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1. A Swift study of long-term changes in the X-ray flaring properties of Sagittarius A

Author

A Andrés, J van den Eijnden, N Degenaar, P A Evans, K Chatterjee, M Reynolds, J M Miller, J Kennea, R Wijnands, S Markoff, D Altamirano, C O Heinke, A Bahramian, G Ponti, D Haggard, and High Energy Astrophys. & Astropart. Phys (API, FNWI)

Subjects
High Energy Astrophysical Phenomena (astro-ph.HE), Space and Planetary Science, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics::Solar and Stellar Astrophysics, Astronomy and Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics::Galaxy Astrophysics
Abstract

The radiative counterpart of the supermassive black hole at the Galactic Centre, Sagittarius A*, displays flaring emission in the X-ray band atop a steady, quiescent level. Flares are also observed in the near-infrared band. The physical process producing the flares is not fully understood and it is unclear if the flaring rate varies, although some recent works suggest it has reached unprecedented variability in recent years. Using over a decade of regular X-ray monitoring of Neil Gehrels Swift Observatory, we studied the variations in count rate of Sgr A* on time scales of years. We decomposed the X-ray emission into quiescent and flaring emission, modelled as a constant and power law process, respectively. We found that the complete, multi-year dataset cannot be described by a stationary distribution of flare fluxes, while individual years follow this model better. In three of the ten studied years, the data is consistent with a purely Poissonian quiescent distribution, while for five years only an upper limit of the flare flux distribution parameter could be determined. We find that these possible changes cannot be explained fully by the different number of observations per year. Combined, these results are instead consistent with a changing flaring rate of Sgr A*, appearing more active between 2006-2007 and 2017-2019, than between 2008-2012. Finally, we discuss this result in the context of flare models and the passing of gaseous objects, and discuss the extra statistical steps taken, for instance to deal with the background in the Swift observations., 14 pages, 10 figures, Accepted for publication in MNRAS

Published
2022
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2. The First Swift Intensive AGN Accretion Disk Reverberation Mapping Survey

Author

R. Edelson, J. Gelbord, E. Cackett, B. M. Peterson, Keith Horne, A. J. Barth, D. A. Starkey, M. Bentz, W. N. Brandt, M. Goad, M. Joner, K. Korista, H. Netzer, K. Page, P. Uttley, S. Vaughan, A. Breeveld, S. B. Cenko, C. Done, P. Evans, M. Fausnaugh, G. Ferland, D. Gonzalez-Buitrago, J. Gropp, D. Grupe, J. Kaastra, J. Kennea, G. Kriss, S. Mathur, M. Mehdipour, D. Mudd, J. Nousek, T. Schmidt, M. Vestergaard, and C. Villforth

Subjects
Astrophysics
Abstract

Swift intensive accretion disk reverberation mapping of four AGN yielded light curves sampled ∼200–350 times in 0.3–10 keV X-ray and six UV/optical bands. Uniform reduction and cross-correlation analysis of these data sets yields three main results: (1) The X-ray/UV correlations are much weaker than those within the UV/optical, posing severe problems for the lamp-post reprocessing model in which variations in a central X-ray corona drive and power those in the surrounding accretion disk. (2) The UV/optical interband lags are generally consistent with t μ l4 3 as predicted by the centrally illuminated thin accretion disk model. While the average interband lags are somewhat larger than predicted, these results alone are not inconsistent with the thin disk model given the large systematic uncertainties involved. (3) The one exception is the U band lags, which are on average a factor of ∼2.2 larger than predicted from the surrounding band data and fits. This excess appears to be due to diffuse continuum emission from the broad-line region (BLR). The precise mixing of disk and BLR components cannot be determined from these data alone. The lags in different AGN appear to scale with mass or luminosity. We also find that there are systematic differences between the uncertainties derived by JAVELIN versus more standard lag measurement techniques, with JAVELIN reporting smaller uncertainties by a factor of 2.5 on average. In order to be conservative only standard techniques were used in the analyses reported herein.

