big Bang are not markedly different from those producing GRBs about 10,000,000,000 years later.
    Nature 10/2009; 461(7268):1258-60. · 38.60 Impact Factor
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    ABSTRACT: The Swift X-ray Telescope has now studied hundreds of X-ray afterglows of Gamma-Ray Bursts. One surprising finding is the apparent absence of jet breaks in the XRT light curves, suggesting that the Swift GRBs may have larger jet opening angles than those studied before the launch of Swift. We have undertaken a program of late-time observations of GRB afterglows by the Chandra X-ray Observatory to search for possible jet breaks at very late times, after the afterglow becomes too faint for Swift to monitor. These Chandra observations push the flux limits down by an order of magnitude, from ˜2E-14 cgs to ˜2E-15 cgs. I will report on the results of this on-going program, which has found very late jet breaks in some cases, and failed to find evidence of jet breaks to very late times in other afterglows. The results are consistent with the recent findings of Racusin et al., that suggest that some jet breaks occur at very late times but that the opening angles are typically still of order 5-10 degrees.
    09/2009;
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    ABSTRACT: The UVOT telescope on the Swift observatory has detected optical afterglow emission from GRB 050319. The flux declined with a power-law slope of α = -0.57 between the start of observations some 230 s after the burst onset (90 s after the burst trigger) until it faded below the sensitivity threshold of the instrument after ~5 × 104 s. There is no evidence for the rapidly declining component in the early light curve that is seen at the same time in the X-ray band. The afterglow is not detected in UVOT shortward of the B band, suggesting a redshift of about 3.5. The optical V-band emission lies on the extension of the X-ray spectrum, with an optical-to-X-ray slope of β = -0.8. The relatively flat decay rate of the burst suggests that the central engine continues to inject energy into the fireball for as long as a few × 104 s after the burst.
    The Astrophysical Journal 12/2008; 639(1):311. · 6.73 Impact Factor
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    ABSTRACT: We present a new measurement of the cosmic X-ray background (CXRB) in the 1.5-7 keV energy band, performed by exploiting the Swift X-ray telescope (XRT) data archive. We also present a CXRB spectral model in a wider energy band (1.5-200 keV), obtained by combining these data with the recently published Swift-BAT measurement. From the XRT archive we collect a complete sample of 126 high Galactic latitude gamma-ray burst (GRB) follow-up observations. This provides a total exposure of 7.5 Ms and a sky-coverage of 7 square degrees which represents a serendipitous survey, well suited for a direct measurement of the CXRB in the 1.5-10 keV interval. Our work is based on a complete characterization of the instrumental background and an accurate measurement of the stray-light contamination and vignetting calibration. We find that the CXRB spectrum in the 1.5-7 keV energy band can be equally well fitted by a single power-law with photon index Gamma=1.47+/-0.07 or a single power-law with photon index Gamma=1.41+/-0.06 and an exponential roll-off at 41 keV. The measured flux in the 2-10 keV energy band is 2.18+/-0.13 E-11 erg/(cm2 s deg2) in the 2-10 keV band. Combining Swift-XRT with Swift-BAT (15-200 keV) we find that, in the 1.5-200 keV band, the CXRB spectrum can be well described by two smoothly-joined power laws with the energy break at 29.0+/-0.5 keV corresponding to a nu F_nu peak located at 22.4+/-0.4 keV. Taking advantage of both the Swift high energy instruments (XRT and BAT), we produce an analytical description of the CXRB spectrum over a wide (1.5-200 keV) energy band. This model is marginally consistent with the HEAO1 measurement (~10% higher at energies higher than 20 keV, while it is significantly (30%) higher at low energies (2-10 keV). Comment: Accepted for publication by A&A; 9 pages, 11 figures. Typo corrected in units of Tab. 2; update Fig. 11
    11/2008;
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    ABSTRACT: Swift very fast follow up observations of Gamma‐Ray Bursts have allowed us to discover a new feature of GRB afterglows: a phase of shallow decay, usually attributed to energy injection in the burst ejecta, which can last for several thousands of seconds both in the X‐ray and optical bands. Here I shall discuss this phase in the cases of Swift GRBs 050401, 050801 and 050802. © 2007 American Institute of Physics
    AIP Conference Proceedings. 08/2007; 924(1):437-440.
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    ABSTRACT: Aims. The aim of this paper is to study the Gamma Ray Burst (GRB) environment through the analysis of the optical absorption features due to the gas surrounding the GRB. Methods. To this purpose we analyze high resolution spectroscopic observations (R=20000-45000, corresponding to 14 km/s at 4200Å and 6.6 km/s at 9000Å) of the optical afterglow of GRB050730, obtained with UVES@VLT ∼ 4 hours after the GRB trigger. Results. The spectrum shows that the ISMof the GRB host galaxy at z = 3.967 is complex, with at least five components contributing to the main absorption system. We detect strong CII*, Si II*, OI* and Fe II* fine structure absorption lines associated to the second and third component. Conclusions. For the first three components we derive information on the relative distance from the site of the GRB explosion. Component 1, which has the longest wavelength, highest positive velocity shift, does not present any fine structure nor low ionization lines; it only shows very high ionization features, such as CIV and OVI, suggesting that this component is very close to the GRB site. From the analysis of low and high ionization lines and fine structure lines, we find evidences that the distance of component 2 from the site of the GRB explosion is 10-100 times smaller than that of component 3. We evaluated the mean metallicity of the z=3.967 system obtaining values ≈ 10−2 of the solar metallicity or less. However, this should not be taken as representative of the circumburst medium, since the main contribution to the hydrogen column density comes from the outer regions of the galaxy while that of the other elements presumably comes from the ISMcloser to the GRB site. Furthermore, difficulties in evaluating dust depletion correction can modify significantly these values. The mean [C/Fe] ratio agrees well with that expected by single star-formation event models. Interestingly the [C/Fe] of component 2 is smaller than that of component 3, in agreement with GRB dust destruction scenarios, if component 2 is closer than component 3 to the GRB site.
