-
[show abstract]
[hide abstract]
ABSTRACT: [Abridged] The central field of the Andromeda galaxy (M 31) has been
monitored, using the Chandra HRC-I detector (about 0.1-10 keV energy range)
from 2006 to 2012 with the main aim to detect X-rays from optical novae. We
present a systematic analysis of all X-ray sources found in the 41 nova
monitoring observations, along with 23 M 31 central field HRC-I observations
available from the Chandra data archive starting in December 1999. Based on
these observations, we studied the X-ray long-term variability of the source
population and especially of X-ray binaries in M 31. We created a catalogue of
sources, detected in the 64 available observations, which add up to a total
exposure of about 1 Ms. We present a point-source catalogue, containing 318
X-ray sources with detailed long-term variability information, 28 of which are
published for the first time. The spatial and temporal resolution of the
catalogue allows us to classify 115 X-ray binary candidates showing high X-ray
variability or even outbursts in addition to 14 globular cluster X-ray binary
candidates showing no significant variability. The analysis may suggest, that
outburst sources are less frequent in globular clusters than in the field of M
31. We detected 7 supernova remnants, one of which is a new candidate and in
addition resolved the first X-rays from a known radio supernova remnant.
Besides 33 known optical nova/X-ray source correlations, we also discovered one
previously unknown super-soft X-ray outburst and several new nova candidates.
The catalogue contains a large sample of detailed long-term X-ray light curves
in the M 31 central field, which helps to understand the X-ray population of
our neighbouring spiral galaxy M 31.
04/2013;
-
A. A. Hakobyan,
A. R. Petrosian,
G. A. Mamon,
B. McLean,
D. Kunth,
M. Turatto,
E. Cappellaro,
F. Mannucci,
R. J. Allen,
N. Panagia, M. Della Valle,
G. V. Petrosyan
[show abstract]
[hide abstract]
ABSTRACT: Based on the database of 56 supernovae (SNe) events discovered in 3838 galaxies of the southern hemisphere, we compute the rate of SNe of different types along the Hubble sequence normalized to the optical and near-infrared (NIR) luminosities as well as to the stellar mass of the galaxies. We find that the rates of Type Ia SNe show a dependence on both morphology and colors of the galaxies, and therefore, on the star-formation activity. The rate of SNe Ia can be explained by assuming that at least 15% of Ia events in spiral galaxies originate in relatively young stellar populations. We also find that the rates show no modulation with nuclear activity or environment.
International Astronomical Union Symposium 281, Padova, Italy; 01/2013
-
M. Henze,
W. Pietsch,
F. Haberl, M. Della Valle,
A. Riffeser,
G. Sala,
D. Hatzidimitriou,
F. Hofmann,
D. H. Hartmann,
J. Koppenhoefer,
S. Seitz,
G. G. Williams,
K. Hornoch,
K. Itagaki,
F. Kabashima,
K. Nishiyama,
G. Xing, C. H. Lee,
E. Magnier,
K. Chambers
[show abstract]
[hide abstract]
ABSTRACT: [Abridged] Classical novae (CNe) represent the main class of supersoft X-ray
sources (SSSs) in the central region of our neighbouring galaxy M 31. Only
three confirmed novae and three SSSs have been discovered in globular clusters
(GCs) of any galaxy so far, of which one nova and two SSSs (including the nova)
were found in M 31 GCs. To study the SSS state of CNe we carried out a
high-cadence X-ray monitoring of the M 31 central area with XMM-Newton and
Chandra. We analysed X-ray and optical data of a new transient X-ray source in
the M 31 GC Bol 126, discovered serendipitously in Swift observations. Our
optical data set was based on regular M 31 monitoring programmes from five
different small telescopes. Additionally, we made use of Pan-STARRS 1 data
obtained during the PAndromeda survey. Our observations reveal that the X-ray
source in Bol 126 is the third SSS in an M 31 GC and can be confirmed as the
second CN in the M 31 GC system. This nova is named M31N 2010-10f. Its
properties in the X-ray and optical regimes agree with a massive white dwarf
(M_WD >~ 1.3 M_sun) in the binary system. Incorporating the data on previously
found (suspected) novae in M 31 GCs we used our high-cadence X-ray monitoring
observations to estimate a tentative nova rate in the M 31 GC system of 0.05
/yr/GC. An optical estimate, based on the recent 10.5-year WeCAPP survey, gives
a lower nova rate, which is compatible with the X-ray rate on the 95%
confidence level. There is growing evidence that the nova rate in GCs is higher
than expected from primordial binary formation and under conditions as in the
field. Dynamical binary formation and/or additional accretion from the
intracluster medium are possible scenarios for an increased nova rate, but
observational confirmation for this enhancement has been absent, so far.
