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NASA NTRS2010

Recent Progress on GRBs with Swift

We are in an exciting period of discovery for gamma-ray bursts. The Swift observatory is detecting 100 bursts per year, providing arcsecond localizations and sensitive observations of the prompt and afterglow emission. In addition, rapid-response telescopes on the ground have new capabilities to study optical emission during the prompt phase and spectral signatures of the host galaxies. The combined data set is enabling great advances in our understanding of GRBs including afterglow physics, short burst origin, and supernova physics.

Gehrels, N.↗
NASA NTRS2011

The Swift BAT Perspective on Non-Thermal Emission in HIFLUGCS Galaxy Clusters

The search for diffuse non-thermal, inverse Compton (IC) emission from galaxy clusters at hard X-ray energies has been underway for many years, with most detections being either of low significance or controversial. Until recently, comprehensive surveys of hard X-ray emission from clusters were not possible; instead, individually proposed-for. long observations would be collated from the archive. With the advent of the Swift BAT all sky survey, any c1u,;ter's emission above 14 keV can be probed with nearly uniform sensitivity. which is comparable to that of RXTE, Beppo-SAX, and Suzaku with the 58-month version of the survey. In this work. we search for non-thermal excess emission above the exponentially decreasing, high energy thermal emission in the flux-limited HIFLUGCS sample. The BAT emission from many of the detected clusters is marginally extended; we are able to extract the total flux for these clusters using fiducial models for their spatial extent. To account for thermal emission at BAT energies, XMM-Newton EPIC spectra are extracted from coincident spatial regions so that both the thermal and non-thermal spectral components can be determined simultaneou,;ly in joint fits. We find marginally significant IC components in 6 clusters, though after closer inspection and consideration of systematic errors we are unable to claim a clear detection in any of them. The spectra of all clusters are also summed to enhance a cumulative non-thermal signal not quite detectable in individual clusters. After constructing a model based on single temperature

Wik, Daniel R.↗
NASA NTRS2010

Discovery of Eclipses from the Accreting Millisecond X-Ray Pulsar Swift J1749.4-2807

We report the discovery of X-ray eclipses in the recently discovered accreting millisecond X-ray pulsar SWIFT J1749.4-2807. This is the first detection of X-ray eclipses in a system of this type and should enable a precise neutron star mass measurement once the companion star is identified and studied. We present a combined pulse and eclipse timing solution that enables tight constraints on the orbital parameters and inclination and shows that the companion mass is in the range 0.6-0.8 solar mass for a likely range of neutron star masses, and that it is larger than a main-sequence star of the same mass. We observed two individual eclipse egresses and a single ingress. Our timing model shows that the eclipse features are symmetric about the time of 90 longitude from the ascending node, as expected. Our eclipse timing solution gives an eclipse duration (from the mid-points of ingress to egress) of 2172+/-13 s. This represents 6.85% of the 8.82 hr orbital period. This system also presents a potential measurement of "Shapiro" delay due to general relativity; through this technique alone, we set an upper limit to the companion mass of 2.2 Solar mass .

Markwardt, C. B.↗
NASA NTRS2010

Ultraviolet+Infrared Star Formation Rates: Hickson Compact Groups with Swift and SPitzer

