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Its membership of about 7, individuals also includes physicists, mathematicians, geologists, engineers, and others whose research and educational interests lie within the broad spectrum of subjects comprising contemporary astronomy. The mission of the AAS is to enhance and share humanity's scientific understanding of the universe. The Institute of Physics IOP is a leading scientific society promoting physics and bringing physicists together for the benefit of all.
It has a worldwide membership of around 50 comprising physicists from all sectors, as well as those with an interest in physics. It works to advance physics research, application and education; and engages with policy makers and the public to develop awareness and understanding of physics. Its publishing company, IOP Publishing, is a world leader in professional scientific communications. Leo P. Singer 32,1,2Mansi M. Kasliwal 3S. Bradley Cenko 2,4Daniel A. Perley 33,5Gemma E. Anderson 6,7G. Fender 6,7Derek B. Rebbapragada 12Tim D. Staley 6,7Dmitry Svinkin 29C. The American Astronomical Society.
All rights reserved. Singer et al ApJ What is article data? Get permission to re-use this article. PetersburgRussia. Receive alerts on all new research papers in American Astronomical Society A A S journals as soon as they are published. Select your desired journals and corridors below. You will need to select a minimum of one corridor. What are corridors? However, the coarse localizations of tens to a hundred square degrees provided by the Fermi GRB Monitor instrument have posed a formidable obstacle to locating the bursts' host galaxies, measuring their redshifts, and tracking their panchromatic afterglows.
We have built a target-of-opportunity mode for the intermediate Palomar Transient Factory in order to perform targeted searches for Fermi afterglows. Here, we present the of one year of this program: 8 afterglow discoveries out of 35 searches. We present our broadband follow-up including spectroscopy as well as X-ray, UV, optical, millimeter, and radio observations.
We identify one new outlier on the Amati relation. We find that two bursts are consistent with a mildly relativistic shock breaking out from the progenitor star rather than the ultra-relativistic internal shock mechanism that powers standard cosmological bursts. Finally, in the context of the Zwicky Transient Facility, we discuss how we will continue to expand this effort to find optical counterparts of binary neutron star mergers that may soon be detected by Advanced LIGO and Virgo.
PTF has even blindly detected the optical emission Cenko et al. Cenko et al. PTF has also detected explosions that optically resemble GRB afterglows but may entirely lack gamma-ray emission Cenko et al. GRBs and their broadband afterglows are notoriously challenging to capture. They naturally evolve from bright to faint, and from high gamma- and hard X-ray to low optical and radio photon energies, with information encoded Iso a needle in a haystack energy scales from 1 to 10 16 GHz Perley et al. Only with a rapid sequence of handoffs between facilities graded by energy passband, FOV, and position accuracy have we been able to find them, pinpoint their host galaxies, and constrain their physics.
The Swift mission Gehrels et al. Consequently, their redshifts and the properties of their afterglows have remained largely unknown. This target-of-opportunity TOO capability uses and briefly redirects the infrastructure of our ongoing synoptic survey, notably the machine learning software and the instrumental pipeline composed of the Palomar 48 inch Oschin telescope P48; Rahmer et al.
In Singer et al. First, it was detected by Fermi LAT. Third, due to its low redshift, an accompanying SN was spectroscopically detectable. In each of the eight cases, the association between the optical transient and the GRB was proven by the presence of high-redshift absorption lines in the optical spectra and the coincident detection of a rapidly fading X-ray source with Swift XRT. In two cases, the positions were further corroborated by accurate Fermi LAT error circles, and in four cases by accurate Inter Planetary Network IPN triangulations involving distant spacecraft.
In one case GRB Athe IPN triangulation was performed rapidly and was instrumental in selecting which optical transient candidates to follow up. In six cases, radio afterglows were detected. Our discovery rate of 8 out of 35 events is consistent with the ages and searched areas of the GBM bursts, combined with the luminosity function of optical afterglows. We provide basic physical interpretations of the broadband spectral energy distributions SEDs of these afterglows. We find that seven of the events are consistent with the classic model of synchrotron cooling of electrons that have been accelerated by a single forward shock encountering either the constant-density circumburst interstellar medium ISM; broadband behavior predicted in Sari et al.
We find that although the gamma-ray energetics of these eight bursts are broadly similar to the Swift sample, two low-luminosity bursts GRB A and B have ificantly lower kinetic energies. We conclude by discussing prospects for targeted optical transient searches in wide areas. This is especially relevant for optical counterparts of gravitational wave GW events.
Upon receiving either kind of notice, the TOO Marshal determines if the best-estimate sky position is observable from Palomar at any time within the 24 hr after the trigger. The criterion for observability is that the position is at an altitude i. Paciesas et al. We use the weighted rms of these two values. The total error radius is then.
We construct a Fisher—von Mises distribution, centered on the best-estimate position, with a concentration parameter of. If the localization has ificant asymmetry, we also retrieve a 2D FITS image whose pixel values correspond to the GBM localization ificance, and use this instead of the Fisher—von Mises distribution. Giving preference to fields for which deep co-added reference images exist, the TOO Marshal selects 10 P48 fields spanning an area of deg 2 to maximize the probability of enclosing the true but as yet unknown location of the source, assuming the above distribution.
The Marshal then immediately contacts a team of humans the authors by SMS text message, telephone, and e-mail. The humans are directed to a mobile-optimized web application to trigger the P48 see Figure 11 in the Appendix.
Within the above constraints, we decide whether to follow up the burst based on the following criteria. We discard any bursts that are detected and accurately localized by Swift BAT, because these are more efficiently followed up by conventional means. We also give preference to events that are out of the Galactic plane and that are observable for at least 3 hr. There are some exceptional circumstances that override these considerations.