Regular X-ray monitoring observations of M 31 provide a promising strategy to
find these novae.
11/2012;
-
[show abstract]
[hide abstract]
ABSTRACT: Classical novae (CNe) represent a major class of supersoft X-ray sources
(SSSs) in the central region of our neighbouring galaxy M 31. Significantly
different SSS properties of CNe in the M 31 bulge and disk were indicated by
recent X-ray population studies, which however considered only a small number
of disk novae. We initiated a target of opportunity (ToO) program with
XMM-Newton to observe the SSS phases of CNe in the disk of M 31 and improve the
database for further population studies. We analysed two XMM-Newton ToO
observations triggered in Aug 2011 and Jan 2012, respectively, and extracted
X-ray spectra and light curves. We report the discovery of an X-ray counterpart
to the M 31 disk nova M31N 2008-05d. The X-ray spectrum of the object allows us
to classify it as a SSS parametrised by a blackbody temperature of 32+/-6 eV.
More than three years after the nova outburst, the X-ray light curve of the SSS
exhibits irregular, broad dip features. These dips affect primarily the very
soft part of the X-ray spectrum, which might indicate absorption effects.
Dipping SSS light curves are rarely observed in M 31 novae. As well as
providing an unparalleled statistical sample, the M 31 population of novae with
SSS counterparts produces frequent discoveries of unusual objects, thereby
underlining the importance of regular monitoring.
07/2012;
-
A. Melandri,
E. Pian,
P. Ferrero,
V. D'Elia,
E. S. Walker,
G. Ghirlanda,
S. Covino,
L. Amati,
P. D'Avanzo,
P. A. Mazzali, [......],
K. Nomoto,
E. Palazzi,
F. Patat,
S. Piranomonte,
R. Salvaterra,
I. Saviane,
R. L. C. Starling,
G. Tagliaferri,
M. Tanaka,
S. D. Vergani
[show abstract]
[hide abstract]
ABSTRACT: The association of Type Ic SNe with long-duration GRBs is well established.
We endeavor, through accurate ground-based observational campaigns, to
characterize these SNe at increasingly high redshifts. We obtained a series of
optical photometric and spectroscopic observations of the Type Ic SN2012bz
associated with the Swift long-duration GRB120422A (z=0.283) using the 3.6-m
TNG and the 8.2-m VLT telescopes. The peak times of the light curves of
SN2012bz in various optical filters differ, with the B-band and i'-band light
curves reaching maximum at ~9 and ~23 rest-frame days, respectively. The
bolometric light curve has been derived from individual bands photometric
measurements, but no correction for the unknown contribution in the
near-infrared (probably around 10-15%) has been applied. Therefore, the present
light curve should be considered as a lower limit to the actual UV-optical-IR
bolometric light curve. This pseudo-bolometric curve reaches its maximum (Mbol
= -18.56 +/- 0.06) at 13 +/- 1 rest-frame days; it is similar in shape and
luminosity to the bolometric light curves of the SNe associated with z<0.2 GRBs
and more luminous than those of SNe associated with XRFs. A comparison with the
model generated for the bolometric light curve of SN2003dh suggests that
SN2012bz produced only about 15% less 56Ni than SN2003dh, about 0.35 Msol.
Similarly the VLT spectra of SN2012bz, after correction for Galactic extinction
and for the contribution of the host galaxy, suggest comparable explosion
parameters with those observed in SN2003dh (EK~3.5 x 10^52 erg, Mej~7 Msol) and
a similar progenitor mass (~25-40 Msol). GRB120422A is consistent with the
Epeak-Eiso and the EX,iso-Egamma,iso-E_peak relations. GRB120422A/SN2012bz
shows the GRB-SN connection at the highest redshift so far accurately monitored
both photometrically and spectroscopically.