We present Swift UVOT ultraviolet (UV; 1600-3000 A) data with complete three-band UV photometry for a sample of 41 galaxies in 11 nearby (<4500 km/s) Hickson Compact Groups (HCGs) of galaxies. We use UVOT uvw2-band (2000A) photometry to estimate the dust-unobscured component, SFR(sub uv), of the total star formation rate, SFR(sub TOTAL). We use Spitzer MIPS 24 micron photometry to estimate SFR(sub IR), the component of SFR(sub TOTAL) that suffers dust extinction in the UV and is re-emitted in the IR. By combining the two components, we obtain SFR(sub TOTAL) estimates for all HCG galaxies. We obtain total stellar mass, M(sub *) estimates by means of Two Micron All Sky Survey K(sub s)-band luminosities, and use them to calculate specific star formation rates, SSFR is identical with SFR(sub TOTAL)/ M (sub *). SSFR values show a clear and significant bimodality, with a gap between low (approximately <3.2 x 10(exp -11) / yr) and high-SSFR (approximately > 1.2 x lO)exp -10)/yr) systems. We compare this bimodality to the previously discovered bimodality in alpha-IRAC, the MIR activity index from a power-law fit to the Spitzer IRAC 4.5-8 micron data for these galaxies. We find that all galaxies with alpha-IRAC <= 0 (> 0) are in the high- (low-) SSFR locus, as expected if high levels of star-forming activity power MIR emission from polycyclic aromatic hydrocarbon molecules and a hot dust continuum. Consistent with this finding, all elliptical/SO galaxies are in the low-SSFR locus, while 22 out of 24 spirals / irregulars are in the high-SSFR locus, with two borderline cases. We further divide our sample into three subsamples (I, II, and III) according to decreasing H I richness of the parent galaxy group to which a galaxy belongs. Consistent with the SSFR and alpha-IRAC bimodality, 12 out of 15 type I (11 out of 12 type III) galaxies are in the high- (low-) SSFR locus, while type II galaxies span almost the full range of SSFR values. We use the Spitzer Infrared Nearby Galaxy Survey (SINGS) to construct a comparison subsample of galaxies that (1) match HCG galaxies in J-band total galaxy luminosity and (2) are not strongly interacting and largely isolated. This selection eliminates mostly low-luminosity dwarfs and galaxies with some degree of peculiarity, providing a substantially improved, quiescent control sample. Unlike HCG galaxies, galaxies in the comparison SINGS subsample are continuously distributed both in SSFR and alpha-IRAC, although they show ranges in SFR(sub TOTAL) values, morphologies and stellar masses similar to those for HCG systems. We test the SSFR bimodality against a number of uncertainties, and find that these can only lead to its further enhancement. Excluding galaxies belonging to HCGs with three giant galaxies (triplets) leaves both the SSFR and the alpha-IRAC bimodality completely unaffected. We interpret these results as further evidence that an environment characterized by high galaxy number densities and low galaxy velocity dispersions, such as the one found in compact groups, plays a key role in accelerating galaxy evolution by enhancing star formation processes in galaxies and favoring a fast transition to quiescence.

Tzanavaris, P.↗
NASA NTRS2011

Host Galaxy Properties of the Swift BAT Ultra Hard X-Ray Selected AGN

We have assembled the largest sample of ultra hard X-ray selected (14-195 keV) AGN with host galaxy optical data to date, with 185 nearby (z<0.05), moderate luminosity AGN from the Swift Burst Alert Telescope (BAT) sample. The BAT AGN host galaxies have intermediate optical colors (u -- r and g -- r) that are bluer than a comparison sample of inactive galaxies and optically selected AGN from the Sloan Digital Sky Survey (SDSS) which are chosen to have the same stellar mass. Based on morphological classifications from the RC3 and the Galaxy Zoo, the bluer colors of BAT AGN are mainly due to a higher fraction of mergers and massive spirals than in the comparison samples. BAT AGN in massive galaxies (log Stellar Mass >10.5) have a 5 to 10 times higher rate of spiral morphologies than in SDSS AGN or inactive galaxies. We also see enhanced far-IR emission in BAT AGN suggestive of higher levels of star formation compared to the comparison samples. BAT AGN are preferentially found in the most massive host galaxies with high concentration indexes indicative of large bulge-to-disk ratios and large supermassive black holes. The narrow-line (NL) BAT AGN have similar intrinsic luminosities as the SDSS NL Seyferts based on measurements of [O III] Lambda 5007. There is also a correlation between the stellar mass and X-ray emission. The BAT AGN in mergers have bluer colors and greater ultra hard X-ray emission compared to the BAT sample as whole. In agreement with the Unified Model of AGN, and the relatively unbiased nature of the BAT sources, the host galaxy colors and morphologies are independent of measures of obscuration such as X-ray column density or Seyfert type. The high fraction of massive spiral galaxies and galaxy mergers in BAT AGN suggest that host galaxy morphology is related to the activation and fueling of local AGN.

