-
G. A. Kriss,
N. Arav,
J. S. Kaastra,
J. Ebrero,
C. Pinto,
B. Borguet,
D. Edmonds,
E. Costantini,
K. C. Steenbrugge,
R. G. Detmers,
E. Behar,
S Bianchi, A. J. Blustin,
G. Branduardi-Raymont,
M. Cappi,
M. Mehdipour,
P. Petrucci,
G. Ponti
[show abstract]
[hide abstract]
ABSTRACT: We observed Mrk 509 during the fall of 2009 during a multiwavelength campaign
using XMM-Newton, Chandra, HST/COS, SWIFT, and Integral. The 600-ks XMM/RGS
spectrum finds two kinematic components and a discrete distribution of ionized
absorbers. Our high S/N COS spectrum detects additional complexity in the known
UV absorption troughs from a variety of sources in Mrk 509, including the
outflow from the active nucleus, the ISM and halo of the host galaxy, and
infalling clouds or stripped gas from a merger that are illuminated by the AGN.
The UV absorption only partially covers the emission from the AGN nucleus with
covering fractions lower than those previously seen with STIS, and are
comparable to those seen with FUSE. Given the larger apertures of COS and FUSE
compared to STIS, we favor scattered light from an extended region near the AGN
as the explanation for the partial covering. As observed in prior X-ray and UV
spectra, the UV absorption has velocities comparable to the X-ray absorption,
but the bulk of the ultraviolet absorption is in a lower ionization state with
lower total column density than the gas responsible for the X-ray absorption.
Variability compared to prior UV spectra lets us set limits on the location,
density, mass flux, and kinetic energy of the outflowing gas. For component 1
at $-400 \rm km s^{-1}$, the kinetic energy flux of both the UV and the X-ray
outflow is insufficient to have a significant impact on further evolution of
the host galaxy.
01/2012;
-
[show abstract]
[hide abstract]
ABSTRACT: There exists a significant population of broad line, z∼ 2 quasi-stellar objects (QSOs) which have heavily absorbed X-ray spectra. Follow-up observations in the submillimetre show that these QSOs are embedded in ultraluminous starburst galaxies, unlike most unabsorbed QSOs at the same redshifts and luminosities. Here we present X-ray spectra from XMM–Newton for a sample of five such X-ray-absorbed QSOs that have been detected at submillimetre wavelengths. We also present spectra in the rest-frame ultraviolet from ground-based telescopes. All the five QSOs are found to exhibit strong C iv absorption lines in their ultraviolet spectra with equivalent width >5 Å. The X-ray spectra are inconsistent with the hypothesis that these objects show normal QSO continua absorbed by low-ionization gas. Instead, the spectra can be modelled successfully with ionized absorbers, or with cold absorbers if they possess unusually flat X-ray continuum shapes and unusual optical to X-ray spectral energy distributions. We show that the ionized absorber model provides the simplest, most self-consistent explanation for their observed properties. We estimate that the fraction of radiated power that is converted into kinetic luminosity of the outflowing winds is typically ∼4 per cent, in agreement with recent estimates for the kinetic feedback from QSOs required to produce the M–σ relation, and consistent with the hypothesis that the X-ray-absorbed QSOs represent the transition phase between obscured accretion and the luminous QSO phase in the evolution of massive galaxies.
