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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. IceCube Alert 240424.08: Global MASTER-Net observations report
  2. LIGO/Virgo/KAGRA S240422ed: Magellan Detection of a Potential Electromagnetic Counterpart
  3. LIGO/Virgo/KAGRA S240422ed: SAGUARO upper limits from CSS
  4. LIGO/Virgo/KAGRA S240422ed: Subaru/MOIRCS near-infrared observations by J-GEM Collaboration
  5. LIGO/Virgo/KAGRA S240422ed: LAST optical observations
  6. LIGO/Virgo/KAGRA S240422ed: Potential Candidates from Magellan galaxy-based search
  7. LIGO/Virgo/KAGRA S240422ed: WINTER J-band upper limits on the Swift/XRT source S240422ed_X61
  8. IceCube-240419A: Upper limits from a search for additional neutrino events in IceCube
  9. LIGO/Virgo/KAGRA S240421ar: Updated Sky localization
  10. LIGO/Virgo/KAGRA S240422ed: GW-MMADS DECam upper limits on the Swift/XRT source S240422ed_X61
  11. LIGO/Virgo/KAGRA S240422ed: no candidate counterparts from Pan-STARRS observations of the skymap
  12. LIGO/Virgo/KAGRA S240422ed: GOTO counterpart search
  13. LIGO/Virgo/KAGRA S240422ed: No Counterparts in DDOTI/OAN Optical Observations
  14. GRB 240419A: Swift-BAT refined analysis
  15. GRB 240418A: Swift-BAT refined analysis
  16. LXT240402A/GRB240402B: Chandra X-ray detection
  17. LIGO/Virgo/KAGRA S240423br: Retraction of GW compact binary merger candidate
  18. LIGO/Virgo/KAGRA S240422ed: no candidate counterparts from ATLAS observations
  19. GRB 240419A: Possible ATCA radio detection
  20. GRB 240421B: ATCA radio observations
  21. LIGO/Virgo/KAGRA S240422ed: WINTER near-infrared J-band observations
  22. LIGO/Virgo S240422ed: No counterpart candidates in INTEGRAL SPI-ACS prompt observation
  23. LIGO/Virgo/KAGRA S240422ed: Zwicky Transient Facility observations and candidates
  24. LIGO/Virgo/KAGRA S240422ed: GW-MMADS DECam observations
  25. LIGO/Virgo/KAGRA S240422ed: Magellan Observations
  26. LIGO/Virgo/KAGRA S240422ed: Updated NED Galaxies in the Localization Volume
  27. LIGO/Virgo/KAGRA S240422ed: AstroSat CZTI non-detection and upper limits
  28. LIGO/Virgo/KAGRA S240422ed: Upper limits from Fermi-GBM Observations
  29. LIGO/Virgo/KAGRA S240422ed: Updated Sky localization and EM Bright Classification
  30. LIGO/Virgo/KAGRA S240421ar: Upper limits from Swift/BAT-GUANO
  31. LIGO/Virgo/KAGRA S240422ed: Coverage and upper limits from MAXI/GSC observations
  32. LIGO/Virgo/KAGRA S240422ed: MeerLICHT and BlackGEM observations report
  33. LIGO/Virgo/KAGRA S240422ed: Identification of a GW compact binary merger candidate
  34. LIGO/Virgo/Kagra S240422ed: NED Galaxies in the Localization Volume
  35. LIGO/Virgo/KAGRA S240422ed: Global MASTER-Net observations report
  36. Fermi trigger No 735470374: Global MASTER-Net observations report
  37. GRB 240421A: Glowbug gamma-ray detection
  38. GRB 240414A: radio detection with the VLA
  39. Fermi-LAT gamma-ray observations of IceCube-240419A
  40. GRB 240414A: AMI-LA radio observations
  41. GRB 240414A: LBT optical detection
  42. GRB 240419B : MITSuME Akeno optical upper limits
  43. GRB 240415B: Swift-XRT observations
  44. GRB 240415A: Swift-XRT refined Analysis
  45. Fermi GRB 240422A: Global MASTER-Net observations report
  46. GRB 240421B: AstroSat CZTI detection
  47. GRB 240422A: Fermi GBM Final Real-time Localization
  48. GRB240421B: Zadko Observations
  49. Fermi GRB 240421B: Global MASTER-Net observations report
  50. Swift GRB 240421B: Global MASTER-Net observations report
  51. GRB 240421B: Fermi GBM Observation
  52. GRB 240421B: Swift-XRT refined Analysis
  53. GRB240421B: BOOTES-5/JGT optical upper limit
  54. GRB 240421B: J-band upper limits from WINTER
  55. GRB 240421B: Swift/UVOT Upper Limits
  56. GRB 240421B: Enhanced Swift-XRT position
  57. Fermi GRB 240421A: Global MASTER-Net observations report
  58. EP240417a: no counterpart detection by SOAR
  59. EP240420a: TNT upper limit to its optical counterpart
  60. EP240420a: Xinglong decaying optical counterpart
  61. GRB 240421B: Swift detection of a burst
  62. EP240420a: Nanshan optical counterpart observations
  63. EP240420a: GWAC-F50A optical upper limit
  64. LIGO/Virgo/KAGRA S240421ar: Identification of a GW unmodeled transient candidate
  65. GRB 240421A: Fermi GBM Final Real-time Localization
  66. EP240420a: detection of fading X-ray emission with refined position by EP-FXT
  67. EP240420a: NOT optical counterpart candidate and potential host
  68. Fermi trigger No 735280430: Global MASTER-Net observations report
  69. GRB240419A: Skynet Optical Afterglow Analysis
  70. GRB240418A - Candidate afterglow from NIRES
  71. IceCube Alert 240419.98: Global MASTER-Net observations report
  72. GRB 240419B: Swift/UVOT Upper Limits
  73. IceCube-240419A - IceCube observation of a high-energy neutrino candidate track-like event
  74. IceCube-240419A - IceCube observation of a high-energy neutrino candidate track-like event
  75. EP240420a: EP-WXT detection of a fast X-ray transient
  76. GRB 240419A: Swift/UVOT Upper Limits
  77. GRB 240419B: Swift-XRT refined Analysis
  78. GRB 240419B: optical afterglow from the NOT
  79. LIGO/Virgo/KAGRA S240420aw: Retraction of GW compact binary merger candidate
  80. EP240414a: Near-IR observations with NIRES and WINTER
  81. Swift GRB 240419B: Global MASTER-Net observations report
  82. EP240414A: Terskol Zeiss-2000 optical upper limit
  83. GRB 240419B: Enhanced Swift-XRT position
  84. Swift GRB 240419A: Global MASTER-Net observations report
  85. GRB 240418A: Swift/UVOT Upper Limits
  86. GRB 240419A: REM NIR afterglow detection
  87. GRB 240419A: Swift-XRT refined Analysis
  88. GRB 240418A: Swift-XRT refined Analysis
  89. GRB 240419B: Swift detection of a burst
  90. GRB 240411B: Swift/UVOT Detection
  91. EP240417a: YAHPT Optical Upper Limits
  92. GRB240418A: YAHPT Upper Limits
  93. GRB 240419A: VLT/UVES redshift of z = 5.178
  94. GRB 240419A: VLT optical afterglow detection
  95. GRB 240419A: Enhanced Swift-XRT position
  96. Fermi trigger No 735089036: Global MASTER-Net observations report
  97. EP240416a: J-band observations with WINTER
  98. EP240414a: GMG observation
  99. GRB 240419A: Prompt enhanced Swift-XRT position
  100. GRB 240419A: Swift detection of a burst

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