Koss, Michael↗
NASA NTRS2011

The Successful Synergy of Swift and Fermi/GBM in Magnetars

The magnetar rate of discovery has increased dramatically in the last decade. Five sources were discovered in the last three years alone as a result of the very efficient synergy among three X- and .gamma-ray instruments on NASA satellites: the Swift/Burst Alert Telescope (BAT), the Fermi/Gamma ray Burst Monitor (GBM), and the Rossi X-Ray Timing Explorer; RXTE/Proportional Counter Array (PCA). To date, there are approx. 25 magnetar candidates, of which two are (one each) in the Large and Small Magellanic Cloud and the rest reside on the Galactic plane of our Milky Way. I will discuss here the main properties of the Magnetar Population and the common projects that can be achieved with the synergy of Swift and GBM.

Kouveliotou, Chryssa↗
NASA NTRS2012

First INTEGRAL and Swift Observations of a Giant Outburst of A 0535+26

The Be/X-ray binary A 0535+26 has shown three giant outbursts since 2005, after a long period of quiescence. The giant outbursts in 2005 (approx.5.2 Crab, 15-50 keY range) and 2009 (approx.5.6 Crab) could not be observed by most X-ray observatories due to Sun observing constraints. Finally, a giant outburst in February 2011, that reached a flux of approx.3.8 Crab, was monitored with INTEGRAL and Swift TOO observations. We present first results these observations, with a special focus on the cyclotron lines present in the X-ray spectrum of the source.

Caballero, I.↗
NASA NTRS2011

Simultaneous Planck, Swift, and Fermi Observations of X-Ray and gamma-Ray Selected Blazars

We present simultaneous Planck, Swift, Fermi, and ground-based data for 105 blazars belonging to three samples with flux limits in the soft X-ray, hard X-ray, and -ray bands, and we compare our results to those of a companion paper presenting simultaneous Planck and multi-frequency observations of 104 radio-loud northern active galactic nuclei selected at radio frequencies. While we confirm several previous results, our unique data set has allowed us to demonstrate that the selection method strongly influences the results, producing biases that cannot be ignored. Almost all the BL Lac objects have been detected by Fermi Large Area Telescope (LAT), whereas 30 to 40% of the flat-spectrum radio quasars (FSRQs) in the radio, soft X-ray, and hard X-ray selected samples are still below the gamma ray detection limit even after integrating 27 months of Fermi-LAT data. The radio to sub-millimetre spectral slope of blazars is quite flat, with [alpha] approximately 0 up to about 70 GHz, above which it steepens to [alpha] approximately -0.65. BL Lacs have significantly flatter spectra than FSRQs at higher frequencies. The distribution of the rest-frame synchrotron peak frequency (v(sup IC) (sub (PEAK)), ranges from 10(sup 21) to 10(sup 22) HZ. The distribution of the rest-frame synchrotron peak frequency (v(sup s)(sub peak)) in the spectral energy distribution (SED) of FSRQs is the same in all the blazar samples with (v(sup s)(sub peak) = 10(sup 13:1 plus or minus 0.1) Hz, while the mean inverse-Compton peak frequency,(v(sup IC)(sub peak) ranges from 10(sup 21) to 10(sup 22) Hz. The distributions of v(sup S)(sub peak) and of v(sup IC)(sub peak) of BL Lacs are much broader and are shifted to higher energies than those of FSRQs; their shapes strongly depend on the selection method. The Compton dominance of blazars ranges from less than 0.2 to nearly 100, with only FSRQs reaching values larger than about 3. Its distribution is broad and depends strongly on the selection method, with gamma-ray selected blazars peaking at approximately 7 or more, and radio-selected blazars at values close to 1, thus implying that the common assumption that the blazar power budget is largely dominated by high-energy emission is a selection effect. A comparison of our multi-frequency data with theoretical predictions shows that simple homogeneous SSC models cannot explain the simultaneous SEDs of most of the gamma-ray detected blazars in all samples. The SED of the blazars that were not detected by Fermi-LAT may instead be consistent with SSC emission. Our data challenge the correlation between bolometric luminosity and v(sup S)(sub peak) predicted by the blazar sequence.

