-
D. A. Perley,
A. J. Levan,
N. R. Tanvir,
S. B. Cenko,
J. S. Bloom,
J. Hjorth,
T. Kruehler,
A. V. Filippenko,
A. Fruchter,
J. P. U. Fynbo,
P. Jakobsson,
J. Kalirai,
B. Milvang-Jensen, A. N. Morgan,
J. X. Prochaska,
J. M. Silverman
[show abstract]
[hide abstract]
ABSTRACT: We present observations and analysis of the host galaxies of 23 heavily
dust-obscured gamma-ray bursts (GRBs) observed by the Swift satellite between
the years 2005-2009, a sample representing all GRBs during this period with an
unambiguous host-frame extinction of at least A_V>1 mag. Deep observations with
Keck, Gemini, VLT, HST, and Spitzer successfully detect the host galaxies and
establish redshifts for all 23 events, enabling us to provide measurements of
the host stellar masses, star-formation rates (SFRs), and mean extinctions.
Compared to the hosts of unobscured GRBs at similar redshifts, we find that the
hosts of dust-obscured GRBs are (on average) more massive by about an order of
magnitude and are also significantly more rapidly star-forming and more
dust-obscured. However, while the inclusion of this population of dust-obscured
hosts shows that GRBs populate all types of star-forming galaxies including the
most massive, luminous systems at z~2, at redshifts below z<1.5 the overall GRB
population continues to show a highly significant aversion away from massive
galaxies and a corresponding preference for low-mass systems relative to would
be expected given a purely SFR-selected galaxy sample. This supports the notion
that the GRB rate is strongly dependent on metallicity, and may suggest that
the most massive galaxies in the universe underwent an significant transition
in their chemical properties approximately 9 Gyr ago. We also conclude that,
based on the absence of unobscured GRBs in massive galaxies and the absence of
obscured GRBs in low-mass galaxies, the dust distributions of both the
lowest-mass and the highest-mass galaxies are relatively homogeneous, while
intermediate-mass galaxies (~10^9 M_sun) have much more diverse internal dust
properties.
01/2013;
-
T Zafar,
D Watson,
Á {El'i}asdóttir,
J ~P ~U Fynbo,
T Krühler,
P Schady,
G Leloudas,
P Jakobsson,
C ~C Thöne,
D ~A Perley, A ~N Morgan,
J Bloom,
J Greiner
apj. 07/2012; 753:82.
-
O. M. Littlejohns,
R. Willingale,
P. T. O'Brien,
A. P. Beardmore,
S. Covino,
D. A. Perley,
N. R. Tanvir,
E. Rol,
F. Yuan,
C. Akerlof, [......],
S. Kobayashi,
W. Li, A. N. Morgan,
C. G. Mundell,
K. Page,
E. Palazzi,
R. M. Quimby,
S. Schulze,
I. A. Steele,
A. de Ugarte Postigo
[show abstract]
[hide abstract]
ABSTRACT: We present broadband multi-wavelength observations of GRB 080310 at redshift
z = 2.43. This burst was bright and long-lived, and unusual in having extensive
optical and near IR follow-up during the prompt phase. Using these data we
attempt to simultaneously model the gamma-ray, X-ray, optical and IR emission
using a series of prompt pulses and an afterglow component. Initial attempts to
extrapolate the high energy model directly to lower energies for each pulse
reveal that a spectral break is required between the optical regime and 0.3 keV
to avoid over predicting the optical flux. We demonstrate that afterglow
emission alone is insufficient to describe all morphology seen in the optical
and IR data. Allowing the prompt component to dominate the early-time optical
and IR and permitting each pulse to have an independent low energy spectral
indices we produce an alternative scenario which better describes the optical
light curve. This, however, does not describe the spectral shape of GRB 080310
at early times. The fit statistics for the prompt and afterglow dominated
models are nearly identical making it difficult to favour either. However one
enduring result is that both models require a low energy spectral index
consistent with self absorption for at least some of the pulses identified in
the high energy emission model.