Monthly Notices of the Royal Astronomical Society 08/2011; 416(4):2792 - 2801. · 4.90 Impact Factor
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M Mehdipour,
G Branduardi-Raymont,
J S Kaastra,
P O Petrucci,
G A Kriss,
G Ponti, A J Blustin,
S Paltani,
M Cappi,
R G Detmers,
K C Steenbrugge
[show abstract]
[hide abstract]
ABSTRACT: We present the analysis of XMM-Newton and Swift optical-UV and X-ray observations of the Seyfert-1/QSO Mrk 509, part of an unprecedented multi-wavelength campaign, investigating the nuclear environment of this AGN. The XMM-Newton data are from a series of 10 observations of about 60 ks each, spaced from each other by about 4 days, taken in Oct-Nov 2009. During our campaign, Mrk 509 was also observed with Swift for a period of about 100 days, monitoring the behaviour of the source before and after the XMM-Newton observations. With these data we have established the continuum spectrum in the optical-UV and X-ray bands and investigated its variability on the timescale of our campaign with a resolution time of a few days. In order to measure and model the continuum as far as possible into the UV, we also made use of Hubble Space Telescope (HST) Cosmic Origin Spectrograph (COS) observations of Mrk 509 (part of our coordinated campaign) and of an archival Far Ultraviolet Spectroscopic Explorer (FUSE) observation. We have found that in addition to an X-ray power-law, the spectrum displays soft X-ray excess emission below 2 keV, which interestingly varies in association with the thermal optical-UV emission from the accretion disc. The change in the X-ray power-law component flux (albeit smaller than that of the soft excess), on the other hand, is uncorrelated to the flux variability of the soft X-ray excess and the disc component on the probed timescale. The results of our simultaneous broad-band spectral and timing analysis suggest that, on a resolution time of a few days, the soft X-ray excess of Mrk 509 is produced by the Comptonisation of the thermal optical-UV photons from the accretion disc by a warm (0.2 keV) optically thick (τ ∼ 17) corona surrounding the inner regions of the disc. This makes Mrk 509, with a black hole mass of about 1–3 ×10 8 M ⊙ , the highest mass known system to display such behaviour and origin for the soft X-ray excess.
08/2011;
-
J. S. Kaastra,
P. O. Petrucci,
M. Cappi,
N. Arav,
E. Behar,
S Bianchi,
J. Bloom, A. J. Blustin,
G. Branduardi-Raymont,
E. Costantini, [......],
P. Lubinski,
J. Malzac,
M. Mehdipour,
S. Paltani,
C. Pinto,
G. Ponti,
E. M. Ratti,
R. A. N. Smith,
K. C. Steenbrugge,
C. P. de Vries
[show abstract]
[hide abstract]
ABSTRACT: (Abridged) Active galactic nuclei show a wealth of interesting physical
processes, some of which are poorly understood. We want to address a number of
open questions, including the location and physics of the outflow from AGN, the
nature of the continuum emission, the geometry and physical state of the X-ray
broad emission line region, the Fe-K line complex, the metal abundances of the
nucleus and finally the interstellar medium of our own Galaxy. We study one of
the best targets for these aims, the Seyfert 1 galaxy Mrk 509 with a
multiwavelength campaign using five satellites (XMM-Newton, INTEGRAL, Chandra,
HST and Swift) and two ground-based facilities (WHT and PAIRITEL). Our
observations cover more than five decades in frequency, from 2 um to 200 keV.
The combination of high-resolution spectroscopy and time variability allows us
to disentangle and study the different components. Our campaign covers 100 days
from September to December 2009, and is centred on a simultaneous set of deep
XMM-Newton and INTEGRAL observations with regular time intervals, spanning
seven weeks. We obtain a continuous light curve in the X-ray and UV band,
showing a strong, up to 60% flux increase in the soft X-ray band during the
three weeks in the middle of our deepest monitoring campaign, and which is
correlated with an enhancement of the UV flux. This allows us to study the time
evolution of the continuum and the outflow. By stacking the observations, we
have also obtained one of the best X-ray and UV spectra of a Seyfert galaxy
ever obtained. In this paper we also study the effects of the spectral energy
distribution (SED) that we obtained on the photo-ionisation equilibrium. Thanks
to our broad-band coverage, uncertainties on the SED do not strongly affect the
determination of this equilibrium.
07/2011;
-
G. A. Kriss,
N. Arav,
J. S. Kaastra,
J. Ebrero,
C. Pinto,
B. Borguet,
D. Edmonds,
E. Costantini,
K. C. Steenbrugge,
R. G. Detmers,
E. Behar,
S Bianchi, A. J. Blustin,
G. Branduardi-Raymont,
M. Cappi,
M. Mehdipour,
P. Petrucci,
G. Ponti
[show abstract]
[hide abstract]
ABSTRACT: We present medium resolution (R~20,000) HST/COS ultraviolet spectra covering
1155-1760 A of the Seyfert 1 Mrk 509 obtained simultaneously with a
Chandra/LETGS spectrum as part of a multiwavelength campaign in 2009 that
included observations with XMM-Newton, SWIFT, and Integral. Our high S/N
spectrum detects additional complexity in the absorption troughs from a variety
of sources in Mrk 509, including the outflow from the active nucleus, the ISM
and halo of the host galaxy, and infalling clouds or stripped gas from a merger
that are illuminated by the AGN. Variability between the STIS and COS
observation of the -400 km/s component allows us to set an upper limit on its
distance of < 250 pc. Similarly, variability of a component at +150 km/s
between two prior FUSE observations limits its distance to < 1.5 kpc. The UV
absorption only partially covers the emission from the AGN nucleus. Covering
fractions are lower than those previously seen with STIS, and are comparable to
those seen with FUSE. Given the larger apertures of COS and FUSE compared to
STIS, we favor scattered light from an extended region near the AGN as the
explanation for the partial covering. As observed in prior X-ray and UV
spectra, the UV absorption has velocities comparable to the X-ray absorption,
but the bulk of the ultraviolet absorption is in a lower ionization state with
lower total column density than the gas responsible for the X-ray absorption.
