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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').
Advanced Search

To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"
  1. LIGO/Virgo/KAGRA S240422ed: WINTER near-infrared J-band observations
  2. LIGO/Virgo S240422ed: No counterpart candidates in INTEGRAL SPI-ACS prompt observation
  3. LIGO/Virgo/KAGRA S240422ed: Zwicky Transient Facility observations and candidates
  4. LIGO/Virgo/KAGRA S240422ed: GW-MMADS DECam observations
  5. LIGO/Virgo/KAGRA S240422ed: Magellan Observations
  6. LIGO/Virgo/KAGRA S240422ed: Updated NED Galaxies in the Localization Volume
  7. LIGO/Virgo/KAGRA S240422ed: AstroSat CZTI non-detection and upper limits
  8. LIGO/Virgo/KAGRA S240422ed: Upper limits from Fermi-GBM Observations
  9. LIGO/Virgo/KAGRA S240422ed: Updated Sky localization and EM Bright Classification
  10. LIGO/Virgo/KAGRA S240421ar: Upper limits from Swift/BAT-GUANO
  11. LIGO/Virgo/KAGRA S240422ed: Coverage and upper limits from MAXI/GSC observations
  12. LIGO/Virgo/KAGRA S240422ed: MeerLICHT and BlackGEM observations report
  13. LIGO/Virgo/KAGRA S240422ed: Identification of a GW compact binary merger candidate
  14. LIGO/Virgo/Kagra S240422ed: NED Galaxies in the Localization Volume
  15. LIGO/Virgo/KAGRA S240422ed: Global MASTER-Net observations report
  16. Fermi trigger No 735470374: Global MASTER-Net observations report
  17. GRB 240421A: Glowbug gamma-ray detection
  18. GRB 240414A: radio detection with the VLA
  19. Fermi-LAT gamma-ray observations of IceCube-240419A
  20. GRB 240414A: AMI-LA radio observations
  21. GRB 240414A: LBT optical detection
  22. GRB 240419B : MITSuME Akeno optical upper limits
  23. GRB 240415B: Swift-XRT observations
  24. GRB 240415A: Swift-XRT refined Analysis
  25. Fermi GRB 240422A: Global MASTER-Net observations report
  26. GRB 240421B: AstroSat CZTI detection
  27. GRB 240422A: Fermi GBM Final Real-time Localization
  28. GRB240421B: Zadko Observations
  29. Fermi GRB 240421B: Global MASTER-Net observations report
  30. Swift GRB 240421B: Global MASTER-Net observations report
  31. GRB 240421B: Fermi GBM Observation
  32. GRB 240421B: Swift-XRT refined Analysis
  33. GRB240421B: BOOTES-5/JGT optical upper limit
  34. GRB 240421B: J-band upper limits from WINTER
  35. GRB 240421B: Swift/UVOT Upper Limits
  36. GRB 240421B: Enhanced Swift-XRT position
  37. Fermi GRB 240421A: Global MASTER-Net observations report
  38. EP240417a: no counterpart detection by SOAR
  39. EP240420a: TNT upper limit to its optical counterpart
  40. EP240420a: Xinglong decaying optical counterpart
  41. GRB 240421B: Swift detection of a burst
  42. EP240420a: Nanshan optical counterpart observations
  43. EP240420a: GWAC-F50A optical upper limit
  44. LIGO/Virgo/KAGRA S240421ar: Identification of a GW unmodeled transient candidate
  45. GRB 240421A: Fermi GBM Final Real-time Localization
  46. EP240420a: detection of fading X-ray emission with refined position by EP-FXT
  47. EP240420a: NOT optical counterpart candidate and potential host
  48. Fermi trigger No 735280430: Global MASTER-Net observations report
  49. GRB240419A: Skynet Optical Afterglow Analysis
  50. GRB240418A - Candidate afterglow from NIRES
  51. IceCube Alert 240419.98: Global MASTER-Net observations report
  52. GRB 240419B: Swift/UVOT Upper Limits
  53. IceCube-240419A - IceCube observation of a high-energy neutrino candidate track-like event
  54. IceCube-240419A - IceCube observation of a high-energy neutrino candidate track-like event
  55. EP240420a: EP-WXT detection of a fast X-ray transient
  56. GRB 240419A: Swift/UVOT Upper Limits
  57. GRB 240419B: Swift-XRT refined Analysis
  58. GRB 240419B: optical afterglow from the NOT
  59. LIGO/Virgo/KAGRA S240420aw: Retraction of GW compact binary merger candidate
  60. EP240414a: Near-IR observations with NIRES and WINTER
  61. Swift GRB 240419B: Global MASTER-Net observations report
  62. EP240414A: Terskol Zeiss-2000 optical upper limit
  63. GRB 240419B: Enhanced Swift-XRT position
  64. Swift GRB 240419A: Global MASTER-Net observations report
  65. GRB 240418A: Swift/UVOT Upper Limits
  66. GRB 240419A: REM NIR afterglow detection
  67. GRB 240419A: Swift-XRT refined Analysis
  68. GRB 240418A: Swift-XRT refined Analysis
  69. GRB 240419B: Swift detection of a burst
  70. GRB 240411B: Swift/UVOT Detection
  71. EP240417a: YAHPT Optical Upper Limits
  72. GRB240418A: YAHPT Upper Limits
  73. GRB 240419A: VLT/UVES redshift of z = 5.178
  74. GRB 240419A: VLT optical afterglow detection
  75. GRB 240419A: Enhanced Swift-XRT position
  76. Fermi trigger No 735089036: Global MASTER-Net observations report
  77. EP240416a: J-band observations with WINTER
  78. EP240414a: GMG observation
  79. GRB 240419A: Prompt enhanced Swift-XRT position
  80. GRB 240419A: Swift detection of a burst
  81. GRB 240418A: TSHAO Zeiss-1000 optical upper limit
  82. GRB 240418A: NOT optical upper limits
  83. GRB 240418A: Enhanced Swift-XRT position
  84. GRB 240418A: AKO Upper Limit
  85. GRB 240411A: GOTO early optical upper limits
  86. Swift GRB240418.85: Global MASTER-Net observations report
  87. GRB 240418A: Swift detection of a burst
  88. EP240417a: EP-WXT detection of a fast X-ray transient
  89. Fermi GRB 240417A: Global MASTER-Net observations report
  90. LIGO/Virgo/KAGRA S240413p: X-ray upper limits from EP-WXT for the candidate AGN counterpart
  91. EP240416A: Terskol Zeiss-2000 optical upper limit
  92. EP240416A: Khureltogoot optical upper limit
  93. Improved IPN triangulation of GRB 240411A
  94. EP240416a: BOOTES-2/TELMA Optical Upper Limit
  95. EP240414a: GSP detects optical candidate counterpart AT2024gsa
  96. LIGO/Virgo/KAGRA S240413p: DECam GW-MMADS candidates
  97. IceCube-Cascade 240416A: Upper limits from a search for additional neutrino events in IceCube
  98. GRB 240417A: Fermi GBM Final Real-time Localization
  99. EP240414a: Pan-STARRS detects re-brightening of the candidate counterpart AT2024gsa
  100. LIGO/Virgo/KAGRA S240413p: historical ATLAS and ZTF observations of the candidate AGN counterpart

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