01/2012;
-
American Astronomical Society Meeting Abstracts; 01/2012
-
[show abstract]
[hide abstract]
ABSTRACT: The known host galaxies of short-hard gamma-ray bursts (GRBs) to date are
characterized by low to moderate star-formation rates and a broad range of
stellar masses. In this paper, we positionally associate the recent
unambiguously short-hard Swift GRB 100206A with a disk galaxy at redshift
z=0.4068 that is rapidly forming stars at a rate of ~30 M_sun/yr, almost an
order of magnitude higher than any previously identified short GRB host. Using
photometry from Gemini, Keck, PAIRITEL, and WISE, we show that the galaxy is
very red (g-K = 4.3 AB mag), heavily obscured (A_V ~ 2 mag), and has the
highest metallicity of any GRB host to date (12 + log[O/H]_KD02 = 9.2): it is a
classical luminous infrared galaxy (LIRG), with L_IR ~ 4 x 10^11 L_sun. While
these properties could be interpreted to support an association of this GRB
with very recent star formation, modeling of the broadband spectral energy
distribution also indicates that a substantial stellar mass of mostly older
stars is present. The current specific star-formation rate is modest (specific
SFR ~ 0.5 Gyr^-1), the current star-formation rate is not substantially
elevated above its long-term average, and the host morphology shows no sign of
recent merger activity. Our observations are therefore equally consistent with
an older progenitor, similar to what is inferred for other short-hard GRBs.
Given the precedent established by previous short GRB hosts and the significant
fraction of the Universe's stellar mass in LIRG-like systems at z >~0.3, an
older progenitor represents the most likely origin of this event.
12/2011;
-
A J Levan,
N R Tanvir,
S B Cenko,
D A Perley,
K Wiersema,
J S Bloom,
A S Fruchter,
A de Ugarte Postigo,
P T O'Brien,
N Butler, [......],
N Singh,
L van Spaandonk,
R L C Starling,
R G Strom,
J C Tello,
O Vaduvescu,
P J Wheatley,
R A M J Wijers,
J M Winters,
D Xu
[show abstract]
[hide abstract]
ABSTRACT: Variable x-ray and γ-ray emission is characteristic of the most extreme physical processes in the universe. We present multiwavelength observations of a unique γ-ray-selected transient detected by the Swift satellite, accompanied by bright emission across the electromagnetic spectrum, and whose properties are unlike any previously observed source. We pinpoint the event to the center of a small, star-forming galaxy at redshift z = 0.3534. Its high-energy emission has lasted much longer than any γ-ray burst, whereas its peak luminosity was ∼100 times higher than bright active galactic nuclei. The association of the outburst with the center of its host galaxy suggests that this phenomenon has its origin in a rare mechanism involving the massive black hole in the nucleus of that galaxy.
Science 06/2011; 333(6039):199-202. · 31.20 Impact Factor
-
C. Guidorzi,
S Kobayashi,
D. A. Perley,
G. Vianello,
J. S. Bloom,
P Chandra,
D. A. Kann,
W Li,
C. G. Mundell,
A. Pozanenko, [......],
E. Klunko,
A. Melandri,
S. Mereghetti, A. N. Morgan,
P. T. O'Brien,
V. Rumyantsev,
R. J. Smith,
I. A. Steele,
N. R. Tanvir,
A. Volnova
[show abstract]
[hide abstract]
ABSTRACT: We report the detection of a faint optical flash by the 2-m Faulkes Telescope
North simultaneously with the second of two prompt gamma-ray pulses in INTEGRAL
gamma-ray burst (GRB) 080603A, beginning at t_rest = 37 s after the onset of
the GRB. This optical flash appears to be distinct from the subsequent emerging
afterglow emission, for which we present comprehensive broadband radio to X-ray
light curves to 13 days post-burst and rigorously test the standard fireball
model. The intrinsic extinction toward GRB 080603A is high (A_V,z = 0.8 mag),
and the well-sampled X-ray-to-near-infrared spectral energy distribution is
interesting in requiring an LMC2 extinction profile, in contrast to the
majority of GRBs. Comparison of the gamma-ray and extinction-corrected optical
flux densities of the flash rules out an inverse-Compton origin for the prompt
gamma-rays; instead, we suggest that the optical flash could originate from the
inhomogeneity of the relativistic flow. In this scenario, a large velocity
irregularity in the flow produces the prompt gamma-rays, followed by a milder
internal shock at a larger radius that would cause the optical flash. Flat
gamma-ray spectra, roughly F propto nu^-0.1, are observed in many GRBs. If the
flat spectrum extends down to the optical band in GRB 080603A, the optical
flare could be explained as the low-energy tail of the gamma-ray emission. If
this is indeed the case, it provides an important clue to understanding the
nature of the emission process in the prompt phase of GRBs and highlights the
importance of deep (R> 20 mag), rapid follow-up observations capable of
detecting faint, prompt optical emission.