Giommi, P.↗
NASA NTRS2011

Properties of Supergiant Fast X-Ray Transients as Observed by Swift

We present the most recent results from our investigation on Supergiant Fast X-ray Transients, a class of High-Mass X-ray Binaries, with a possible counterpart in the gamma-ray energy band. Since 2007 Swift has contributed to this new field by detecting outbursts from these fast transients with the BAT and by following them for days with the XRT. Thus, we demonstrated that while the brightest phase of the outburst only lasts a few hours, further activity is observed at lower fluxes for a remarkably longer time, up to weeks. Furthermore, we have performed several campaigns of intense monitoring with the XRT, assessing the fraction of the time these sources spend in each phase, and their duty cycle of inactivity.

Romano, P.↗
NASA NTRS2012

The Lag-Luminosity Relation in the GRB Source-Frame: An Investigation with Swift BAT Bursts

Spectral lag, which is defined as the difference in time of arrival of high and low energy photons, is a common feature in Gamma-ray Bursts (GRBs). Previous investigations have shown a correlation between this lag and the isotropic peak luminosity for long duration bursts. However, most of the previous investigations used lags extracted in the observer-frame only. In this work (based on a sample of 43 Swift long GRBs with known redshifts), we present an analysis of the lag-luminosity relation in the GRB source-frame. Our analysis indicates a higher degree of correlation -0.82+/-0.05 (chance probability of approx 5.5 X 10(exp -5) between the spectral lag and the isotropic peak luminosity, L(sub iso), with a best-fit power-law index of -1.2 +/- 0.2, such that L(sub iso) varies as lag(exp -1.2). In addition, there is an anti-correlation between the source-frame spectral lag and the source-frame peak energy of the burst spectrum, E(sub pk)(1 + z).

Ukwatta, T. N.↗
NASA NTRS2012

Swift X-Ray Upper Limits on Type Ia Supernova Environments

We have considered 53 Type Ia supernovae (SNe Ia) observed by the Swift X-Ray Telescope. None of the SNe Ia are individually detected at any time or in stacked images. Using these data and assuming that the SNe Ia are a homogeneous class of objects, we have calculated upper limits to the X-ray luminosity (0.2-10 keV) and mass-loss rate of L(sub 0.2-10) < 1.7 X 10(exp 38) erg/s and M(dot) < l.l X 10(exp -6) solar M/ yr x (V(sub w))/(10 km/s), respectively. The results exclude massive or evolved stars as the companion objects in SN Ia progenitor systems, but allow the possibility of main sequence or small stars, along with double degenerate systems consisting of two white dwarfs, consistent with results obtained at other wavelengths (e.g., UV, radio) in other studies.

Russell, B. R.↗
NASA NTRS2011

Can a Double Component Outflow Explain the X-Ray and Optical Lightcurves of Swift Gamma-Ray Bursts?

An increasing sample of Gamma-Ray Bursts (GRBs) observed by Swift show evidence of 'chromatic breaks', i.e. breaks that are present in the X-ray but not in the optical. We find that in a significant fraction of these GRB afterglows the X-ray and the optical emission cannot be produced by the same component. We propose that these afterglow lightcurves are the result of a two-component jet, in which both components undergo energy injection for the whole observation and the X-ray break is due to a jet break in the narrow outflow. Bursts with chromatic breaks also explain another surprising finding, the paucity of late achromatic breaks. We propose a model that may explain the behaviour of GRB emission in both X-ray and optical bands. This model can be a radical and noteworthy alternative to the current interpretation for the 'canonical' XRT and UVOT lightcurves, and it bears fundamental implications for GRB physics.

