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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
  1. LIGO/Virgo/KAGRA S240430ca: Identification of a GW compact binary merger candidate
  2. LIGO/Virgo/KAGRA S240422ed: GECKO/7DT ToO observations
  3. Additional DECam GW-MMADS Candidates from three nights of observations
  4. GRB 240425A: GRBAlpha detection
  5. Fermi-LAT gamma-ray observations of IceCube-240424A
  6. LIGO/Virgo/KAGRA S240426s: Updated Sky localization
  7. LIGO/Virgo/KAGRA S240422ed: SRG/eROSITA archival upper limit for EP240426a
  8. LIGO/Virgo/KAGRA S240426dl: Updated Sky localization
  9. GRB 240429A: Fermi GBM Final Real-time Localization
  10. LIGO/Virgo/KAGRA S240428dr: Updated Sky localization
  11. LIGO/Virgo/KAGRA S240422ed: GECKO/KMTNet ToO observations
  12. LIGO/Virgo/KAGRA S240429an: Retraction of GW compact binary merger candidate
  13. LIGO/Virgo/KAGRA S240422ed: ENGRAVE VLT/XShooter spectroscopy of the host galaxy of J-GEM24a
  14. LIGO/Virgo/KAGRA S240428dr: Identification of a GW compact binary merger candidate
  15. Fermi GRB 240428A: Global MASTER-Net observations report
  16. GRB 240428A: Fermi GBM Final Real-time Localization
  17. LIGO/Virgo/KAGRA S240422ed: J-band non-detection of J-GEM24a
  18. LIGO/Virgo/KAGRA S240422ed: DDOTI Optical Upper Limit for J-GEM24a
  19. EP240426b: AST3-2 optical upper limit
  20. LIGO/Virgo/KAGRA S240422ed: Observations with 1.6m Mephisto
  21. LIGO/Virgo/KAGRA S240422ed: A transient discovered from Subaru/MOIRCS near-infrared observations by J-GEM Collaboration
  22. LIGO/Virgo S240422ed: Swift XRT observation of EP240426a
  23. LIGO/Virgo/KAGRA S240422ed: NOT optical observations of EP240426a
  24. EP240426b: EP-WXT detection of a new fast X-ray transient
  25. LIGO/Virgo/KAGRA S240422ed: Archival radio detection of EP240426a
  26. LIGO/Virgo/KAGRA S240422ed: Swope Follow-up of AT2024hfq, AT2024hfr, AT2024hfs, and AT2024hfx
  27. LIGO/Virgo/KAGRA S240422ed: BOOTES-6/DPRT optical upper limits for EP240426a
  28. LIGO/Virgo/KAGRA S240422ed: GRANDMA Optical Upper Limits for EP240426a
  29. LIGO/VIRGO/KAGRA S240422ed: Historical variability for EP240426a
  30. GRB 240426A: AstroSat CZTI detection
  31. EP240426a: YAHPT optical upper limit
  32. XMM-Newton observation of EP240426a
  33. LIGO/Virgo/KAGRA S240426dl: Identification of a GW compact binary merger candidate
  34. LIGO/Virgo/KAGRA S240422ed: BOOTES-4/MET Optical Upper Limits for EP240426a
  35. LIGO/Virgo/KAGRA S240422ed: EP-FXT Detection of the Potential Opitcal Electromagnetic Counterpart AT 2024hfq Reported by DECam
  36. GRB 240414A: NOEMA detection
  37. LIGO/Virgo/KAGRA S240422ed: EP240426a possible optical detection
  38. LIGO/Virgo/KAGRA S240422ed: Continued Magellan Observations
  39. EP240426a: GMG optical upper limit
  40. LVK S240422ed: Further Swift-XRT followup of three sources
  41. LIGO/Virgo/KAGRA S240422ed: EP-FXT detection of a candidate counterpart EP240426a
  42. LIGO/Virgo/KAGRA S240426s: Identification of a GW compact binary merger candidate
  43. LIGO/Virgo/KAGRA S240422ed: Magellan Follow-up Observations of Swift/XRT candidates
  44. LIGO/Virgo/KAGRA S240422ed: Zwicky Transient Facility contuinued observations of S240422ed and candidate analysis
  45. IceCube-240424A: Upper limits from a search for additional neutrino events in IceCube
  46. LIGO/Virgo/KAGRA S240422ed: GOTO counterpart search update and AT2024hfx, AT2024hgl observations
  47. S240422ed: BlackGEM/MeerLICHT transient detection AT2024hgl/MLTJ080628.10-250116.4
  48. LIGO/Virgo/KAGRA S240422ed: PRIME near-infrared observations
  49. LIGO/Virgo/KAGRA S240422ed: 2.5m PRL Telescope follow-up of the Swift/XRT source S240422ed_X190
  50. S240422ed: MeerLICHT/BlackGEM photometry on AT2024hfx and archival ZTF detection
  51. LIGO/Virgo/KAGRA S240422ed: Second night Pan-STARRS observations of the skymap
  52. LIGO/Virgo/KAGRA S240422ed: Further near-infrared observations with Subaru/MOIRCS by J-GEM Collaboration