    D'Elia, V. and Fiore, F. and Meurs, E.J.A. and Chincarini, G. and Melandri, A. and Norci, Laura and Pellizza, L. and Perna, R. and Piranomonte, S. and Sbordone, L. and Stella, L. and Tagliaferri, G. and Vergani, Susanna D. and Ward, P.A. and Angelini, L. and Antonelli, L.A. and Burrows, D.N. and Campana, M. and Capalbi, M. and Cimatti, A. and Costa, E. and Cusumano, G. and Della Valle, M. and Filliatre, P. and Fontana, A. and Frontera, F. and Fugazza, D. and Gehrels, N. and Giannini, T. and Giommi, P. and Goldoni, P. and Guetta, D. and Israel, G. and Lazzati, D. and Malesani, D. and Marconi, G. and Mason, K. and Mereghetti, S. and Mirabel, F. and Molinari, E. and Moretti, A. and Nousek, J. and Perri, M. and Piro, L. and Stratta, G. and Testa, V. and Vietri, M. (2007) UVES/VLT high resolution spectroscopy of GRB 050730 afterglow: probing the features of the GRB environment. Astronomy & Astrophysics, 467 (2). pp. 629-639. ISSN 0004-6361. 01/2007;
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    ABSTRACT: We report time-resolved imaging UV photometry of Comet 9P/Tempel 1 during the interval 2005 June 29–2005 July 21, including intensive coverage of the collision with the Deep Impact probe and its immediate aftermath. The nuclear flux of the comet begins to rise within minutes of the collision, and peaks about 3 h after impact. There is no evidence for a prompt flash at the time of impact. The comet exhibits a significant re-brightening about 40 h after the initial outburst, consistent with the rotation period of the comet, with evidence for further periodic re-brightenings on subsequent rotations. Modelling of the brightness profile of the coma as a function of time suggests two distinct velocity systems in the ejecta, at de-projected expansion speeds of 190 and 550 m/s, which we suggest are due to dust and gas, respectively. There is a distinct asymmetry in the slower-moving (dust) component as a function of position angle on the sky. This is confirmed by direct imaging analysis, which reveals an expanding plume of material concentrated in the impact hemisphere. The projected expansion velocity of the leading edge of this plume, measured directly from the imaging data, is 190 m/s, consistent with the velocity of the dust component determined from the photometric analysis. From our data we determine that a total of (1.4±0.2)×1032 water molecules were ejected in the impact, together with a total scattering area of dust at 300 nm of 190±20 km2.
    Icarus 01/2007; · 3.16 Impact Factor
  • GRB Coordinates Network. 01/2007;
  • Nuovo Cimento B Serie. 12/2006; 121:1531-1533.
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    ABSTRACT: Results are presented of early X-ray afterglow observations of GRB 060105 by Swift and Suzaku. The bright, long gamma-ray burst GRB 060105 triggered the Swift Burst Alert Telescope (BAT) at 06:49:28 on 5 January 2006. The Suzaku team commenced a pre-planned target of opportunity observation at 19 ks (5.3 hr) after the Swift trigger. Following the prompt emission and successive very steep decay, a shallow decay was observed from T_0+187 s to T_0+1287 s. After an observation gap during T_0 +(1.5-3) ks, an extremely early steep decay was observed in T_0+(4-30) ks. The lightcurve flattened again at T_0+30 ks, and another steep decay followed from T_0+50 ks to the end of observations. Both steep decays exhibited decay indices of 2.3 - 2.4. This very early break, if it is a jet break, is the earliest case among X-ray afterglow observations, suggesting a very narrow jet whose opening angle is well below 1 degree. The unique Suzaku/XIS data allow us to set very tight upper limits on line emission or absorption in this GRB. For the reported pseudo-redshift of z=4.0+/-1.3 the upper limit on the iron line equivalent width is 50 eV.
    10/2006;
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    ABSTRACT: Further observations with the Swift/XRT have allowed us to refine the position of the faint Galactic Center X-ray transient Swift J174540.2-290005 (ATEL #920). The new position is as follows: RA(J2000) = 17h 45m 40.1s Dec(J200) = -29d 00m 06.4s with an estimated error radius of 3.6 arcseconds (90% containment). This places the transient 0.7 arcseconds from CXOGC J174540.0-290005 (e.g.
    The Astronomer's Telegram. 10/2006;
  • Nuovo Cimento B Serie. 10/2006; 121:1253-1256.
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    ABSTRACT: Swift/XRT monitoring of the Galactic Center region has detected a faint transient source, Swift J174540.2-290005.3, close to Sgr A*. The source is detected in observations starting on Oct 20th, 2006, and is observed to peak at a flux of 5x10-12 erg/s/cm2 (0.5-10 keV) on Oct 22nd, 2006. Observations of archival data have shown no XRT detection of this source prior to Oct 20th.
    The Astronomer's Telegram. 10/2006;
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    ABSTRACT: IGR J17497-2821 (e.g. Soldi et al., ATEL #885) has been observed by the Swift/XRT on 4 occasions from Sept 19th, 2006 to Sept 26th, 2006, since being initially detected by INTEGRAL on Sept 17th, 2006. We report on a refined analysis of these combined data. Swift/XRT positions for this source previously reported have been inconsistent (e.g. Walter et al., ATEL #889, Chaty et al., ATEL #897), this is most likely due to the point source falling on hot columns in the XRT detector, making accurate centroiding of the source difficult.
    The Astronomer's Telegram. 09/2006;