Catching GRBS from the Ground

arXiv:1102.2112 [pdf, ps, other]

Catching GRBs with atmospheric Cherenkov telescopes

Rudy C. Gilmore, Joel R. Primack, Aurelien Bouvier, A. Nepomuk Otte

Comments: 4 pages, 3 figures, to appear in the Proceedings of "Gamma Ray Bursts 2010", held Nov. 1-4, 2010 in Annapolis, MD

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Fermi has shown GRBs to be a source of >10 GeV photons. We present an estimate of the detection rate of GRBs with a next generation Cherenkov telescope. Our predictions are based on the observed properties of GRBs detected by Fermi, combined with the spectral properties and redshift determinations for the bursts population by instruments operating at lower energies. While detection of VHE emission from GRBs has eluded ground-based instruments thus far, our results suggest that ground-based detection may be within reach of the proposed Cherenkov Telescope Array (CTA), albeit with a low rate, 0.25 - 0.5/yr. Such a detection would help constrain the emission mechanism of gamma-ray emission from GRBs. Photons at these energies from distant GRBs are affected by the UV-optical background light, and a ground-based detection could also provide a valuable probe of the Extragalactic Background Light (EBL) in place at high redshift.

Record Setting Binary

arXiv:1102.2102 [pdf, ps, other]

MAXI J1659-152: the shortest orbital period black-hole binary

E. Kuulkers (1), C. Kouveliotou (2), A.J. van der Horst (3), T. Belloni (4), J. Chenevez (5), A. Ibarra (1), T. Munoz-Darias (4), A. Bazzano (6), M. Cadolle Bel (1), G. De Cesare(6), M. Diaz Trigo (7), E. Jourdain (8), P. Lubinski (9), L. Natalucci (6), J.-U. Ness (1), A. Parmar (1), A.M.T. Pollock (1), J. Rodriguez (10), J.-P. Roques (8), C. Sanchez-Fernandez (1), P. Ubertini (6), C. Winkler (11) ((1) ESA/ESAC, Spain (2) NASA/MSFC, USA (3) USRA, USA (4) INAF - Brera Observatory, Italy (5) DTU Space, Copenhagen, Denmark (6) INAF/IASF Rome, Italy (7) ESO, Garching, Germany (8) IRAP, Toulouse, France (9) NCAC, Torun, Poland (10) CEA, Saclay, France (11) ESA/ESTEC, The Netherlands)

Comments: 5 pages, 4 figures, to be published in the proceedings of the 4th International MAXI Workshop `The First Year of MAXI: Monitoring variable X-ray sources', 2010 Nov 30 - Dec 2, Tokyo, Japan

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Following the detection of a bright new X-ray source, MAXI J1659-152, a series of observations was triggered with almost all currently flying high-energy missions. We report here on XMM-Newton, INTEGRAL and RXTE observations during the early phase of the X-ray outburst of this transient black-hole candidate. We confirm the dipping nature in the X-ray light curves. We find that the dips recur on a period of 2.4139+/-0.0005 hrs, and interpret this as the orbital period of the system. It is thus the shortest period black-hole X-ray binary known to date. Using the various observables, we derive the properties of the source. The inclination of the accretion disk with respect to the line of sight is estimated to be 60-75 degrees. The companion star to the black hole is possibly a M5 dwarf star, with a mass and radius of about 0.15 M_sun and 0.23 R_sun, respectively. The system is rather compact (orbital separation is about 1.35 R_sun) and is located at a distance of roughly 7 kpc. In quiescence, MAXI J1659-152 is expected to be optically faint, about 28 mag in the V-band.

Where are all the supernovae?

arXiv:1102.1977 [pdf, ps, other]

The Cosmic Core-collapse Supernova Rate does not match the Massive-Star Formation Rate

Shunsaku Horiuchi, John F. Beacom, Christopher S. Kochanek, Jose L. Prieto, K. Z. Stanek, Todd A. Thompson

Comments: 16 pages, 5 figures

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Solar and Stellar Astrophysics (astro-ph.SR)

We identify a "supernova rate problem": the measured cosmic core-collapse supernova rate is a factor ~ 2 smaller (with significance ~ 2 sigma) than that predicted from the measured cosmic massive-star formation rate. This comparison is critical for topics from galaxy evolution and enrichment to the abundance of neutron stars and black holes. We systematically explore possible resolutions. The precision and accuracy of the star formation rate data and conversion to the supernova rate are well supported, and proposed changes would have far-reaching consequences. The likely explanation is that many supernovae are missed because they are either optically faint or dark, whether intrinsically or due to obscuration. We investigate supernovae too faint to have been discovered in cosmic surveys by a detailed study of all supernova discoveries in the local volume. If possible supernova impostors are included, then faint supernovae are common enough by fraction to solve the supernova rate problem. If they are not included, then the rate of dark core collapses is likely substantial. The remaining alternative is that there is a surprising change required in the understanding of star formation or supernova rates. These possibilities can be distinguished by upcoming supernova surveys, searches for disappearing massive stars, and measurements of supernova neutrinos.

Black-Hole-Spheroid Mass Relation

arXiv:1102.1975 [pdf, ps, other]

The Relation between Black Hole Mass and Host Spheroid Stellar Mass out to z~2

Vardha Nicola Bennert (1), Matthew W. Auger (1), Tommaso Treu (1), Jong-Hak Woo (2), Matthew A. Malkan (3) ((1) UCSB, (2) Seoul National University, (3) UCLA)

Comments: 7 pages, 3 figures. Submitted to the Astrophysical Journal Letters

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We combine Hubble Space Telescope images from the Great Observatories Origins Deep Survey with archival Very Large Telescope and Keck spectra of a sample of 11 X-ray selected broad-line active galactic nuclei in the redshift range 1<z<2 to study the black hole mass - stellar mass relation out to a lookback time of 10 Gyrs. Stellar masses of the spheroidal component are derived from multi-filter surface photometry. Black hole masses are estimated from the width of the broad MgII emission line and the 3000A nuclear luminosity. We find evolution in the form M_BH/M_spheroid ~ (1+z)^(2.1+/-0.3), in agreement with our earlier studies based on spheroid luminosity. However, this result is more accurate because it does not require a correction for luminosity evolution and therefore avoids the related and dominant systematic uncertainty. We also measure total stellar masses. Combining our sample with data from the literature, we find M_BH/M_host ~ (1+z)^(1.41+/-0.12), consistent with the hypothesis that black holes (in the range M_BH ~ 10^8-9 M_sun) predate the formation of their host galaxies. Roughly one third of our objects reside in spiral galaxies with the majority showing no evidence of a bulge component; none of the host galaxies reveal signs of interaction or merger activity. Combined, our results indicate that secular evolution plays a non-negligible role in growing spheroids.