We conclude that the outflow from the active nucleus is a multiphase wind.
07/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: There exists a significant population of broad line, z~2 QSOs which have
heavily absorbed X-ray spectra. Follow up observations in the submillimetre
show that these QSOs are embedded in ultraluminous starburst galaxies, unlike
most unabsorbed QSOs at the same redshifts and luminosities. Here we present
X-ray spectra from XMM-Newton for a sample of 5 such X-ray absorbed QSOs that
have been detected at submillimetre wavelengths. We also present spectra in the
restframe ultraviolet from ground based telescopes. All 5 QSOs are found to
exhibit strong C IV absorption lines in their ultraviolet spectra with
equivalent width > 5 Angstroms. The X-ray spectra are inconsistent with the
hypothesis that these objects show normal QSO continua absorbed by
low-ionization gas. Instead, the spectra can be modelled successfully with
ionized absorbers, or with cold absorbers if they posess unusually flat X-ray
continuum shapes and unusual optical to X-ray spectral energy distributions. We
show that the ionized absorber model provides the simplest, most
self-consistent explanation for their observed properties. We estimate that the
fraction of radiated power that is converted into kinetic luminosity of the
outflowing winds is typically ~4 per cent, in agreement with recent estimates
for the kinetic feedback from QSOs required to produce the M - sigma relation,
and consistent with the hypothesis that the X-ray absorbed QSOs represent the
transition phase between obscured accretion and the luminous QSO phase in the
evolution of massive galaxies.
06/2011;
-
A. A. Breeveld,
P. A. Curran,
E. A. Hoversten,
S. Koch,
W. Landsman,
F. E. Marshall,
M. J. Page,
T. S. Poole,
P. Roming,
P. J. Smith, [......],
S. Immler,
M. Ivanushkina,
T. Kennedy,
K. O. Mason,
A. N. Morgan,
S. Oates,
M. De Pasquale,
P. Schady,
M. Siegel,
D. Vanden Berk
[show abstract]
[hide abstract]
ABSTRACT: The Ultraviolet/Optical Telescope (UVOT) is one of three instruments onboard the Swift observatory. The photometric calibration has been published, and this paper follows up with details on other aspects of the calibration including a measurement of the point spread function with an assessment of the orbital variation and the effect on photometry. A correction for large-scale variations in sensitivity over the field of view is described, as well as a model of the coincidence loss which is used to assess the coincidence correction in extended regions. We have provided a correction for the detector distortion and measured the resulting internal astrometric accuracy of the UVOT, also giving the absolute accuracy with respect to the International Celestial Reference System. We have compiled statistics on the background count rates, and discuss the sources of the background, including instrumental scattered light. In each case, we describe any impact on UVOT measurements, whether any correction is applied in the standard pipeline data processing or whether further steps are recommended.