Published
2019
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3. XMM-Newton observations of a sample of radio pulsars

Author

R. Much, J. Kennea, F. A. Cordova, and T. Oosterbroek

Subjects
Physics, On board, Nuclear and High Energy Physics, Pulsar, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Short exposure, Sample (graphics), Atomic and Molecular Physics, and Optics
Abstract

Results of a search for X-ray counterparts of radio pulsars with the EPIC-PN instrument on board XMM-Newton are presented. Despite the mostly relatively short exposure times (

Published
2004
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4. The X-ray flaring properties of Sgr A* during six years of monitoring with Swift

Author

N. Degenaar, J. M. Miller, J. Kennea, N. Gehrels, M. T. Reynolds, R. Wijnands, and High Energy Astrophys. & Astropart. Phys (API, FNWI)

Subjects
Physics, Swift, High Energy Astrophysical Phenomena (astro-ph.HE), Supermassive black hole, Astrophysics::High Energy Astrophysical Phenomena, Spectral properties, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Luminosity, law.invention, Telescope, Sagittarius A, Space and Planetary Science, law, Astrophysics::Solar and Stellar Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, computer, Astrophysics::Galaxy Astrophysics, Line (formation), computer.programming_language
Abstract

Starting in 2006, Swift has been targeting a region of ~21'X21' around Sagittarius A* (Sgr A*) with the onboard X-ray telescope. The short, quasi-daily observations offer an unique view of the long-term X-ray behavior of the supermassive black hole. We report on the data obtained between 2006 February and 2011 October, which encompasses 715 observations with a total accumulated exposure time of ~0.8 Ms. A total of six X-ray flares were detected with Swift, which all had an average 2-10 keV luminosity of Lx (1-4)E35 erg/s (assuming a distance of 8 kpc). This more than doubles the number of such bright X-ray flares observed from Sgr A*. One of the Swift-detected flares may have been softer than the other five, which would indicate that flares of similar intensity can have different spectral properties. The Swift campaign allows us to constrain the occurrence rate of bright (Lx > 1E35 erg/s) X-ray flares to be ~0.1-0.2 per day, which is in line with previous estimates. This analysis of the occurrence rate and properties of the X-ray flares seen with Swift offers an important calibration point to asses whether the flaring behavior of Sgr A* changes as a result of its interaction with the gas cloud that is projected to make a close passage in 2013., 8 pages, 5 figures, 3 tables. Shortened, accepted to ApJ

Published
2012

5. A gamma-ray burst at a redshift of z approximately 8.2

Author

N R, Tanvir, D B, Fox, A J, Levan, E, Berger, K, Wiersema, J P U, Fynbo, A, Cucchiara, T, Krühler, N, Gehrels, J S, Bloom, J, Greiner, P A, Evans, E, Rol, F, Olivares, J, Hjorth, P, Jakobsson, J, Farihi, R, Willingale, R L C, Starling, S B, Cenko, D, Perley, J R, Maund, J, Duke, R A M J, Wijers, A J, Adamson, A, Allan, M N, Bremer, D N, Burrows, A J, Castro-Tirado, B, Cavanagh, A, de Ugarte Postigo, M A, Dopita, T A, Fatkhullin, A S, Fruchter, R J, Foley, J, Gorosabel, J, Kennea, T, Kerr, S, Klose, H A, Krimm, V N, Komarova, S R, Kulkarni, A S, Moskvitin, C G, Mundell, T, Naylor, K, Page, B E, Penprase, M, Perri, P, Podsiadlowski, K, Roth, R E, Rutledge, T, Sakamoto, P, Schady, B P, Schmidt, A M, Soderberg, J, Sollerman, A W, Stephens, G, Stratta, T N, Ukwatta, D, Watson, E, Westra, T, Wold, and C, Wolf

Subjects
Astrophysics::High Energy Astrophysical Phenomena, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics::Galaxy Astrophysics
Abstract

Long-duration gamma-ray bursts (GRBs) are thought to result from the explosions of certain massive stars, and some are bright enough that they should be observable out to redshifts of z > 20 using current technology. Hitherto, the highest redshift measured for any object was z = 6.96, for a Lyman-alpha emitting galaxy. Here we report that GRB 090423 lies at a redshift of z approximately 8.2, implying that massive stars were being produced and dying as GRBs approximately 630 Myr after the Big Bang. The burst also pinpoints the location of its host galaxy.

Published
2009

7. Identification of the Hard X-Ray Source Dominating the E > 25 keV Emission of the Nearby Galaxy M31.

Author

M. Yukita, A. Ptak, A. E. Hornschemeier, D. Wik, T. J. Maccarone, K. Pottschmidt, A. Zezas, V. Antoniou, R. Ballhausen, B. D. Lehmer, A. Lien, B. Williams, F. Baganoff, P. T. Boyd, T. Enoto, J. Kennea, K. L. Page, and Y. Choi

Subjects
HARD X-rays, EMISSION-line galaxies, PULSARS, NEUTRON stars, PHOTON statistics, X-ray binaries
Abstract