  53. LIGO/Virgo/KAGRA S240422ed: X-ray Upper Limits from EP-FXT for the Potential Electromagnetic Counterparts Reported by Swift and DECam
  54. LIGO/Virgo/KAGRA S240422ed: Upper limits from GECAM Observations
  55. LIGO/Virgo/KAGRA S240422ed: No significant candidates in GRANDMA and Kilonova-Catcher galaxy targeting observations
  56. LIGO/Virgo/KAGRA S240422ed: Additional DECam GW-MMADS Candidates from the first two nights of observations
  57. LIGO/Virgo/KAGRA S240422ed: ANU 2.3m followup of candidate counterparts
  58. LIGO/Virgo/KAGRA S240422ed: Magellan Spectrum of GW-MMADS Candidate AT2024hdo Indicates a Type II SN
  59. GRB 240425A: Fermi GBM Final Real-time Localization
  60. Fermi trigger No 735697285: Global MASTER-Net observations report
  61. LIGO/Virgo/KAGRA S240422ed: SRG/eROSITA archival upper limits for Swift/XRT candidates
  62. GRB 240419B: Swift-BAT refined analysis
  63. GRB 240421B: Swift-BAT refined analysis
  64. GRB 240422A: Glowbug gamma-ray detection
  65. LIGO/Virgo/KAGRA S240422ed: Archival BlackGEM/MeerLICHT detections of AT 2024hdr & AT 2024hdq
  66. LIGO/Virgo/KAGRA S240413p: DESGW DECam Follow-Up
  67. LIGO/Virgo/KAGRA S240422ed: Himalayan Chandra Telescope follow-up of the Swift/XRT source S240422ed_X101
  68. LIGO/Virgo/KAGRA S240422ed: No significant counterpart candidates in HAWC observations
  69. LIGO/Virgo/KAGRA S240422ed: Vetting of DECam Candidates Using Real-Time Resources and SAGUARO Infrastructure
  70. LIGO/Virgo/KAGRA S240422ed: No significant candidates in GRANDMA/FRAM Observations
  71. IceCube-240424A - IceCube observation of a high-energy neutrino candidate track-like event
  72. LIGO/Virgo/KAGRA S240422ed: X-ray Upper Limits from EP-WXT for the Potential Electromagnetic Counterparts Reported by Swift and DECam
  73. LIGO/Virgo/KAGRA S240422ed: MOSFIRE spectroscopy of the DECam GW-MMADS candidate AT 2024hdn
  74. LIGO/Virgo/KAGRA S240422ed: ATCA follow-up of candidate counterparts
  75. LIGO/Virgo/KAGRA S240422ed: MOSFIRE imaging of the DECam GW-MMADS candidate AT 2024hdm
  76. LIGO/Virgo S240422ed: Swift-XRT detection of 3 possible counterparts
  77. LIGO/Virgo/KAGRA S240422ed: Early X-ray Upper Limits from EP-WXT for the LVK Sky Localization Region
  78. LIGO/Virgo/KAGRA S240422ed: J-band non-detection of Mag24a
  79. LIGO/Virgo/KAGRA S240422ed: Continued Imaging of Mag24a
  80. LIGO/Virgo/KAGRA S240422ed: Archival DECaPSs2 observations of the field of Mag24a
  81. LIGO/Virgo/KAGRA S240422ed: DECam GW-MMADS Candidates
  82. LIGO/Virgo/KAGRA S240422ed: Potential Magellan candidates from GCN 36263 are unrelated.
  83. LIGO/Virgo/KAGRA S240422ed: NOT J-band upper limit on the Swift/XRT source S240422ed_X61
  84. LIGO/Virgo/KAGRA S240422ed: X-ray Upper Limits from EP-WXT for the Three Potential Electromagnetic Counterparts Reported So Far
  85. GRB 240421B: GRBAlpha detection
  86. IceCube Alert 240424.08: Global MASTER-Net observations report
  87. LIGO/Virgo/KAGRA S240422ed: Magellan Detection of a Potential Electromagnetic Counterpart
  88. LIGO/Virgo/KAGRA S240422ed: SAGUARO upper limits from CSS
  89. LIGO/Virgo/KAGRA S240422ed: Subaru/MOIRCS near-infrared observations by J-GEM Collaboration
  90. LIGO/Virgo/KAGRA S240422ed: LAST optical observations
  91. LIGO/Virgo/KAGRA S240422ed: Potential Candidates from Magellan galaxy-based search
  92. LIGO/Virgo/KAGRA S240422ed: WINTER J-band upper limits on the Swift/XRT source S240422ed_X61
  93. IceCube-240419A: Upper limits from a search for additional neutrino events in IceCube
  94. LIGO/Virgo/KAGRA S240421ar: Updated Sky localization
  95. LIGO/Virgo/KAGRA S240422ed: GW-MMADS DECam upper limits on the Swift/XRT source S240422ed_X61
  96. LIGO/Virgo/KAGRA S240422ed: no candidate counterparts from Pan-STARRS observations of the skymap
  97. LIGO/Virgo/KAGRA S240422ed: GOTO counterpart search
  98. LIGO/Virgo/KAGRA S240422ed: No Counterparts in DDOTI/OAN Optical Observations
  99. GRB 240419A: Swift-BAT refined analysis
  100. GRB 240418A: Swift-BAT refined analysis

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