06/2012;
-
[show abstract]
[hide abstract]
ABSTRACT: Supernovae Ib/c are likely to be associated to long GRBs, therefore it is
important to compare the SN rate in galaxies with the GRB rate. To do that we
computed Type Ib/c SN rates in galaxies of different morphological type by
assuming different histories of star formation and different supernova Ib/c
progenitors. We included some recent suggestions about the dependence of the
minimum mass of single Wolf-Rayet (WR) stars upon the stellar metallicity and
therefore upon galactic chemical evolution. We adopted several cosmic star
formation rates as functions of cosmic time, either observationally or
theoretically derived, including the one computed with our galaxy models. Then
we computed the cosmic Type Ib/c SN rates. We derived the following
conclusions: i) the ratio cosmic GRB - Type Ib/c rate varies in the range
10^{-2}-10^{-4} in the whole redshift range, thus suggesting that only a small
fraction of all the Type Ib/c SNe gives rise to GRBs. ii) The metallicity
dependence of Type Ib/c SN progenitors produces lower cosmic SN Ib/c rates at
early times, for any chosen cosmic star formation rate. iii) Different
theoretical cosmic star formation rates, computed under different scenarios of
galaxy formation, produce SN Ib/c cosmic rates which differ mainly at very high
redshift. However, it is difficult to draw firm conclusions on the high
redshift trend because of the large uncertainties in the data. iv) GRBs can be
important tracers of star formation at high redshift if their luminosity
function does not vary with redshift and they can help in discriminating among
different galaxy formation models.
04/2012;
-
S Campana,
G Lodato,
P D'Avanzo,
N Panagia,
E M Rossi, M Della Valle,
G Tagliaferri,
L A Antonelli,
S Covino,
G Ghirlanda,
G Ghisellini,
A Melandri,
E Pian,
R Salvaterra,
G Cusumano,
V D'Elia,
D Fugazza,
E Palazzi,
B Sbarufatti,
S D Vergani
[show abstract]
[hide abstract]
ABSTRACT: The tidal disruption of a solar-mass star around a supermassive black hole has been extensively studied analytically and numerically. In these events, the star develops into an elongated banana-shaped structure. After completing an eccentric orbit, the bound debris falls into the black hole, forming an accretion disk and emitting radiation. The same process may occur on planetary scales if a minor body passes too close to its star. In the Solar System, comets fall directly into our Sun or onto planets. If the star is a compact object, the minor body can become tidally disrupted. Indeed, one of the first mechanisms invoked to produce strong gamma-ray emission involved accretion of comets onto neutron stars in our Galaxy. Here we report that the peculiarities of the 'Christmas' gamma-ray burst (GRB 101225A) can be explained by a tidal disruption event of a minor body around an isolated Galactic neutron star. This would indicate either that minor bodies can be captured by compact stellar remnants more frequently than occurs in the Solar System or that minor-body formation is relatively easy around millisecond radio pulsars. A peculiar supernova associated with a gamma-ray burst provides an alternative explanation.
Nature 12/2011; 480(7375):69-71. · 36.28 Impact Factor
-
S. Campana,
G. Lodato,
P. D'Avanzo,
N. Panagia,
E. M. Rossi, M. Della Valle,
G. Tagliaferri,
L. A. Antonelli,
S. Covino,
G Ghirlanda,
G. Ghisellini,
A. Melandri,
E. Pian,
R. Salvaterra,
G. Cusumano,
V. D'Elia,
D. Fugazza,
E. Palazzi,
B. Sbarufatti,
S. D. Vergani
[show abstract]
[hide abstract]
ABSTRACT: The tidal disruption of a solar mass star around a supermassive black hole
has been extensively studied analytically and numerically. In these events the
star develops into an elongated banana-shaped structure. After completing an
eccentric orbit, the bound debris fall onto the black hole, forming an
accretion disk and emitting radiation. The same process may occur on planetary
scales, if a minor body orbits too close to its star. In the Solar System,
comets fall directly onto our Sun or onto planets. If the star is a compact
object, the minor body can become tidally disrupted. Indeed, one of the first
mechanisms invoked to produce strong gamma-ray emission involved accretion of
comets onto neutron stars in our Galaxy. Here we report that the peculiarities
of the `Christmas' gamma-ray burst (GRB 101225A) can be explained by a tidal
disruption event of a minor body around a Galactic isolated neutron star. This
result would indicate either that minor bodies can be captured by compact
stellar remnants more frequently than it occurs in our Solar System or that
minor body formation is relatively easy around millisecond radio pulsars. A
peculiar Supernova associated to a GRB may provide an alternative explanation.