05/2011;
-
S. B. Cenko,
D. A. Frail,
F. A. Harrison,
J. B. Haislip,
D. E. Reichart,
N. R. Butler,
B. E. Cobb,
A. Cucchiara,
E. Berger,
J. S. Bloom, [......],
A. V. Filippenko,
K. Glazebrook,
K. M. Ivarsen,
M. M. Kasliwal,
S. R. Kulkarni,
A. P. LaCluyze,
S. Lopez, A. N. Morgan,
M. Pettini,
and V. R. Rana
[show abstract]
[hide abstract]
ABSTRACT: We present broadband (radio, optical, and X-ray) light curves and spectra of the afterglows of four long-duration gamma-ray bursts (GRBs; GRBs 090323, 090328, 090902B, and 090926A) detected by the Gamma-Ray Burst Monitor and Large Area Telescope (LAT) instruments on the Fermi satellite. With its wide spectral bandpass, extending to GeV energies, Fermi is sensitive to GRBs with very large isotropic energy releases (1054 erg). Although rare, these events are particularly important for testing GRB central-engine models. When combined with spectroscopic redshifts, our afterglow data for these four events are able to constrain jet collimation angles, the density structure of the circumburst medium, and both the true radiated energy release and the kinetic energy of the outflows. In agreement with our earlier work, we find that the relativistic energy budget of at least one of these events (GRB 090926A) exceeds the canonical value of 1051 erg by an order of magnitude. Such energies pose a severe challenge for models in which the GRB is powered by a magnetar or a neutrino-driven collapsar, but remain compatible with theoretical expectations for magnetohydrodynamical collapsar models (e.g., the Blandford-Znajek mechanism). Our jet opening angles (θ) are similar to those found for pre-Fermi GRBs, but the large initial Lorentz factors (Γ0) inferred from the detection of GeV photons imply θΓ0 70-90, values which are above those predicted in magnetohydrodynamic models of jet acceleration. Finally, we find that these Fermi-LAT events preferentially occur in a low-density circumburst environment, and we speculate that this might result from the lower mass-loss rates of their lower-metallicity progenitor stars. Future studies of Fermi-LAT afterglows at radio wavelengths with the order-of-magnitude improvement in sensitivity offered by the Extended Very Large Array should definitively establish the relativistic energy budgets of these events.
The Astrophysical Journal 04/2011; 732(1):29. · 6.02 Impact Factor
-
D. A. Perley, A. N. Morgan,
A. Updike,
F. Yuan,
C. W. Akerlof,
A. A. Miller,
J. S. Bloom,
S. B. Cenko,
W. Li,
A. V. Filippenko, [......],
N. R. Tanvir,
A. J. Levan,
N. R. Butler,
P. Christian,
D. H. Hartmann,
P. Milne,
E. S. Rykoff,
W. Rujopakarn,
J. C. Wheeler,
and G. G. Williams
[show abstract]
[hide abstract]
ABSTRACT: We present early-time optical through infrared photometry of the bright Swift gamma-ray burst (GRB) 080607, starting only 6 s following the initial trigger in the rest frame. Complemented by our previously published spectroscopy, this high-quality photometric data set allows us to solve for the extinction properties of the redshift 3.036 sightline, giving perhaps the most detailed information to date on the ultraviolet continuum absorption properties of any sightline outside our Local Group. The extinction properties are not adequately modeled by any ordinary extinction template (including the average Milky Way, Large Magellanic Cloud, and Small Magellanic Cloud curves), partially because the 2175 Å feature (while present) is weaker by about a factor of two than when seen under similar circumstances locally. However, the spectral energy distribution is exquisitely fitted by the more general Fitzpatrick & Massa parameterization of Local-Group extinction, putting it in the same family as some peculiar Milky Way extinction curves. After correcting for this (considerable, AV = 3.3 ± 0.4 mag) extinction, GRB 080607 is revealed to have been among the most optically luminous events ever observed, comparable to the naked-eye burst GRB 080319B. Its early peak time (t rest < 6 s) indicates a high initial Lorentz factor (Γ>600), while the extreme luminosity may be explained in part by a large circumburst density. Only because of its early high luminosity could the afterglow of GRB 080607 be studied in such detail in spite of the large attenuation and great distance, making this burst an excellent prototype for the understanding of other highly obscured extragalactic objects, and of the class of "dark" GRBs in particular.