If the burst's position estimate is accessible within an hour after the burst, we may select it even if the observability window is very brief. If the burst is very well localized or has the possibility of a substantially improved localization later due to a LAT or IPN detection, we may select it even if it is in the Galactic plane.
The default observing program is three epochs of P48 images at a minute cadence. The human may shorten or lengthen the cadence if the burst is very young or old see the discussion of Equation 2 in Section 2. The robot adds the requested fields to the night's schedule with the highest possible priority, ensuring that they are observed as soon as they are visible. Nugent et al. The real-time pipeline creates difference images between the new P48 observations and co-added references composed of observations from months or years earlier. It generates candidates by performing source extraction on the difference images.
Table 1 lists the of candidates that remain after each stage of candidate selection. When the image subtraction pipeline has finished analyzing at least two successive epochs of any one field, the TOO Marshal contacts the humans again Iso a needle in a haystack the surviving candidates are presented to the humans via the Treasures portal. The remaining candidate vetting steps currently involve human participation and are informed by the nature of the other transients that iPTF commonly detects: foreground SNe slowly varying and in low- z host galaxiesactive galactic nuclei AGNscataclysmic variables, and M-dwarf flares.
We visually assess each candidate's image subtraction residual compared to the neighboring stars of similar brightness in the new image. If the residual resembles the new image's point-spread function, then the candidate is considered likely to be a genuine transient or variable source. Next, we look at the photometric history of the candidates. Given the time, tof the optical observation relative to the burst and the cadence,we expect that a typical optical afterglow that decays as a power lawwithwould fade by mag over the course of our observations.
Any source that exhibits statistically ificant fading consistent with an afterglow decay becomes a prime target. Note that a decay in brightness requires such a source to be. Noting that long GRBs preferentially occur at high redshifts and in intrinsically small, faint galaxies Svensson et al.
If a Iso a needle in a haystack source is near a spatially resolved galaxy, then we compute its distance modulus using the galaxy's redshift or photometric redshift from SDSS. Therefore, if the candidate's pd host galaxy would give it an absolute magnitude mag, it is considered promising. The human saves all candidates that are considered promising by these measures to the iPTF Transient Marshal database. This step baptizes them with an iPTF transient name, which consists of the last two digits of the year and a sequential alphabetic deation.
Once named in the Transient Marshal, we perform archival vetting of each candidate using databases including VizieR Ochsenbein et al. M dwarfs can produce bright, blue, rapidly Iso a needle in a haystack optical flares that can mimic optical afterglows. Therefore, a source that is detectable in WISE but that is either absent from or very faint in the iPTF reference images suggests a quiescent dwarf star.
If, by this point, data from Fermi LAT or from IPN satellites are available, we can use the improved localization to select an even smaller of follow-up targets. For sources whose photometric evolution is not clear, we perform photometric follow-up. We may schedule additional observations of some of the P48 fields if a ificant of candidates are in the same field. We may also use the P48 to gather more photometry for sources that are superimposed on a quiescent source or galaxy, in order to make use of the image subtraction pipeline to automatically obtain host-subtracted magnitudes. For isolated sources, we schedule one or more epochs of r -band photometry with the P If, by this point, any candidates show strong evidence of fading, we begin multicolor photometric monitoring with the P A spectrum that has a relatively featureless continuum and high-redshift absorption lines secures the classification of the candidate as an optical afterglow.
Detection of a radio or X-ray afterglow typically confirms the nature of the optical transient, even without spectroscopy. To monitor the optical evolution of afterglows identified by our program, we typically request nightly observations in ri and occasionally gz filters for as long as the afterglow remained detectable. Bias subtraction, flat-fielding, and other basic reductions are performed automatically at Palomar by the P60 automated pipeline using standard techniques.
Photometry of the optical afterglow is then performed in IDL using a custom aperture-photometry routine, calibrated relative to SDSS secondary standards in the field when available or using our own solution for secondary field standards constructed during a photometric night for fields outside the SDSS footprint. Standard CCD reduction techniques e. All observations are conducted at 93 GHz in single-polarization mode in the array's C, D, or E configuration.
Targets are typically observed once for 1—3 hr within a few days after the GRB, establishing the phase calibration using periodic observations of a nearby phase calibrator and the bandpass and the flux calibration by observations of a standard source at the start of the track.
If detected, we acquire additional observations in approximately logarithmically spaced time intervals until the afterglow flux falls below detection limits. We look for radio afterglows at 6. The calibration is performed using the VLA calibration pipeline. After running the pipeline, we inspect the data calibrators and target source and apply further flagging when needed.
The VLA measurement errors are a combination of the rms map error, which measures the contribution of small unresolved fluctuations in the background emission and random map fluctuations due to receiver noise, and a basic fractional error here estimated to bewhich s for inaccuracies of the flux density calibration. These errors are added in quadrature, and total errors are reported in Table 3.
Starting in August, we also look for radio emission with AMI. AMI is composed of eight For further details on the reduction and analysis performed on the AMI observations please see Anderson et al. To date, we have successfully followed up 35 Fermi GBM bursts and detected eight optical afterglows. The detections are listed in Table 4and all of the P48 tilings are listed in Table 5. Figure 1 shows the GBM localizations and P48 tilings for the detected bursts.
In Figure 2the light curves are shown in the context of a comprehensive sample of long GRB afterglows compiled by D. Kannprivate communication. Figure 1. The positions of the optical transients are marked with black diamonds. Only a portion of this table is shown here to demonstrate its form and content.Iso a needle in a haystack
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Iso a needle in a haystack