11/2011;
-
A. A. Hakobyan,
A. R. Petrosian,
G. A. Mamon,
B. McLean,
D. Kunth,
M. Turatto,
E. Cappellaro,
F. Mannucci,
R. J. Allen,
N. Panagia, M. Della Valle
[show abstract]
[hide abstract]
ABSTRACT: Based on the database compiled in the first article of this series, with 56 SN events discovered in 3838 galaxies of the southern hemisphere, we compute the rate of supernovae (SNe) of different types along the Hubble sequence normalized to the optical and near-infrared luminosities as well as to the stellar mass of the galaxies. We find that the rates of all SN types show a dependence on both morphology and colors of the galaxies, and therefore, on the star-formation activity. The rate of core-collapse (CC) SNe is confirmed to be closely related to the Star Formation Rate (SFR) and only indirectly to the total mass of the galaxies. The rate of SNe Ia can be explained by assuming that at least 15% of Ia events in spiral galaxies originates in relatively young stellar populations. We find that the rates show no modulation with nuclear activity or environment. The ratio of SN rates between types Ib/c and II shows no trend with spiral type.
Astrophysics 09/2011; 54(3):301-314. · 0.47 Impact Factor
-
D. A. Kann,
S. Klose,
B. Zhang,
S. Covino,
N. R. Butler,
D. Malesani,
E. Nakar,
A. C. Wilson,
L. A. Antonelli,
G. Chincarini, [......],
P. Ferrero,
D. Fugazza,
J. Gorosabel,
G. L. Israel,
F. Mannucci,
S. Piranomonte,
S. Schulze,
L. Stella,
G. Tagliaferri,
and K. Wiersema
[show abstract]
[hide abstract]
ABSTRACT: Gamma-ray bursts (GRBs) have been separated into two classes, originally along the lines of duration and spectral properties, called "short/hard" and "long/soft." The latter have been conclusively linked to the explosive deaths of massive stars, while the former are thought to result from the merger or collapse of compact objects. In recent years, indications have been accumulating that the short/hard versus long/soft division does not map directly onto what would be expected from the two classes of progenitors, leading to a new classification scheme called Type I and Type II which is based on multiple observational criteria. We use a large sample of GRB afterglow and prompt-emission data (adding further GRB afterglow observations in this work) to compare the optical afterglows (or the lack thereof) of Type I GRBs with those of Type II GRBs. In comparison to the afterglows of Type II GRBs, we find that those of Type I GRBs have a lower average luminosity and show an intrinsic spread of luminosities at least as wide. From late and deep upper limits on the optical transients, we establish limits on the maximum optical luminosity of any associated supernova (SN), confirming older works and adding new results. We use deep upper limits on Type I GRB optical afterglows to constrain the parameter space of possible mini-SN emission associated with a compact-object merger. Using the prompt-emission data, we search for correlations between the parameters of the prompt emission and the late optical afterglow luminosities. We find tentative correlations between the bolometric isotropic energy release and the optical afterglow luminosity at a fixed time after the trigger (positive), and between the host offset and the luminosity (negative), but no significant correlation between the isotropic energy release and the duration of the GRBs. We also discuss three anomalous GRBs, GRB 060505, GRB 060614, and GRB 060121, in light of their optical afterglow luminosities.
The Astrophysical Journal 05/2011; 734(2):96. · 6.02 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: For the He/N nova M31N 2007-12b, we analyzed XMM-Newton EPIC and Chandra
HRC-I observations of our monitoring program performed at intervals of ten days
and added results of a XMM-Newton target of opportunity observation and Swift
XRT observations. The supersoft source (SSS) emission started between 21 and 30
d after the optical outburst and ended between 60 and 120 d after outburst,
making M31N 2007-12b one of the few novae with the shortest SSS phase known.