The Astronomical Journal 12/2010; 141(2):36. · 4.03 Impact Factor
-
Daniel A. Perley,
J. S. Bloom,
C. R. Klein,
S. Covino,
T. Minezaki,
P. Woźniak,
W. T. Vestrand,
G. G. Williams,
P. Milne,
N. R. Butler, [......],
L. Cowie,
P. Ferrero,
J. Greiner,
D. H. Hartmann,
Y. Kakazu,
A. Küpcü Yoldaş, A. N. Morgan,
P. A. Price,
J. X. Prochaska,
Y. Yoshii
[show abstract]
[hide abstract]
ABSTRACT: We present observations and analysis of the broad-band afterglow of Swift GRB 071025. Using optical and infrared (RIYJHK) photometry, we derive a photometric redshift of 4.4 < z < 5.2; at this redshift our simultaneous multicolour observations begin at ∼30 s after the gamma-ray burst trigger in the host frame, during the initial rising phase of the afterglow. We associate the light-curve peak at ∼580 s in the observer frame with the formation of the forward shock, giving an estimate of the initial Lorentz factor Γ0∼ 200. The red spectral energy distribution (even in regions not affected by the Lyman α break) provides secure evidence of a large dust column. However, the inferred extinction curve shows a prominent flat component between 2000 and 3000 Å in the rest frame, inconsistent with any locally observed template but well fitted by models of dust formed by supernovae. Time-dependent fits to the extinction profile reveal no evidence of dust destruction and limit the decrease in the extinction column to ΔA3000 < 0.54 mag after t= 50 s in the rest frame. Together with studies of high-z quasars, our observations suggest a transition in dust properties in the early Universe, possibly associated with a transition between supernova-dominated and asymptotic giant branch-dominated modes of dust production.
Monthly Notices of the Royal Astronomical Society 08/2010; 406(4):2473 - 2487. · 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.
Monthly Notices of the Royal Astronomical Society 06/2010; 406(3):1687 - 1700. · 4.90 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We report SMARTS, Gemini and Swift-UVOT observations of the optical transient (OT) associated with gamma-ray burst (GRB) 091127, at redshift 0.49, taken between 0.9 hr and 102 days following the Swift trigger. In our early-time observations, the OT fades in a manner consistent with previously observed GRB afterglows. However, after 9 days post-burst, the OT is observed to brighten for a period of ~2 weeks, after which the source resumes fading. A comparison of this late-time "bump" to SN 1998bw (the broad-lined Type Ic supernova associated with GRB 980425), and several other GRB supernovae (SNe), indicates that the most straightforward explanation is that GRB 091127 was accompanied by a contemporaneous SN (SN 2009nz) that peaked at a magnitude of M_V=-19.0+/-0.2. SN 2009nz is globally similar to other GRB supernovae, but evolves slightly faster than SN 1998bw and reaches a slightly dimmer peak magnitude. We also analyze the early-time UV-optical-IR spectral energy distribution of the afterglow of GRB 091127 and find that there is little to no reddening in the host galaxy along the line-of-slight to this burst. Comment: minor edits, accepted by ApJ Letters
05/2010;
-
S. B. Cenko,
D. A. Frail,
F. A. Harrison,
J. B. Haislip,
D. E. Reichart,
N. R. Butler,
B. E. Cobb,
A. Cucchiara,
E. Berger,
J. S. Bloom, [......],
A. V. Filippenko,
K. Glazebrook,
K. M. Ivarsen,
M. M. Kasliwal,
S. R. Kulkarni,
A. P. LaCluyze,
S. Lopez, A. N. Morgan,
M. Pettini,
V. R. Rana
[show abstract]
[hide abstract]
ABSTRACT: We present broadband (radio, optical, and X-ray) light curves and spectra of the afterglows of four long-duration gamma-ray bursts (GRBs 090323, 090328, 090902B, and 090926A) detected by the Gamma-Ray Burst Monitor (GBM) and Large Area Telescope (LAT) instruments on the Fermi satellite. With its wide spectral bandpass, extending to GeV energies, Fermi is sensitive to GRBs with very large isotropic energy releases (10e54 erg). Although rare, these events are particularly important for testing GRB central-engine models. When combined with spectroscopic redshifts, our afterglow data for these four events are able to constrain jet collimation angles, the density structure of the circumburst medium, and both the true radiated energy release and the kinetic energy of the outflows. In agreement with our earlier work, we find that the relativistic energy budget of at least one of these events (GRB 090926A) exceeds the canonical value of 10e51 erg by an order of magnitude. Such energies pose a severe challenge for models in which the GRB is powered by a magnetar or neutrino-driven collapsar, but remain compatible with theoretical expectations for magneto-hydrodynamical (MHD) collapsar models. Our jet opening angles (theta) are similar to those found for pre-Fermi GRBs, but the large initial Lorentz factors (Gamma_0) inferred from the detection of GeV photons imply theta Gamma_0 ~ 70-90, values which are above those predicted in MHD models of jet acceleration. Finally, we find that these Fermi-LAT events preferentially occur in a low-density circumburst environment, and we speculate that this might result from the lower mass-loss rates of their lower-metallicity progenitor stars. Future studies of Fermi-LAT afterglows in the radio with the order-of-magnitude improvement in sensitivity offered by the EVLA should definitively establish the relativistic energy budgets of these events. Comment: 29 pages, 11 figures, submitted to ApJ. Comments welcome. v2 - Minor typos corrected.