We report the identification of a bright hard X-ray source dominating the M31 bulge above 25 keV from a simultaneous NuSTAR–Swift observation. We find that this source is the counterpart to Swift J0042.6+4112, which was previously detected in the Swift BAT All-sky Hard X-ray Survey. This Swift BAT source had been suggested to be the combined emission from a number of point sources; our new observations have identified a single X-ray source from 0.5 to 50 keV as the counterpart for the first time. In the 0.5–10 keV band, the source had been classified as an X-ray Binary candidate in various Chandra and XMM-Newton studies; however, since it was not clearly associated with Swift J0042.6+4112, the previous E < 10 keV observations did not generate much attention. This source has a spectrum with a soft X-ray excess (kT ∼ 0.2 keV) plus a hard spectrum with a power law of and a cutoff around 15–20 keV, typical of the spectral characteristics of accreting pulsars. Unfortunately, any potential pulsation was undetected in the NuSTAR data, possibly due to insufficient photon statistics. The existing deep HST images exclude high-mass (>3 ) donors at the location of this source. The best interpretation for the nature of this source is an X-ray pulsar with an intermediate-mass (<3 ) companion or a symbiotic X-ray binary. We discuss other possibilities in more detail. [ABSTRACT FROM AUTHOR]

Published
2017
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8. GRB 130427A: a nearby ordinary monster.

Author

Maselli A, Melandri A, Nava L, Mundell CG, Kawai N, Campana S, Covino S, Cummings JR, Cusumano G, Evans PA, Ghirlanda G, Ghisellini G, Guidorzi C, Kobayashi S, Kuin P, La Parola V, Mangano V, Oates S, Sakamoto T, Serino M, Virgili F, Zhang BB, Barthelmy S, Beardmore A, Bernardini MG, Bersier D, Burrows D, Calderone G, Capalbi M, Chiang J, D'Avanzo P, D'Elia V, De Pasquale M, Fugazza D, Gehrels N, Gomboc A, Harrison R, Hanayama H, Japelj J, Kennea J, Kopac D, Kouveliotou C, Kuroda D, Levan A, Malesani D, Marshall F, Nousek J, O'Brien P, Osborne JP, Pagani C, Page KL, Page M, Perri M, Pritchard T, Romano P, Saito Y, Sbarufatti B, Salvaterra R, Steele I, Tanvir N, Vianello G, Wiegand B, Wiersema K, Yatsu Y, Yoshii T, and Tagliaferri G

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) ergs per second) and its relative proximity (z = 0.34), GRB 130427A reached the highest fluence observed in the γ-ray band. Here, we present a comprehensive multiwavelength view of GRB 130427A with Swift, the 2-meter 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.

Published
2014
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9. A gamma-ray burst at a redshift of z approximately 8.2.

Author

Tanvir NR, Fox DB, Levan AJ, Berger E, Wiersema K, Fynbo JP, Cucchiara A, Krühler T, Gehrels N, Bloom JS, Greiner J, Evans PA, Rol E, Olivares F, Hjorth J, Jakobsson P, Farihi J, Willingale R, Starling RL, Cenko SB, Perley D, Maund JR, Duke J, Wijers RA, Adamson AJ, Allan A, Bremer MN, Burrows DN, Castro-Tirado AJ, Cavanagh B, de Ugarte Postigo A, Dopita MA, Fatkhullin TA, Fruchter AS, Foley RJ, Gorosabel J, Kennea J, Kerr T, Klose S, Krimm HA, Komarova VN, Kulkarni SR, Moskvitin AS, Mundell CG, Naylor T, Page K, Penprase BE, Perri M, Podsiadlowski P, Roth K, Rutledge RE, Sakamoto T, Schady P, Schmidt BP, Soderberg AM, Sollerman J, Stephens AW, Stratta G, Ukwatta TN, Watson D, Westra E, Wold T, and Wolf C

Abstract

Long-duration gamma-ray bursts (GRBs) are thought to result from the explosions of certain massive stars, and some are bright enough that they should be observable out to redshifts of z > 20 using current technology. Hitherto, the highest redshift measured for any object was z = 6.96, for a Lyman-alpha emitting galaxy. Here we report that GRB 090423 lies at a redshift of z approximately 8.2, implying that massive stars were being produced and dying as GRBs approximately 630 Myr after the Big Bang. The burst also pinpoints the location of its host galaxy.

Published
2009
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10. Fermi observations of high-energy gamma-ray emission from GRB 080916C.