Monthly Notices of the Royal Astronomical Society 06/2010; 406(3):1687 - 1700. · 4.90 Impact Factor
-
A. A. Breeveld,
P. A. Curran,
E. A. Hoversten,
S. Koch,
W. Landsman,
F. E. Marshall,
M. J. Page,
T. S. Poole,
P. Roming,
P. J. Smith, [......],
S. Immler,
M. Ivanushkina,
T. Kennedy,
K. O. Mason,
A. N. Morgan,
S. Oates,
M. De Pasquale,
P. Schady,
M. Siegel,
D. Vanden Berk
[show abstract]
[hide abstract]
ABSTRACT: The Ultraviolet/Optical Telescope (UVOT) is one of three instruments onboard the Swift observatory. The photometric calibration has been published, and this paper follows up with details on other aspects of the calibration including a measurement of the point spread function with an assessment of the orbital variation and the effect on photometry. A correction for large scale variations in sensitivity over the field of view is described, as well as a model of the coincidence loss which is used to assess the coincidence correction in extended regions. We have provided a correction for the detector distortion and measured the resulting internal astrometric accuracy of the UVOT, also giving the absolute accuracy with respect to the International Celestial Reference System. We have compiled statistics on the background count rates, and discuss the sources of the background, including instrumental scattered light. In each case we describe any impact on UVOT measurements, whether any correction is applied in the standard pipeline data processing or whether further steps are recommended. Comment: Accepted for publication in MNRAS. 15 pages, 21 figures, 4 tables
04/2010;
-
K. O. Mason, A. J. Blustin,
P. Boyd,
S. T. Holland,
M. J. Page,
P. Roming,
M. Still,
B. Zhang,
A. Breeveld,
M. de Pasquale, [......],
C. Gronwall,
S. Hunsberger,
M. Ivanushkina,
W. Landsman,
K. McGowan,
J. Nousek,
T. Poole,
J. Rhoads,
S. Rosen,
and P. Schady
[show abstract]
[hide abstract]
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. · 6.02 Impact Factor
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G. L. Israel,
P. Romano,
V. Mangano,
S. Dall'Osso,
G. Chincarini,
L. Stella,
S. Campana,
T. Belloni,
G. Tagliaferri, A. J. Blustin,
T. Sakamoto,
K. Hurley,
S. Zane,
A. Moretti,
D. Palmer,
C. Guidorzi,
D. N. Burrows,
N. Gehrels,
and H. A. Krimm
[show abstract]
[hide abstract]
ABSTRACT: In 2006 March the soft gamma-ray repeater SGR 1900+14 resumed its bursting activity after ~2 yr of quiescence. The Swift mission observed the source several times. We report on the intense burst "forest" recorded on March 29, which lasted for ~30 s, when Swift was pointing at the source with the narrow field of view instruments. More than 40 bursts were detected by BAT and XRT, 7 of which were rare intermediate flares (IFs). The BAT data were used to carry out time-resolved spectroscopy in the 14-100 keV range down to 8 ms timescales. BAT and XRT simultaneous data were used to characterize the broadband energy spectra of IFs and verify the results obtained from the BAT-only spectral fits. This unique data set allowed us to test the magnetar model predictions, such as the magnetically trapped fireball and twisted magnetosphere, over an unprecedented range of fluxes and with large statistics. We confirmed that a two-blackbody component adequately fits the time-resolved and integrated spectra of IFs. However, Comptonization models give comparably good reduced χ2. Moreover, we found a change of behavior, around ~1041 erg s−1, above which the softer blackbody shows a sort of saturation, while the harder one still grows to a few times 1041 erg s−1, and a rather sharp correlation between temperature and radii of the blackbodies (R2 kT−3), which holds for the most luminous parts of the flares (~Ltot ≥ 1041 erg s−1). Within the magnetar model, the majority of these findings are accounted for in terms of thermalized emission from the E-mode and O-mode photospheres. Interestingly, the maximum observed luminosity coming from a region of ~15 km matches the magnetic Eddington luminosity at the same radius, for a surface dipole field of ~8 × 1014 G (virtually equal to that deduced from the spin-down of SGR 1900+14).
The Astrophysical Journal 12/2008; 685(2):1114. · 6.02 Impact Factor
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P. J. Brown,
S. T. Holland,
C. James,
P. Milne,
P. W. A. Roming,
K. O. Mason,
K. L. Page,
A. P. Beardmore,
D. Burrows,
A. Morgan, [......],
A. Breeveld,
M. de Pasquale,
S. Hunsberger,
M. Ivanushkina,
W. Landsman,
K. McGowan,
T. Poole,
S. Rosen,
P. Schady,
and N. Gehrels
[show abstract]
[hide abstract]
ABSTRACT: We present ultraviolet and optical light curves in six broadband filters and grism spectra obtained by Swift's Ultraviolet/Optical Telescope for the Type Ia supernova SN 2005am. The data were collected beginning about 4 days before the B-band maximum, with excellent coverage of the rapid decline phase and later observations extending out to 69 days after the peak. The optical and near-UV light curve match well those of SN 1992A. The other UV observations constitute the first set of light curves shorter than 2500 Å and allow us to compare the light curve evolution in three UV bands. One interesting feature is that the decay in the intermediate UVM2 band is shallower than in the filters on either side and may result from the bump in the interstellar extinction curve. The UV behavior of this and other low-redshift supernovae can be used to constrain theories of progenitor evolution or to interpret optical light curves of high-redshift supernovae. Using Swift's X-Ray Telescope, we also report the upper limit to SN 2005am's X-ray luminosity to be 6 × 1039 ergs s-1 in the 0.3-10 keV. This result is derived from 58 ks of exposure time spread out over 7 weeks beginning 4 days before the B-band maximum.