The X-ray spectrum was supersoft and can be fitted with a white dwarf (WD)
atmosphere model with solar abundances absorbed by the Galactic foreground. The
temperature of the WD atmosphere seems to increase at the beginning of the SSS
phase from ~70 to ~80 eV. The luminosity of M31N 2007-12b during maximum was at
the Eddington limit of a massive WD and dropped by ~30% in the observation 60 d
after outburst. The radius of the emission region is ~6x10^8 cm. In the four
bright state observations, we detected a stable 1110 s pulsation, which we
interpret as the WD rotation period. In addition, we detect dips in three
observations that might represent a 4.9 h or 9.8 h binary period of the system.
Nova envelope models with <50% mixing between solar-like accreted material and
the degenerate core of the WD can be used to describe the data. We derive a WD
mass of 1.2 Msun, as well as an ejected and burned mass of 2.0x10^{-6} Msun}
and 0.2x10^{-6} Msun, respectively. The observed periodicities indicate that
nova M31N 2007-12b erupted in an intermediate polar (IP) system. The WD
photospheric radius seems to be larger than expected for a non-magnetic WD but
in the range for magnetic WDs in an IP system. (abridged)
05/2011;
-
C. Inserra,
M. Turatto,
A. Pastorello,
S. Benetti,
E. Cappellaro,
M. L. Pumo,
L. Zampieri,
I. Agnoletto,
F. Bufano,
M. T. Botticella, M. Della Valle,
N. Elias-Rosa,
T Iijima,
S. Spiro,
S. Valenti
[show abstract]
[hide abstract]
ABSTRACT: Ultraviolet (UV), optical and near infrared (NIR) observations of the type
IIP supernova (SN) 2007od are presented, covering from the maximum light to the
late phase, allowing to investigate in detail different physical phenomena in
the expanding ejecta. These data turn this object into one of the most peculiar
IIP ever studied. The early light curve of SN 2007od is similar to that of a
bright IIPs with a short plateau, a bright peak (MV = -18 mag), but a very
faint optical light curve at late time. However, with the inclusion of mid
infrared (MIR) observations during the radioactive decay we have estimate a
M(56Ni) ~ 2\times10^-2 M\odot. Modeling the bolometric light curve, ejecta
expansion velocities and black-body temperature, we estimate a total ejected
mass was 5 - 7.5 M\odot with a kinetic energy of at least 0.5 \times 10^51 erg.
The early spectra reveal a boxy H{\alpha} profile and high velocities features
of the Balmer series that suggest interaction between the ejecta and a close
circum-stellar matter (CSM). SN 2007od may be, therefore, an intermediate case
between a Type IIn SN and a typical Type IIP SN. Also late spectra show a clear
evidence of CSM and the presence of dust formed inside the ejecta. The episodes
of mass loss short before explosion, the bright plateau, along with the
relatively small amount of 56Ni and the faint [O I] observed in the nebular
spectra are consistent with a super-asympthotic giant branch (super-AGB)
progenitor (M~9.7 - 11 M\odot).
