88 research outputs found
The nature of supernovae 2010O and 2010P in Arp 299 - II. Radio emission
We report radio observations of two stripped-envelope supernovae (SNe), 2010O
and 2010P, which exploded within a few days of each other in the luminous
infrared galaxy Arp 299. Whilst SN 2010O remains undetected at radio
frequencies, SN 2010P was detected (with an astrometric accuracy better than 1
milli arcsec in position) in its optically thin phase in epochs ranging from ~1
to ~3yr after its explosion date, indicating a very slow radio evolution and a
strong interaction of the SN ejecta with the circumstellar medium. Our
late-time radio observations toward SN 2010P probe the dense circumstellar
envelope of this SN, and imply a mass-loss rate (Msun/yr) to wind velocity (in
units of 10 km/s) ratio of (3.0-5.1)E-05, with a 5 GHz peak luminosity of
~1.2E+27 erg/s/Hz on day ~464 after explosion. This is consistent with a Type
IIb classification for SN 2010P, making it the most distant and most slowly
evolving Type IIb radio SN detected to date.Comment: 14 pages, 8 tables and 7 figures. Accepted for publication in MNRA
The ALMA Frontier Fields Survey - IV. Lensing-corrected 1.1 mm number counts in Abell 2744, MACSJ0416.1-2403 and MACSJ1149.5+2223
[abridged] Characterizing the number counts of faint, dusty star-forming
galaxies is currently a challenge even for deep, high-resolution observations
in the FIR-to-mm regime. They are predicted to account for approximately half
of the total extragalactic background light at those wavelengths. Searching for
dusty star-forming galaxies behind massive galaxy clusters benefits from strong
lensing, enhancing their measured emission while increasing spatial resolution.
Derived number counts depend, however, on mass reconstruction models that
properly constrain these clusters. We estimate the 1.1 mm number counts along
the line of sight of three galaxy clusters, i.e. Abell 2744, MACSJ0416.1-2403
and MACSJ1149.5+2223, which are part of the ALMA Frontier Fields Survey. We
perform detailed simulations to correct these counts for lensing effects. We
use several publicly available lensing models for the galaxy clusters to derive
the intrinsic flux densities of our sources. We perform Monte Carlo simulations
of the number counts for a detailed treatment of the uncertainties in the
magnifications and adopted source redshifts. We find an overall agreement among
the number counts derived for the different lens models, despite their
systematic variations regarding source magnifications and effective areas. Our
number counts span ~2.5 dex in demagnified flux density, from several mJy down
to tens of uJy. Our number counts are consistent with recent estimates from
deep ALMA observations at a 3 level. Below 0.1 mJy, however,
our cumulative counts are lower by 1 dex, suggesting a flattening in
the number counts. In our deepest ALMA mosaic, we estimate number counts for
intrinsic flux densities 4 times fainter than the rms level. This
highlights the potential of probing the sub-10 uJy population in larger samples
of galaxy cluster fields with deeper ALMA observations.Comment: 19 pages, 14 figures, 3 tables. Accepted for publication in A&
Serendipitous discovery of the long-sought AGN in Arp 299-A
Context: The dusty nuclear regions of luminous infra-red galaxies (LIRGs) are
heated by either an intense burst of massive star formation, an active galactic
nucleus (AGN), or a combination of both. Disentangling the contribution of each
of those putative dust-heating agents is a challenging task, and direct imaging
of the innermost few pc can only be accomplished at radio wavelengths, using
very high-angular resolution observations. Aims: We observed the nucleus A of
the interacting starburst galaxy Arp 299, using very long baseline
interferometry (VLBI) radio observations at 1.7 and 5.0 GHz. Our aim was to
characterize the compact sources in the innermost few pc region of Arp 299-A,
as well as to detect recently exploded core-collapse supernovae. Methods: We
used the European VLBI Network (EVN) to image the 1.7 and 5.0 GHz compact radio
emission of the parsec-scale structure in the nucleus of Arp 299-A with
milliarcsecond resolution. Results: Our EVN observations show that one of the