The Astrophysical Journal 12/2008; 635(2):1192. · 6.02 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Broad absorption line quasars (commonly termed BALQSOs) contain the most dramatic examples of AGN-driven winds. The high absorbing columns in these winds, ~10^24 cm^-2, ensure that BALQSOs are generally X-ray faint. This high X-ray absorption means that almost all BALQSOs have been discovered through optical surveys, and so what little we know about their X-ray properties is derived from very bright optically-selected sources. A small number of X-ray selected BALQSOs (XBALQSOs) have, however, recently been found in deep X-ray survey fields. In this paper we investigate the X-ray and rest-frame UV properties of five XBALQSOs for which we have obtained XMM-Newton EPIC X-ray spectra and deep optical imaging and spectroscopy. We find that, although the XBALQSOs have an alpha_ox steeper by ~0.5 than normal QSOs, their median alpha_ox is nevertheless flatter by 0.30 than that of a comparable sample of optically selected BALQSOs (OBALQSOs). We rule out the possibility that the higher X-ray to optical flux ratio is due to intrinsic optical extinction. We find that the amount of X-ray and UV absorption due to the wind in XBALQSOs is similar, or perhaps greater than, the corresponding wind absorption in OBALQSOs, so the flatter alpha_ox cannot be a result of weaker wind absorption. We conclude that these XBALQSOs have intrinsically higher X-ray to optical flux ratios than the OBALQSO sample with which we compare them.
09/2008;
-
G. L. Israel,
P. Romano,
V. Mangano,
S. Dall'Osso,
G. Chincarini,
L. Stella,
S. Campana,
T. Belloni,
G. Tagliaferri, A. J. Blustin,
T Sakamoto,
K. Hurley,
S. Zane,
A. Moretti,
D Palmer,
C. Guidorzi,
D. N. Burrows,
N. Gehrels,
H. A. Krimm
[show abstract]
[hide abstract]
ABSTRACT: We report on the intense burst ``forest'' recorded on 2006 March 29 which lasted for ~30s. More than 40 bursts were detected both by BAT and by XRT, seven of which are rare intermediate flares (IFs): several times 10^{42} ergs were released. The BAT data were used to carry out time-resolved spectroscopy in the 14-100keV range down to 8ms timescales. This unique dataset allowed us to test the magnetar model predictions such as the magnetically trapped fireball and the twisted magnetosphere over an unprecedented range of fluxes and with large statistics (in terms of both photons and IFs). We confirmed that a two blackbody component fits adequately the time-resolved and integrated spectra of IFs. However, Comptonization models give comparable good reduced chi^2. Moreover, we found: i) a change of behavior, around ~10^{41} erg/s, above which the softer blackbody shows a sort of saturation while the harder one still grows to a few times 10^{41} erg/s; ii) a rather sharp correlation between temperature and radii of the blackbodies (R^2 prop kT^{-3}), which holds for the most luminous parts of the flares (approximately for L_{tot} > 10^{41} erg/s). Within the magnetar model, the majority of these findings can be accounted for in terms of thermalised emission from the E-mode and O-mode photospheres. Interestingly, the maximum observed luminosity coming from a region of ~15km matches the magnetic Eddington luminosity at the same radius, for a surface dipole field of ~8 x 10^{14} G (virtually equal to the one deduced from the spindown of SGR 1900+14). Comment: Accepted for publication on ApJ, 15 pages, 10 figures
05/2008;
-
M. De Pasquale,
S. R. Oates,
A. Beardmore,
K. L. Page, A. J. Blustin,
S. Zane,
M. J. Page,
K. O’Mason,
D. N. Burrows,
D. Palmer,
N. Gehrels,
J. Nousek,
P. Roming,
P. Price,
B. Zhang
[show abstract]
[hide abstract]
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.