02/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: [Abridged] Classical novae (CNe) represent the major class of supersoft X-ray sources (SSSs) in the central region of our neighbouring galaxy M 31. We performed a dedicated monitoring of the M 31 central region with XMM-Newton and Chandra between Nov 2007 and Feb 2008 and between Nov 2008 and Feb 2009 respectively, in order to find SSS counterparts of CNe, determine the duration of their SSS phase and derive physical outburst parameters. We systematically searched our data for X-ray counterparts of CNe and determined their X-ray light curves and spectral properties. We detected in total 17 X-ray counterparts of CNe in M 31, only four of which were known previously. These latter sources are still active 12.5, 11.0, 7.4 and 4.8 years after the optical outburst. From the 17 X-ray counterparts 13 were classified as SSSs. Four novae displayed short SSS phases (< 100 d). Based on these results and previous studies we compiled a catalogue of all novae with SSS counterparts in M 31 known so far. We used this catalogue to derive correlations between the following X-ray and optical nova parameters: turn-on time, turn-off time, effective temperature (X-ray), t2 decay time and expansion velocity of the ejected envelope (optical). Furthermore, we found a first hint for the existence of a difference between SSS parameters of novae associated with the stellar populations of the M 31 bulge and disk. Additionally, we conducted a Monte Carlo Markov Chain simulation on the intrinsic fraction of novae with SSS phase. This simulation showed that the relatively high fraction of novae without detected SSS emission might be explained by the inevitably incomplete coverage with X-ray observations in combination with a large fraction of novae with short SSS states, as expected from the WD mass distribution. In order to verify our results with an increased sample further monitoring observations are needed. Comment: 31 pages, 23 figures, 10 tables; submitted to A&A
10/2010;
-
M. Henze,
W. Pietsch,
F. Haberl,
M. Hernanz,
G. Sala, M. Della Valle,
D. Hatzidimitriou,
A. Rau,
D. H. Hartmann,
J. Greiner,
V. Burwitz,
J. Fliri
[show abstract]
[hide abstract]
ABSTRACT: (Abridged) Classical novae (CNe) have recently been reported to represent the major class of supersoft X-ray sources (SSSs) in the central region of our neighbour galaxy M 31. We carried out a dedicated monitoring of the M 31 central region with XMM-Newton and Chandra in order to find SSS counterparts of CNe, determine the duration of their SSS phase and derive physical outburst parameters. We systematically searched our data for X-ray counterparts of CNe and determined their X-ray light curves and spectral properties. Additionally, we determined luminosity upper limits for all novae from previous studies which are not detected anymore and for all CNe in our field of view with optical outbursts between May 2005 and March 2007. We detected eight X-ray counterparts of CNe in M 31, four of which were not previously known. Seven sources can be classified as SSSs, one is a candidate SSS. Two SSSs are still visible more than nine years after the nova outburst, whereas two other nova counterparts show a short SSS phase of less than 150 days. Of the latter sources, M31N 2006-04a exhibits a short-time variable X-ray light curve with an apparent period of (1.6+-0.3) h. This periodicity could indicate the binary period of the system. From the 14 SSS nova counterparts known from previous studies, ten are not detected anymore. Additionally, we found four SSSs in our XMM-Newton data without a nova counterpart, one of which is a new source. Out of eleven SSSs detected in our monitoring, seven are counterparts of CNe. We therefore confirm the earlier finding that CNe are the major class of SSSs in the central region of M 31. We use the measured SSS turn-on and turn-off times to estimate the mass ejected in the nova outburst and the mass burned on the white dwarf. Classical novae with short SSS phases seem to be an important contributor to the overall population. Comment: 17 pages, 10 figures, 9 tables, accepted for publication in A&A, reduced image resolution of Fig.1
09/2010;
-
D. A. Kann,
S. Klose,
B. Zhang,
D. Malesani,
E. Nakar,
A. Pozanenko,
A. C. Wilson,
N. R. Butler,
P. Jakobsson,
S. Schulze, [......],
L. Stella,
G. Tagliaferri,
N. R. Tanvir,
J. Telting,
V. Testa,
A. C. Updike,
A. Volnova,
D. Watson,
K. Wiersema,
and D. Xu
[show abstract]
[hide abstract]
ABSTRACT: We have gathered optical photometry data from the literature on a large sample of Swift-era gamma-ray burst (GRB) afterglows including GRBs up to 2009 September, for a total of 76 GRBs, and present an additional three pre-Swift GRBs not included in an earlier sample. Furthermore, we publish 840 additional new photometry data points on a total of 42 GRB afterglows, including large data sets for GRBs 050319, 050408, 050802, 050820A, 050922C, 060418, 080413A, and 080810. We analyzed the light curves of all GRBs in the sample and derived spectral energy distributions for the sample with the best data quality, allowing us to estimate the host-galaxy extinction. We transformed the afterglow light curves into an extinction-corrected z = 1 system and compared their luminosities with a sample of pre-Swift afterglows. The results of a former study, which showed that GRB afterglows clustered and exhibited a bimodal distribution in luminosity space, are weakened by the larger sample. We found that the luminosity distribution of the two afterglow samples (Swift-era and pre-Swift) is very similar, and that a subsample for which we were not able to estimate the extinction, which is fainter than the main sample, can be explained by assuming a moderate amount of line-of-sight host extinction. We derived bolometric isotropic energies for all GRBs in our sample, and found only a tentative correlation between the prompt energy release and the optical afterglow luminosity at 1 day after the GRB in the z = 1 system. A comparative study of the optical luminosities of GRB afterglows with echelle spectra (which show a high number of foreground absorbing systems) and those without, reveals no indication that the former are statistically significantly more luminous. Furthermore, we propose the existence of an upper ceiling on afterglow luminosities and study the luminosity distribution at early times, which was not accessible before the advent of the Swift satellite. Most GRBs feature afterglows that are dominated by the forward shock from early times on. Finally, we present the first indications of a class of long GRBs, which form a bridge between the typical high-luminosity, high-redshift events and nearby low-luminosity events (which are also associated with spectroscopic supernovae) in terms of energetics and observed redshift distribution, indicating a continuous distribution overall.