De Pasquale, Massimiliano↗
NASA NTRS2011

The Lag-Luminosity Relation in the GRB Source Frame: An Investigation with Swift BAT Bursts

Spectral lag. which is defined as the difference in time of arrival of high- and low-energy photons. is a common feature in gamma-ray bursts (GRBs). Previous investigations have shown a correlation between this lag and the isotropic peak luminosity for long duration bursts. However. most of the previous investigations used lags extracted in the observer frame only. In this work (based on a sample of 43 Swift long GRBs with known redshifts). we present an analysis of the lag-luminosity relation in the GRB source frame. Our analysis indicates a higher degree of correlation -0.82 +/- 0.05 (chance probability of approx. 5.5 x 10(exp -5) between the spectral lag and the isotropic peak luminosity, L(sub iso). with a best-fitting power-law index of -1.2 +/- 0.2. In addition, there is an anticorrelation between the source-frame spectral lag and the source-frame peak energy of the burst spectrum.

Ukwatta, T. N.↗
NASA NTRS2012

Simultaneous Planck, Swift, and Fermi Observations of X-ray and Gamma-ray Selected Blazars

We present simultaneous Planck, Swift, Fermi, and ground-based data for 105 blazars belonging to three samples with flux limits in the soft X-ray, hard X-ray, and gamma-ray bands, with additional 5 GHz flux-density limits to ensure a good probability of a Planck detection. We compare our results to those of a companion paper presenting simultaneous Planck and multi-frequency observations of 104 radio-loud northern active galactic nuclei selected at radio frequencies. While we confirm several previous results, our unique data set allows us to demonstrate that the selection method strongly influences the results, producing biases that cannot be ignored. Almost all the BL Lac objects have been detected by the Fermi Large Area Telescope (LAT), whereas 30% to 40% of the flat-spectrum radio quasars (FSRQs) in the radio, soft X-ray, and hard X-ray selected samples are still below the gamma-ray detection limit even after integrating 27 months of Fermi-LAT data. The radio to sub-millimetre spectral slope of blazars is quite flat, with (alpha) approx 0 up to about 70GHz, above which it steepens to (alpha) approx -0.65. The BL Lacs have significantly flatter spectra than FSRQs at higher frequencies. The distribution of the rest-frame synchrotron peak frequency (nu(sup s)(sub peak)) in the spectral energy distribution (SED) of FSRQs is the same in all the blazar samples with (nu(sup s)(sub peak)) = 10(exp 13.1 +/- 0.1) Hz, while the mean inverse Compton peak frequency, (nu(sup IC)(sub peak)), ranges from 10(exp 21) to 10(exp 22) Hz. The distributions of nu(sup s)(sub peak) and nu(sup IC)(sub peak) of BL Lacs are much broader and are shifted to higher energies than those of FSRQs; their shapes strongly depend on the selection method. The Compton dominance of blazars. defined as the ratio of the inverse Compton to synchrotron peak luminosities, ranges from less than 0.2 to nearly 100, with only FSRQs reaching values larger than about 3. Its distribution is broad and depends strongly on the selection method, with gamma-ray selected blazars peaking at approx 7 or more, and radio-selected blazars at values close to 1, thus implying that the common assumption that the blazar power budget is largely dominated by high-energy emission is a selection effect. A comparison of our multi-frequency data with theoretical predictions shows that simple homogeneous SSC models cannot explain the simultaneous SEDs of most of the gamma-ray detected blazars in all samples. The SED of the blazars that were not detected by Fermi~LAT may instead be consistent with SSC emission. Our data challenge the correlation between bolometric luminosity and nu(sup s)(sub peak) predicted by the blazar sequence.

Giommi, P.↗
NASA NTRS2010

Prompt Emission Properties of Swift GRBs

We present the results from the second Swift BAT catalog of 476 gamma-ray bursts, which contains bursts detected by the BAT between 2004 December 19 and 2009 December 21. In addition to the spectral and temporal parameters extracted from the first BAT GRB catalog, 3324 time-resolved spectra have been extracted and analyzed. We show and discuss 1) the duration distribution, 2) the hardness of short GRBs, 3) Epeak distribution, 4) the line of death problem and 5) an additional power-law component in the prompt emission spectrum.