04/2010;
-
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;
-
A. Brunthaler,
I. Marti-Vidal,
K. M. Menten,
M. J. Reid,
C. Henkel,
G. C. Bower,
H. Falcke,
H. Feng,
P. Kaaret,
N. R. Butler, A. N. Morgan,
A Weiss
[show abstract]
[hide abstract]
ABSTRACT: We present observations of the recently discovered supernova 2008iz in M82 with the VLBI High Sensitivity Array at 22 GHz, the Very Large Array at frequencies of 1.4, 4.8, 8.4, 22 and 43 GHz, and the Chandra X-ray observatory. The supernova was clearly detected on two VLBI images, separated by 11 months. The source shows a ring-like morphology and expands with a velocity of ~23000 km/s. The most likely explosion date is in mid February 2008. The measured expansion speed is a factor of ~2 higher than expected under the assumption that synchrotron self-absorption dominates the light curve at the peak, indicating that this absorption mechanism may not be important for the radio emission. We find no evidence for an asymmetric explosion. The VLA spectrum shows a broken power law, indicating that the source was still optically thick at 1.4 GHz in April 2009. Finally, we report upper limits on the X-ray emission from SN 2008iz and a second radio transient recently discovered by MERLIN observations. Comment: accepted Astronomy & Astrophysics, 9 pages, 8 figures, also available at http://www.mpifr-bonn.mpg.de/staff/abrunthaler/pub.shtml
03/2010;
-
Daniel A. Perley,
J. S. Bloom,
C. R. Klein,
S. Covino,
T. Minezaki,
P. Wozniak,
W. T. Vestrand,
G. G. Williams,
P. Milne,
N. R. Butler, [......],
L. Cowie,
P. Ferrero,
J. Greiner,
D. H. Hartmann,
Y. Kakazu,
A. Küpcü Yoldas, A. N. Morgan,
P. A. Price,
J. X. Prochaska,
Y Yoshii
[show abstract]
[hide abstract]
ABSTRACT: We present observations and analysis of the broadband afterglow of Swift GRB 071025. Using optical and infrared (RIYJHK) photometry, we derive a photometric redshift of 4.4 < z < 5.2; at this redshift our simultaneous multicolour observations begin at ~30 s after the GRB trigger in the host frame and during the initial rising phase of the afterglow. We associate the light curve peak at 580 s in the observer frame with the formation of the forward shock, giving an estimate of the initial Lorentz factor Gamma_0 ~ 200. The red spectral energy distribution (even in regions not affected by the Lyman-alpha break) provides secure evidence of a large dust column. However, the inferred extinction curve shows a prominent flat component between 2000-3000 Angstroms in the rest-frame, inconsistent with any locally observed template but well-fit by models of dust formed by supernovae. Time-dependent fits to the extinction profile reveal no evidence of dust destruction and limit the decrease in the extinction column to Delta A_3000 < 0.54 mag after t = 50 s in the rest frame. Our observations provide evidence of a transition in dust properties at z~5, in agreement with studies of high-z quasars, and suggest that SN-formed dust continues to dominate the opacity of typical galaxies at this redshift. Comment: Resubmitted to MNRAS following referee report. Contains additional figure and some extra analysis/discussion
12/2009;
-
S. B. Cenko,
N. R. Butler,
E. O. Ofek,
D. A. Perley, A. N. Morgan,
D. A. Frail,
J. Gorosabel,
J. S. Bloom,
A. J. Castro-Tirado,
J. Cepa,
P. C. Chandra,
A. de Ugarte Postigo,
A. V. Filippenko,
C. R. Klein,
S. R. Kulkarni,
A. A. Miller,
P. E. Nugent,
D. L. Starr
[show abstract]
[hide abstract]