The Astrophysical Journal 08/2010; 720(2):1513. · 6.02 Impact Factor
-
A. A. Hakobyan,
A. R. Petrosian,
G. A. Mamon,
B. McLean,
D. Kunth,
M. Turatto,
E. Cappellaro,
F. Mannucci,
R. J. Allen,
N. Panagia, M. Della Valle
[show abstract]
[hide abstract]
ABSTRACT: The database for 3838 galaxies that were monitored for SNe events includes newly determined morphologies and newly measured apparent blue and red magnitudes, angular diameters, axial ratios and position angles, Two Micron All Sky Survey (2MASS) J, H and Ks and Deep Near-Infrared Southern Sky Survey (DENIS) I, J and Ks magnitudes, as well as activity classes from the NASA/IPAC Extragalactic Database (NED), and numbers of neighboring objects in a circle of radius 50 kpc. The optical parameters (morphologies and axial ratios) for the Five SN survey (FSS) galaxies were extracted as follows: 10'x10' regions centered on each FSS galaxy were extracted from the POSS-II IIIa-J and IIIa-F plates and from the UKST IIIa-J and IIIa-F plates. The creation of this homogeneous database is aimed to support all future studies and to minimize possible selection effects and errors which often arise when information are selected from different sources and catalogues.
-
F Vitali,
G Chincarini,
M Zannoni,
S Covino,
E Molinari,
S Benetti,
C Bonoli,
F Bortoletto,
E Cascone,
R Cosentino, [......],
R Mazzoleni,
L Nicastro,
A Riva,
M Riva,
R Salvaterra,
P Spanò,
M Sperandio,
M Stefanon,
G Tosti,
V Testa
Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series; 07/2010
-
P. D'Avanzo,
M. Perri,
D. Fugazza,
R. Salvaterra,
G. Chincarini,
R. Margutti,
X. F. Wu,
C. C. Thoene,
A. Fernandez-Soto,
T. N. Ukwatta,
D. N. Burrows,
N. Gehrels,
P. Meszaros,
K Toma,
B Zhang,
S. Covino,
S. Campana,
V. D'Elia, M. Della Valle,
S. Piranomonte
[show abstract]
[hide abstract]
ABSTRACT: Gamma-ray bursts have been proved to be detectable up to distances much larger than any other astrophysical object, providing the most effective way, complementary to ordinary surveys, to study the high redshift universe. To this end, we present here the results of an observational campaign devoted to the study of the high-z GRB 090205. We carried out optical/NIR spectroscopy and imaging of GRB 090205 with the ESO-VLT starting from hours after the event up to several days later to detect the host galaxy. We compared the results obtained from our optical/NIR observations with the available Swift high-energy data of this burst. Our observational campaign led to the detection of the optical afterglow and host galaxy of GRB 090205 and to the first measure of its redshift, z=4.65. Similar to other, recent high-z GRBs, GRB 090205 has a short duration in the rest-frame with T_{90,rf}=1.6 s, which suggests the possibility that it might belong to the short GRBs class. The X-ray afterglow of GRB 090205 shows a complex and interesting behaviour with a possible rebrightening at 500-1000s from the trigger time and late flaring activity. Photometric observations of the GRB 090205 host galaxy argue in favor of a starburst galaxy with a stellar population younger than ~ 150 Myr. Moreover, the metallicity of Z > 0.27 Z_Sun derived from the GRB afterglow spectrum is among the highest derived from GRB afterglow measurement at high-z, suggesting that the burst occurred in a rather enriched envirorment. Finally, a detailed analysis of the afterglow spectrum shows the existence of a line corresponding to Lyman-alpha emission at the redshift of the burst. GRB 090205 is thus hosted in a typical Lyman-alpha emitter (LAE) at z=4.65. This makes the GRB 090205 host the farthest GRB host galaxy, spectroscopically confirmed, detected to date. Comment: Accepted for publication in Astronomy and Astrophysics; 8 pages, 7 figures
06/2010;
-
G. Chincarini,
M. Zannoni,
S. Covino,
E Molinari,