Sakamoto, T.↗
NASA NTRS2012

The Second SWIFT Burst Alert Telescope (BAT) Gamma-Ray Burst Catalog

We present the second Swift Burst Alert Telescope (BAT) catalog of gamma-ray bursts. (GRBs), which contains 476 bursts detected by the BAT between 2004 December 19 and 2009 December 21. This catalog (hereafter the BAT2 catalog) presents burst trigger time, location, 90% error radius, duration, fluence, peak flux, time-averaged spectral parameters and time-resolved spectral parameters measured by the BAT. In the correlation study of various observed parameters extracted from the BAT prompt emission data, we distinguish among long-duration GRBs (L-GRBs), short-duration GRBs (S-GRBs), and short-duration GRBs with extended emission (S-GRBs with E.E.) to investigate differences in the prompt emission properties. The fraction of L-GRBs, S-GRBs and S-GRBs with E.E. in the catalog are 89%, 8% and 2% respectively. We compare the BAT prompt emission properties with the BATSE, BeppoSAX and HETE-2 GRB samples.. We also correlate the observed prompt emission properties with the redshifts for the GRBs with known redshift. The BAT T(sub 90) and T(sub 50) durations peak at 70 s and 30 s, respectively. We confirm that the spectra of the BAT S-GRBs are generally harder than those of the L-GRBs.

Sakamoto, T.↗
NASA NTRS2012

Multiwavelength Observations of the AGN 1ES 0414+009 with Veritas, Fermi-LAT, Swift-XRT, and MDM

We present observations of the BL Lac object 1ES 0414+009 in the greater than 200 GeV gamma-ray band by the VERITAS array of Cherenkov telescopes. 1ES 0414+009 was observed by VERITAS between January 2008 and February 2011, resulting in 56.2 hours of good quality pointed observations. These observations resulted in a detection of 822 events from the source corresponding to a statistical significance of 6.4 standard deviations (6.4 sigma) above the background. The source flux, showing no evidence for variability, is measured as (5.2 plus or minus 1.1(sub stat) plus or minus 2.6(sub sys) x 10(exp 12) photons per square centimeter per second above 200 GeV, equivalent to approximately 2% of the Crab Nebula flux above this energy. The differential photon spectrum from 230 GeV to 850 GeV is well fit by a power law with an photon index of TAU = 3.4 plus or minus 0.5(sub stat) plus or minus 0.3(sub sys) and a flux normalization of (1.6 plus or minus 0.3(sub stat) plus or minus 0.8(sub sys) x 10(exp -11) photons per square centimeter per second at 300 GeV. We also present multiwavelength results taken in the optical (MDM), X-ray (Swift-XRT), and GeV (Fermi-LAT) bands and use these results to construct a broadband spectral energy distribution (SED). Modeling of this SED indicates that homogenous one-zone leptonic scenarios are not adequate to describe emission from the system, with a lepto-hadronic model providing a better fit to the data.

Aliu, E.↗
NASA NTRS2012

Swift Follow-Up Observations of Candidate Gravitational-Wave Transient Events

We present the first multi-wavelength follow-up observations of two candidate gravitational-wave (GW) transient events recorded by LIGO and Virgo in their 2009-2010 science run. The events were selected with low latency by the network of GW detectors (within less than 10 minutes) and their candidate sky locations were observed by the Swift observatory (within 12 hr). Image transient detection was used to analyze the collected electromagnetic data, which were found to be consistent with background. Off-line analysis of the GW data alone has also established that the selected GW events show no evidence of an astrophysical origin; one of them is consistent with background and the other one was a test, part of a "blind injection challenge." With this work we demonstrate the feasibility of rapid follow-ups of GW transients and establish the sensitivity improvement joint electromagnetic and GW observations could bring. This is a first step toward an electromagnetic follow-up program in the regime of routine detections with the advanced GW instruments expected within this decade. In that regime, multi-wavelength observations will play a significant role in completing the astrophysical identification of GW sources. We present the methods and results from this first combined analysis and discuss its implications in terms of sensitivity for the present and future instruments.

Evans, P. A.↗