-
T. S. Poole,
A. A. Breeveld,
M. J. Page,
W. Landsman,
S. T. Holland,
P. Roming,
N. P. M. Kuin,
P. J. Brown,
C. Gronwall,
S. Hunsberger, [......],
H. Huckle,
S. Immler,
M. Ivanushkina,
T. Kennedy,
F. Marshall,
A. Morgan,
S. Pandey,
M. De Pasquale,
P. J. Smith,
M. Still
[show abstract]
[hide abstract]
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 broadband 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 1600-8000A 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. Comment: Minor improvements after referees report. Accepted for publication in MNRAS
08/2007;
-
S. R. Oates,
M. De Pasquale,
M. J. Page, A. J. Blustin,
S. Zane,
K. McGowan,
K. O. Mason,
T. S. Poole,
P. Schady,
P. W. A. Roming,
K. L. Page,
A Falcone,
N. Gehrels
[show abstract]
[hide abstract]
ABSTRACT: This paper investigates GRB 050802, one of the best examples of a it Swift gamma-ray burst afterglow that shows a break in the X-ray lightcurve, while the optical counterpart decays as a single power-law. This burst has an optically bright afterglow of 16.5 magnitude, detected throughout the 170-650nm spectral range of the UVOT on-board Swift. Observations began with the XRT and UVOT telescopes 286s after the initial trigger and continued for 1.2 x 10^6s. The X-ray lightcurve consists of three power-law segments: a rise until 420s, followed by a slow decay with alpha_2 = 0.63 +/- 0.03 until 5000s, after which, the lightcurve decays faster with a slope of alpha_3 = 1.59 +/- 0.03. The optical lightcurve decays as a single power-law with alpha_O = 0.82 +/- 0.03 throughout the observation. The X-ray data on their own are consistent with the break at 5000s being due to the end of energy injection. Modelling the optical to X-ray spectral energy distribution, we find that the optical afterglow can not be produced by the same component as the X-ray emission at late times, ruling out a single component afterglow. We therefore considered two-component jet models and find that the X-ray and optical emission is best reproduced by a model in which both components are energy injected for the duration of the observed afterglow and the X-ray break at 5000s is due to a jet break in the narrow component. This bright, well-observed burst is likely a guide for interpreting the surprising finding of Swift that bursts seldom display achromatic jet breaks. Comment: 13 pages, 5 figures, accepted MNRAS
06/2007;
-
Massimiliano De Pasquale,
S. R. Oates,
M. J. Page,
D. N. Burrows, A. J. Blustin,
S. Zane,
K. O. Mason,
P. W. A. Roming,
D Palmer,
N. Gehrels,
B Zhang
[show abstract]
[hide abstract]
ABSTRACT: We present results of Swift optical, UV and X-ray observations of the afterglow of GRB 050801. The source is visible over the full optical, UV and X-ray energy range of the Swift UVOT and XRT instruments.Both optical and X-ray lightcurves exhibit a broad plateau (\Delta t/t ~ 1) during the first few hundred seconds after the gamma-ray event. We investigate the multiwavelength spectral and timing properties of the afterglow, and we suggest that the behaviour at early times is compatible with an energy injection by a newly born magnetar with a period of a few tenths of a millisecond, which keeps the forward shock refreshed over this short interval by irradiation. Reverse shock emission is not observed. Its suppression might be due to GRB ejecta being permeated by high magnetic fields, as expected for outflows powered by a magnetar.Finally, the multiwavelength study allows a determination of the burst redshift, z=1.56. Comment: 13 pages, 7 figs, Accepted for publication in MNRAS
03/2007;
-
P. Giommi,
M. Capalbi,
E. Cavazzuti,
S. Colafrancesco,
A. Cucchiara,
A Falcone,
J. Kennea,
R. Nesci,
M. Perri,
G. Tagliaferri, [......], A. J. Blustin,
G. Branduardi-Raymont,
D. N. Burrows,
G. Chincarini,
A. J. Dean,
N. Gehrels,
H. Krimm,
F. Marshall,
A. M. Parsons,
B Zhang
[show abstract]
[hide abstract]