compact VLBI sources, A1, previously detected at 5.0 GHz, has a flat spectrum
between 1.7 and 5.0 GHz and is the brightest source at both frequencies. Our
1.7 GHz EVN image shows also diffuse, low-surface brightness emission extending
westwards from A1 and displays a prominent core-jet structure. Conclusions: The
morphology, radio luminosity, spectral index and ratio of radio-to-X-ray
emission of the A1-A5 region is consistent with a low-luminosity AGN (LLAGN),
and rules out the possibility that it is a chain of young radio supernovae
(RSNe) and supernova remnants (SNRs). We therefore conclude that A1-A5 is the
long-sought AGN in Arp 299-A. This finding may suggest that both starburst and
AGN are frequently associated phenomena in mergers.Comment: Accepted for publication in Letters to Astronomy and Astrophysics on
12 August 2010. 4 pages, 1 figur
Core-collapse and Type Ia supernovae with the SKA
Core-collapse SNe (CCSNe): Systematic searches of radio emission from CCSNe
are still lacking, and only targeted searches of radio emission from just some
of the optically discovered CCSNe in the local universe have been carried out.
Optical searches miss a significant fraction of CCSNe due to dust obscuration;
CCSN radio searches are thus more promising for yielding the complete,
unobscured star-formation rates in the local universe. The SKA yields the
possibility to piggyback for free in this area of research by carrying out
commensal, wide-field, blind transient survey observations. SKA1-SUR should be
able to discover several hundreds of CCSNe in just one year, compared to about
a dozen CCSNe that the VLASS would be able to detect in one year, at most. SKA,
with an expected sensitivity ten times that of SKA1, is expected to detect
CCSNe in the local Universe by the thousands. Therefore, commensal SKA
observations could easily result in an essentially complete census of all CCSNe
in the local universe, thus yielding an accurate determination of the
volumetric CCSN rate. Type Ia SNe: We advocate for the use of the SKA to search
for the putative prompt (~first few days after the explosion) radio emission of
any nearby type Ia SN, via target-of-opportunity observations. The huge
improvement in sensitivity of the SKA with respect to its predecessors will
allow to unambiguously discern which progenitor scenario (single-degenerate vs.
double-degenerate) applies to them.Comment: Proceedings of Science: Advancing Astrophysics with the Square
Kilometre Array. Accepted version, including comments by the refere
The nature of supernovae 2010O and 2010P in Arp 299-I. Near-infrared and optical evolution
We present near-infrared and optical photometry, plus optical spectroscopy of two stripped-envelope supernovae (SNe) 2010O and 2010P that exploded in two different components of an interacting luminous infrared galaxy Arp 299 within only a few days of one another. SN 2010O is found to be photometrically and spectroscopically similar to many normal Type Ib SNe and our multiwavelength observations of SN 2010P suggest it to be a Type IIb SN. No signs of clear hydrogen features or interaction with the circumstellar medium are evident in the optical spectrum of SN 2010P. We derive estimates for the host galaxy line-of-sight extinctions for both SNe, based on both light curve and spectroscopic comparison finding consistent results. These methods are also found to provide much more robust estimates of the SN host galaxy reddening than the commonly used empirical relations between extinction and equivalent width of Na i D absorption features. The SN observations also suggest that different extinction laws are present in different components of Arp 299. For completeness, we study high-resolution pre-explosion images of Arp 299 and find both SNe to be close to, but not coincident with, extended sources that are likely massive clusters. A very simple model applied to the bolometric light curve of SN 2010O implies a rough estimate for the explosion parameters of E-k approximate to 3 x 10(51) erg, M-ej approximate to 2.9 M-circle dot and M-Ni approximate to 0.16 M-circle dot.</p
NUSTAR Unveils a Heavily Obscured Low-luminosity Active Galactic Nucleus in the Luminous Infrared Galaxy NGC 6286
