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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"

32502 results found.

  1. GRB 250315A/EP250315A: Fermi-GBM Sub-Threshold Detection
  2. GRB 250314A: EP-FXT afterglow detection
  3. EP250315a: refined analysis of the EP-WXT and EP-FXT observations
  4. GRB 250314A: Swift/UVOT Upper Limits
  5. GRB 250312B: GRBAlpha detection
  6. GRB 250314A: Swift XRT Detection
  7. EP250315a: optical counterpart candidate detected by Gemini North
  8. GRB 250314A: VLT/X-shooter dropout, redshift z ~ 7.3
  9. GRB 250226A: Mondy AZT-33IK and Koshka Zeiss-1000 Optical Upper Limits
  10. SVOM/MXT upper limit on GRB 250314A
  11. GRB 250314A: SVOM/VT upper limit
  12. GRB 250314A: NOT near-infrared candidate counterpart
  13. GRB 250313A: Fermi GBM Detection
  14. GRB 250313A: CALET Gamma-Ray Burst Monitor detection
  15. GRB 250312B: Fermi GBM Observation
  16. GRB250314A: SVOM/VT lack of bright optical candidate from VHF data
  17. Konus-Wind detection of GRB 250313A
  18. Konus-Wind detection of GRB 250308A
  19. EP250311a/GRB 250311A: Correction to EP-WXT detection time
  20. GRB 250313A: SVOM/GRM observation of a bright long burst
  21. FRB 20250206A: Nondetection of Repeating Bursts from FRB 20250206A with FAST
  22. GRB 250313A: AstroSat CZTI detection of a bright long burst
  23. IceCube-250309A: MASTER detection of J140105.33-091631.6 blazar flare with Zhirkov effect
  24. GRB 250313A: Fermi-LAT detection
  25. GRB 250313A: Swift ToO observations
  26. EP250304a: Pan-STARRS r and i-band imaging and photometry
  27. GRB 250312B: Swift/BAT-GUANO localization skymap of a burst
  28. EP trigger ID 01709061302: Lick/Kast spectroscopy with the 3 m Shane telescope
  29. Fermi GRB 250313A: Global MASTER-Net observations report
  30. GRB 250309B: PRIME near-infrared upper limits in 2nd epoch
  31. EP250304a: SVOM/VT optical observation
  32. EP250311a/GRB 250311A: EP-FXT follow-up observation
  33. ATCA detection of the radio counterpart of GRB 250309B-AT2025dws
  34. EP250302a: Chandra X-ray Detection
  35. Fermi GRB 250312B: Global MASTER-Net observations report
  36. GRB 250226B: Fermi GBM Observation
  37. Swift GRB 250312A: Global MASTER-Net observations report
  38. GRB 250302A: Fermi GBM Observation
  39. GRB 250309B/AT2025dws: Daochen/RC-10 optical counterpart observation
  40. GRB 241213A: VIRT Optical Upper Limit
  41. GRB 241228A: VIRT Optical Upper Limit
  42. GRB 250311A/EP250311a: Optical upper limits with Kinder observations
  43. GRB 250223B: Fermi GBM Observation
  44. GRB 250311A: Swift-XRT observations
  45. GRB 250228A: Fermi GBM Observation
  46. GRB 250309B: 1.3m DFOT Optical observations
  47. IceCube-250309A: Upper limits from a search for additional neutrino events in IceCube
  48. EP250311a: Global MASTER-Net observations report
  49. GRB 250308A: Swift/BAT-GUANO localization skymap of a short burst
  50. GRB 250302A: Swift/BAT-GUANO localization skymap of a burst
  51. GRB 250228A: Swift/BAT-GUANO localization skymap of a likely short burst
  52. GRB 250226B: Swift/BAT-GUANO localization skymap of a likely long GRB
  53. GRB 250226A: Swift/BAT-GUANO localization skymap of a long GRB
  54. GRB 250223B: Swift/BAT-GUANO localization skymap of a short burst
  55. GRB 250309B: PRIME near-infrared detection
  56. EP250304a: Chandra detection
  57. GRB 250225B: Swift-BAT refined analysis
  58. GRB 250311A/EP250311a: TRT optical upper limit
  59. IceCube-250309A: MITSuME Akeno and Seimei/TriCCS optical observations
  60. GRB 250311A: Tiled Swift observations
  61. EP250311a/GRB 250311A: EP-WXT detection
  62. GRB 250308A: CALET Gamma-Ray Burst Monitor detection
  63. GRB 250309B: SVOM/VT optical observation
  64. GRB 250309B / AT2025dws: further SAO RAS optical observations
  65. IceCube-250309A: Upper limits from Fermi-GBM Observations
  66. EP250308a: 1.6m Mephisto optical upper limits
  67. Konus-Wind detection of GRB 250309B
  68. GRB 250309B / AT2025dws: KMTNet-CTIO optical observations
  69. IPN triangulation of GRB 250308A (short)
  70. IPN triangulation of GRB 250309B
  71. IceCube-241224A: MASTER detection of PKS 1217+02 blazar flare with Zhirkov effect
  72. GRB 250309B/AT2025dws : COLIBRÍ Detection of the Optical Counterpart
  73. GRB 250309B: Swift-XRT refined Analysis
  74. GRB 250309B / IceCube-250309A: GECAM-B observations
  75. GRB 250309B / AT2025dws: OSIRIS+/GTC spectroscopy z=1.898
  76. Liverpool Telecope observations of AT 2025dws / GRB 250309B
  77. GRB 250309B / AT2025dws: SAO RAS optical observations
  78. GRB 250309B / AT2025dws: Swift-UVOT detection
  79. AT 2025dws, likely optical counterpart of GRB 250309B: LCO confirmation of fast fading
  80. GRB 250309B: Fermi GBM Observation
  81. Fermi GRB 250309B: Global MASTER-Net observations report
  82. Fermi GRB 250309A: Global MASTER-Net observations report
  83. GRB250309B: One candidate counterpart from the Zwicky Transient Facility
  84. IceCube-250309A: No candidates from the Zwicky Transient Facility
  85. Fermi-LAT gamma-ray observations of IceCube-250309A
  86. GRB 250308A: SVOM/GRM detection of QPO in the tail emission
  87. Correction to GCN 39633 - Swift is observing GRB 250309B/IceCube-250309A!
  88. GRB 230509B: Tiled Swift observations
  89. IceCube-250309A - IceCube observation of a high-energy neutrino candidate track-like event
  90. EP250308a: Global MASTER-Net observations report
  91. EP250308a: GSP optical upper limit
  92. GRB 250306A: EIRSAT-1 GMOD detection
  93. Fermi GRB 250307A: Global MASTER-Net observations report
  94. Konus-Wind detection of GRB 250306A
  95. GRB 250306A: Swift-BAT refined analysis
  96. GRB 250306A: NuSTAR detection of the prompt emission
  97. EP250304a: MeerKAT detection of a possible radio counterpart
  98. IceCube-241016A: MASTER flaring blazar 5BZU J073038.29-320820.2 with Zhirkov effect
  99. GRB 250305A: AstroSat CZTI detection
  100. EP250302a:Xinglong optical observations

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