ABSTRACT: Almost the totality of the bright foreground sources in the WMAP CMB maps are blazars, a class of sources that show usually also X-ray emission. However, 23 objects in a flux-limited sample of 140 blazars of the WMAP catalog (first year) were never reported before as X-ray sources. We present here the results of 41 Swift observations which led to the detection of all these 23 blazars in the 0.3-10 keV band. We conclude that all micro-wave selected blazars are X-ray emitters and that the distribution of the micro-wave to X-ray spectral slope $\alpha_{mu x}$ of LBL blazars is very narrow, confirming that the X-ray flux of most blazars is a very good estimator of their micro-wave emission. The X-ray spectral shape of all the objects that were observed long enough to allow spectral analysis is flat and consistent with inverse Compton emission within the commonly accepted view where the radiation from blazars is emitted in a Sychrotron-Inverse-Compton scenario. We predict that all blazars and most radio galaxies above the sensitivity limit of the WMAP and of the Planck CMB missions are X-ray sources detectable by the present generation of X-ray satellites. An hypothetical all-sky soft X-ray survey with sensitivity of approximately $10^{-15}$ erg/s would be crucial to locate and remove over 100,000 blazars from CMB temperature and polarization maps and therefore accurately clean the primordial CMB signal from the largest population of extragalactic foreground contaminants. Comment: 13 pages, 4 figures, 5 tables, A&A in press
03/2007;
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S. Campana,
V. Mangano, A. J. Blustin,
P. Brown,
D. N. Burrows,
G. Chincarini,
J. R. Cummings,
G. Cusumano,
M. Della Valle,
D. Malesani, [......],
P. Giommi,
O. Godet,
J. A. Kennea,
H. Krimm,
L. Angelini,
S. D. Barthelmy,
P. T. Boyd,
D. M. Palmer,
A. A. Wells,
N. E. White
Nature 08/2006; 442(7106):1008-1010. · 36.28 Impact Factor
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S. R. Oates,
C. G. Mundell,
S. Piranomonte,
K. L. Page,
M. De Pasquale,
A. Monfardini,
A. Melandri,
S. Zane,
C. Guidorzi,
D. Malesani, [......],
M. Capalbi,
D Carter,
P. D'Avanzo,
S Kobayashi,
H. A. Krimm,
P. T. O'Brien,
M. J. Page,
R. J. Smith,
I. A. Steele,
N. Tanvir
[show abstract]
[hide abstract]
ABSTRACT: We report the first detection of an optical afterglow of a GRB (060108) that would have been classified as 'dark' in the absence of deep, rapid ground-based optical imaging with the 2-m robotic Faulkes Telesscope (FTN). Our multiwavelength analysis reveals an X-ray light curve typical of many Swift long GRBs (3-segments plus flare). Its optical afterglow, however, was already fainter than the detection limit of the UVOT within 100s of the burst. Optical imaging in BVRi' filters with the FTN began 2.75 minutes after the burst and resulted in the detection of the optical afterglow at 5.3 minutes, with a UKIRT K-band identification at ~45 mins. R and i'-band light curves are consistent with a single power law decay in flux, F(t) prop t^-a where a=0.43+/-0.08, or a 2-segment light curve with a steep decay a_1 <0.88, flattening to a_2 ~ 0.31, with evidence for rebrightening at i' band. Deep VLT R-band imaging at ~12 days reveals a faint, extended object (R ~23.5 mag) at the location of the afterglow. Although the brightness is compatible with the extrapolation of the a_2 slow decay, significant flux is likely due to a host galaxy. This implies that the optical light curve had a break before 12 days, akin to what observed in the X-rays. We derive a maximum photometric redshift z<3.2 for GRB 060108 and a best-fitting optical-to-X-ray SED at 1000 s after the burst consistent with a power law with index beta_OX = 0.54 and a small amount of extinction. The unambiguous detection at B-band and the derived photometric redshift rule out a high redshift as the reason for the optical faintness of GRB 060108. Instead, the hard opt/X-ray spectral index confirms it as one of the optically-darkest bursts detected and with modest host extinction explains the UVOT non-detection (abridged). Comment: 12 pages, 8 figures, accepted for publication in MNRAS; replaces incorrect paper version previously posted
07/2006;