We report the detection of a heavily obscured active galactic nucleus (AGN) in the luminous infrared galaxy (LIRG) NGC 6286 identified in a 17.5 ks Nuclear Spectroscopic Telescope Array observation. The source is in an early merging stage and was targeted as part of our ongoing NuSTAR campaign observing local luminous and ultra-luminous infrared galaxies in different merger stages. NGC 6286 is clearly detected above 10 keV and by including the quasi-simultaneous Swift/XRT and archival XMM-Newton and Chandra data, we find that the source is heavily obscured (NH sime(0.95ā1.32) Ć 1024 cmā2) with a column density consistent with being Compton-thick (CT, ). The AGN in NGC 6286 has a low absorption-corrected luminosity (L2ā10 keV ~ 3ā20 Ć 1041 erg sā1) and contributes lesssim1% to the energetics of the system. Because of its low luminosity, previous observations carried out in the soft X-ray band (<10 keV) and in the infrared did not notice the presence of a buried AGN. NGC 6286 has multiwavelength characteristics typical of objects with the same infrared luminosity and in the same merger stage, which might imply that there is a significant population of obscured low-luminosity AGNs in LIRGs that can only be detected by sensitive hard X-ray observations
The Core-Collapse Supernova Rate in Arp299 Revisited
We present a study of the CCSN rate in nuclei A and B1 of the luminous
infrared galaxy Arp299, based on 11 years of Very Large Array monitoring of
their radio emission at 8.4 GHz. Significant variations in the nuclear radio
flux density can be used to identify the CCSN activity in the absence of
high-resolution very long baseline interferometry observations. In the case of
the B1-nucleus, the small variations in its measured diffuse radio emission are
below the fluxes expected from radio supernovae, thus making it well-suited to
detect RSNe through flux density variability. In fact, we find strong evidence
for at least three RSNe this way, which results in a lower limit for the CCSN
rate of 0.28 +/- 0.16 per year. In the A-nucleus, we did not detect any
significant variability and found a SN detection threshold luminosity which
allows only the detection of the most luminous RSNe known. Our method is
basically blind to normal CCSN explosions occurring within the A-nucleus, which
result in too small variations in the nuclear flux density, remaining diluted
by the strong diffuse emission of the nucleus itself. Additionally, we have
attempted to find near-infrared counterparts for the earlier reported RSNe in
the Arp299 nucleus A, by comparing NIR adaptive optics images from the Gemini-N
telescope with contemporaneous observations from the European VLBI Network.
However, we were not able to detect NIR counterparts for the reported radio SNe
within the innermost regions of nucleus A. While our NIR observations were
sensitive to typical CCSNe at 300 mas from the centre of the nucleus A,
suffering from extinction up to A_v~15 mag, they were not sensitive to such
highly obscured SNe within the innermost nuclear regions where most of the EVN
sources were detected. (abridged)Comment: 12 pages, 4 figures and 7 tables. Accepted for publication in MNRA
SN 1978K: An evolved supernova outside our Local Group detected at millimetre wavelengths
Supernova 1978K is one of the oldest-known examples of the class of Type IIn supernovae that show evidence for strong interaction between the blast wave and a dense, pre-existing circumstellar medium. Here we report detections of SN 1978K at both 34 GHz and 94 GHz, making it only the third extragalactic supernova (after SN 1987A and SN 1996cr) to be detected at late-times at these frequencies. We find SN 1978K to be >400 times more luminous than SN 1987A at millimetre wavelengths in spite of the roughly nine year difference in ages, highlighting the risk in adopting SN 1987A as a template for the evolution of core-collapse supernovae in general. Additionally, from new VLBI observations at 8.4 GHz, we measure a deconvolved diameter for SN 1978K of ~5 milli-arcsec, and a corresponding average expansion velocity of <1500 km s-1. These observations provide independent evidence of an extremely dense circumstellar medium surrounding the progenitor star
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