Author

Abdo AA, Ackermann M, Arimoto M, Asano K, Atwood WB, Axelsson M, Baldini L, Ballet J, Band DL, Barbiellini G, Baring MG, Bastieri D, Battelino M, Baughman BM, Bechtol K, Bellardi F, Bellazzini R, Berenji B, Bhat PN, Bissaldi E, Blandford RD, Bloom ED, Bogaert G, Bogart JR, Bonamente E, Bonnell J, Borgland AW, Bouvier A, Bregeon J, Brez A, Briggs MS, Brigida M, Bruel P, Burnett TH, Burrows D, Busetto G, Caliandro GA, Cameron RA, Caraveo PA, Casandjian JM, Ceccanti M, Cecchi C, Celotti A, Charles E, Chekhtman A, Cheung CC, Chiang J, Ciprini S, Claus R, Cohen-Tanugi J, Cominsky LR, Connaughton V, Conrad J, Costamante L, Cutini S, Deklotz M, Dermer CD, de Angelis A, de Palma F, Digel SW, Dingus BL, do Couto E Silva E, Drell PS, Dubois R, Dumora D, Edmonds Y, Evans PA, Fabiani D, Farnier C, Favuzzi C, Finke J, Fishman G, Focke WB, Frailis M, Fukazawa Y, Funk S, Fusco P, Gargano F, Gasparrini D, Gehrels N, Germani S, Giebels B, Giglietto N, Giommi P, Giordano F, Glanzman T, Godfrey G, Goldstein A, Granot J, Greiner J, Grenier IA, Grondin MH, Grove JE, Guillemot L, Guiriec S, Haller G, Hanabata Y, Harding AK, Hayashida M, Hays E, Hernando Morat JA, Hoover A, Hughes RE, Jóhannesson G, Johnson AS, Johnson RP, Johnson TJ, Johnson WN, Kamae T, Katagiri H, Kataoka J, Kavelaars A, Kawai N, Kelly H, Kennea J, Kerr M, Kippen RM, Knödlseder J, Kocevski D, Kocian ML, Komin N, Kouveliotou C, Kuehn F, Kuss M, Lande J, Landriu D, Larsson S, Latronico L, Lavalley C, Lee B, Lee SH, Lemoine-Goumard M, Lichti GG, Longo F, Loparco F, Lott B, Lovellette MN, Lubrano P, Madejski GM, Makeev A, Marangelli B, Mazziotta MN, McBreen S, McEnery JE, McGlynn S, Meegan C, Mészáros P, Meurer C, Michelson PF, Minuti M, Mirizzi N, Mitthumsiri W, Mizuno T, Moiseev AA, Monte C, Monzani ME, Moretti E, Morselli A, Moskalenko IV, Murgia S, Nakamori T, Nelson D, Nolan PL, Norris JP, Nuss E, Ohno M, Ohsugi T, Okumura A, Omodei N, Orlando E, Ormes JF, Ozaki M, Paciesas WS, Paneque D, Panetta JH, Parent D, Pelassa V, Pepe M, Perri M, Pesce-Rollins M, Petrosian V, Pinchera M, Piron F, Porter TA, Preece R, Rainò S, Ramirez-Ruiz E, Rando R, Rapposelli E, Razzano M, Razzaque S, Rea N, Reimer A, Reimer O, Reposeur T, Reyes LC, Ritz S, Rochester LS, Rodriguez AY, Roth M, Ryde F, Sadrozinski HF, Sanchez D, Sander A, Saz Parkinson PM, Scargle JD, Schalk TL, Segal KN, Sgrò C, Shimokawabe T, Siskind EJ, Smith DA, Smith PD, Spandre G, Spinelli P, Stamatikos M, Starck JL, Stecker FW, Steinle H, Stephens TE, Strickman MS, Suson DJ, Tagliaferri G, Tajima H, Takahashi H, Takahashi T, Tanaka T, Tenze A, Thayer JB, Thayer JG, Thompson DJ, Tibaldo L, Torres DF, Tosti G, Tramacere A, Turri M, Tuvi S, Usher TL, van der Horst AJ, Vigiani L, Vilchez N, Vitale V, von Kienlin A, Waite AP, Williams DA, Wilson-Hodge C, Winer BL, Wood KS, Wu XF, Yamazaki R, Ylinen T, and Ziegler M

Abstract

Gamma-ray bursts (GRBs) are highly energetic explosions signaling the death of massive stars in distant galaxies. The Gamma-ray Burst Monitor and Large Area Telescope onboard the Fermi Observatory together record GRBs over a broad energy range spanning about 7 decades of gammaray energy. In September 2008, Fermi observed the exceptionally luminous GRB 080916C, with the largest apparent energy release yet measured. The high-energy gamma rays are observed to start later and persist longer than the lower energy photons. A simple spectral form fits the entire GRB spectrum, providing strong constraints on emission models. The known distance of the burst enables placing lower limits on the bulk Lorentz factor of the outflow and on the quantum gravity mass.

Published
2009
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