S. Benetti,
F. Vitali,
C. Bonoli,
F. Bortoletto,
E. Cascone,
R. Cosentino, [......],
R. Mazzoleni,
L. Nicastro,
A. Riva,
M Riva,
R. Salvaterra,
P. Spano,
M. Sperandio,
M. Stefanon,
G. Tosti,
V. Testa
[show abstract]
[hide abstract]
ABSTRACT: The approach of Observational Astronomy is mainly aimed at the construction of larger aperture telescopes, more sensitive detectors and broader wavelength coverage. Certainly fruitful, this approach turns out to be not completely fulfilling the needs when phenomena related to the formation of black holes (BH), neutron stars (NS) and relativistic stars in general are concerned. Recently, mainly through the Vela, Beppo-SAX and Swift satellites, we reached a reasonable knowledge of the most violent events in the Universe and of some of the processes we believe are leading to the formation of black holes (BH). We plan to open a new window of opportunity to study the variegated physics of very fast astronomical transients, particularly the one related to extreme compact objects. The innovative approach is based on three cornerstones: 1) the design (the conceptual design has been already completed) of a 3m robotic telescope and related focal plane instrumentation characterized by the unique features: "No telescope points faster"; 2) simultaneous multi-wavelengths observations (photometry, spectroscopy o\& polarimetry); 3) high time resolution observations. The conceptual design of the telescope and related instrumentation is optimized to address the following topics: High frequency a-periodic variability, Polarization, High z GRBs, Short GRBs, GRB-Supernovae association, Multi-wavelengths simultaneous photometry and rapid low dispersion spectroscopy. This experiment will turn the "exception" (like the optical observations of GRB 080319B) to "routine". Comment: To be published in the proceedings of the conference "The Shocking Universe", San Servolo Venice, September 14-18, 2009.
05/2010;
-
G. Chincarini,
J Mao,
R. Margutti,
M. G. Bernardini,
C. Guidorzi,
F. Pasotti,
D. Giannios, M. Della Valle,
A. Moretti,
P. Romano,
P. D'Avanzo,
G. Cusumano,
P. Giommi
[show abstract]
[hide abstract]
ABSTRACT: We present an updated catalog of 113 X-ray flares detected by Swift in the ~33% of the X-ray afterglows of Gamma-Ray Bursts (GRB). 43 flares have a measured redshift. For the first time the analysis is performed in 4 different X-ray energy bands, allowing us to constrain the evolution of the flare temporal properties with energy. We find that flares are narrower at higher energies: their width follows a power-law relation w~E^{-0.5} reminiscent of the prompt emission. Flares are asymmetric structures, with a decay time which is twice the rise time on average. Both time scales linearly evolve with time, giving rise to a constant rise-to-decay ratio: this implies that both time scales are stretched by the same factor. As a consequence, the flare width linearly evolves with time to larger values: this is a key point that clearly distinguishes the flare from the GRB prompt emission. The flare 0.3-10 keV peak luminosity decreases with time, following a power-law behaviour with large scatter: L_{pk}~ t_{pk}^{-2.7}. When multiple flares are present, a global softening trend is established: each flare is on average softer than the previous one. The 0.3-10 keV isotropic energy distribution is a log-normal peaked at 10^{51} erg, with a possible excess at low energies. The flare average spectral energy distribution (SED) is found to be a power-law with spectral energy index beta~1.1. These results confirmed that the flares are tightly linked to the prompt emission. However, after considering various models we conclude that no model is currently able to account for the entire set of observations. Comment: MNRAS submitted
04/2010;