ABSTRACT: We present broadband (gamma-ray, X-ray, near-infrared, optical, and radio) observations of the gamma-ray burst (GRB) 090709A and its afterglow in an effort to ascertain the origin of this high-energy transient. Previous analyses suggested that GRB 090709A exhibited quasi-periodic oscillations with a period of 8.06 s, a trait unknown in long-duration GRBs but typical of flares from soft gamma-ray repeaters. When properly accounting for the underlying shape of the power-density spectrum of GRB 090709A, we find no conclusive (> 3 sigma) evidence for the reported periodicity. In conjunction with the location of the transient (far from the Galactic plane and absent any nearby host galaxy in the local universe) and the evidence for extinction in excess of the Galactic value, we consider a magnetar origin relatively unlikely. A long-duration GRB, however, can account for the majority of the observed properties of this source. GRB 090709A is distinguished from other long-duration GRBs primarily by the large amount of obscuration from its host galaxy (A_K,obs >~ 2 mag). Comment: 12 pages; 6 figures; Submitted to AJ; Comments welcome
The Astronomical Journal 11/2009; · 4.03 Impact Factor
-
A. N. Morgan,
D. E. Vanden Berk,
P. W. A. Roming,
J. A. Nousek,
T. S. Koch,
A. A. Breeveld,
M. de Pasquale,
S. T. Holland,
N. P. M. Kuin,
M. J. Page,
and M. Still
[show abstract]
[hide abstract]
ABSTRACT: We present a technique for optimal co-addition of image data for rapidly varying sources, with specific application to gamma-ray burst (GRB) afterglows. Unweighted co-addition of rapidly fading afterglow light curve data becomes counterproductive relatively quickly. It is better to stop co-addition of the data once noise dominates late exposures. A better alternative is to optimally weight each exposure to maximize the signal-to-noise ratio (S/N) of the final co-added image data. By using information about GRB light curves and image noise characteristics, optimal image co-addition increases the probability of afterglow detection and places the most stringent upper limits on nondetections. For a temporal power-law flux decay typical of GRB afterglows, optimal co-addition has the greatest potential to improve the S/N of afterglow imaging data (relative to unweighted co-addition) when the decay rate is high, the source count rate is low, and the background rate is high. The optimal co-addition technique is demonstrated with applications to Swift Ultraviolet/Optical Telescope (UVOT) data of several GRBs, with and without detected afterglows.
The Astrophysical Journal 12/2008; 683(2):913. · 6.02 Impact Factor
-
P. W. A. Roming,
P. Schady,
D. B. Fox,
B Zhang,
E. Liang,
K. O. Mason,
E. Rol,
D. N. Burrows,
A. J. Blustin,
P. T. Boyd, [......],
V. Mangano,
P. Meszaros, A. N. Morgan,
J. A. Nousek,
J. P. Osborne,
D. M. Palmer,
T. Poole,
M. D. Still,
G. Tagliaferri,
S. Zane
[show abstract]
[hide abstract]
ABSTRACT: Very early observations with the Swift satellite of gamma-ray burst (GRB) afterglows reveal that the optical component is not detected in a large number of cases. This is in contrast to the bright optical flashes previously discovered in some GRBs (e.g. GRB 990123 and GRB 021211). Comparisons of the X-ray afterglow flux to the optical afterglow flux and prompt gamma-ray fluence is used to quantify the seemingly deficient optical, and in some cases X-ray, light at these early epochs. This comparison reveals that some of these bursts appear to have higher than normal gamma-ray efficiencies. We discuss possible mechanisms and their feasibility for explaining the apparent lack of early optical emission. The mechanisms considered include: foreground extinction, circumburst absorption, Ly-alpha blanketing and absorption due to high redshift, low density environments, rapid temporal decay, and intrinsic weakness of the reverse shock. Of these, foreground extinction, circumburst absorption, and high redshift provide the best explanations for most of the non-detections in our sample. There is tentative evidence of suppression of the strong reverse shock emission. This could be because of a Poynting-flux-dominated flow or a pure non-relativistic hydrodynamical reverse shock. Comment: 22 pages, 5 figures. Accepted for publication in ApJ
09/2005;
-
A. Brunthaler,
I. Martí-Vidal,
K. M. Menten,
M. J. Reid,
C. Henkel,
G. C. Bower,
H. Falcke,
H. Feng,
P. Kaaret,
N. R. Butler, A. N. Morgan,
A. Weiß
http://dx.doi.org/10.1051/0004-6361/201014133.
